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Marine Ecology and Fisheries
... Although fish spawning and larval recruitment in the marine environment have been shown to be closely related to water temperature, photoperiod and seasonal plankton production (e.g. Royce 1972;Cushing 1975;Bye 1984;Sherman et al. 1984; Allen and Barker 1990), only a few studies have investigated ecological relationships between estuarine-spawned larval fishes and both hydrodynamics and plankton cycles in estuaries. These few studies have found that peak spawning for some species is in synchrony with seasonal increases in abundance of their dominant copepod prey (Sherman et al. 1984;Townsend 1984), with maximum catch rates of dominant larval fishes closely coupled to zooplankton dynamics. ...
... These few studies have found that peak spawning for some species is in synchrony with seasonal increases in abundance of their dominant copepod prey (Sherman et al. 1984;Townsend 1984), with maximum catch rates of dominant larval fishes closely coupled to zooplankton dynamics. For example, the 'match-mismatch' hypothesis of Cushing (1975Cushing ( , 1990 proposes that the spawning of marine fish should be timed such that the appearance of larvae overlaps with seasonal plankton blooms. Conversely, other species have developed a ubiquitous spawning strategy, producing larvae over a protracted period, thus allowing these populations to increase rapidly in response to favourable conditions and prey that are temporally restricted (Sherman et al. 1984). ...
... In addition, interspecific competition for food would be reduced for black bream larvae during late spring, because the peak in gobylgudgeon spawning occurred after this time. Therefore, the black bream does appear to conform to the strategy of the 'match-mismatch' hypothesis of Cushing (1975Cushing ( , 1990; see also Bollens et al. 1992). ...
The ichthyoplankton assemblage of the Hopkins River estuary, Victoria, was dominated by estuarine taxa that included demersal (goby, gudgeon) and pelagic (black bream, estuary perch, anchovy) species. The two seasonal peaks in fish larvae abundance were related to (1) the springlsummer zooplankton increase that occurred after flooding of the estuary and was comprised predominantly of copepod nauplii, thereby providing a good prey field for very young fish larvae, and (2) the autumn zooplankton maxima, which would provide a wide selection of copepod stages and meroplankton and promote dietary partitioning and flexibility among older larval stages. The two peaks in fish larvae abundance occurred well before and well after the attainment of maximum water temperature in the estuary. Goby, gudgeon, estuary perch and anchovy larvae were in the plankton over an extended period coinciding with the more stable conditions of salt-wedge presence and maximum zooplankton densities. The spawning of black bream and anchovies in the estuary was clearly related to physical conditions, such as salinity and water temperature, and habitat-although spawning of both species also occurred at times of high concentrations of potential prey organisms for their larvae. Adults of all the above fish species appear to have evolved spawning strategies that are adapted to the average hydrological and biological conditions in the estuary that would lead to the enhanced survival of their larvae. With the exception of the black bream, it appears that a ubiquitous and prolonged rather than a synchronous and confined spawning strategy is more widely used by estuarine-spawning fishes in the Hopkins River estuary. This type of spawning strategy, combined with the generally high density of food available to fish larvae in estuaries, suggests that the match-mismatch hypothesis of Cushing may be less relevant in the estuarine than in the marine environment.
... The 'match-mismatch hypothesis' (Cushing, 1974(Cushing, , 1975 predicts that changes in synchrony will impact species' fitness, but findings to date have been inconsistent across studies (Dunn et al., 2011;Renner & Zohner, 2018;Samplonius et al., 2021;Zhemchuzhnikov et al., 2021). Some studies have linked disruptions in synchrony to decreases in consumer fitness ('phenological mismatch') for some interacting species (Doiron et al., 2015;Plard et al., 2014;Post & Forchhammer, 2007); while others have found no link (Burthe et al., 2012;Vatka et al., 2011). ...
