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Scale-dependent effects of habitat on movements and path structure of reef sharks at a predator-dominated atoll
Ecology
Abstract
The effects of habitat on the ecology, movements, and foraging strategies of marine apex predators are largely unknown. We used acoustic telemetry to quantify the movement patterns of blacktip reef sharks (Carcharhinus melanopterus) at Palmyra Atoll National Wildlife Refuge, in the Pacific Ocean. Sharks had relatively small home ranges over a timescale of days to weeks (0.55 +/- 0.24 km2) and showed strong site fidelity to sand-flat ledges within the west lagoon over a three-year period. Sharks showed evidence of diel and tidal movements, and they utilized certain regions of the west lagoon disproportionately. There were ontogenetic shifts in habitat selection, with smaller sharks showing greater selection for sand-flat habitats, and pups (total length 35-61 cm) utilizing very shallow waters on sand-flats, potentially as nursery areas. Adult sharks selected ledge habitats and had lower rates of movement when over sand-flats and ledges than they did over lagoon waters. Fractal analysis of movements showed that over periods of days, sharks used patches that were 3-17% of the scale of their home range. Repeat horizontal movements along ledge habitats consisted of relatively straight movements, which theoretical models consider the most efficient search strategy when forage patches may be spatially and temporally unpredictable. Although sharks moved using a direct walk while in patches, they appeared to move randomly between patches. Microhabitat quantity and quality had large effects on blacktip reef shark movements, which have consequences for the life-history characteristics of the species and potentially the spatial distribution of behaviorally mediated effects on lower trophic levels throughout the Palmyra ecosystem.
... A few sharks in that study appeared to exhibit an equally strong affinity to two receivers, some of which were not adjacent suggesting that some individuals show sitefidelity to more than one area. This is similar to movements observed in blacktip reef sharks where individuals moved between 'patches' within their core area or home range [92]. Alternatively, site-fidelity may be spatially and temporally dynamic [92], the primary receiver site of an individual may have shifted from one to another receiver site over time. ...
... This is similar to movements observed in blacktip reef sharks where individuals moved between 'patches' within their core area or home range [92]. Alternatively, site-fidelity may be spatially and temporally dynamic [92], the primary receiver site of an individual may have shifted from one to another receiver site over time. However, data from the present study are not able to give conclusive information on shifting site-fidelity due to the low number of detections and spatiotemporal variation in acoustic coverage. ...
... While these findings could be an artefact due to the greater detection range of V16 compared to that of V9 tags (used in very small sharks of < 110 cm TL), ontogenetic differences in space use are common in many sharks [9,10,28] and thought to be linked to individual energy requirements. Generally, larger individuals have greater energy requirements than smaller ones [97][98][99] and therefore, need more resources and consequently more space [reviewed in 83,85,92]. In contrast, smaller sharks tend to cruise more slowly [98] and to stay within core areas in order to avoid predation [94]; consequently they move between receivers less frequently and avoid movements across deeper water. ...
Understanding how reef-associated sharks use coastal waters through their ontogeny is important for their effective conservation and management. This study used the horizontal movements of acoustically tagged Caribbean reef sharks ( Carcharhinus perezi ) to examine their use of coastal space around the Cayman Islands between 2009 and 2019. A total of 39 (59.1%) tagged sharks (male = 22, female = 17, immature = 18, mature = 21) were detected on the islands wide network of acoustic receivers. The detection data were used to calculate values of Residency Index (RI), Site-Fidelity Index (SFI) and minimum linear displacement (MLD), as well as for network analysis of individual shark movements to test for differences between demographics, seasons, and diel periods. Sharks were detected for up to 1,598 days post-tagging and some individuals showed resident behaviour but the majority of tagged individuals appear to have been one-off or only occasional transient visitors to the area. Generally, individuals showed strong site-fidelity to different areas displaying linear home ranges of < 20 km. The evidence indicates that there was no pattern of diel behaviour. Tagged sharks generally showed increased movements within and between islands during the summer (April–September), which may be related to breeding activity. Some individuals even made occasional excursions across 110 km of open water > 2,000 m deep between Grand Cayman and Little Cayman. One mature female shark showed a displacement of 148.21 km, the greatest distance reported for this species. The data shows that the distances over which some sharks moved, greatly exceeded the extent of any one of the islands’ marine protected areas indicating that this species may be more mobile and dispersive than previously thought. This study provides support for the blanket protection to all sharks throughout Cayman waters, which was incorporated within the National Conservation Act in 2015.
... Many coastal species of sharks appear to show periodicity in their presence on subtidal reefs within their home ranges, with some species showing 24-h periodicity relating to circadian rhythms (Papastamatiou et al. 2009;Speed et al. 2011;Barnett et al. 2012), whereas others show 8-12-h periodicity in detections relating to tidal movements (Papastamatiou et al. 2009;Field et al. 2011;Speed et al. 2011). In the case of blacktip reef sharks (Carcharhinus melanopterus, Papastamatiou et al. 2009) and grey reef sharks (Carcharhinus amblyrhynchos, Field et al. 2011), individuals showed both 24-h periodicity and 8-12-h periodicity. ...
... Many coastal species of sharks appear to show periodicity in their presence on subtidal reefs within their home ranges, with some species showing 24-h periodicity relating to circadian rhythms (Papastamatiou et al. 2009;Speed et al. 2011;Barnett et al. 2012), whereas others show 8-12-h periodicity in detections relating to tidal movements (Papastamatiou et al. 2009;Field et al. 2011;Speed et al. 2011). In the case of blacktip reef sharks (Carcharhinus melanopterus, Papastamatiou et al. 2009) and grey reef sharks (Carcharhinus amblyrhynchos, Field et al. 2011), individuals showed both 24-h periodicity and 8-12-h periodicity. ...
... Many coastal species of sharks appear to show periodicity in their presence on subtidal reefs within their home ranges, with some species showing 24-h periodicity relating to circadian rhythms (Papastamatiou et al. 2009;Speed et al. 2011;Barnett et al. 2012), whereas others show 8-12-h periodicity in detections relating to tidal movements (Papastamatiou et al. 2009;Field et al. 2011;Speed et al. 2011). In the case of blacktip reef sharks (Carcharhinus melanopterus, Papastamatiou et al. 2009) and grey reef sharks (Carcharhinus amblyrhynchos, Field et al. 2011), individuals showed both 24-h periodicity and 8-12-h periodicity. This is understandable, given the importance of tide and diel cycles in driving the behaviour of marine organisms (e.g. ...
Limited information exists about the temporal residency patterns of marine predators, especially at the individual level. Temporal partitioning of resources can reduce intra-specific competition, but this has seldom been examined in predators in marine ecosystems. Here, we used 8 years of acoustic telemetry data from 27 receivers deployed in a large coastal embayment to examine the temporal residency of 51 Port Jackson sharks (Heterodontus portusjacksoni), during their breeding season. We found that the residency lengths of male and female Port Jackson sharks on breeding reefs differed throughout the breeding season, with males showing longer residency at the start of the season and females showing longer residency at the end of the season. Port Jackson sharks also showed a 24-h or diel periodicity in their detection patterns. Although the majority of individuals were nocturnal, a small proportion of sharks was detected more frequently during the day, possibly to reduce competition for resources. Surprisingly, there was no difference in the sex ratio nor the size of diurnal and nocturnal individuals. This study provides long-term insight into the temporal residency patterns of mesopredatory sharks at a breeding site and, more broadly, our results highlight the importance of studying temporal variation at the individual level in movement ecology studies.
... Two polygons between T1 and T3 and T1 and T4 represent the home range of sharks captured at T1 that were recaptured at T3 and T4, respectively than the area of Tepee (Table 1), although no shark was tracked outside of the MPA containing Tepee. Mark-recapture did not allow us to estimate KUDs, although this approach could also be used to calculate the maximum linear dimension metric (Papastamatiou et al. 2009). Further, MCP from mark-recapture will be influenced by the distance between nets (i.e., 200-600 m) and barriers (e.g., coastline, channels). ...
... Neonates tracked in this study exhibited much smaller home ranges than blacktip reef shark neonates from other populations (Papastamatiou et al. 2009;Chin et al. 2016;Oh et al. 2017b). Home ranges of blacktip reef sharks (TL = 100.0 ...
... Home ranges of blacktip reef sharks (TL = 100.0 ± 17.0 cm) at Palmyra Atoll were actively monitored for 4-72 h and had 95% KUDs of 0.5 ± 0.2 km 2 (Papastamatiou et al. 2009). Differences in home ranges between individuals monitored in this study and the population at Palmyra, which were tracked over similar durations, could reflect differences in habitat availability between high island narrow lagoon and atoll systems. ...
Sharks play important functional roles in coral reef ecosystems. Studying reef shark populations' spatial ecology also contributes important data for effective conservation planning. The purpose of this study was to define the home range of neonatal blacktip reef sharks (Carcharhinus melanopterus) around Moorea, French Polynesia, and compare estimates using both mark-recapture surveys and active acoustic telemetry. Mark-recapture surveys produced a minimum convex polygon (MCP) of 0.07 km 2 that was significantly larger than the MCP derived from acoustic telemetry (0.02 km 2). Acoustic telemetry produced 50 and 95% kernel utilization densities that were smaller (0.02 km 2) and larger (0.14 km 2) than home range estimates from mark-recapture surveys, respectively. Home range estimates from this study are the smallest that have been documented for neonatal blacktip reef sharks, possibly owing to the study sites' proximity to deep channels. Mark-recapture and active acoustic telemetry are complementary approaches worthy of consideration where passive telemetry is impractical.
... It is the third most commonly encountered shark in the GBR reef line fishery [59] and the most common reef shark caught in the commercial net fishery operating within inshore waters of the GBR [45]. High site-attachment is reported for C. melanopterus on atolls [60][61][62], remote high islands [63] and in several coastal bays [64,65] with localised movement and comparatively small home ranges observed across various habitat types and life history stages [44,60,64,65]. Males reach sexual maturity at~1000 mm, females between 1100-1335 mm [reviewed in 66], with mating and parturition reported to occur locally between November and March [65,67,68]. ...
... To date, most studies examining movement and space use of reef sharks have been conducted on offshore reefs, remote islands or atolls with high site-fidelity and restricted space use a common trait observed for many species including the lemon shark, Negaprion brevirostris [84][85][86], Caribbean reef shark, Carcharhinus perezi [33,87], whitetip reef shark, Triaenodon obesus [41] and C. amblyrhynchos [31,34,41,42]. Similarly, results from the current study showed C. melanopterus to be strongly site-attached to reef habitats inshore, supporting previous research conducted on this species in remote reef [35,44,62,63] and coastal environments [64,65]. High residency and low roaming values at Orpheus Island remained relatively constant throughout most of the study period indicating limited movement and high reuse of inshore reef areas across the sample population. ...
... While large-scale movements are primarily observed for adults [43,95], they have also been documented among juveniles [92,98] and are thought to assist with gene dispersal, reducing inter-and intra-specific competition and identifying new suitable habitats/resources [16]. Several studies on C. melanopterus have documented occasional long-range excursions within reef systems for reasons likely related to reproduction [62,63,88]. For example, interisland migrations were observed for adult female C. melanopterus in French Polynesia, with sharks observed to travel 50 km over open ocean to give birth in natal habitats [63]. ...
Information on the spatial ecology of reef sharks is critical to understanding life-history patterns , yet gaps remain in our knowledge of how these species move and occupy space. Previous studies have focused on offshore reefs and atolls with little information available on the movement and space use of sharks utilising reef habitats closer to shore. Cross-shelf differences in physical and biological properties of reefs can alter regional ecosystem processes resulting in different movement patterns for resident sharks. Passive acoustic telem-etry was used to examine residency, space use and depth use of 40 blacktip reef sharks, Carcharhinus melanopterus, on an inshore reef in Queensland, Australia, and assess temporal or biological influences. All sharks showed strong site-attachment to inshore reefs with residency highest among adult females. Sharks exhibited a sex-based, seasonal pattern in space use where males moved more, occupied more space and explored new areas during the reproductive season, while females utilised the same amount of space throughout the year, but shifted the location of the space used. A positive relationship was also observed between space use and size. There was evidence of seasonal site fidelity and long-distance movement with the coordinated, annual migration of two adult males to the study site during the mating season. Depth use was segregated with some small sharks occupying shallower depths than adults throughout the day and year, most likely as refuge from predation. Results highlight the importance of inshore reef habitats to blacktip reef sharks and provide evidence of connectivity with offshore reefs, at least for adult males.
... For example, blacktip reef and sicklefin lemon sharks Negaprion acutidens use shallow-water nurseries in lagoons (e.g. Papastamatiou et al. 2009, Matich et al. 2017). As they grow, sicklefin lemon sharks move to waters along the forereef and beyond, while adult blacktip reef sharks continue to use both forereef and lagoon waters frequently , Heupel et al. 2018b). ...
... Finally, while blacktip reef sharks use lagoon areas as nurseries (e.g. Papastamatiou et al. 2009, Matich et al. 2017), this does not appear to be the case for grey reef sharks. Variation in abundances of whitetip reef sharks, the third most abundant species, was poorly explained by the parameters in our models. ...
... For example, blacktip reef and sicklefin lemon sharks Negaprion acutidens use shallow-water nurseries in lagoons (e.g. Papastamatiou et al. 2009, Matich et al. 2017). As they grow, sicklefin lemon sharks move to waters along the forereef and beyond, while adult blacktip reef sharks continue to use both forereef and lagoon waters frequently , Heupel et al. 2018b). ...
... Finally, while blacktip reef sharks use lagoon areas as nurseries (e.g. Papastamatiou et al. 2009, Matich et al. 2017), this does not appear to be the case for grey reef sharks. Variation in abundances of whitetip reef sharks, the third most abundant species, was poorly explained by the parameters in our models. ...
Populations of sharks, including those inhabiting coral reefs, have experienced dramatic global declines. Setting appropriate targets for restoring reef shark populations requires estimates of expected relative abundances in the absence of intense fishing. It is therefore important to identify factors that drive the carrying capacity of sharks in relatively intact reef systems and to determine whether expected shark abundance varies according to easy to assess variables. These variables could then be used by managers for setting restoration targets, or prioritizing resource allocation, for particular areas in the absence of detailed data. French Polynesia, the world’s largest shark sanctuary, provides a model system for addressing this question. We used baited remote underwater video surveys to assess relative abundance of sharks on 35 reefs across the broad geographic range of French Polynesia. Boosted regression tree models revealed that relative abundance of sharks varied significantly with island geomorphology. Overall, relative shark abundances at high islands were nearly 3 times lower than on atolls, and among atoll geomorphology types, open atolls had abundances nearly 20% higher than closed atolls. Island group, temperature, and net primary productivity had more limited effects. Human pressure (measured as market gravity) was not a significant factor. Although species-specific patterns varied, our findings suggest that environmental factors, particularly island geomorphology, should be taken into account when setting shark abundance recovery targets. Using this easy to assess factor can facilitate the allocation of conservation effort and improve assessments of species recovery efforts for islands in the Indo-Pacific region.
