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Executive Summary
Introduction
Although Indo-Pacific bottlenose dolphins (Tursiops aduncus) are a valued component of the Swan-Canning Estuary and the Swan Canning Riverpark, little is known about the health and ecology of the small community of dolphins inhabiting the estuary.
To improve the scientific basis for management, we examined the popula...
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... samples were collected using the PAXARMS biopsy system, a modified 0.22 caliber rifle with a detachable barrel, a valve to adjust firing pressure in the chamber and a biopsy dart (Figures 1 and 2; Krützen et al., 2002). The PAXARMS biopsy system is regarded as a safe and cost-effective method, commonly used for obtaining skin and blubber samples from live dolphins ( Krützen et al., 2002). ...
Citations
... While increased toxins and heavy metals have been associated with nervous, endocrine, neoplastic, and immune disorders in marine wildlife including sea turtles, the pathogenesis of toxicities including the cumulative and synergistic effects of such contaminants are not well understood (Kannan et al. 2000, Holyoake et al. 2011, Poppenga 2017, Barraza et al. 2021). Although sea turtles can withstand significant physical injuries they are particularly intolerant to chemical agents and biotoxins (i.e., cyanobacteria and microalgal toxins) . ...
The current state of sea turtle health in the Indian Ocean is largely unknown, especially for the endemic flatback turtle (Natator depressus) which is listed as ‘vulnerable’ in Western Australia (WA) and ‘data deficient’ globally. Anecdotally, the causes of illness, injury, and death in Western Australian turtles are comparable to those in other parts of Australia and the world (e.g., spirorchiidiasis, fibropapillomatosis, and marine debris interaction) but scientific studies to validate these reports are particularly limited in this region. To address these knowledge gaps, causes of both live and dead turtle strandings in WA were investigated through an array of veterinary diagnostic techniques including necropsy, clinical pathology, diagnostic imaging, histopathology, parasitology, microbiology, toxicology, and molecular analyses. Health assessments were conducted on live animals to determine baseline levels of health and disease for specific populations, predominately nesting and foraging flatback turtles.
Through these health and disease investigations, baselines were developed, along with the discovery of new diseases in flatback turtles including a novel haemoparasite, Haemocystidium spp., occurring specifically in the foraging life stage; a potentially emerging zoonotic bacterium, Streptococcus iniae associated with a multi-species mass mortality event involving post-hatchlings; as well as spirorchiidiasis, previously unreported in this species. Other unusual and emerging diseases were also reported in sea turtles in this study, including microsporidial myopathy, salt gland adenitis, gout, and pseudogout.
In this study, natural disease-related causes of mortality occurred more frequently than direct anthropogenic causes, with parasitoses the most frequently occurring natural disease. Spirorchiidiaisis was the most common cause of mortality (32.0%) with a prevalence of 93.2% in turtles susceptible to the disease (i.e., excluding the post-hatchling life stage). The next most common cause of mortality was unknown (17.3%), followed by trauma (13.3%), endoparasitosis (10.7%), infectious disease (6.7%), and pneumonia (6.7%), with the remaining mortality categories each accounting for less than 5% of cases (including systemic inflammation, osmoregulatory disorder, gastrointestinal impaction, gastrointestinal foreign body, fibropapillomatosis, and metabolic disorder).
We developed the first flatback turtle reference intervals (RIs) in Reference Value Advisor (RefVal v2.1) following the American Society of Veterinary Clinical Pathology (ASVCP) guidelines. We found flatback turtle RIs were generally similar to other published sea turtle RIs and reference values (RVs) but detected significant differences in our study for the various boundary conditions including life stage (nesting or foraging), as well for measurement methodology (field or laboratory tests), justifying the establishment of separate RIs/RVs for nesting and foraging flatbacks, and for field and laboratory techniques.
This study was the first sea turtle health and disease investigation in WA and the eastern Indian Ocean to offer broader insights into sea turtle health and disease status on a regional scale. These essential baselines provided a number of crucial functions which include serving as a reference point for future studies to monitor changes in population health and disease levels. Specifically, these baseline data will be useful for future comparative studies of the same population where changes are an indication of a changing environment. The blood RIs can be used for disease diagnosis, monitoring progress and assessing prognosis of clinical flatback turtle cases in rehabilitation. Considering that diseases in the marine environment are predicted to rise with increasing anthropogenic pressures, detection of new and emerging diseases is of significance to the global knowledge of sea turtle diseases; and for understanding and mitigating disease threats to sea turtle populations. Finally, this study provided a framework to integrate health into future conservation management decisions to ensure the long-term survival of sea turtles.