... For shifts in synchrony to lead to changes in consumer fitness, there must be a relationship between consumer fitness and the timing of the interaction with the resource (i.e. the match-mismatch hypothesis; Cushing, 1974Cushing, , 1975. This hypothesis predicts that consumers should temporally 'match' the peak of their most energetically demanding period with the peak of resource availability ( Figure 1). ...
... First, the consumer and resource must present a certain degree of seasonality relative to each other, otherwise there is effectively no timing to match (or disrupt). Second, the resource must be the major controller of consumer fitness (Cushing, 1974(Cushing, , 1975(Cushing, , 1990, meaning that the consumer must be bottom-up controlled (Shurin et al., 2005;Borer et al., 2006;Gruner et al., 2008). Otherwise, other factors would determine consumer fitness and any relationship with timing of the resource would be weakened. ...
Climate change has led to widespread shifts in the timing of key life history events between interacting species (phenological asynchrony) with hypothesized cascading negative fitness impacts on one or more of the interacting species—often termed ‘mismatch’. Yet, predicting the types of systems prone to mismatch remains a major hurdle. Recent reviews have argued that many studies do not provide strong evidence of the underlying match‐mismatch hypothesis, but none have quantitatively analysed support for it. Here, we test the hypothesis by estimating the prevalence of mismatch across antagonistic trophic interactions in terrestrial systems and then examine whether studies that meet the assumptions of the hypothesis are more likely to find a mismatch. Despite a large range of synchrony to asynchrony, we did not find general support for the hypothesis. Our results thus question the general applicability of this hypothesis in terrestrial systems, but they also suggest specific types of data missing to robustly refute it. We highlight the critical need to define resource seasonality and the window of ‘match’ for the most rigorous tests of the hypothesis. Such efforts are necessary if we want to predict systems where mismatches are likely to occur.
... We contend that these performance criteria are in intuitive accord with the fundamental factors affecting fish stocks and fisheries (c.f. Beverton and Holt, 1957;Cushing, 1975). These factors are discussed below. ...
... The stock biomass and production dynamics depend on particular environmental conditions at various stages of the life cycle for optimal growth and recruitment, such as temperature, salinity, oxygen, food type and availability, ocean currents, and limitations on pollution or other forms of human encroachment that degrade habitats (Beverton and Holt, 1957;Cushing, 1975;Laevastu and Favorite, 1988;Bakun, 1996;McFarlane et al., 2000). The ‗ocean climate' and its variability forces many of the above-mentioned variables and so plays a major role in determining the productivity of the stock, be it directly or indirectly. ...
... Climate forcing has been identified as a major driver of environmental, ecosystem and fish stock dynamics (Cushing, 1975, ICES, 1994Ottersen et al., 2010). In particular, the stock biomass and production dynamics, and fluctuations thereof, often depend on particular environmental (abiotic) conditions (e.g., gradients in temperature, salinity, stratification/density, oxygen, and the forcing of these by ocean currents), at various stages of the life cycle for optimizing recruitment and survival (manifested in abundance), distributions and migrations in space and time, and body growth and reproduction (Rijnsdorp et al., 2009). ...
The UNCOVER project ‘Understanding the mechanisms of stock recovery’ has produced a rational scientific basis for developing Long-Term Management Plans (LTMPs) and recovery strategies for 11 of the ecologically and socioeconomically most important fish stocks/ fisheries in the Norwegian and Barents Seas (Northeast Arctic cod,
Norwegian spring-spawning herring, Barents Sea capelin), the North Sea (North Sea cod, Autumn spawning herring, North Sea plaice), the Baltic Sea (Eastern Baltic cod, Baltic sprat) and the Bay of Biscay and Iberian Peninsula (Northern hake, Southern hake, Bay of Biscay anchovy). UNCOVER’s objectives were to identify changes
experienced during stock depletion/collapses, to understand prospects for recovery, to enhance the scientific understanding of the mechanisms of fish stock/fishery recovery, and to formulate recommendations how best to implement LTMPs/recovery plans.