... The demographic compositions observed, including numerous immature individuals, indicate that there are breeding populations of both Caribbean reef and nurse sharks within the area, supporting the evidence that both species are substantially resident through their range (Carrier and Pratt, 1998). Since shallow lagoons provide nursery grounds for sharks elsewhere, including insular populations (Feldheim et al., 2002;Garla et al., 2006b;Papastamatiou et al., 2009;Papastamatiou et al., 2015;Bond et al., 2017), it would be useful to undertake visual surveys for juveniles across suitable mangrove and reef flat areas; however preliminary searches of these areas did not detect any concentrations of juveniles, such as are known for lemon shark nursery areas in the Bahamas (Feldheim et al., 2002(Feldheim et al., , 2014. The occasional sighting of small juveniles both on BRUVS and while SCUBA diving suggests that Caribbean reef sharks may in contrast use structurally complex reef slope areas for pupping and to provide shelter for juveniles. ...
... Acoustic telemetry showed that larger individuals move greater distances than smaller Caribbean reef sharks in Cayman (Kohler, 2022). Ontogenetic expansion of home range size has also been reported in Caribbean reef sharks from Belize which is thought to be due to the higher energy requirements of larger sharks compared to that of smaller individuals (Papastamatiou et al., 2009;Grubbs, 2010;Speed et al., 2010). The larger home ranges in this study might be likely due to a combination of competition, resource availability and sampling. ...
The assessment of parameters population size and individual home range is important for effective conservation management of sharks. This study uses the novel application of photo identification (photo-ID) to BRUVS footage as a non-invasive alternative to tagging in order to generate individual capture histories. These were used in mark-recapture models to estimate effective population sizes and to determine home ranges. In the Cayman Islands a total of 499 shark sightings of six coastal shark species were recorded on BRUVS from 2015 - 2018, but re-sighting rates were only sufficient for the determination of population parameters for two species - Caribbean reef shark (Carcharhinus perezi) and nurse shark (Ginglymostoma cirratum). The calculated super-population sizes for Caribbean reef shark (180 ± 37 SE) and nurse shark (336 ± 61 SE) were greater than the estimates for each species based on a closed-population model (Caribbean reef shark: 128 ± 40 SE, nurse shark: 249 ± 48 SE), though both measures indicated that there were about twice as many nurse sharks (1.3 - 1.8 sharks/km²) as Caribbean reef sharks (0.7 – 1 shark/km²) within the study area. The demographic compositions included numerous immature individuals, indicating that breeding of both species takes place within the study area of 188 km². Most recognizable individuals of both species showed linear home ranges of <20 km, but a few individuals were observed to have moved longer distances (Caribbean reef shark: 125.37 km, nurse shark: 156.07 km). The data indicate that the home ranges and long-distance movements of individual sharks observed within the islands’ marine protected areas (MPAs) often extend to areas beyond the MPA’s boundary, potentially exposing them to fishing activities. This study provides the first estimates of population size for Caribbean reef and nurse sharks in the Cayman Islands and the first estimate of a Caribbean reef shark population globally.
... These sharks were more likely to be observed in shallow depths (< 25 m), but within this range we found evidence of species-specific depth preferences. C. melanopterus were most likely to be observed in the shallowest deployments (0-4 m), and this species is known to inhabit complex habitats on reef flats within shallow lagoons [44][45][46] . C. amblyrhynchos were found at intermediate depths (4-9 m), whereas T. obesus were most likely to be observed in deeper deployments (16-25 m). ...
... Our study examined patterns in the abundance and behaviour of sharks during the day, but it is important to note that habitat use 54 , activity levels 44,55 , and depth distributions 56 of sharks can alter at night. Despite this sampling bias, our study provided a comprehensive survey of patterns in the distribution and abundance of sharks across hundreds of kilometres of tropical and sub-tropical reef. ...
Quantifying the drivers of population size in reef sharks is critical for the development of appropriate conservation strategies. In north-west Australia, shark populations inhabit coral reefs that border growing centres of human population, industry, and tourism. However, we lack baseline data on reef sharks at large spatial scales (hundreds of km) that might enable managers to assess the status of shark populations in the face of future development in this region. Here, we examined the occurrence, abundance and behaviour of apex (Galeocerdo cuvier, Carcharhinus plumbeus) and reef (C. amblyrhynchos, C. melanopterus, Triaenodon obesus) sharks using > 1200 deployments of baited remote underwater stereo-video systems (stereo-BRUVs) across > 500 km of coastline. We found evidence for species-specific influences of habitat and fishing activities on the occurrence (probability of observation), abundance (MaxN) and behaviour of sharks (time of arrival to the stereo-BRUVs and likelihood of feeding). Although the presence of management zoning (No-take areas) made little difference to most species, C. amblyrhynchos were more common further from boat ramps (a proxy of recreational fishing pressure). Time of arrival for all species was also influenced by distance to boat ramp, although patterns varied among species. Our results demonstrate the capacity for behavioural metrics to complement existing measures of occurrence and abundance in assessing the potential impact of human activities on shark populations.
... To understand the assortative forces which underpin the structural properties of the system is challenging for elusive underwater animals. As the blacktip reef shark displays a high degree of site fidelity (Papastamatiou et al. 2009) and shares some of its areas with many conspecifics (Mourier et al. 2012), exploring this network holds the potential to work out the relationship between spatial, social, and genetic structure in a reef shark. Size, sex, and gregariousness of sharks have been shown to influence assortment at the population and community levels (Mourier et al. 2012;Mourier et al. 2017). ...
... Taking into account the confounding effects of five structural variables (spatial and temporal overlap, gregariousness, size, and sex), which are known to influence association patterns (e.g., Godde et al. 2013;Diaz-Aguirre et al. 2019;Machado et al. 2019;Perryman et al. 2019), we found that blacktip reef sharks in Moorea had structured associations and affiliations, although most of the network structure was driven by spatio-temporal overlap. However, social proximity was not predicted by the genetic relatedness between sharks both at the association, affiliation and community levels. ...
Genetic relatedness in animal societies is often a factor that drives the structure of social groups. In the marine world, most studies which have investigated this question have focused on marine mammals such as whales and dolphins. For sharks, recent studies have demonstrated preferential associations among individuals from which social communities emerge. Assortment patterns have been found according to phenotypic or behavioral traits, but the role of genetic relatedness in shaping the social structure of adult shark populations has, to the best of our knowledge, never been investigated. Here, we used a social network analysis crossed with DNA microsatellite genotyping to investigate the role of the genetic relatedness in the social structure of a blacktip reef shark (Carcharhinus melanopterus) population. Based on the data from 156 groups of sharks, we used generalized affiliation indices to isolate social preferences from nonsocial associations, controlling for the contribution of sex, size, gregariousness, spatial, and temporal overlap on social associations, to test for the influence of genetic relatedness on social structure. A double-permutation procedure was employed to confirm our results and account for issues arising from potentially elevated type I and type II error rates. Kinship was not a predictor of associations and affiliations among sharks at the dyad or community levels as individuals tended to associate independently of the genetic relatedness among them. The lack of parental care in this species may contribute to the breakdown of family links in the population early in life, thereby preventing the formation of kin-based social networks.
... The blacktip reef shark Carcharhinus melanopterus, the target species for the artificial feeding, is one of the most abundant and a common shark species in the coral reefs of the Indo-Pacific (Vignaud et al., 2014), inhabiting shallow reefs and sand-flats of both atolls and high islands (Papastamatiou et al., 2009;Speed et al., 2011;Mourier, Mills & Planes, 2013;Chin et al., 2016). Blacktip reef sharks demonstrate a high degree of site attachment and individual spatial overlap (Papastamatiou et al., 2009;Mourier, Vercelloni & Planes, 2012), with individuals displaying larger range of movements only during the reproductive period Speed et al., 2016). ...
... The blacktip reef shark Carcharhinus melanopterus, the target species for the artificial feeding, is one of the most abundant and a common shark species in the coral reefs of the Indo-Pacific (Vignaud et al., 2014), inhabiting shallow reefs and sand-flats of both atolls and high islands (Papastamatiou et al., 2009;Speed et al., 2011;Mourier, Mills & Planes, 2013;Chin et al., 2016). Blacktip reef sharks demonstrate a high degree of site attachment and individual spatial overlap (Papastamatiou et al., 2009;Mourier, Vercelloni & Planes, 2012), with individuals displaying larger range of movements only during the reproductive period Speed et al., 2016). These sharks have limited home ranges and are resident to specific reefs for periods of at least several years (up to 10 years or more in Moorea; Mourier et al., 2012). ...
While the negative effects of consumptive pressures on marine predators are well established, the effects of increasing non‐consumptive activities such as wildlife tourism are still understudied. As such, the long‐term effects of the provision of bait on shark behaviour are still unclear. Here, we assessed the effects of provisioning using a Control‐Impact design on the spatial use and level of residency of the blacktip reef shark Carcharhinus melanopterus over a 2‐year period. We used effect sizes to model the relative changes in residency between provisioning and non‐provisioning sites. Sharks showed a high degree of residency and significant changes in their habitat use which persisted overnight while the activity ceased. We suggest that provisioning activities can affect species with high level of residency such as the blacktip reef shark. Further research is needed to better understand how these behavioural modifications can alter the fitness of this species. It is important to adapt shark provisioning activities to limit the induced changes in habitat use.
... High use of areas of the Sebastopol Lagoon by lemon sharks where high fish abundance was recorded, especially near mangrove-lined shores, suggest that these areas confer a benefit of access to abundant prey as well as refuge from predators. Other species such as blacktip and blacktip reef sharks have also shown movement patterns that demonstrate trade-offs between predator avoidance and access to prey (Heupel and Simpfendorfer 2005;Papastamatiou et al. 2009). Although apparently of little significance at Los Roques, specific environmental conditions (i.e. ...
Use of a small tropical nursery in the Los Roques Archipelago by lemon sharks (Negaprion brevirostris) was investigated using acoustic telemetry. Twelve juvenile lemon sharks of three size classes were tracked between February 2014 and August 2015 in the Sebastopol Lagoon. Sharks were strongly site attached and remained in the lagoon for the duration of the study. Individuals in the smallest size class exhibited restricted movements within the innermost area of the lagoon in shallow water (< 1 m), over muddy substrate and along mangrove-lined shores. Sharks in the two larger size classes ranged further, in deeper water, over a wider range of substrates and more frequently near the lagoon entrance. Activity space varied among size classes, with home range (95% kernel utilization densities–KUD) of 0.42 km² and core area (50% KUD) of 0.13 km² for individuals in the smallest size class. For the medium and large size classes home ranges were 1.11 and 1.15 km² and core areas were 0.33 and 0.35 km² respectively. Space use as Minimum Convex Polygons differed among size classes, with overlap between the two largest size classes of 89%, compared with 40% between medium and smallest and 43% for largest and smallest size classes. Space use of lemon sharks in the Los Roques nursery illustrates variable use of habitat with varying environmental characteristics, likely reflecting a balance between predator avoidance and prey acquisition. Greater understanding of the use of nursery habitats for species such as lemon sharks, which use small, discrete nurseries over a broad geographical range can enhance our understanding of relationships between life history traits and environmental variability and management of populations.
... This result could be due to differences in energy requirements and risk of predation. Larger sharks generally have higher energetic requirements than smaller ones (Carlson et al. 2004;Espinoza et al. 2015a), and consequently, their activity space tends to increase as they grow to look for more potential prey (Papastamatiou et al. 2009;Grubbs 2010). The direct exposure to open waters in Roca Partida favors the presence of pelagic fish of higher trophic level, which attracts large predators, compared to the reef fish communities of the other islands of the Revillagigedo Archipelago (Fourrière et al. 2019). ...
The silvertip shark (Carcharhinus albimarginatus) is a reef-associated shark widely distributed across the Indo-Pacific. However, it has been poorly studied and little is known about its spatial ecology, particularly about long-range travels. In this study, we investigated the residency and movement patterns of silvertip sharks in a widespread remote archipelago offshore the Pacific coast of Mexico, the Revillagigedo Archipelago. An array of 10 VR2W receivers was deployed around the archipelago to monitor the movement of 45 silvertip sharks during 11 years. Among the 40 sharks detected during the study, 34 exhibited high site fidelity with 70% of their daily detections recorded in one particular site. Residency index ranged from 0.049 to 0.99 with an average residency of 0.49 ± 0.27 (SD). The sharks exhibited strong diurnal patterns in horizontal and vertical movements with two peaks of detections at sunrise and sunset and a presence in deeper waters during daytime. Eleven individuals (7 adult females) traveled from one island to another (separated by distances ranging from 60 to 425 km). Geographical ontogenetic segregation was observed within the archipelago with juveniles being present only around San Benedicto and Socorro islands. Five sharks tagged as juveniles left their tagging island once they had reached adulthood, three males between 8 and 10 years old and two females at 11 years old.
... Other than food resources, coastal areas and shallow waters of the lagoon offer more protection from predators such as large sharks, and hence, represent a suitable environment for potential nurseries. In New Caledonia, the detection of juvenile individuals remains sporadic, and neonates are even scarcer, although lagoons are places of nursery grounds for reef manta rays in Raja Ampat, Indonesia [62] and for other elasmobranchs [66][67][68]. Further investigations in suspected adequate nursery grounds using aerial surveys and accurate measurement methods to quantify maturation stages might lead to the discovery of nurseries in New Caledonia. ...
The reef manta ray, Mobula alfredi (Krefft, 1868), is a highly mobile and plankton-feeding species, classified vulnerable to extinction on the IUCN Red List for Threatened Species. Knowledge on their spatial ecology and the extent of their dispersal remain incomplete, especially within island-fragmented habitats as found in New Caledonia. Satellite telemetry was used to investigate the horizontal movement ecology of reef manta rays in New Caledonia. A total of 21 reef manta rays were tagged with pop-up satellite archival transmitting tags (21 Fastloc and 2 MiniPAT) that remained deployed for a duration ranging from 3 to 180 days (mean ± SE = 76.7 ± 50.3). Rays presented a strong site fidelity and an important affinity for coastal waters. Long-distance migrations (>300 km) were also observed, mainly through coastal and shallow water paths. Horizontal movements were compared to a home range area and classified into four distinct patterns: Fidelity, Excursion, Fidelity + Relocation and Relocation. The most dominant pattern was Fidelity, where manta rays remained within their home range for the whole duration of the tag deployment. Our findings may assist in the design of more appropriate management strategies for the species in New Caledonia and other regions worldwide. Key Contribution: This paper presents unique information on the horizontal movement ecology of reef manta rays (Mobula alfredi) in a context of an archipelago that combines continuous coastlines and islands separated by deep waters. The main results show a consistent use of shallow coastal waters for dispersal and that deep water might be a restraining factor but not a complete barrier to connectivity.
... Other than food resources, coastal areas and shallow waters of the lagoon offer more protection from predators such as large sharks and hence, represent a suitable environment for potential nurseries. In New Caledonia, the detection of juvenile individuals remains sporadic, and neonates are even scarcer, although lagoons are places of nursery grounds for reef manta rays in Raja Ampat, Indonesia [64] and for other elasmobranchs [68][69][70]. Further investigations in suspected adequate nursery grounds using aerial surveys and accurate measurement methods to quantify maturation stages might lead to the discovery of nurseries in New Caledonia. ...
The reef manta ray (Mobula alfredi) is a highly mobile and plankton-feeding species, classified vulnerable to extinction on the IUCN Red List for Threatened Species. Knowledge on their spatial ecology and the extent of their dispersal remain incomplete, especially within island-fragmented habitats as found in New Caledonia. Satellite telemetry was used to investigate the horizontal movement ecology of reef manta rays in New Caledonia. A total of 21 manta rays were tagged with pop-up satellite archival transmitting tags (21 Fastloc and 2 MiniPAT) that remained deployed for a duration ranging from 3 to 180 days (mean ± SE = 76.7 ± 50.3). Rays presented a strong site fidelity and an important affinity for coastal waters. Long-distance migrations (> 300 km) were also observed, mainly through coastal and shallow water paths. Horizontal movements were compared to a home range area and classified into four distinct patterns: Fidelity, Excursion, Fidelity + Relocation and Relocation. The most dominant pattern was Fidelity where manta rays remained within their home range for the whole duration of the tag deployment. Our findings may assist the design of more appropriate management strategies for the species in New Caledonia and other regions worldwide.