... McCluskey et al., 2021). This is consistent with findings from other studies as, generally, individuals showing high site fidelity to estuaries or near coastal areas have higher δ 13 C values than the gradually lower values observed the further from coast the individual's activity space is located (Barros et al., 2010;Gibbs, Harcourt & Kemper, 2011;Holyoake et al., 2011;McCluskey et al., 2021). Although the relative δ 13 C values suggest members of the estuarine community rely on estuarine primary production and are part of the estuarine food web, the high variability in δ 15 N values suggests considerable intra-community partitioning in diet. ...
... Similar to some studies (Barros et al., 2010;Gibbs, Harcourt & Kemper, 2011) and in contrast to others (Holyoake et al., 2011;McCluskey et al., 2021), this study found that dolphins with high site fidelity to estuaries feed at a lower trophic position than their coastal counterparts. Differences in δ 15 N values may reflect variability in trophic level occupied by dolphins in different ecosystems but may also reflect variation in nitrogen isotope signatures of basal resources (Fry, 2006;Phillips, 2012;Lorrain et al., 2015). ...
• Investigations of population structure across multiple niche dimensions can identify discrete management units within populations. This study examined social, spatial and isotopic niche partitioning in Indo-Pacific bottlenose dolphins (Tursiops aduncus) across ca. 600 km² of coastal and estuarine waters in south-western Australia, to evaluate whether estuarine dolphins should be treated as a discrete management unit.
• Photo-identification data and tissue samples were collected in 2016 and 2017 in a study area covering the Peel-Harvey Estuary (PHE) and adjacent coastal waters. A total of 1,038 dolphin groups were encountered, and 481 individuals were identified. Tissue samples for stable isotope (δ¹³C and δ¹⁵N) analyses were collected from 96 individuals. Social structure and complexity analyses were conducted, full and core activity spaces were identified, and their size estimated for identified social communities. Differences in stable isotope composition among individuals and communities were examined.
• A socially, spatially and isotopically distinct dolphin community occurred in the PHE. The coastal waters contained four socially and spatially, but not isotopically, distinct communities as well as a substantial number of dolphins (n = 185) that were sighted infrequently and therefore were not assigned to any community. Individuals formed three levels of relationships; the majority (78%) were weak association relationships (mean half-weight index 0.006). The estuarine community had significantly higher mean δ¹³C and significantly lower mean δ¹⁵N values than any of the coastal communities.
• There is a strong scientific basis for treating the PHE dolphin community as a discrete management unit. The estuarine and coastal communities occupied different social environments, with coastal individuals sharing space with more transient individuals. This study shows the value of integrating information from multiple niche dimensions when identifying management units, and the need to consider all encountered individuals in management planning.
... Growing evidence indicates the importance of major estuarine systems in Australia for localised resident populations of Indo-Pacific bottlenose dolphins (Chabanne et al. 2012a;Fury and Harrison 2008;Passadore et al. 2018;Wiszniewski et al. 2010;Zanardo et al. 2016). In recent years, concerns have increased in relation to the impacts of threats including coastal development, habitat degradation, pollutants, poor habitat quality, fishing interactions and vessel traffic, on dolphin populations inhabiting estuarine areas in Australia (Bossley et al. 2016;Bossley and Woolfall 2008;Chabanne et al. 2012a;Chabanne et al. 2017;Holyoake et al. 2010;Holyoake et al. 2011). These cumulative pressures increase the vulnerability of dolphins to the risk of displacement, injury, entanglement, disease and mortality (Chabanne et al. 2012b;Fury and Reif 2012;Holyoake et al. 2011;Marley et al. 2017;Paiva et al. 2015;Stephens et al. 2014). ...
... In recent years, concerns have increased in relation to the impacts of threats including coastal development, habitat degradation, pollutants, poor habitat quality, fishing interactions and vessel traffic, on dolphin populations inhabiting estuarine areas in Australia (Bossley et al. 2016;Bossley and Woolfall 2008;Chabanne et al. 2012a;Chabanne et al. 2017;Holyoake et al. 2010;Holyoake et al. 2011). These cumulative pressures increase the vulnerability of dolphins to the risk of displacement, injury, entanglement, disease and mortality (Chabanne et al. 2012b;Fury and Reif 2012;Holyoake et al. 2011;Marley et al. 2017;Paiva et al. 2015;Stephens et al. 2014). Despite these concerns, there remains very little knowledge of the status of regional dolphin populations and the relationships between estuarine health and dolphin health (on an individual, community and population level). ...
... The Fremantle Inner Harbour, located in south-western Australia, is a year-round hotspot for about 45 individuals from two resident communities of Indo-Pacific bottlenose dolphins (T. aduncus) [10][11][12][13]: one occurring mainly in Cockburn Sound just west of Fremantle and in the open water, and the other in the Swan-Canning River estuary. The Fremantle Inner Harbour is located at the entrance of the Swan-Canning River estuary and connects Cockburn Sound to the estuary, thus bordering the core home range areas of the two communities. ...