This UNCOVER report is aimed at a knowledgeable readership comprising, in particular, scientists, scientific advisors and administrators/managers in the fishery and environmental fields. The report provides an overview of the project’s aims and scope, approaches and methodologies, and detailed documentation of the deliverables and results which places these in relation to current and emerging challenges, constraints and opportunities.
UNCOVER emphasizes that it is essential to set ‘realistic’ long-term objectives and strategies for achieving successful LTMPs/recovery plans. It is recommended that such plans ideally should include:
1) Consideration of stock-regulating environmental processes;
2) Incorporation of fisheries effects on stock structure and reproductive potential;
3) Consideration of changes in habitat dynamics due to global change;
4) Incorporation of biological multispecies interactions;
5) Incorporation of technical multispecies interactions and mixed-fisheries issues;
6) Integration of economically optimized harvesting;
7) Exploration of the socio-economic implications and political constraints from the implementation of existing and alternative recovery plans;
8) Investigations on the acceptance of the plans by stakeholders and specifically incentives for compliance by the fishery;
9) Agreements with and among stakeholders.
UNCOVER has provided imperative policy support underpinning the following fundamental areas: a) Evolution of the Common Fisheries Policy with respect to several aims of the ‘Green Paper’; b) Contributing to the Marine Strategy Framework Directive with respect to fish stocks/communities; c) Furthering the aims of the 2002 Johannesburg Declaration of the World Summit on Sustainable Development regarding achieving Maximum Sustainable Yield (MSY) for depleted fish stocks. This has been done by contributing to LTMPs/recovery plans for fish stocks/fisheries, demonstrating how to shift from scientific advice based on limit reference points towards setting and attaining targets such as MSY, and furthering ecosystem-based management through incorporating multispecies, environmental and habitat, climate variability/change, and human dimensions into these plans.
... The feeding and swimming abilities of larval fish are often poor (Wanzenböck and Schiemer 1989;Webb 1994;Wolter and Arlinghaus 2003) and limited food resources are likely to reduce larval growth and survival, ultimately influencing overall fish recruitment and productivity (Werner and Blaxter 1980;Hart and Werner 1987;Mills et al. 1989). As fluctuations in prey density can occur both spatially and temporally (e.g., Threlkeld 1983), fish reproduction timed to coincide with peak prey abundance would likely benefit the survival and growth of young fish (Cushing 1975;Bakun 1996Bakun , 1998Humphries et al. 2013). ...
... Their complimentary nature is recognised in the recent "Riverscape Recruitment Synthesis Model" (RRSM; Humphries et al. 2020), which synthesises many of the tenets of previous models into a single conceptual framework. These models include the "Match-Mismatch Hypothesis" (MMH; Cushing 1975), "Flood-pulse Concept" (FPC; Junk et al. 1989), "Fundamental Triad" (Bakun 1996(Bakun , 1998, and "Low-flow Recruitment Hypothesis" (LFRH; Humphries et al. 1999). The RRSM authors propose that it may be potentially applicable for predicting riverine fish recruitment across a wide range of settings; however, as a unifying concept, the RRSM is largely untested, as are a number of key elements in the model (see Humphries et al. 2020). ...
... (3) Do seasonally and aseasonally spawning taxa respond similarly to these variables? Results are evaluated with respect to the key processes and mechanisms hypothesised in the MMH (Cushing 1975), Fundamental Triad (Bakun 1996(Bakun , 1998, FPC (Junk et al. 1989), LFRH (Humphries Fig ...
Several hypotheses and conceptual models propose to explain mechanisms mediating riverine fish abundance, but few empirical studies to date have explored their utility in tropical systems. This study assesses key components of previous fish recruitment models by exploring spatiotemporal variation in larval fish assemblages in response to predicted key drivers in a tropical Australian river catchment. Data on larval fish composition and abundance, alongside hydrological, hydraulic, habitat and food variables, were collected monthly to bimonthly over one year at eight sites. Variables which best predicted larval fish abundance and diversity were determined with Boosted Regression Trees. The most commonly important predictors were microfauna abundance, structural habitat complexity and temperature, with high values of each predicting high larval fish abundance and diversity. Maximum larval diversity occurred when discharge was highest because several wet-season spawning taxa occurred alongside aseasonally spawning taxa. These findings support previous generic fish recruitment models, demonstrating the utility of their inclusion in the recent Riverine Recruitment Synthesis Model and the applicability of this model for describing processes important for tropical riverine fish recruitment.