... They rarely moved in a straight line for more than a few minutes". Papastamatiou et al. (2009b) described blacktips at Palmyra Atoll (Line Islands) using patches that were 3 to 17% of the scale of their home range for periods of days. They repeated straight movements along ledge habitats, which was theorized to be the most efficient search strategy when foraging is unpredictable. ...
The chondrichthyan lineage diverged from the osteichthyan line around 440 million years ago, resulting in a vast evolutionary gulf between modern elasmobranchs and other vertebrates. Though this has supported the assumption that as an ancient line, elasmobranchs are dangerously stupid, intelligent actions including social interactions have been noted in the field, while laboratory studies have confirmed a variety of cognitive capacities. Yet, due to fear of sharks and the difficulties of observing them in their aquatic environments, few ethological studies have been done, so their natural behaviour remains little known. On noting that the blacktip reef shark, Carcharhinus melanopterus , displayed complex actions during incidental meetings, a long-term ethological study of the species was carried out on the north shore of Mo’orea Island, French Polynesia. During the 6.5 years of the study, new behaviours continued to present. The 35 context-specific actions identified as comprising the behavioural repertoire of C. melanopterus are described.
... Indeed, sub-adult and adult blacktip reef and lemon sharks are abundant at St. Joseph Atoll and occur within reef habitats around the atoll, and in the central lagoon adjacent to the shallow intertidal reef flats (Filmalter et al. 2013;Lea et al. 2016Lea et al. , 2020. With the incoming tides, adult sharks gain access to these shallower areas (Lea et al. 2020), thus juvenile sharks may seek the shallowest areas of the atoll for refuge (Papastamatiou et al. 2009;Guttridge et al. 2012). Such tidal dependent movements are not unique to St. ...
The coexistence of ecologically and morphologically similar species is often facilitated by the partitioning of ecological niches. While subordinate species can reduce competition with dominant competitors through spatial and/or trophic segregation, empirical support from wild settings, particularly those involving large-bodied taxa in marine ecosystems, are rare. Shark nursery areas provide an opportunity to investigate the mechanisms of coexistence. We used experimental and field studies of sympatric juvenile sharks (blacktip reef shark, Carcharhinus melanopterus; sicklefin lemon shark, Negaprion acutidens) to investigate how competitive ability influenced realized niches at St. Joseph Atoll, Seychelles. Captive trials revealed that sicklefin lemon sharks were dominant over blacktip reef sharks, consistently taking food rewards. In the field, blacktip reef sharks were captured over a broader area than sicklefin lemon sharks, but daily space use of actively tracked sharks showed a high degree of overlap across microhabitats. While stomach contents analysis revealed that blacktip reef shark diets included a broader range of prey items, stable isotope analysis demonstrated significantly higher mean δ¹³C values for sicklefin lemon sharks, suggesting diverging dietary preferences. Overall, our results matched theoretical predictions of subordinate competitors using a greater range of habitats and displaying broader feeding niches than competitively dominant species. While separating the realized and fundamental niche of marine predators is complicated, we provide evidence that resource partitioning is at least partially driven by interspecific competition.
... This comparison suggests considerable variability among the Caspian, Aral, Azov, and Mediterranean populations in the maximum size attained by the species. It has been stated that the differences in the maximum size among populations may be due to different ecological conditions among the areas, most probably due to differences in the temperature and limiting the food resources (Nikolskii, 1963;Basilone et al., 2004;Papastamatiou et al., 2009), causing different growth rate of populations. In general, the difference in maximum size attained by a species during its lifespan is interpreted as a result of local adaptation and genetic differences among the populations of this species (Anvarinia et al., 2020). ...
... They rarely moved in a straight line for more than a few minutes". Papastamatiou et al. (2009b) described blacktips at Palmyra Atoll (Line Islands) using patches that were 3 to 17% of the scale of their home range for periods of days. They repeated straight movements along ledge habitats, which was theorized to be the most efficient search strategy when foraging is unpredictable. ...
The chondrichthyan lineage diverged from the osteichthyan line around 440 million years ago, resulting in a vast evolutionary gulf between modern elasmobranchs and other vertebrates. Though this has supported the assumption that sharks are ancient, dangerous, and binary-minded, intelligent actions including social interactions have been noted in the field, while laboratory studies have confirmed a variety of cognitive capacities. Yet, due to fear of sharks and the difficulties of observing them in their aquatic environments, few ethological studies have been done, so their natural behaviour remains little known. On noting that Carcharhinus melanopterus displayed complex actions during incidental meetings, a long-term ethological study of the species was carried out on the north shore of Mo’orea Island, French Polynesia. During the 6.5 years of the study, new behaviours continued to present. The 35 context-specific actions identified as comprising the behavioural repertoire of C. melanopterus are described.
... Beberapa penelitian menunjukkan bahwa terdapat variasi ukuran panjang yang ditemukan di beberapa lokasi dan adanya kecenderungan panjang maksimum tubuh individu betina C. melanopterus yang dilaporkan lebih besar dibandingkan dengan individu jantan (White, 2007;Papastamatiou et al., 2009a;Speed et al., 2011;Chin et al., 2012;Mourier et al., 2013). Hal ini diduga disebabkan diantaranya karena adanya variasi kompetisi sumber makanan baik interspesies maupun antar spesies (Papastamatiou et al., 2009b). Tekanan antropogenik (seperti degradasi habitat, ekploitasi penangkapan dan aktivitas wisata) kemungkinan juga dapat menjadi faktor yang mempengaruhi kondisi perkembangan dan pertumbuhan (Clua et al., 2010). ...
Perairan Wakatobi merupakan koridor penting bagi pergerakan atau migrasi beberapa spesies laut karismatik seperti penyu, paus dan hiu. Studi ini bertujuan untuk mengidentifikasi habitat ideal bagi spesies hiu yang ada di Perairan Wakatobi. Pengumpulan data dilakukan pada tahun 2017 sampai 2019 dengan menggunakan metode underwater visual census (UVC) di tujuh lokasi penyelaman yang ada di Kabupaten Wakatobi. Hasil studi ini menunjukkan bahwa spesies hiu yang umumnya ditemukan di Perairan Wakatobi adalah hiu karang sirip hitam (Carcharhinus melanopterus) dengan 211 kali kemunculan dan hiu karang sirip putih (Triaenodon obesus) dengan 3 kali kemunculan. Individu yang dijumpai merupakan hiu dewasa dan remaja, yaitu 46% dewasa dan 54% remaja untuk C. melanopterus, sedangkan T. obesus dewasa sebanyak 34% dan remaja 67%. Kedua jenis tersebut ditemukan pada terumbu karang dengan tipe terumbu tepi (fringing reef). Carcharhinus. melanopterus ditemukan pada profil terumbu berbentuk lereng (reef slope) dan tebing (reff wall) pada kedalaman 10-30 meter dengan kondisi tidak berarus, dan visibilitas ± 10 meter, sedangkan T. obesus ditemukan pada profil terumbu berbentuk tebing (reff wall) pada kedalaman 21-30 meter dengan kondisi tidak berarus dan visibilitas ± 10 meter.
... Other than food resources, coastal areas and shallow waters of the lagoon offer more protection from predators such as large sharks and hence, also represent a suitable environment for potential nurseries. In New Caledonia, the detection of juvenile individuals remains sporadic, and neonates are even more scarce, although lagoons are places of nursery grounds for reef manta rays in Raja Ampat, Indonesia (Setyawan et al. 2020) and for other elasmobranchs (Heupel et al. 2007;Papastamatiou et al. 2009;Dale et al. 2011). Further investigations in suspected adequate nursery grounds using aerial surveys and accurate measurement methods to quantify maturation stages might lead to the discovery of nurseries in New ...
Espèce emblématique et néanmoins menacée qui peuple les mers des régions tropicales et subtropicales du monde entier, la raie manta de récif (Mobula alfredi) est bien présente en Nouvelle-Calédonie. La population de l’archipel n’a cependant encore jamais été étudiée et la compréhension de sa biologie, son écologie, sa dynamique des populations et ses mouvements est encore limitée à l’échelle globale. L’acquisition de connaissances de références pourrait jouer un rôle essentiel pour la conservation de l’espèce. Cette thèse tente de décrire la population, sa structure et l’écologie spatiale de raies manta de Nouvelle-Calédonie en utilisant des approches diverses combinant la science participative à la télémétrie satellite et la génomique. Un suivi de cinq ans permettant la collecte de 1741 photo-identifications de raies manta a permis de connaitre les caractéristiques et la distribution de la population, d’estimer son abondance et d’obtenir un premier aperçu de son utilisation de l’espace et des potentielles sources de blessures. L’utilisation de 21 balises satellites a permis d’obtenir des données de déplacements et de comportements de plongées plus. Finalement, le séquençage du génome de 92 échantillons dont 73 provenant de quatre sites en Nouvelle-Calédonie et 19 de deux sites sur la côte Est de l’Australie a permis de révéler l’existence d’une structure génétique à l’échelle régionale et locale. Les résultats présentés dans cette thèse apportent les premières données sur la population de raies manta de récifs en Nouvelle-Calédonie et proposent les mesures et précautions qui devraient être prises pour évaluer et mitiger les possibles perturbations présentes et futures.
... This separation among the size-classes was also evident from the results of the annual CPUE-weighted mean centers of relative abundance which showed neonates distributed more northerly of juveniles. Ontogenetic resource partitioning in shark nurseries is common (Bethea et al. 2004;Froeschke et al. 2010b;Tickler et al. 2017), wherein animals expand their habitat utilization to exploit available resources with increasing size and associated reduced mortality risk (Papastamatiou et al. 2009;Conrath and Musick 2010;Matich and Heithaus 2015). Although the aforementioned abiotic niche variables certainly play a role in structuring the spatial distributions of fishes, an important biotic niche variable not formally considered in this study was prey availability (due to a lack of synoptic sampling for both predators and prey). ...
Characterizing ontogenetic niches of species is fundamental to understanding ecosystem structure and how habitat utilization changes across life-stages. Niche partitioning over temporal and spatial domains is also key to the coexistence of interspecific and intraspecific competitors. This study utilized fisheries-independent bottom longline survey data collected from 2013 to 2020 to develop ecological niche models for neonate and juvenile sandbar sharks (Carcharhinus plumbeus) inhabiting the lower Chesapeake Bay nursery area. Modeled relationships in combination with auxiliary environmental data yielded size-specific habitat suitability estimates that were used to develop projected spatiotemporal distributions and assess ontogenetic niche equivalency. Results showed appreciable differences among the two size-classes in the relationships of relative abundance with measured abiotic variables. High neonate (observed size range 45.5–70.5 cm total length, TL) relative abundance was associated with high bottom temperatures, low bottom dissolved oxygen levels, and intermediate depths and bottom salinities. In contrast, high juvenile (observed size range 71–116 cm TL) relative abundance was linked with intermediate bottom temperatures and bottom dissolved oxygen levels, deeper depths, and lower bottom salinities. Fine-scale coexistence among the two size-classes was low, and annual maps of projected habitat suitabilities showed temporally consistent spatial separation of favorable abiotic niche conditions for neonates and juveniles. Niche equivalency results revealed that overlap among the size-specific niches was low to moderate with statistically significant differences detected annually and seasonally within years. Taken together, these results yield valuable insights on neonate and juvenile sandbar shark ecology by providing a nuanced delineation of stage-specific ecological niches and evidence of niche separation within a large nursery ecosystem.
... They move in response to seasonal changes in water temperature or prey movements (Klimley and Butler 1988;Klimley 1993;Bruce et al. 2005;Heupel et al. 2010;Ketchum et al. 2014a). They also move locally to improve their foraging success or benefit from cleaning by small fishes (Ackerman et al. 2000;Robbins 2007;Papastamatiou et al. 2009;Werry et al. 2012). Finally, they may move into different temperature environments to maintain optimal metabolic rates (Kimball et al. 2004;Whitney et al. 2012a;Ward-Paige et al. 2015). ...
In the southwestern Gulf of California one of the most successful marine protected areas (MPA) worldwide is found: Cabo Pulmo National Park (CPNP). Due to the level of protection and availability of prey, a large population of bull sharks (Carcharhinus leucas) exists in this MPA. Historical records about the abundance and distribution of these sharks in the park are scarce. Here we describe the movement patterns of 32 bull sharks within CPNP using a passive acoustic telemetry array (N = 13) located along the park to examine how the residency of the species change spatially and temporally. Environmental variables were taken in situ (HOBOs) and complemented with satellite information (MODIS aqua). The mean residence index (RI) was 0.365 (SD ± 0.2143). Sharks were resident from December to May, whereas they were absent from August to October. Most bull sharks preferred water temperatures below 28 ºC and depths as shallow as 14 m as well as deeper waters ranging from 70 to 160 m. They thus occupy a wide range of habitats with diverse prey, from shallow to mesophotic reefs. Differences in the residency of males and females occur in response to temperature during the different seasons, resulting in sexual segregation. Our results suggest that females segregate from males probably for reproductive reasons (pupping in another area) or to feed on more energy-rich prey resulting in increased growth rates. This study provides information germane to the protection and management of bull sharks in CPNP.
... Migration increases local genetic diversity and decreases structuring across the range of a species, leading towards migration-drift equilibrium during a range expansion (Mona et al. 2014). Although both C. amblyrhynchos and C. melanopterus generally exhibit site fidelity (Bonnin et al. 2021;Chin et al. 2013;Espinoza et al. 2015aEspinoza et al. , 2015bMourier et al. 2012;Papastamatiou et al. 2009;Speed et al. 2011), C. amblyrhynchos has a larger average dispersal distance (Dwyer et al. 2020), activity space (Speed et al. 2016), and utilizes offshore resources more frequently (McCauley et al. 2012;Papastamatiou et al. 2018). Furthermore, only C. amblyrhynchos has been observed to undertake repeated migrations of several hundred kilometres (Bonnin et al. 2019)-sometimes more than 900 kilometres (White et al. 2017)-across oceanic expanses. ...
Analyses of genetic diversity can shed light on both the origins of biodiversity hotspots, as well as the conservation status of species that are impacted by human activities. With these objectives, we assembled a genomic dataset of 14,935 single nucleotide polymorphisms from 513 grey reef sharks (Carcharhinus amblyrhynchos) sampled across 17 locations in the tropical Indo-Pacific. We analysed geographic variation in genetic diversity, estimated ancient and contemporary effective population size (Ne) across sampling locations (using coalescent and linkage disequilibrium methods) and modelled the history of gene flow between the Coral Triangle and the Coral Sea. Genetic diversity decreased with distance away from the Coral Triangle and north-western Australia, implying that C. amblyrhynchos may have originated in this region. Increases in Ne were detected across almost all sampling locations 40,000–90,000 generations ago (approximately 0.6–1.5 mya, given an estimated generation time of 16.4 years), suggesting a range expansion around this time. More recent, secondary increases in Ne were inferred for the Misool and North Great Barrier Reef sampling locations, but joint modelling did not clarify whether these were due to population growth, migration, or both. Despite the greater genetic diversity and ancient Ne observed at sites around Australia and the Coral Triangle, remote reefs around north-western New Caledonia had the highest contemporary Ne, demonstrating the importance of using multiple population size assessment methods. This study provides insight into both the past and present demographics of C. amblyrhynchos and contributes to our understanding of evolution in marine biodiversity hotspots.