Bottlenose dolphins use whistles to communicate with their conspecifics and maintain group cohesion. We recorded 477 whistles of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the Fremantle Inner Harbour, Western Australia, on nine occasions over a six-week period during May/June 2013. Over half (57 %) of the whistles had complex contours exhibiting at least one local extremum, while 32 % were straight upsweeps, 5 % downsweeps and 6 % constant-frequency. About 60 % of whistles occurred in trains. Fundamental frequency ranged from 1.1 to 18.4 kHz and whistle duration from 0.05 to 1.15 s. The maximum numbers of local extrema and inflection points were 7 and 9, respectively. Whistle parameters compared well to those of measurements made from other T. aduncus populations around Australia. Observed differences might be due to ambient noise rather than geographic separation.
... The most easterly area of the Fremantle Inner Harbour is also the mouth of the Swan River system which is inhabited by several species of fish which a resident community of Indo-Pacific bottlenose dophins prey upon [27]. Dolphins have been documented to swim upstream and downstream of the channel on a regular basis [28,29]. ...
Research involving marine mammals often requires costly field programs. This paper assessed whether the benefits of using cameras outweighs the implications of having personnel performing marine mammal detection in the field. The efficacy of video and still cameras to detect Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the Fremantle Harbour (Western Australia) was evaluated, with consideration on how environmental conditions affect detectability. The cameras were set on a tower in the Fremantle Port channel and videos were perused at 1.75 times the normal speed. Images from the cameras were used to estimate position of dolphins at the water's surface. Dolphin detections ranged from 5.6 m to 463.3 m for the video camera, and from 10.8 m to 347.8 m for the still camera. Detection range showed to be satisfactory when compared to distances at which dolphins would be detected by field observers. The relative effect of environmental conditions on detectability was considered by fitting a Generalised Estimation Equations (GEEs) model with Beaufort, level of glare and their interactions as predictors and a temporal auto-correlation structure. The best fit model indicated level of glare had an effect, with more intense periods of glare corresponding to lower occurrences of observed dolphins. However this effect was not large (-0.264) and the parameter estimate was associated with a large standard error (0.113). The limited field of view was the main restraint in that cameras can be only applied to detections of animals observed rather than counts of individuals. However, the use of cameras was effective for long term monitoring of occurrence of dolphins, outweighing the costs and reducing the health and safety risks to field personal. This study showed that cameras could be effectively implemented onshore for research such as studying changes in habitat use in response to development and construction activities.
... Though both T. aduncus and T. truncatus haplotypes have been documented in the Perth region, the inshore form is considered to be T. aduncus (Holyoake et al. 2011). Cheal and Gales (1992) reported that, for captive bottlenose dolphins that were captured in the Perth area, females reached sexual maturity at 11-13 years of age and at lengths between 227 and 238 cm, while males reached sexual maturity at lengths between 222 and 233 cm. ...
... It is unclear, based on current information, whether the resident community in the Riverpark represents a discrete demographic unit (i.e. a population with little or no demographic connectivity with populations in adjacent coastal areas) (Holyoake et al. 2011). This study does, however, present some insights as to the demographic processes likely to be affecting the community. ...
... The two best-fitting demographic models for LIR identified emigration, immigration, and mortality as potentially relevant processes. This, along with observations indicating resident dolphins also range within coastal areas, suggests some connectivity between the estuarine community and coastal areas and coastal populations (or communities) which may support gene flow (Karczmarski et al. 2005;Möller et al. 2007;Holyoake et al. 2011) and allow for expanded social networks (Lusseau and Newman 2004). ...
... Though both T. aduncus and T. truncatus haplotypes have been documented in the Perth region, the inshore form is considered to be T. aduncus (Holyoake et al. 2011). Cheal and Gales (1992) reported that, for captive bottlenose dolphins that were captured in the Perth area, females reached sexual maturity at 11-13 years of age and at lengths between 227 and 238 cm, while males reached sexual maturity at lengths between 222 and 233 cm. ...
... It is unclear, based on current information, whether the resident community in the Riverpark represents a discrete demographic unit (i.e. a population with little or no demographic connectivity with populations in adjacent coastal areas) (Holyoake et al. 2011). This study does, however, present some insights as to the demographic processes likely to be affecting the community. ...
... The two best-fitting demographic models for LIR identified emigration, immigration, and mortality as potentially relevant processes. This, along with observations indicating resident dolphins also range within coastal areas, suggests some connectivity between the estuarine community and coastal areas and coastal populations (or communities) which may support gene flow (Karczmarski et al. 2005;Möller et al. 2007;Holyoake et al. 2011) and allow for expanded social networks (Lusseau and Newman 2004). ...