... Although fish spawning and larval recruitment in the marine environment have been shown to be closely related to water temperature, photoperiod and seasonal plankton production (e.g. Royce 1972;Cushing 1975;Bye 1984;Sherman et al. 1984; Allen and Barker 1990), only a few studies have investigated ecological relationships between estuarine-spawned larval fishes and both hydrodynamics and plankton cycles in estuaries. These few studies have found that peak spawning for some species is in synchrony with seasonal increases in abundance of their dominant copepod prey (Sherman et al. 1984;Townsend 1984), with maximum catch rates of dominant larval fishes closely coupled to zooplankton dynamics. ...
... These few studies have found that peak spawning for some species is in synchrony with seasonal increases in abundance of their dominant copepod prey (Sherman et al. 1984;Townsend 1984), with maximum catch rates of dominant larval fishes closely coupled to zooplankton dynamics. For example, the 'match-mismatch' hypothesis of Cushing (1975Cushing ( , 1990 proposes that the spawning of marine fish should be timed such that the appearance of larvae overlaps with seasonal plankton blooms. Conversely, other species have developed a ubiquitous spawning strategy, producing larvae over a protracted period, thus allowing these populations to increase rapidly in response to favourable conditions and prey that are temporally restricted (Sherman et al. 1984). ...
... In addition, interspecific competition for food would be reduced for black bream larvae during late spring, because the peak in gobylgudgeon spawning occurred after this time. Therefore, the black bream does appear to conform to the strategy of the 'match-mismatch' hypothesis of Cushing (1975Cushing ( , 1990; see also Bollens et al. 1992). ...
The ichthyoplankton assemblage of the Hopkins River estuary, Victoria, was dominated by estuarine taxa that included demersal (goby, gudgeon) and pelagic (black bream, estuary perch, anchovy) species. The two seasonal peaks in fish larvae abundance were related to (1) the springlsummer zooplankton increase that occurred after flooding of the estuary and was comprised predominantly of copepod nauplii, thereby providing a good prey field for very young fish larvae, and (2) the autumn zooplankton maxima, which would provide a wide selection of copepod stages and meroplankton and promote dietary partitioning and flexibility among older larval stages. The two peaks in fish larvae abundance occurred well before and well after the attainment of maximum water temperature in the estuary. Goby, gudgeon, estuary perch and anchovy larvae were in the plankton over an extended period coinciding with the more stable conditions of salt-wedge presence and maximum zooplankton densities. The spawning of black bream and anchovies in the estuary was clearly related to physical conditions, such as salinity and water temperature, and habitat-although spawning of both species also occurred at times of high concentrations of potential prey organisms for their larvae. Adults of all the above fish species appear to have evolved spawning strategies that are adapted to the average hydrological and biological conditions in the estuary that would lead to the enhanced survival of their larvae. With the exception of the black bream, it appears that a ubiquitous and prolonged rather than a synchronous and confined spawning strategy is more widely used by estuarine-spawning fishes in the Hopkins River estuary. This type of spawning strategy, combined with the generally high density of food available to fish larvae in estuaries, suggests that the match-mismatch hypothesis of Cushing may be less relevant in the estuarine than in the marine environment.