... Predatory fish show preferences for particular habitat types such as forereef ledges (Papastamatiou et al., 2009), outer atolls and shelf areas (Cappo et al., 2007;Skinner et al., 2020) that are associated with abrupt changes in depth. Such habitats are characterised by increased depth that can provide refuge to a wide variety of reef predator populations (Tyler et al., 2009;Stefanoudis et al., 2019). ...
Coral reefs across the world face significant threats from fishing and climate change, which tends to be most acute in shallower waters. This is the case off Pemba Island, Tanzania, yet the effects of these anthropogenic stressors on the distribution and abundance of economically and ecologically important predatory reef fish, including how they vary with depth and habitat type, is poorly understood. Thus, we deployed 79 baited remote underwater video stations (BRUVs) in variable water depths and habitats off Pemba Island, and modeled the effects of depth and habitat on abundance of predatory reef fish. Predatory reef fish types/taxa were significantly predicted by depth and habitat types. Habitats in relatively deeper waters and dominated by hard and soft corals hosted high species richness and abundance of predatory reef fish types/taxa compared to mixed sandy and rubble habitats. The findings add to the growing evidence that deep waters around coral reefs are important habitats for predatory reef fish. Thus, careful management, through effective area and species protection measures, are needed to prevent further depletion of predatory reef-associated populations and conservation of this biologically important area.
... Adult female bull sharks move seasonally into estuarine habitats to pup (give birth), where juveniles may remain for several years before transitioning to higher salinity habitats (Heupel et al., 2010). As the most abundant shark in estuaries of the northwest Gulf of Mexico (nwGoM) (Froeschke et al., 2010;Plumlee et al., 2018), and perhaps across the GoM, bull sharks may play an important role in structuring estuarine food webs via direct or indirect effects (Papastamatiou et al., 2009). Previous studies of bull shark diet have included stable isotope, stomach content, and fecal metabarcoding analyses (Matich and Heithaus, 2014;Tillett et al., 2014;van Zinnicq Bergmann et al., 2021), and highlight the cosmopolitan nature of their diets. ...
A combination of stomach content and stable isotope (δ ¹³ C, δ ¹⁵ N, and δ ³⁴ S) analyses were used to characterize and examine spatiotemporal and ontogenetic trends in the feeding ecology of juvenile bull sharks ( Carcharhinus leucas ) captured in estuaries throughout the northwest Gulf of Mexico (GoM) between 2013 and 2016. Shark diets were dominated by fish prey taxa [>98% index of relative importance (%IRI)], and of those identified to the family level, two families comprised greater than 50% IRI, Mugilidae (mullets: ∼32%) and Sciaenidae (drums and croakers: 27%). Clupeidae (herrings: 14%) and Ariidae (sea catfishes: 15%) also contributed substantially to the diet of juvenile sharks, though consumption of Ariidae increased as consumption of Clupeidae decreased in juvenile sharks larger than 893 mm Fork Length (FL) (∼1 year old). Values of δ ¹⁵ N increased significantly with shark size, indicating a shift toward larger or higher trophic level prey with increasing shark size. Latitudinal and temporal trends in δ ¹³ C and δ ³⁴ S suggest isotopic variation occurred in correspondence with shifts in primary producer assemblages and environmental drivers of sampled estuaries. These results highlight the importance of teleost prey resources along the freshwater-marine continuum in the diet of juvenile bull sharks, as well as the utility of natural tracers in tracking ontogenetic trends in feeding ecology.
... Active acoustic tracking, although arduous and time consuming, provides some of the highest spatial resolution on sharks' movements (Towner et al., 2016) and can also be used to track smallbodied or juvenile sharks ( Morrissey & Gruber, 1993b;George et al., 2019). Active tracking has also been used to investigate activity space and fine-scale movements of various elasmobranchs (Papastamatiou et al., 2009b;McCauley et al., 2014;Towner et al., 2016;George et al., 2019), and can further be used to identify different modes of movements, e.g. area restricted searching (ARS; Fauchald & Tveraa, 2003). ...
In areas of sympatry, closely related and morphologically similar species are expected to occupy different ecological niches in order to avoid competition. However, without knowledge on competitive abilities (e.g. dominance hierarchies) and population characteristics (e.g. growth rates, fitness traits), the origin and the potential effects of niche pattern (segregation and overlap) are unknown. I found compelling evidence that juvenile blacktip reef sharks Carcharhinus melanopterus and juvenile sicklefin lemon sharks Negaprion acutidens from St. Joseph Atoll, Seychelles exhibit fine-scale segregation patterns as a means to avoid competition. In contrast, slight differences in population characteristics were more likely to be caused by prey availability, intraspecific competition, and anthropogenic impacts. This thesis highlights the need for multi-disciplinary investigations to unveil the underlaying mechanisms of coexistence.
... The global decline of sharks has been attributed to a combination of slow reproductive life-history characteristics (Cortés 2000), high levels of fishing pressure (Baum & Myers 2004, Myers et al. 2007, García et al. 2008, and habitat degradation (Knip et al. 2010, Espinoza et al. 2014. As coastal reef ecosystems become increasingly affected by anthropogenic impacts and global warming (Bellwood et al. 2004, De'ath et al. 2012, understanding how reefassociated sharks utilise coastal reef habitats through -out their ontogeny is increasingly important for the effective management of these species and ecosystems, both globally and locally (Papastamatiou et al. 2009, Heupel et al. 2019. Ontogenetic shifts in habitat use occur in many shark species, caused by changes in species-specific diet, foraging behaviour and vulnerability to predation (Dahlgren & Eggleston 2000, Knip et al. 2011, Werry et al. 2011. ...
Understanding how reef-associated sharks utilise coastal reef habitats throughout their ontogeny is essential for their effective management. In this study, we assessed the distribution of sharks in the northern Caribbean Netherlands (Saba, Saba Bank and St Eustatius) and ontogenetic shifts in habitat and depth use of the 2 most observed species: Caribbean reef shark Carcharhinus perezi and nurse shark Ginglymostoma cirratum . We used stereo baited remote underwater video (stereo-BRUV) surveys at 376 sites. A total of 126 shark sightings (6 species) were recorded, with C. perezi (n = 72) and G. cirratum (n = 42) most frequently observed. The probability of recording at least 1 shark per deployment ranged from 0.19 to 0.37 and is comparable with shark occurrences in the small number of other stereo-BRUV studies in the Wider Caribbean Region. Habitat type was the most important factor driving reef-associated shark occurrences, with the highest probability of observing C. perezi and G. cirratum in soft-coral habitat. Additionally, occurrences of C. perezi were significantly influenced by the management zone, with highest probabilities of occurrence in no-fishing zones. Almost all observed reef-associated sharks (95.6%) were juveniles, indicating that the study area may be a nursery area. Overall, both species were observed in deeper waters with increasing size, indicating ontogenetic shifts in depth use. Our findings imply that protected areas should not be limited to a single habitat or depth, but focus on protecting a large area with the range of habitats and depths necessary for reef-associated sharks to complete their life cycle.
... However, the reason for these differences in abundance is unknown. Seasonal differences in abundance seemingly contradict existing data that show blacktip reef sharks, bluespotted maskrays, and bluespotted ribbontail rays are highly reef associated and non-migratory species [58][59][60]. Blacktip reef sharks comprised 89% of sharks observed in this study and have not been observed to be seasonally resident in other regions of the world [61,62]. Males on inshore reefs moved more and further distances during the reproductive season (Nov-Mar in Australia) [61], equivalent to the wet season in Bau Bau, which may explain their higher abundances at that time. ...
Baited remote underwater video stations (BRUVS) are increasingly being used to evaluate and monitor reef communities. Many BRUVS studies compare multiple sites sampled at single time points that may differ from the sampling time of another site. As BRUVS use grows in its application to provide data relevant to sustainable management, marine protected area success, and overall reef health, understanding repeatability of sampling results is vital. We examined the repeatability of BRUVS results for the elasmobranch community both within and between seasons and years, and explored environmental factors affecting abundances at two sites in Indonesia. On 956 BRUVS, 1139 elasmobranchs (69% rays, 31% sharks) were observed. We found consistent results in species composition and abundances within a season and across years. However, elasmobranch abundances were significantly higher in the wet season. The elasmobranch community was significantly different between the two sites sampled, one site being more coastal and easily accessed by fisher-men. Our results demonstrate that while BRUVS are a reliable and repeatable method for surveying elasmobranchs, care must be taken in the timing of sampling between different regions to ensure that any differences observed are due to inherent differences amongst sampling areas as opposed to seasonal dissimilarities.
... Seasonal differences in abundance seemingly contradict existing data that show blacktip reef sharks, bluespotted maskrays, and bluespotted fantail rays are highly reef associated and non-migratory species (Papastamatiou et al. 2009 Bluespotted maskrays comprised 47% of all rays observed and although no data on their movement patterns exist, one study captured individuals after 3 years of liberty within 40 km of where they were tagged, suggesting relatively small home ranges (Pierce and Bennett 2009). There is no distinct breeding season in maskrays and in a captive population, mating occurred soon after parturition (Janse and Schrama 2010). ...
... Most individuals of Blacktip reef shark were found in the shallow sand flats of the transition zone (lagoon). Papastamatiou et al. (2009Papastamatiou et al. ( , 2015 reported that Blacktip Reef Sharks have a relatively small home range (0.55 ± 0.24 km 2 ) and show high site fidelity within lagoon atolls. Grey Reef Sharks were observed in the fore reef habitat (Figure 7). ...
The remote Kanton (Abariringa) Atoll, in the South Pacific Phoenix Islands Protected Area, was assessed using rapid techniques to describe the infrastructure, fish, coral, birds, vegetation, sharks, turtles and marine mammals. Median live coral cover was 28% (8% - 93%) with 11 coral genera, the most abundant being tabular Acropora spp. A total of 130 species of fish (9365 individuals) showed highest abundance in the fore reef habitat. The most abundant bird was the brown noddy (Anous stolidus) with 3600 individuals counted. Nine species of plants were identified, with beach saltbush (Scaevola sericea) being the most abundant. The human subsistence catch was 345 fish and invertebrates with a weight of 103.5kg over a 5-day period. Assessment of the aesthetics of dive sites identified two excellent sites: the shipwreck of President Taylor, and Cascades, with very high abundances of coral and reef fish. The condition of infrastructure on the island, including the Kanton port, airfield and road network were rated as ‘Poor’ for Port (above water), Jetty, Road, Water and Waste Management; followed by ‘Fair’ for Road and Energy and ‘Good’ for Port (below water).
... Additional support for this hypothesis comes from divers participating in this eOceans program who have been photographing and recording individual blacktip reef sharks, which show that some sharks are repeatedly observed at the same sites (e.g., orientalsea.com/ID-oversigt.htm). As well, blacktip reef sharks have been shown to undergo ontogenetic shifts in habitat selection, where adults used ledge habitats and pups used shallow waters, potentially as nursery areas (Papastamatiou et al., 2009). In the current study, four sites had high maximum school sizes (n = 11-45 individuals), all were near to, but not in, sheltered bays. ...
Many marine animals around the world are threatened by a variety of anthropogenic activities, yet there is often a paucity of data to monitor patterns in abundance and distribution or to evaluate human interventions. The new citizen science program eOceans helps to fill this gap by gathering observations of various marine animals from worldwide ocean explorers. In 2012, a dedicated Thailand-wide census of sharks, and other animals, began as collaboration between eOceans scientists and the dive tourism industry. Using the observations from 9,524 dives (9,357 hours underwater) logged by >169 divers on 153 sites, we describe the spatial and temporal patterns of sharks in coastal Thailand. A total of 12 shark species were encountered, most commonly (67%) as individuals, and were observed on 11% of all dives, on 59% of sites, in all months and years. The two most frequently encountered species were blacktip reef ( Carcharhinus melanopterus ) and leopard sharks ( Stegostoma fasciatum ). Many species had peak encounter rates in summer, but aggregated in various seasons in different years. Mating events and nursery sites were observed rarely, and only for blacktip reef and whitetip reef ( Triaenodon obesus ) sharks. These results could be of value to species-or region-specific biologists, ecologists and fisheries scientists, as well as to managers and policy makers that could use the findings to monitor future trends and prioritize conservation strategies. Moreover, this study highlights the value that collaborative eOceans citizen science projects could have in support of marine science, management and conservation efforts worldwide.
... Instead, previous studies have suggested that oscillatory diving provides an effective search strategy for an animal that feeds on prey both at the surface and near the seabed [2,11]. More recently, tiger sharks tagged at Ningaloo Reef have been found to make oscillatory dives during the tortuous movements associated with area-restricted search [15], a search pattern that has been linked with increased foraging success in many marine animals [16][17][18]. Oscillatory dives by tiger sharks, however, also occurred throughout directional swimming, suggesting that factors other than foraging also contribute to these patterns [15]. ...
Tiger sharks, Galeocerdo cuvier , are a keystone, top-order predator that are assumed to engage in cost-efficient movement and foraging patterns. To investigate the extent to which oscillatory diving by tiger sharks conform to these patterns, we used a biologging approach to model their cost of transport. High-resolution biologging tags with tri-axial sensors were deployed on 21 tiger sharks at Ningaloo Reef for durations of 5–48 h. Using overall dynamic body acceleration as a proxy for energy expenditure, we modelled the cost of transport of oscillatory movements of varying geometries in both horizontal and vertical planes for tiger sharks. The cost of horizontal transport was minimized by descending at the smallest possible angle and ascending at an angle of 5–14°, meaning that vertical oscillations conserved energy compared to swimming at a level depth. The reduction of vertical travel costs occurred at steeper angles. The absolute dive angles of tiger sharks increased between inshore and offshore zones, presumably to reduce the cost of transport while continuously hunting for prey in both benthic and surface habitats. Oscillatory movements of tiger sharks conform to strategies of cost-efficient foraging, and shallow inshore habitats appear to be an important habitat for both hunting prey and conserving energy while travelling.
... Thorburn et al. 2015). Some species appear to display residency (Papastamatiou et al. 2009, Andrews et al. 2009 ...
... The observed tidal habitat switching is consistent with other studies showing that blacktip reef sharks move into tidal flats at high tides, and favor shallower edge habitats away from the deepest parts of the lagoon even at lower tides (Stevens, 1984;Papastamatiou et al., 2009b). Previous work on sicklefin lemon sharks at St Joseph also found that occupancy in the deep lagoon was higher at lower tides (Filmalter et al., 2013). ...
Coexistence of ecologically similar species occupying the same geographic location (sympatry) poses questions regarding how their populations persist without leading to competitive exclusion. There is increasing evidence to show that micro-variations in habitat use may promote coexistence through minimizing direct competition for space and resources. We used two sympatric marine predators that show high fidelity to a small, remote coral atoll as a model to investigate how temporally dynamic partitioning of space use may promote coexistence. Using novel methods (difference network analysis and dynamic space occupancy analysis), we revealed that even though blacktip reef sharks Carcharhinus melanopterus and sicklefin lemon sharks Negaprion acutidens both show focused use of the same atoll habitats, the spatio-temporal dynamics of their use was partitioned such that they only shared the same microhabitats 26% of the time. Moreover, the degree of overlap was strongly influenced by the tidal cycle, peaking at ∼35% at higher tides as both species appear to target similar intertidal micro-habitats despite the increase in available space. Our work provides a rare example of how two marine predators with similar ecological roles and habitat preferences may coexist in the same place through dynamic segregation of habitat use in space and time, potentially reflecting adaptive behavioral traits for minimizing interactions. The strong influence of small tidal variation on species habitat use and partitioning also raises concerns over how atoll ecosystem dynamics may be influenced by sea level rises that could alter tidal dynamics.