... anguillid eels) but also for species that only travel modest distances to offshore spawning sites, e.g. the sciaenid Micropogonias undulatus, Baltic herring Clupea harengus membras) (Arula et al. 2014), the semi-catadromous European pleuronectid Platichthys flesus (Amorim et al. 2016) or the centropomid Centropomus undecimalis that spawns in nearshore coastal waters of the Gulf of Mexico close to adult estuarine habitats (Adams et al. 2009). Poor selection of spawning sites or poor timing of spawning that fails to coincide with favourable conditions for egg and larvae survival (Harden-Jones 1968, Cushing 1975, Secor 2015) has implications for recruitment success. For example, the consequences of misdirected drift of eggs and larvae (the 'denatant drift') related to poor selection of spawning sites can result in failure by early-life stages to reach estuarine nurseries and favourable feeding areas and ultimately recruitment failure (Cushing 1975, Secor 2002. ...
... Poor selection of spawning sites or poor timing of spawning that fails to coincide with favourable conditions for egg and larvae survival (Harden-Jones 1968, Cushing 1975, Secor 2015) has implications for recruitment success. For example, the consequences of misdirected drift of eggs and larvae (the 'denatant drift') related to poor selection of spawning sites can result in failure by early-life stages to reach estuarine nurseries and favourable feeding areas and ultimately recruitment failure (Cushing 1975, Secor 2002. ...
... Under favourable conditions, the probability of successful recruitment may be enhanced in estuarine environments. Success in recruitment of marine fishes is dependent on connectivity amongst habitats, often in well-defined, evolved pathways that assure linkages amongst life stages (Harden-Jones 1968, Cushing 1975, Pineda et al. 2007, Sheaves 2009, Secor 2015, Duffy-Anderson et al. 2015, Amorim et al. 2016, Teodosio et al. 2016, and often between offshore and estuary habitats. Hydrodynamic processes are important in guiding connectivity, creating pathways, delivering early-life stages to estuaries and retaining early-life stages in estuaries (Wolanski 2017). ...
The patterns of reproduction and ontogeny in the taxonomically rich estuary- associated fishes from around the world, including all the major groups from elasmobranchs to bony fishes, are as diverse as documented for fishes living in other ecosystems. Further, the diversity in the life histories of bony fishes, the dominant group in estuaries, is complex with egg, larval, juvenile and adult stages having different ecologies. Moreover, some stages that use estuaries also use the adjacent, downstream ocean and upstream
freshwaters for parts of their life history. Given these complexities in patterns and modes of reproduction, it is not surprising that recruitment processes of estuary- associated fishes are also diverse. In Introduction, we listed six broad topic areas that framed the scope of the chapter. We summarise major conclusions in the six areas.
... Wide inter annual as well as decadal scale oscillations are observed in the catches of these species, the reasons for which are not yet fully understood. To large extent year-class strength is dependent on the growth and mortality rates associated with ontogeny, as explained by the matchmismatch hypothesis of Cushing (1975) and/or the stability hypothesis of Lasker (1985). Fish larvae are most susceptible during the transition from yolk-sac stage to the planktivorous stage (Lasker, 1975). ...
... However, the present observations are restricted to the period mid-May to mid-August (upwelling season) and therefore the possibility of spawning during March-April (Krishnakumar et al., 2008) or October -November (Ganga, 2010), could not be established. It is known that fish stocks release its larvae into the annual production cycle at the best time to secure food (Cushing, 1975) and the right environmental conditions (Lasker, 1981) to ensure good survival (Cury and Roy, 1989). Indian mackerels are believed to be microzooplankton feeders in their critical stage of ontogeny (Madhupratap et al., 1994) whereas more advanced mackerel larvae feed predominantly on calanoid copepods (Arthur, 1976;Ostergaard et al., 2005). ...
... Havforskerne på denne tida var altså mer eller mindre samstemte om at fisketrykket spilte en sekundaer rolle for hvor sterk en fiskebestand var (Sinclair, 2009). Cushing (1975) skapte imidlertid et vendepunkt i den fastgrodde oppfatninga med sin 'Store syntese' eller 'Grand Synthesis'. Denne syntesen etablerte et skille mellom vekstoverfiske og rekrutteringsoverfiske. ...
... Først ble det lovlig å fiske etter småsild i ni av årets tolv måneder fra og med 1963 (Fiksen & Slotte, 2002). Denne forvaltningsstrategien resulterte imidlertid i vekstoverfiske (Cushing, 1975). For det andre, i takt med økende underskudd, forhandlet Norges Fiskarlag (fiskernes fagforening) med staten i 1963 om økonomisk støtte i form av pris-eller frakttilskudd (Hersoug et al., 2015). ...
This historical analysis shows that the great herring collapse that took place in the 1960s represented a fundamental shock in Norwegian fisheries. The authorities’ initial response to the crisis was to allow the fishing of small herring and introduce subsidies to save the fishermen’s income. But this was a complete failure. Eventually, the tremors led to the termination of the management practice of free fishing. At the same time, a ‘package’ of
institutions was built up, which together formed a new quota-regulated management practice. In retrospect, the new practice can be described as an ecological and economic success because it has contributed to rebuilding a sustainable herring fishery. However, the study shows that the institutions that were established have also contributed to redistributing the values that have been created in the past decades in pelagic fishing. Fewer and larger vessels have benefited from the ‘good times’ in the herring industry. A stronger regional concentration of quotas has also taken place. West Norway, in general, and the herring clusters in Austevoll and Herøy, in particular, come out particularly well. The quota concentration that has taken place has reduced the herring industry’s traditional role as a contributor to employment and settlement in Norwegian coastal communities. The study finally raises the issue of whether the extra returns that are created in the herring fishery are distributed fairly between the various stakeholders. It is argued that the Norwegian people, who own the herring resources, and the state, which ensures that they are managed sustainably, also have legitimate claims to the residual return. In line with strategic theory, these groups can use their bargaining power to appropriate their relative
contributions.
... An extended spawning and growing season exists at lower latitudes with higher temperatures (Cushing 1975). In the tropics, species generally experience a narrower range of seasonal variation in sea temperature than temperate species (Munday et al. 2008). ...
... Although most of the GBR is contained within the tropics, there is still a clear gradient in seasonality and variation in water temperatures over 10° of latitude; this in turn can be related to latitudinal growth theories. Most theory is based on temperate to coldtemperate environments where it is argued that fishes at low latitudes generally experience a longer growing season with short pulses of high productivity and peaks in hatching (Cushing 1975). In contrast, at high latitudes, fishes have shorter growing seasons with, on average, consistently high productivity and continuous hatching (Fiedler et al. 1991). ...
Clupeiformes are the most important food fish in the world, and provide a key trophic link in marine food chains. Here we describe broad scale patterns of clupeiform demographic characteristics of the delicate round herring sprat Spratelloides delicatulus on the Great Barrier Reef (GBR). Sampling was conducted over 10° of latitude and two seasons at multiple distances across the GBR shelf. The oldest S. delicatulus sampled was 152 days and the maximum standard length was 74 mm. Age and length maxima increased with latitude conforming with ‘counter gradient theory’ and these patterns were consistent between years. von Bertalanffy relationships showed that growth rates were highest at Northern GBR sites; growth coefficients ranged from 2–6 K year ⁻¹ , and were lowest on southern reefs, i.e. ‘tropical gradient of growth’. Daily survivorship ranged from 91–97% day ⁻¹ at all sites. Hatching dates estimated from counts of daily otolith increments indicated a prolonged spawning season of at least 9 months. Reproductive development indicated a size-based relationship. Males and females matured at similar sizes ranging from 36–38 mm, but fish from southern sites were 30–40 days older. Tropical clupeiforms live fast and die young, and patterns of abundance, composition and demography followed strong environmental gradients which conformed to some existing models.
... Wide inter annual as well as decadal scale oscillations are observed in the catches of these species, the reasons for which are not yet fully understood. To large extent year-class strength is dependent on the growth and mortality rates associated with ontogeny, as explained by the matchmismatch hypothesis of Cushing (1975) and/or the stability hypothesis of Lasker (1985). Fish larvae are most susceptible during the transition from yolk-sac stage to the planktivorous stage (Lasker, 1975). ...