... Similarly, tropical epaulette sharks (Hemiscyllium ocellatum) exhibit some capacity for using behaviour to avoid high temperatures that are associated with reductions in growth rate if acclimation occurs (Gervais et al., 2018). However, it is important to consider that neonatal C. melanopterus around Moorea have very small home ranges (0.04 km 2 ; I. A. Bouyoucos, unpublished data) relative to other C. melanopterus populations, which could restrict their access to a sufficient diversity of habitats to seek thermal refuge (Chin et al., 2016;Oh et al., 2017;Papastamatiou et al., 2009). Thermal preference could be verified ex situ using conventional methods, such as an annular chamber (Cocherell et al., 2014) or shuttle box (Habary et al., 2017), in future studies. ...
Thermal dependence of growth and metabolism can influence thermal preference and tolerance in marine ectotherms, including threatened and data-deficient species. Here, we quantified the thermal dependence of physiological performance in neonates of a tropical shark species (blacktip reef shark, Carcharhinus melanopterus) from shallow, nearshore habitats. We measured minimum and maximum oxygen uptake rates (ṀO2 ), calculated aerobic scope, excess post-exercise oxygen consumption and recovery from exercise, and measured critical thermal maxima (CTmax), thermal safety margins, hypoxia tolerance, specific growth rates, body condition and food conversion efficiencies at two ecologically relevant acclimation temperatures (28 and 31°C). Owing to high post-exercise mortality, a third acclimation temperature (33°C) was not investigated further. Acclimation temperature did not affect ṀO2 or growth, but CTmax and hypoxia tolerance were greatest at 31°C and positively associated. We also quantified in vitro temperature (25, 30 and 35°C) and pH effects on haemoglobin-oxygen (Hb-O2) affinity of wild-caught, non-acclimated sharks. As expected, Hb-O2 affinity decreased with increasing temperatures, but pH effects observed at 30°C were absent at 25 and 35°C. Finally, we logged body temperatures of free-ranging sharks and determined that C. melanopterus neonates avoided 31°C in situ We conclude that C. melanopterus neonates demonstrate minimal thermal dependence of whole-organism physiological performance across a seasonal temperature range and may use behaviour to avoid unfavourable environmental temperatures. The association between thermal tolerance and hypoxia tolerance suggests a common mechanism warranting further investigation. Future research should explore the consequences of ocean warming, especially in nearshore, tropical species.
... Where IOR is the index of refuge, [OV (A1 + A2)] is the area of overlap between two tracks, and (A1 + A2) total area of both tracks. A value of 0 indicates no overlap in space use, and a 1 indicates 100% overlap of space use (Papastamatiou et al. 2009) ...
Teleost fish that form predictable spawning aggregations and undertake reproductive migrations can be particularly vulnerable to overexploitation. To support community-based management of an artisanal fishery that targets bonefish (Albula glossodonta) spawning aggregations, we used a combination of acoustic telemetry, biological sampling, and remote imagery to reveal the spatiotemporal spawning migrations of bonefish on Anaa Atoll in the Tuamotu Archipelago, French Polynesia. The spawning migrations of bonefish tracked with acoustic telemetry were restricted to the northern section of the atoll, with 99.6% of all detections at offshore spawning habitats occurring on fixed acoustic receivers adjacent to the atoll’s artisanal fish trap complex. Male bonefish undertook spawning migrations more frequently than females and these spawning migrations were common during the Austral winter and fall. The movements of bonefish spawning aggregations coincided with the lunar cycle, as a network analysis revealed an increase in network size and the diversity of habitat use within our acoustic array throughout the duration of the waning moon. Our results highlighted the need for the management of the artisanal trap fishery to prevent the overharvest of bonefish during their peak spawning periods. In response to the spatiotemporal management recommendations derived from this research, the local government established an Educational Managed Marine Area that includes the atoll’s bonefish spawning migratory corridor adjacent to Tukuhora village and a Rahui (i.e., seasonal closure) to improve the sustainability of the fishery.
... Hansell et al. (2018) suggested that the shallow flats around Bimini could be a nursery area for this species, which could explain this difference. It is also possible that our study site, which is bounded by deep water on either side, is used as a foraging area by large tiger sharks feeding in the edge habitat that it creates (Heithaus and Dill, 2006;Papastamatiou et al., 2009). This could correspond to tiger sharks leaving the Gulf Stream to feed in shallow habitats around South Bimini (Hansell et al., 2018). ...
Long-term trends in shark abundance offer important insights for fisheries management. Few fisheries-independent, extended time-series data exist for coastal shark species in the northwest Atlantic Ocean or Caribbean outside of the United States. A decades old dataset comprised of standardized longline surveys provided us with the opportunity to characterize diversity and evaluate changes in the relative abundance of sharks in the eastern Bahamas between 1979–1990 and 2011–2013. Caribbean reef sharks Carcharhinus perezi and tiger sharks Galeocerdo cuvier were the two most commonly captured species throughout the survey and were the only two species analyzed in detail. For both species, sex ratios favored females. Using Bayesian generalized linear models, we found that Caribbean reef shark catch-per-unit-effort (CPUE) exhibited a positive relationship with year and temperature, while size exhibited no relationship with year and a negative relationship with temperature. There was no relationship between tiger shark CPUE and year but there was a positive relationship between size and year. These results are presented in the context of Bahamian shark conservation efforts and the results of other surveys in the region.
... Similarly, tropical epaulette sharks (Hemiscyllium ocellatum) exhibit some capacity for using behaviour to avoid high temperatures that are associated with reductions in growth rate if acclimation occurs . However, it is important to consider that neonatal C. melanopterus around Moorea use very small core habitat (0.02 km 2 ; personal observation) relative to other C. melanopterus neonate populations that could restrict their access to a sufficient diversity of habitats to seek thermal refuge (Papastamatiou et al., 2009b;Chin et al., 2016;Oh et al., 2017b). Furthermore, it is necessary to consider the possible confounding effects of other environmental factors (Schlaff et al., 2014) and predator-prey dynamics (George et al., 2019) on the apparent observation of thermal preference in C. melanopterus neonates. ...
Myriad anthropogenic impacts drive declines in global shark populations; yet, the consequences of a newly recognised threat, global climate change, are poorly understood. This thesis tested the hypothesis that global change stressors (ocean acidification and warming) reduce fitness in tropical reef sharks via effects on physiological performance. My specific objectives were to define thermal performance in fitness-enhancing nursery areas, physiological performance in situ, associations between thermal performance, preference, and tolerance, and physiological performance under multiple global change stressors. I found that neonatal blacktip reef sharks (Carcharhinus melanopterus) have superior growth efficiency in nursery areas relative to other habitats, but ocean acidification and warming synergistically reduce performance. This thesis suggests that global change stressors reduce fitness in tropical reef sharks by acting on physiological traits that are associated with nursery areas.
... Sharks and other bony fish use shallow or brackish water environments because of increased prey abundance or to seek refuge from predators (e.g. Ross 2003;Simpfendorfer et al. 2005;Conrath and Musick 2007;Papastamatiou et al. 2009;Guttridge et al. 2012). There are multiple prey species within Winyah Bay that juvenile C. plumbeus may be preying upon, such as blue crab, Callinectes sapidus (Rathbun, 1896), Atlantic stingray, Hypanus sabina (Lesueur, 1824), hogchoker, Trinectes maculatus (Bloch and Schneider, 1801), Atlantic croaker, Micropogonias undulatus, (Linnaeus, 1766), and spot, Leiostomus xanthurus (Lacepède, 1802;Abel et al. 2007;Ellis and Musick 2007;Arnott et al. 2013;Shiffman et al. 2014). ...
In the past decade along the U.S. East coast, the overfished western North Atlantic stock of Carcharhinus plumbeus has been recovering; however, research investigating C. plumbeus habitats and seasonal habitat shifts is lacking. Accordingly, we studied the seasonal residency, catch abundance, and distribution of juvenile C. plumbeus in Winyah Bay, SC, as well as their migration patterns along the western North Atlantic. We set 303 bottom longlines from May through September in 2016 and 2017 and deployed 11 Vemco (V16-4H) acoustic transmitters in juvenile C. plumbeus. Catch abundance did not differ by month or year (p = 0.45) and was not significantly influenced by any tested water parameter (p = 0.58). C. plumbeus catches were dominated by individuals measuring 81–100 cm precaudal length, and mean size only significantly differed by year (p = 0.02) with slightly larger sharks (86.8 cm PCL) caught in 2017 than 2016 (81.4 cm PCL). Tidal stage and Bay region were positively correlated with catches (p = 0.02). From August 2016 through January 2019, juveniles were detected in Winyah Bay from April to November for 1–302 non-consecutive days (μ ± SE = 108.1 ± 32.6 days), with six juveniles exhibiting interannual return. Detection frequency and presence differed by Bay region, with most detections nearshore and in Lower Bay, fewest in Middle Bay, and none in Upper Bay. This study had two primary findings: monitored sharks utilized a previously unknown southern overwintering migration route, and Winyah Bay serves as a secondary nursery for C. plumbeus.
... Cocos plantations with native forest. Therefore, there have been many studies on community structure and habitat connectivity at Palmyra, including surveying fish diversity, abundance and biomass density on the intertidal sand flats (Friedlander et al., 2007;McCauley et al., 2012;McLaughlin, 2018;Papastamatiou et al., 2009). They sought to determine whether eDNA signals might be an efficient way to describe distinct sand-flat fish communities at Palmyra Atoll. ...
At Palmyra Atoll, the environmental DNA (eDNA) signal on tidal sand flats was associated with fish biomass density and captured 98%–100% of the expected species diversity there. Although eDNA spilled over across habitats, species associated with reef habitat contributed more eDNA to reef sites than to sand‐flat sites, and species associated with sand‐flat habitat contributed more eDNA to sand‐flat sites than to reef sites. Tides did not disrupt the sand‐flat habitat signal. At least 25 samples give a coverage >97.5% at this diverse, tropical, marine system.
... Furthermore, as demonstrated by Papastamatiou et al. [42] and Espinoza et al. [43] for reef sharks, larger individuals often require a broad activity space in order to fulfill their energetic requirements. Stingray activity space in early life stages therefore might also be limited by low energy intake requirements. ...
Stingrays are thought to play important ecological roles in coral reef ecosystems. However, little is known about juvenile stingray movement patterns and habitat use in coral reefs. This study used active acoustic telemetry to determine fine-scale diel movement patterns and habitat use of juvenile cowtail stingrays (Pastinachus ater) in a coral reef flat environment. Seven cowtail stingrays (4 males and 3 females) were manually tracked between April and December 2016. Each individual was tracked over 2 days, generating a total of 14 active tracks ranging from 4.91 to 9 h. Specimens moved at an average speed of 2.44 m min⁻¹ ± 0.87 SE, with minimum distances travelled ranging from 546 to 1446 m. Tracking data showed that juvenile cowtail stingrays move in response to tidal cycles, moving faster and in straighter pathways during incoming and outgoing tides. Juvenile cowtail stingrays also showed a strong affinity to sand flat areas and mangrove edge areas. These areas provide food resources and potential refuges for juvenile rays to avoid predators. Coral reef flats were identified as secondary refuge for juveniles during the lowest tides. Future research is necessary to fully unveil the major drivers of juvenile cowtail stingray seasonal and ontogenetic movement patterns and habitat use within coral reef flat environments. This information is important to establish a full understanding of juvenile cowtail stingray ecology, but could also improve management and conservation policies.
... In addition to this spatial refuge from predation, prey species can alter their behaviours to avoid exhibiting "risky" behaviours when predators are active, creating temporal refugia from predation (Smith et al. 2019). Reef sharks are typically nocturnal hunters with higher rates of movement at night (Papastamatiou et al. 2009), so that the perceived level of predation risk to prey species would be elevated from sunset to sunrise. Our camera systems were not equipped with lights, which may in themselves alter behaviour, so we did not explore the effect of diurnal cycles on the behaviour of mesopredatory reef fishes. ...
Predators can exert strong ecological effects on their prey either via consumption or by altering their behaviour and morphology. In marine systems, predators and their prey co‐occur in a three‐dimensional environment, but to date predator–prey studies have largely focussed on behaviours of prey on horizontal (distance from shelter) rather than vertical (height in water column) axes. We used life‐size shape‐models of a blacktip reef shark Carcharhinus melanopterus (threatening shape‐model), a juvenile coral trout Plectropomus leopardus (non‐threatening shape‐model) and a shape‐control to examine the impact of perceived instantaneous (measured by time to first feeding) versus sustained (measured by time to consume the entire bait) predation threats on the feeding behaviour and three‐dimensional use of space by mesopredatory reef fishes in a coral reef environment. We found that mesopredatory fishes such as red snapper Lutjanus bohar and spangled emperor Lethrinus nebulosus took longer to begin feeding and to consume predation assays (fish baits) at greater distances from the shelter of a patch reef across both horizontal and vertical axes and that this phenomenon was stronger in the vertical axis than the horizontal. The presence of a life‐size shape‐model of a shark, which we used to increase the perception of predator threat, magnified the instantaneous effect compared to non‐threatening models, but not the sustained effect. We found no evidence for a difference in the level of predation risk posed by the shape‐model of the juvenile coral trout (a non‐threatening reef fish) and a negative control (no shape‐model). Our study suggests that mesopredators modify their behaviours in response to the perceived risk of predation across both horizontal and vertical axes away from shelter, and that this response is most severe on the vertical axis, potentially limiting daytime foraging behaviour to a hemisphere around shelter sites.
... In both terrestrial and marine systems, predators show a preference for edge habitats (Phillips et al. 2004;Heithaus et al. 2006), such as forest grassland edges (Svobodová et al. 2011), forereef ledges (Papastamatiou et al. 2009) and outer shelf areas (Cappo et al. 2007). Consequently, reef predators may increase in density and diversity from shallow, lagoonal habitats to outer reef slopes (Friedlander et al. 2010;Dale et al. 2011). ...
Predators on coral reefs play an important ecological role structuring reef fish communities and are important fishery targets. It is thought that reef predator assemblages increase in density and diversity from inner lagoonal to outer edge reefs. Oceanic atolls may differ though, as nutrients are available throughout. Reef predator populations are declining, but there is little known about how their distributions may vary across oceanic atolls. Using a combination of underwater visual census and baited remote underwater video, this study aimed to compare reef predator populations between inner and outer reefs of North Malé Atoll (Maldives) and determine which reef metrics may drive any differences in assemblage structure. We found that predator assemblages were significantly different between inner and outer atoll. Body sizes of several predator families were consistently larger in the outer atoll, however, abundance, biomass and species richness were similar between outer edge reefs and inner lagoonal reefs suggesting atoll lagoons may be undervalued habitats. Depth and complexity were consistently important predictors of the predator assemblage. Inner atoll lagoonal habitat is equally as important for reef predator assemblages as outer reef slopes, although the dominant species differ. This study provides important information on reef predator populations in the Maldives, where detailed assessments of the reef predator assemblage are lacking but the reef fishery is thriving and annual catch will continue to increase.
Trawl surveys within and surrounding two northwestern Australian marine parks revealed banded sand catsharks Atelomycterus fasciatus (family Atelomycteridae) taking refuge within large sponges of the family Irciniidae (Demospongiae: Dictyoceratida) and the genus Agelas (Demospongiae: Agelasida: Agelasidae). Five sponges contained a total of 57 A. fasciatus, comprising both sexes and both immature and mature individuals ranging from 102 to 390 mm total length (TL). In the same surveys, only five A. fasciatus were captured unassociated with sponges, suggesting that sponges are an important microhabitat for A. fasciatus and may provide a daytime refuge from predators. A southerly range extension is also reported for this species.
Coastal elasmobranchs tend to be upper-level predators, which may exert top-down impacts on the systems they inhabit; but there remains much to learn about their trophic ecology. In this chapter, we update our knowledge on the trophic interactions of coastal elasmobranchs as prey, predators, and competitors. We also explore factors that affect these relationships and elasmobranch interactions within key coastal habitats.
Regional patterns of fish diversity, abundance, distribution, and assemblage composition are driven by a combination of biotic and abiotic conditions in the marine environment, but these conditions can be altered through anthropogenic activities, such as those associated with oil and gas extraction. The present study utilises data on fish relative abundance and diversity obtained from 1546 baited remote underwater video deployments conducted between 2004 – 2019 in depths of 9 – 170 m across 2000 km of coastline in north-west Australia on natural habitats and subsea pipelines to understand the influence of oil and gas infrastructure on fish assemblages. A total of 450 fish taxa from 56 families was observed, with populations dominated by generalist and invertebrate carnivore taxa. At the regional scale, subsea pipelines had lower diversity (lower taxonomic richness) than natural environments, but possessed a higher abundance of piscivorous and herbivorous fish taxa. Clear patterns in fish assemblage composition were observed in multivariate analyses, reflecting the proximity of oceanic shoals and banks, depth, and to a lesser extent, oil and gas infrastructure. Shallow-water and close to shoals assemblages were characterised by a diversity of site-attached (e.g., wrasses, tuskfish), reef-associated taxa (e.g., emperors). Mesophotic fish assemblages were characterised by commercially important (e.g., goldband snapper), wide-ranging (e.g., sharks) and sand-affiliated (e.g., toadfish, threadfin bream) taxa. Proximity to pipelines and platforms ranked low as predictors in the multivariate analyses suggesting a negligible regional influence of these structures on fish communities in comparison to depth and shoal habitats. Local-scale influences of subsea infrastructure, however, may be important for some fish species (infrastructure vs. immediate surrounds). Our study highlights the influence of abiotic factors on regional-scale patterns in fish assemblage structure across north-west Australia.
Coral reef ecosystems are exceptionally complex with a myriad of trophic pathways and consumer relationships. The application of stable isotopes (SIs) offers numerous advantages over traditional methods towards understanding these intricate systems. We summarize current knowledge derived from the rapidly increasing SI literature base and identify potential gaps and future directions for the use of SI in coral reef ecosystem studies. Using topic modelling, a form of text mining, on 236 identified published works, we determined that SI research on coral reefs broadly falls into five major topics. 1) Organic matter dynamics: SI analyses (SIA) have quantified substantial variability in autochthonous (internal) and allochthonous (external) fluxes across coral reefs. 2) Holobiont metabolism: Coral nutrient acquisition, translocation and partitioning, and coral responses to various endogenous and exogenous factors, have been explored through SIA. 3) Trophic niches: SIA has indicated that considerable variation in resource use facilitates co-occurrence of high densities of consumers, emphasising that many trophic categorisations on reefs are often too simplistic. 4) Fish diet variation and habitat connectivity: SIA has revealed how ontogenetic, larval, and mobile predator movements link adjacent ecosystems. 5) Environmental drivers (both natural and anthropogenic): SIA can track anthropogenic nutrient inputs, revealing impacts of human-derived pollutants on reef systems. There are a number of important knowledge gaps however. Few studies compare feeding strategies across guilds and the literature is biased towards reef fish and hard corals. Furthermore, few studies examine multiple taxonomic groups in situ or consider multiple environmental drivers. Studies also tend to ignore the underlying, but potentially substantial, spatiotemporal variation in SI baselines as demonstrated from 741 mean SI values extracted from the literature, making inferences based on small variations in SI values problematic. Given that coral reefs face global decline, knowledge gaps need to be addressed while acknowledging the limitations of SIA; careful application of SIs can enhance understanding of processes driving environmental change in these iconic marine ecosystems.
Carcharhinus melanopterus in the southern waters of the Makassar Strait is caught with bottom longlines and bottom gill nets as bycatch, caught throughout the year without any management arrangements. The research objective was to obtain information about the size structure and sex ratio of C. melanopterus in the southern waters of the Makassar Strait. The method used is a survey method. Sample measurements were carried out at TPI Paotere Makassar City and TPI Beba Takalar Regency, South Sulawesi Province from July to September 2020. Measurement of total body length (TL:cm) and determining the sex ratio were carried out directly in the field. The results of the study on 144 sample fish showed that the total length range for C. melanopterus landed at the Paotere TPI was the same as those landed at the Beba TPI at sizes between 58 - 135 cm TL with an average length of 91.18 ± 3.32 cm TL and sizes between 51 - 139 cm TL with an average length of 91.1±2.21 cm TL for both male and female sex, respectively.The comparison of C. melanopterus landed in the two fish landing sites was in a balanced state but the male sex was smaller than the female sex.The sex ratio of male and female C. melanopterus is balanced. Most (69.44%) female C. melanopterus caught were relatively young.
Scientific support for the application of Marine Protected Areas (MPAs) for shark and ray (herein elasmobranchs) conservation varies widely in current literature. Several MPAs around the globe have been created with the purpose of protecting elasmobranch species, however, their suitability and effectiveness are often questionable. Telemetry (electronic tagging) is widely used to better understand shark ecology and behaviour, yet the application of insight gained through these studies for conservation and management, particularly with respect to MPA efficacy, is inconsistent. A systematic literature review was conducted to determine how telemetry has been used to monitor and evaluate MPAs for elasmobranch species. Several aspects of telemetric MPA monitoring were investigated including the study area, duration, species, MPA restrictions and methodology. Results of the review are useful to inform the newly designated Laurentian Channel MPA (LCMPA) and its proposed conservation objectives to protect three species of elasmobranch: Porbeagle shark (Lamna nasus), Black Dogfish (Centroscyllium fabricii) and Smooth Skate (Malacoraja senta). Recommendations for an elasmobranch monitoring plan are discussed to inform management of the LCMPA. Carrying out these recommendations will serve to bridge the current gaps in knowledge of these species’ movements and distribution and aid elasmobranch species conservation in Canada.
It is challenging to assess long‐term trends in mobile, long‐lived and relatively rare species such as sharks. Despite ongoing declines in many coastal shark populations, conventional surveys might be too fleeting and too recent to describe population trends over decades to millennia. Placing recent shark declines into historical context should improve management efforts as well as our understanding of past ecosystem dynamics.
A new palaeoecological approach for surveying shark abundance on coral reefs is to quantify dermal denticle assemblages preserved in sediments. This approach assumes that denticle accumulation rates correlate with shark abundances. Here, we test this assumption by comparing the denticle record in surface sediments to three conventional shark survey methods at Palmyra Atoll, Line Islands, central Pacific Ocean, where shark density is high and spatially heterogeneous.
We generally found a significant positive correlation between denticle accumulation rates and shark abundances derived from underwater visual census, baited remote underwater video and hook and line surveys.
Denticle accumulation rates reflected shark abundances, suggesting that denticle assemblages can preserve a signal of time‐averaged shark abundance in low‐energy coral reef environments. We offer suggestions for applying this tool to measure shark abundance over long time‐scales in other contexts.
Mammalian predator-prey systems are behaviorally sophisticated games of stealth and fear. But, traditional mass-action models of predator prey dynamics treat individuals as behaviorally unresponsive "molecules" in Brownian motion. Foraging theory should provide the conceptual framework to envision the interaction. But, current models of predator feeding behavior generally envision a clever predator consuming large numbers of sessile and behaviorally inert prey (e.g., kangaroo rats, Dipodomys, collecting seeds from food patches). Here, we extend foraging theory to consider a predator-prey game of stealth and fear and then embed this game into the modeling of predator-prey population dynamics. The melding of the prey and predator's optimal behaviors with their population and community-level consequences constitutes the ecology of fear. The ecology of fear identifies the endpoints of a continuum of N-driven (population size) versus mu-driven (fear) systems. In N-driven systems, the major direct dynamical feedback involves predators killing prey, whereas mu-driven systems involve the indirect effects from changes in fear levels and prey catchability. In mu-driven systems, prey respond to predators by becoming more vigilant or by moving away from suspected predators. In this way, a predator (e.g., mountain lion, Puma concolor) depletes a food patch (e.g., local herd of mule deer, Odocoileus hemionus) by frightening prey rather than by actually killing prey. Behavior buffers the system: a reduction in predator numbers should rapidly engender less vigilant and more catchable prey. The ecology of fear explains why big fierce carnivores should be and can be rare. In carnivore systems, ignore the behavioral game at one's peril.
Ultrasonic telemetry was used to determine the movements and distribution of juvenile hammerhead sharks (Sphyrna lewini) on their natal grounds in Kaneohe Bay, Oahu, Hawaii. Transmitters were force fed to six pups which were tracked for periods of up to 12 days. All animals showed a high fidelity to a shared daytime core area to which they repeatedly returned after exhibiting wider ranging nocturnal movements. During daytime, the shark pups formed a loose school which moved about within the core area, hovering about 1.5 m off the bay floor. This daytime refuging behavior may serve an antipredation function. Nighttime movements covered the bay floor and bases of patch and fringing reefs and probably represented foraging excursions. Occasional forays away from the core area also occurred during daytime. The small size of the total activity spaces may indicate a healthy forage base for the sharks. Nocturnal swimming speeds were greater than diurnal swimming speeds.
Manual acoustic telemetry techniques were used to study spatial and temporal patterns of movement of juvenile lemon sharks. Ultrasonic transmitters were implanted into the coelom of 38 sharks, yielding trackings totaling 2281 telemetry fixes. Activity space varied from 0.23 km2 to 1.26 km2 and was positively correlated with shark size. Three indices of site attachment demonstrated that juvenile lemon sharks establish a home range. An index of site defense and field observations indicated that no territoriality was observed against conspecifics.
The impact of fishing on chondrichthyan stocks around the world is currently the focus of considerable international concern. Most chondrichthyan populations are of low productivity relative to teleost fishes, a consequence of their different life-history strategies. This is reflected in the poor record of sustainability of target shark fisheries. Most sharks and some batoids are predators at, or near, the top of marine food webs. The effects of fishing are examined at the single-species level and through trophic interactions. We summarize the status of chondrichthyan fisheries from around the world. Some 50% of the estimated global catch of chondrichthyans is taken as by-catch, does not appear in official fishery statistics, and is almost totally unmanaged. When taken as by-catch, they are often subjected to high fishing mortality directed at teleost target species. Consequently, some skates, sawfish, and deep-water dogfish have been virtually extirpated From large regions. Some chondrichthyans are more resilient to fishing and we examine predictions on the vulnerability of different species based on their life-history and population parameters. At the species level, fishing may alter size structure and population parameters in response to changes in species abundance. We review the evidence for such density-dependent change. Fishing can affect trophic interactions and we examine cases of apparent species replacement and shifts in community composition. Sharks and rays learn to associate trawlers with food and feeding on discards may increase their populations. Using ECOSIM, we make some predictions about the long-term response of ecosystems to fishing on sharks. Three different environments are analysed: a tropical shelf ecosystem in Venezuela, a Hawaiian coral reef ecosystem, and a North Pacific oceanic ecosystem. (C) 2000 International Council for the Exploration of the Sea.
Acoustic telemetry techniques were adapted for use with a kayak to facilitate tracking of species that range into shallow habitats that are inaccessible to even small outboard motor powered vessels. Low cost and portability make the tracking kayak a potentially useful tool for tracking aquatic animals in a wide variety of marine and freshwater environments. In the present study, blue-spined unicornfish (Naso unicornis, Acanthuridae) were successfully tracked for periods of up to 22 days in shallow high-energy fringing reef habitat in a Hawaii marine reserve (Waikiki Marine Life Conservation District-MLCD). To date all unicornfish tracked were highly site attached to well-defined home ranges and showed similar diel patterns of behaviour; refuging within holes in the reef by night and moving to a separate daytime area. Unicornfish home ranges were completely encompassed by the boundaries of the 0.32 km2 MLCD.
Mammalian predation influences waterfowl breeding success in the U.S. northern Great Plains, yet little is known about the influence of the landscape on the ability of predators to find waterfowl nests. We used radiotelemetry to record nightly movements of red foxes (Vulpes vulpes) and striped skunks (Mephitis mephitis) in two 41.4-km2 study areas in North Dakota. Study areas contained either 15-20% grassland (low grassland composition) or 45-55% grassland (high grassland composition). Grasslands included planted cover, pastureland, and hayland. We predicted that the type and composition of cover types in the landscape would influence both predator move- ment across the landscape (as measured by the fractal dimension and displacement ratio) as well as localized movement (as measured by the rate of movement and turning angle between locations) within patches of different cover types. Red fox movements were straighter (lower fractal dimensions and higher displacements) across landscapes with a low grassland composition, indicating directed movement between the more isolated patches of planted cover. Striped skunk movements did not differ between landscape types, illustrating their movement along wetland edges, which had similar compositions in both landscape types. The high variability in turning angles by red fox in planted cover and pastureland in both landscape types is consistent with restricted-area foraging. The high rate of movement by red foxes in planted cover and by striped skunks in wetland edges suggests that spatial memory may influence movement patterns. Understanding the behavior of predators in fragmented prairie landscape is essential for managing breeding habitat for grassland birds and for predicting the spatial and temporal dynamics of predators and their prey.
The California sheephead Semicossyphus pulcher Ayres (Labridae) is a temperate, rocky-reef/kelp-bed fish that is sought by recreational and commercial fishermen. Long-term acoustic monitoring was used to ascertain site fidelity and seasonal movement patterns of S, pulcher. We implanted 16 adult (24 to 36 cm standard length) fish with long-term (similar to 1 yr) acoustic transmitters and their presence and movement patterns were monitored in the Catalina Marine Science Center Marine Life Reserve using an acoustic receiver array. A method was developed that explained some of the variability in detection frequencies. A negative relationship between detection frequency and activity (rate of movement) was found for S. pulcher moving within the array. Most fish exhibited high site fidelity to the general area of the reserve, with 13 of the 16 fish detected spending an average of 99 +/- 2% of their total days at liberty in the study area, with a mean of 90 +/- 9% of total residence time spent within a 600 m core area. However, these fish showed some variability in area use between months, exhibiting periods of expansion in their range. Fish also tended to increase activity as seasonal water temperature increased. These expanded movements resulted in some fish crossing the reserve boundary for extended periods or leaving the reserve permanently.
Movement patterns and habitat use of juvenile lemon sharks Negaprion brevirostris were monitored at Atol das Rocas, Brazil, an atypical nursery area for this species, characterized by extreme tides and a lack of seagrass flats and mangroves. Twenty-three sharks carrying transmitters were monitored using an array of bottom-fixed automated receivers during 3 trips over a total of 60 d. Transmitters were recorded on receivers over 13 000 times, and the majority of sharks were detected more than 100 times. Newborn sharks (60 to 80 cm total length, TL) showed restricted but repeated movements between small tide pools on reef flats at low tide and a small, shallow, nearby tidal creek at high tide. Larger sharks (up to 106 cm TL) sampled 6 and 20 mo after the study in March 2000 frequented the tidal creek and several other locations at high tide and a variety of larger pools at low tide, and in general exhibited more extensive movements within the atoll than did newborn sharks. Sharks approaching 2 yr of age were generally observed in specific pools or shallow water locations within the atoll during high and low tides, but also expanded their movements to include more of the atoll. Throughout the study, young lemon sharks appeared to concentrate movements within shal- low-water low-tide refuges and separate high tidal areas. Movement patterns of sharks in Atol das Rocas differ from those at other well-studied lemon shark nursery locations, where individuals con- tinuously occupy shallow flats and mangrove habitats. Nevertheless, lemon sharks in general restrict their movements to shallow-water habitats regardless of the specific nursery area occupied. This behavior is most likely related to predator avoidance. This study provides an example of the inter- action between the physical environment and the biology of animals—in this case, the influence of the physical characteristics of a nursery area and the behavioral ecology of young lemon sharks.
Mammalian predator-prey systems are behaviorally sophisticated games of stealth and fear. But, traditional mass-action models of predator prey dynamics treat individuals as behaviorally unresponsive "molecules" in Brownian motion. Foraging theory should provide the conceptual framework to envision the interaction. But, current models of predator feeding behavior generally envision a clever predator consuming large numbers of sessile and behaviorally inert prey (e.g., kangaroo rats, Dipodomys, collecting seeds from food patches). Here, we extend foraging theory to consider a predator-prey game of stealth and fear and then embed this game into the modeling of predator-prey population dynamics. The melding of the prey and predator's optimal behaviors with their population and community-level consequences constitutes the ecology of fear. The ecology of fear identifies the endpoints of a continuum of N-driven (population size) versus μ-driven (fear) systems. In N-driven systems, the major direct dynamical feedback involves predators killing prey, whereas μ-driven systems involve the indirect effects from changes in fear levels and prey catchability. In μ-driven systems, prey respond to predators by becoming more vigilant or by moving away from suspected predators. In this way, a predator (e.g., mountain lion, Puma concolor) depletes a food patch (e.g., local herd of mule deer, Odocoileus hemionus) by frightening prey rather than by actually killing prey. Behavior buffers the system: a reduction in predator numbers should rapidly engender less vigilant and more catchable prey. The ecology of fear explains why big fierce carnivores should be and can be rare. In carnivore systems, ignore the behavioral game at one's peril.
ABSTRACT: We describe the abundance, biomass, size composition, and trophic structure of fish assemblages of shallow (10 m depth) fore reef habitats at 2 US Pacific atolls (Kingman, Palmyra) and 2 Kiribati-owned atolls (Tabuaeran, Kiritimati) in the northern Line Islands. Our characterization spans several coincident gradients (in human habitation and exploitation, latitude, and nutrient upwelling) from uninhabited, presently unfished, and oligotrophic Kingman to relatively densely populated, fished, and equatorially upwelled Kiritimati. Major findings are most consistent with direct effects of extraction on large-bodied predators and indirect effects on lower-level assemblage structure. Fish assemblages at Palmyra and especially Kingman atolls were characterized by high total standing biomass, large average body sizes, a preponderance of apex predators and other piscivorous fishes in an inverted biomass pyramid, few and small planktivorous fishes, and herbivores dominated by non-territorial species. M
A non-overlapping acoustic receiver array was used to track the movements of two common shark species, nurse Ginglymostoma cirratum (n=25) and Caribbean reef Carcharhinus perezi (n=5), in and around Glover's Reef Marine Reserve (GRMR), off the coast of Belize, between May and October, 2004. Although both species exhibited partial site fidelity in that they were most likely to be detected near the area of original capture, both species also moved widely throughout the 10 by 30 km atoll. One Caribbean reef shark was detected by a monitor at Lighthouse Reef, 30 km from Glover's Reef across deep (>400m) open water. The mean minimum linear dispersal (MLD) was 10.5 km for Caribbean reef sharks and 7.7 km for nurse sharks, with many individuals traveling more than the 10 km width of the no-take "conservation zone" of the marine reserve. Although most sharks were tagged within the conservation zone, individuals were detected outside this part of GRMR on average 48 days out of the 150 days of observations. However, of 7 nurse sharks tagged near the center of the conservation zone, 4 were never detected outside of this part of the reserve. In general, this study suggests that effective conservation of these large roving predators requires an ecosystem-based management approach including a zoned management plan, similar to that used at GRMR, in which a fairly large no-take reserve, incorporating diverse habitats and the connections between them, is surrounded by a larger area in which fishing is regulated.
Underwater visual and photographic observations, over a four year period, monitored the presence of mating wounds on female blackfin reef shark, Carcharhinus melanopterus. Mating begins in November and continues until the end of March as each female follows her own temporal cycle. Correspondingly, parturition begins in September and continues until January. Each female again mates 1.5–2.5months after parturition, thus completing an annual reproductive cycle. The gestation period is 286–305days, with slight individual differences. All resident sharks under observation followed this pattern. Evidence of reproductive events presented by transient females conformed with the pattern of the residents.
We investigated short-term movements of neonate and juvenile sandbar sharks, Carcharhinus plumbeus, on their nursery grounds in Delaware Bay. The majority of sharks tracked limited their movements to water less than 5m deep, remained within 5km of the coastline, and occupied oblong activity spaces along the coast. In addition to site-attached coastal movements observed, several sharks moved entirely across Delaware Bay or spent considerable time in deeper portions of the central bay. Sharks tracked on the New Jersey side of the bay tended to spend more time in deeper water, farther from shore than sharks tracked on the Delaware side. Observation-area curves estimated that optimal tracking time for sandbar sharks in Delaware Bay was 41h. Indices of site attachment showed that movement patterns of tracked sandbar sharks varied from nomadic to home ranging. There was no significant difference in rate of movement for day/night, crepuscular periods, or between juveniles and neonates. In general, young sandbar sharks patrolled the coast and appeared to be site attached to some extent, but were capable of making longer excursions, including movement entirely across Delaware Bay.
Fractal measurements of animal movement paths have been used to analyze how animals view habitats at different spatial scales. One problem has been the absence of error estimates for fractal d estimators. To address this weakness, I present and test 4 new estimators for measuring fractal dimension at different spatial scales, along with estimates of their variation. The estimators are based on dividing the movement path into pairs of steps, forming V's, and then estimating various statistics from each V.I measured the performance of these estimators by comparing them to the traditional divider d method, using data generated by two different animal movement models. The estimator based on the net distance between the two steps and the cos turning angle was most accurate, giving estimates similar to those of the traditionally-used divider d method. Precision increased with longer and straighter paths.Strengths of this new estimator are that it can estimate fractal d at different spatial scales, give an estimate of variation, and combine data from many separate path segments which have been gathered at various spatial scales.
We surgically implanted ultrasonic transmitters in 38 lemon sharks,Negaprion brevirostris, and manually tracked the sharks for 1–153 days. This yielded 2281 positional fixes recorded at 15-min intervals. We used these positional data with availability data of four environmental variables (water depth, temperature, salinity, and bottom type), sampled at 213 stations along 15 transects, to examine usage of habitat. All sharks used contours of water depth, water temperature, and bottom type disproportionately to the availability of these variables in the study site. Specifically, juvenile lemon sharks selected shallower, warmer water with an underlying rocky or sandy substrate, perhaps for predator avoidance. This is the first report on habitat selection by any elasmobranch.
We examined a population of blacktip sharks, Carcharhinus limbatus, within a coastal nursery area to define how individuals use the nursery habitat throughout the summer. We used a series of acoustic hydrophones to passively monitor the movement patterns of sharks for periods up to 167 days. We used passive monitoring data to calculate home range estimates using minimum convex polygon (MCP) and fixed kernel estimators. MCP calculated the extent of an individual's range. Kernel estimates provided information regarding the utilization of space within the home range including core area (50% kernel) and larger excursions outside the core area (95% kernel). Individuals within the nursery area typically used a consistently small core area. All sharks monitored in the study site underwent a home range expansion during the month of July, suggesting a synchronous population-level change in habitat use. This change in habitat use was reflected in all home range calculations. Passive monitoring revealed that young sharks remain within the nursery area for up to 6 months. The long-term use of this nursery area reflects its critical importance to young blacktip sharks.
The movement patterns and long-term site-fidelity of primarily juvenile Caribbean reef sharks, Carcharhinus perezi, were investigated using tag-recapture and automated telemetry at an insular nursery area, the Fernando de Noronha Archipelago, Brazil. Of the 143 externally tagged juvenile sharks (<110cm), 22 (15.3%) were recaptured between 0 and 5km from the site of tagging after 5–800days at liberty, suggesting some site-fidelity in young individuals of this species. Site-fidelity and movement patterns of ten juvenile sharks ranging from 78 to 110cm total length (TL) and one opportunistically captured adult female (224cm TL) were also investigated for periods of up to 2years with an array of automated telemetry receivers. Tagging and telemetry data from both inside and outside a marine protected area (MPA) show that shark abundance and activity is greatest along the part of the archipelago’s coastline least disturbed by human activity. Telemetry tracking also showed that juvenile reef sharks demonstrated a high degree of site-fidelity and occupied specific locations along the coast throughout the year, with some evidence of an increase in activity space with ontogeny. Sharks appeared to range more widely at night and there were no seasonal variations in habitat use. Our results suggest that MPAs may be a useful conservation tool to protect young C. perezi and potentially other reef-dwelling carcharhinid sharks during their early life history.
Understanding the foraging behavior and spatial distribution of top predators is crucial to gaining a complete understanding of communities. However, studies of top predators are often logistically difficult and it is important to develop appropriate methods for identifying factors influencing their spatial distribution. Sharks are top predators in many marine communities, yet no studies have quantified the habitat use of large predatory sharks or determined the factors that might influence shark spatial distributions. We used acoustic telemetry and animal-borne video cameras ("Crittercam") to test the hypothesis that tiger shark (Galeocerdo cuvier) habitat use is determined by the availability of their prey. We also used Crittercam to conduct the first investigation of foraging behavior of tiger sharks. To test for habitat preferences of sharks, the observed proportion of time in each habitat for each individual was compared to the predicted values for that individual based on correlated random walk and track randomization methods. Although there was individual variation in habitat use, tiger sharks preferred shallow seagrass habitats, where their prey is most abundant. Despite multiple encounters with potential prey, sharks rarely engaged in prolonged high-speed chases, and did not attack prey that were vigilant. We propose that the tiger sharks' foraging tactic is one of stealth, and sharks rely upon close approaches to prey in order to be successful. This study shows that using appropriate analysis techniques and a variety of field methods it is possible to elucidate the factors influencing habitat use and gain insights into the foraging behavior of elusive top predators.
Empirical data quantifying the long-term movement patterns of coral reef top predators are needed in order to design marine
protected areas (MPAs) that will provide these fishes with effective, long-term protection. Acoustic telemetry was used to
quantify the movements of a large coral reef top predator (Aprion virescens, Lutjanidae; Hawaiian name ‘uku’) at five atolls in the Northwestern Hawaiian Islands Marine National Monument (NWHIMNM)
from May 2005 to September 2006. The study atolls were located between 23.8°N, 166.2°W and 28.5°N, 178.3°W, and were separated
from their nearest receiver-equipped neighbor by distances ranging from 100 to 478km. No inter-atoll movements by uku were
detected but individuals were seasonally site-attached to core activity areas of up to 12km in length, and ranged up to 19km
across atolls. Within their core areas, tagged uku exhibited diel and tidal habitat shifts, with the latter resulting in round
trips of up to 24km in 24h. Seasonal uku migrations resulted in extended winter (October–April) absences from summer (May–September)
core activity areas and may be linked to summer spawning. Large MPAs (i.e., entire islands, atolls or banks) would probably
be required for full protection of resident populations of adult uku, but such ‘island-scale’ MPAs will not benefit fisheries
unless there is significant larval supply from MPAs to neighboring fished areas, or adult emigration over time scales exceeding
the 16-month monitoring period of this study. A mixed management strategy of combining smaller MPAs with conventional measures
(e.g., minimum size limits, catch, and effort restrictions) may be the best approach for sustaining uku fisheries. However,
this would still require relatively large MPAs (12km in length) to contain uku short-term (diel and tidal) movements, and
seasonal migrations would still take uku beyond the boundaries of MPAs of this size. These fluxes across MPA boundaries could
supply fish to fisheries but, if high exploitation rates exist, fishing could eliminate key MPA benefits such as increased
numbers of large, highly fecund individuals.
Predation is a central feature of ecological communities. Most theoretical and empirical studies of predation focus on the consequences of predators consuming their prey. Predators reduce prey population densities through direct consumption (a density- mediated interaction, DMI), a process that may indirectly affect the prey's resources, com- petitors, and other predators. However, predators can also affect prey population density by stimulating costly defensive strategies. The costs of these defensive strategies can include reduced energy income, energetic investment in defensive structures, lower mating success, increased vulnerability to other predators, or emigration. Theoretical and empirical studies confirm the existence of these induced costs (trait-mediated interactions, TMIs); however, the relative importance of intimidation (TMI) and consumption (DMI) effects remains an open question. We conducted a meta-analysis assessing the magnitude of both TMIs and DMIs in predator-prey interactions. On average, the impact of intimidation on prey de- mographics was at least as strong as direct consumption (63% and 51% the size of the total predator effect, respectively). This contrast is even more pronounced when we consider the cascading effects of predators on their prey's resources: density effects attenuated through food chains, while TMIs remained strong, rising to 85% of the total predator effect. Predators can thus strongly influence resource density even if they consume few prey items. Finally, intimidation was more important in aquatic than terrestrial ecosystems. Our results suggest that the costs of intimidation, traditionally ignored in predator-prey ecology, may actually be the dominant facet of trophic interactions.
Animals live in an environment that is patchy and hierarchical. I present a method of detecting the scales at which animals perceive their world. The hierarchical nature of habitat causes movement path structure to vary with spatial scale, and the patchy nature of habitat causes movement path structure to vary throughout space. These responses can be measured by a combination of path tortuousity (measured with fractal dimension) versus spatial scale, the variation in tortuousity of small path segments along the movement path, and the correlation between tortuousities of adjacent path segments. These statistics were tested using simulated animal movements. When movement paths contained no spatial heterogeneity, then fractal D and variance continuously increased with scale, and correlation was zero at all scales. When movement paths contained spatial heterogeneity, then fractal D sometimes showed a discontinuity at transitions between domains of scale, variation showed peaks at transitions, and correlations showed a statistically significant positive value at scales smaller than patch size, decreasing to below zero at scales greater than patch size. I illustrated these techniques with movement paths from deer mice and red-backed voles. These new analyses should help understand how animals perceive and react to their landscape structure at various spatial scales, and to answer questions about how habitat structure affects animal movement patterns.
The stability of ecological communities largely depends on the strength of interactions between predators and their prey. Here we show that these interaction strengths are structured nonrandomly in a large Caribbean marine food web. Specifically, the cooccurrence of strong interactions on two consecutive levels of food chains occurs less frequently than expected by chance. Even when they occur, these strongly interacting chains are accompanied by strong omnivory more often than expected by chance. By using a food web model, we show that these interaction strength combinations reduce the likelihood of trophic cascades after the overfishing of top predators. However, fishing selectively removes predators that are overrepresented in strongly interacting chains. Hence, the potential for strong community-wide effects remains a threat.
• community stability
• omnivory
• trophic chain
• trophic cascade
• quantitative networks
Quantifying spatial and temporal patterns of prey searching is of primary importance for understanding animals' critical habitat and foraging specialization. In patchy environments, animals forage by exhibiting movement patterns consisting of area-restricted searching (ARS) at various scales. Here, we present a new method, the fractal landscape method, which describes the peaks and valleys of fractal dimension along the animal path. We describe and test the method on simulated tracks, and quantify the effect of track inaccuracies. We show that the ARS zones correspond to the peaks from this fractal landscape and that the method is near error-free when analyzing high-resolution tracks, such as those obtained using the Global Positioning System (GPS). When we used tracks of lower resolution, such as those obtained with the Argos system, 9.6-16.3% of ARS were not identified, and 1-25% of the ARS were found erroneously. The later type of error can be partially flagged and corrected. In addition, track inaccuracies erroneously increased the measured ARS size by a factor of 1.2 to 2.2. Regardless, the majority of the times and locations were correctly flagged as being in or out of ARS (from 83.8 to 89.5% depending on track quality). The method provides a significant new tool for studies of animals' foraging behavior and habitat selection, because it provides a method to precisely quantify each ARS separately, which is not possible with existing methods.
Effective conservation requires rigorous baselines of pristine conditions to assess the impacts of human activities and to evaluate the efficacy of management. Most coral reefs are moderately to severely degraded by local human activities such as fishing and pollution as well as global change, hence it is difficult to separate local from global effects. To this end, we surveyed coral reefs on uninhabited atolls in the northern Line Islands to provide a baseline of reef community structure, and on increasingly populated atolls to document changes associated with human activities. We found that top predators and reef-building organisms dominated unpopulated Kingman and Palmyra, while small planktivorous fishes and fleshy algae dominated the populated atolls of Tabuaeran and Kiritimati. Sharks and other top predators overwhelmed the fish assemblages on Kingman and Palmyra so that the biomass pyramid was inverted (top-heavy). In contrast, the biomass pyramid at Tabuaeran and Kiritimati exhibited the typical bottom-heavy pattern. Reefs without people exhibited less coral disease and greater coral recruitment relative to more inhabited reefs. Thus, protection from overfishing and pollution appears to increase the resilience of reef ecosystems to the effects of global warming.
The striking health of remote coral reefs provides clear evidence that protection from local overfishing and pollution can help mitigate the impacts of global warming.
This chapter discusses the movement and activity pattern of California fishes. There are a number of good examples that suggest that fishes most closely associated with complex habitats tend to move less than those more loosely associated with habitat; however, there also appears to be a large amount of variability in behavior between species and individuals. Nevertheless, the general differences in movements are likely associated with energetic tradeoffs between finding food and mates, and avoiding predation or unsuitable abiotic conditions. In addition, many of the same tradeoffs have likely influenced the evolution of activity patterns seen in marine fishes. Because of the economic importance of many marine fishes in California, the need to understand fish behavior has increased, particularly for its application in resource and fisheries management.
Ten species of shark belonging to three families were recorded from Aldabra Atoll. Carcharhinus melanopterus and Negaprion acutidens were the most abundant species in the lagoon, while Carcharhinus albimarginatus was the most common shark outside the reef. Twelve hundred sharks of six species were tagged and individual recapture rates varied from 15 to 34%. Some specimens of C. melanopterus were caught up to seven times. All five species for which recapture data were available are restricted in their movements at Aldabra. C. melanopterus in particular is very localized, normally remaining in an area of a few square kilometres. Length increment data obtained from tagging demonstrated a slow growth rate for C. melanopterus, averaging 3.5 cm a-1, with no detectable difference between the growth rates of small and large individuals. Limited data for juvenile Negaprion and C. albimarginatus indicated average growth rates of 12.5 and 8.8 cm a-1 respectively. Population densities calculated for several areas in the lagoon varied from 19 to 198 C. melanopterus per square kilometre. It is suggested that C. melanopterus may be food-limited at Aldabra owing to the intensity of intra- and inter-species competition. C. melanopterus and Negaprion have restricted and almost identical reproductive cycles at Aldabra. C. melanopterus females mature at 110 cm total length and breed every second year giving birth to about four pups after a 10-11 month gestation period. Stomach contents of the more abundant species indicate that fish are the most important item in the diet, except for Nebrius concolor which feeds principally on octopus.
Ecologists need a better understanding of how animals make decisions about moving across landscapes. To this end, we developed computer simulations that contrast the effectiveness of various search strategies at finding habitat patches in idealized landscapes (uniform, random, or clumped patches), where searchers have different energy reserves and face different mortality risks. Nearly straight correlated random walks always produced better dispersal success than relatively uncorrelated random walks. However, increasing patch density decreased the degree of correlation that maximized dispersal success. Only under high mortality and low energy reserves in a uniform landscape did absolutely straight-line search perform better than any random walk. With low mortality risks and high energy reserves, exhaustive systematic search was superior to the best correlated random walk; an increase in the perceptual range of the searcher (i.e., patch detectability) also favored exhaustive search over relatively straight random walks. For all conditions examined, the 'average distance rule,' a hybrid search rule incorporating both straight-line and systematic search, was best. Overall, however, our results suggest that a simple and effective search rule for many landscape-explicit models would involve straight or nearly straight movements.
The use of fractal analysis to study animal movement paths has been criticized because the inherent assumptions of the technique are rarely discussed, and most movement paths violate the assumption of scale invariance. While this violation may prohibit the use of the technique for population-level prediction, it need not restrict the analysis of individual variation in movement patterns, an application of fractal theory that has received relatively little research attention. Therefore, we review fractal analysis and its assumptions, highlighting three ways in which it can yield useful information about individual movement paths regardless of whether or not the assumption of scale invariance has been met. We used these techniques to analyze patterns of individual variation and potential causes of variation in the dispersal searching paths of two species of Australian treecreeper (Passeriformes: Climacteridae). By comparing relative fractal D, or the relative tortuosity and thus thoroughness of search paths, we found that individuals faced a trade-off between thoroughness and the extent of searching. Thoroughness also differed between the sexes and the species, possibly as a direct consequence of mating and social systems. For almost all individuals, thoroughness varied depending on the spatial scale at which it was examined, revealing three distinct domains of scale in which movement tactics vary because movement is used for very different purposes. Variability in movement tactics was greatest in the largest spatial-scale domain, the one used exclusively for dispersal movements, suggesting that dispersal tactics show more intraspecific variation than other types of movement because dispersal decisions are influenced by a greater variety of factors. Our results reveal that fractal analysis can provide useful information on the causes of and constraints on individual movement strategies, creating empirically based models of animal movement and thus a firm foundation for modeling movement processes from individual to landscape scales.
Over a 4-year period, free-ranging sharks were studied by ultrasonic telemetry and direct underwater observation. Twenty-six intermittent multi-day trackings were conducted, of from 2-6 (x = 3.5) days of contact, and with overall durations of 2-23 days. Three transmitter attachment methods were used and evaluated: 1) dorsal-fin mount, 2) body-cavity insertion and 3) self-ingestion in bait. Observed activity spaces of the telemetered sharks ranged in area from 0.19 km2 to 53 km2 (x = 4.2 km) and in length from 300 m to 16 km (x = 3.6 km). Movement patterns suggested that: 1) sharks tagged near the ocean reefs were generally nomadic, moving relatively long distances along the reefs and 2) sharks tagged on lagoon reefs or pinnacles had a more home-ranging pattern with different day and night areas, often returning day-after-day to the tagging site. The overall daytime mean rate of movement was 1.7 km/h, while the nighttime rate was significantly higher at 3.3 km/h. Observed daytime grouping patterns were of the following three intergrading types: 1) polarized schools-seen close to bottom over level areas, 2) loose aggregations-usually near ocean-reef dropoffs and 3) lone individuals-usually over shallower reefs and lagoon pinnacles.
The concept of elasmobranch species using nursery areas was introduced in the early 1900s and has been an accepted aspect of shark biology and behavior for several decades. Despite several descriptions of how shark species use nursery areas and what types of regions nurseries may be found in, no explicit definition of what constitutes a shark nursery area has been presented. Here we evaluate the assumptions of the current shark nursery paradigm in light of available data. Based on examination of these assumptions and available methods of quantifying and accurately describing shark nursery areas, a new more quantitative definition of shark nursery areas is proposed. This definition requires 3 criteria to be met for an area to be identified as a nursery: (1) sharks are more commonly encountered in the area than other areas; (2) sharks have a tendency to remain or return for extended periods; and (3) the area or habitat is repeatedly used across years. These criteria make the definition of shark nursery areas more compatible with those for other aquatic species. The improved definition of this concept will provide more valuable information for fisheries managers and shark biologists.
Sharks are marine consumers believed to occupy top positions in marine food webs. But surprisingly, trophic level estimates for these predators are almost non-existent. With the hope of helping better define the ecological role of sharks in marine communities, this paper presents standardized diet compositions and trophic levels calculated for a suite of species. Dietary composition for each species was derived from published quantitative studies using a weighted average index that takes into account sample size in each study. The trophic level (TL) values of the 11 food types used to characterize the diet (obtained from published accounts) were then used to calculate fractional trophic levels for 149 species representing eight orders and 23 families. Sharks as a group are tertiary consumers (TL>4), and significant differences were found among the six orders compared, which were attributable to differences between orectolobiforms (TL<4) and all other orders, and between hexanchiforms and both carcharhiniforms and squatiniforms. Among four families of carcharhiniform sharks, carcharhinids (TL=4.1, n=39) had a significantly higher TL than triakids (TL=3.8, n=19) and scyliorhinids (TL=3.9, n=21), but not sphyrnids (TL=3.9, n=6). When compared to trophic levels for other top predators of marine communities obtained from the literature, mean TL for sharks was significantly higher than for seabirds (n=28), but not for marine mammals (n=97). Trophic level and body size were positively correlated (r s =0.33), with the fit increasing (r s =0.41) when the three predominantly zooplanktivorous sharks were omitted, and especially when considering only carcharhinid sharks (r s =0.55).
In many fish and reptiles, gastric digestion is responsible for the complete breakdown of prey items into semi-liquid chyme. The responses of the stomach to feeding and to periods of fasting are, however, unknown for many lower vertebrates. We inserted data loggers into the stomachs of free-swimming captive adult blacktip reef sharks (Carcharhinus melanopterus) to quantify gastric pH, motility and temperature during fasting and following ingestion of food. Gastric acid secretion was continuous, even during long periods of fasting, with a mean pH of 1.66 ± 0.40 (±1 SD) when the stomach was empty. Stomach contractions were greater following meals of mackerel than for those of squid. Gastric motility following feeding on mackerel, was positively influenced by ambient temperature, and followed a quadratic relationship with meal size, with maximum motility occurring after meals of 0.8–1.0% body weight. Diel changes in gastric motility were apparent, and were most likely caused by diel changes in ambient temperature. Gastric digestion in blacktip reef sharks is affected by both biotic and abiotic variables. We hypothesize that behavioral strategies adopted by sharks in the field may be an attempt to optimize digestion by selecting for appropriate environmental conditions.
In this paper kernel methods for the nonparametric estimation of the utilization distribution from a random sample of locational observations made on an animal in its home range are described. They are of flexible form, thus can be used where simple parametric models are found to be inappropriate or difficult to specify. Two examples are given to illustrate the fixed and adaptive kernel approaches in data analysis and to compare the methods. Various choices for the smoothing parameter used in kernel methods are discussed. Since kernel methods give alternative approaches to the Anderson (1982) Fourier transform methods, some comparisons are made.
This report concerns a study of the feeding behavior in three species of sharks: Carcharhinus menisorrah Muller and Henle, the grey shark (Fig. 1), Carcharhinus melanopterus Quoy and Gaimard, the blacktip shark (Fig. 2), both of the family Carcharhinidae; and Triaenodon obesus Ruppell, the whitetip shark (Fig. 3), of the family Triakidae. The study was conducted in the lagoon at Eniwetok Atoll, Marshall Islands, during the summers of 1959 and 1960. It was a segment of a broad program of investigation of shark behavior in which laboratory and field work were coordinated whenever possible. The overall program, conducted at both the Eniwetok Marine Biological Laboratory and the Hawaii Marine Laboratory, Coconut Island, Hawaii, was under the direction of Dr. Albert 1. Tester, with financial support from the Office of Naval Research (Contract Nom 2756(00), Project NR 104503).
Quantifying animal movement in response to a spatially and temporally heterogeneous environment is critical to understanding the structural and functional landscape influences on population viability. Generalities of landscape structure can easily be extended to the marine environment, as marine predators inhabit a patchy, dynamic system, which influences animal choice and behavior. An innovative use of the fractal measure of complexity, indexing the linearity of movement paths over replicate temporal scales, was applied to satellite tracking data collected from narwhals (Monodon monoceros) (n = 20) in West Greenland and the eastern Canadian high Arctic. Daily movements of individuals were obtained using polar orbiting satellites via the ARGOS data location and collection system. Geographic positions were filtered to obtain a daily good quality position for each whale. The length of total pathway was measured over seven different temporal length scales (step lengths), ranging from one day to one week, and a seasonal mean was calculated. Fractal dimension (D) was significantly different between seasons, highest during summer (D = 1.61, SE 0.04) and winter (D = 1.69, SE 0.06) when whales made convoluted movements in focal areas. Fractal dimension was lowest during fall (D = 1.34, SE 0.03) when whales were migrating south ahead of the forming sea ice. There were no significant effects of size category or sex on fractal dimension by season. The greater linearity of movement during the migration period suggests individuals do not intensively forage on patchy resources until they arrive at summer or winter sites. The highly convoluted movements observed during summer and winter suggest foraging or searching efforts in localized areas. Significant differences between the fractal dimensions on two separate wintering grounds in Baffin Bay suggest differential movement patterns in response to the dynamics of sea ice.
Tiger sharks Galeocerdo cuvier are important predators in a variety of nearshore communities, including the seagrass ecosystem of Shark Bay, Western Australia. Because tiger sharks are known to influence spatial distributions of multiple prey species, it is important to understand how they use habitats at a variety of spatial scales. We used a combination of catch rates and acoustic tracking to determine tiger shark microhabitat use in Shark Bay.
Comparing habitat‐use data from tracking against the null hypothesis of no habitat preference is hindered in Shark Bay, as elsewhere, by the difficulty of defining expected habitat use given random movement. We used randomization procedures to generate expected habitat use in the absence of habitat preference and expected habitat use differences among groups (e.g. males and females). We tested the performance of these protocols using simulated data sets with known habitat preferences.
The technique correctly classified sets of simulated tracks as displaying a preference or not and was a conservative test for differences in habitat preferences between subgroups of tracks (e.g. males vs. females).
Sharks preferred shallow habitats over deep ones, and preferred shallow edge microhabitats over shallow interior ones. The use of shallow edges likely increases encounter rates with potential prey and may have profound consequences for the dynamics of Shark Bay's seagrass ecosystem through indirect effects transmitted by grazers that are common prey of tiger sharks.
Females showed a greater tendency to use shallow edge microhabitats than did males; this pattern was not detected by traditional analysis techniques.
The randomization procedures presented here are applicable to many field studies that use tracking by allowing researchers both to determine overall habitat preferences and to identify differences in habitat use between groups within their sample.
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