... However, the present observations are restricted to the period mid-May to mid-August (upwelling season) and therefore the possibility of spawning during March-April (Krishnakumar et al., 2008) or October -November (Ganga, 2010), could not be established. It is known that fish stocks release its larvae into the annual production cycle at the best time to secure food (Cushing, 1975) and the right environmental conditions (Lasker, 1981) to ensure good survival (Cury and Roy, 1989). Indian mackerels are believed to be microzooplankton feeders in their critical stage of ontogeny (Madhupratap et al., 1994) whereas more advanced mackerel larvae feed predominantly on calanoid copepods (Arthur, 1976;Ostergaard et al., 2005). ...
Along the Kerala-Mangalore coast the peak spawning season of Indian
mackerel coincides with the transition period from Spring Inter-monsoon to Summer Monsoon. The species spawn in the offshore waters (50 to 200 m isobaths) mostly in the South Zone and to a less extent in the North Zone. Mackerel mostly avoid the Central Zone for spawning and as nursery ground. Newly hatched larvae are 1.585 mm in standard Length (SL). Larval growth rates are significantly higher (0.339 mm D-1) in the May-June spawning stock as compared to the July-August spawning stock (0.203 mm D-1). Growth is allometric and involves the yolk-sac stage (1.49 mm to 2.84 mm SL), pre-flexion (1.80 mm to 3.3 mm SL), flexion (2.85 mm to 4.85 mm SL), and post-flexion (4.60 to 11.3 mm SL) stages. Mackerel larvae have only restricted swimming and manoeuvring abilities as their body depth is relatively higher, but have much better feeding abilities owing to their large mouth-gape. In the early stages of ontogeny, the larvae feed predominantly on microzooplankton and switch over to a diet dominated by Calanoid Copepods as they grow further. Main nursery grounds of mackerel larvae are located along the thermal fronts associated with cold-core eddies. Inter-annual variations in the abundance of mackerel larvae are influenced by the strength of winds that favour upwelling.
... The body-length distribution in relation to the depth of collection (Fig. 1) shows a tendency for larger specimens to occur in deeper waters. This effect, called "bigger-deeper" (Macpherson 1979;Macpherson & Duarte 1991;Massutí et al. 2004;Moranta et al. 2004), and also known as "Heincke's law," (Heincke 1913;Cushing 1975) occurs in various species due to ontogenetic displacement to deeper waters. The occurrence of larvae and juveniles up to 25 mm SL in the water column near the surface over deep water suggests that individuals under ~25 mm SL are pelagic, and that they settle at the bottom at about 25 mm SL. ...
Centropristes fusculus Poey, 1861 historically has variously and somewhat perplexingly been assigned to Centropristis Cuvier, 1829, Prionodes Jenyns, 1840, and Serranus Cuvier, 1816. Here, we provide evidence from comparisons of morphology, ecology, and sexual systems for its inclusion in Serranus and redescribe the species based on the holotype and 60 specimens from Brazil, the Caribbean, the United States, and Uruguay. Serranus fusculus is a simultaneous hermaphrodite, a sexual system that is relevant to its generic placement. The inclusion of Serranus fusculus in the genus Serranus increases to 33 the number of currently valid Serranus species, of which two are found in the Western Indian Ocean, six in the eastern Pacific and 25 in the Atlantic Ocean (15 restricted to the western Atlantic and 10 to the eastern and Central Atlantic). An identification key to western Atlantic species of the genus is provided.
... warm and hydraulically benign conditions) predicted by both the low-flow recruitment hypothesis (Humphries et al. 1999) and flood pulse concept (Junk et al. 1989) to drive riverine larval productivity were important within this catchment. Interactions between larval food resources and river discharge indicates that, within rivers, larval productivity cannot be predicted or maximised through simple match-mismatch processes (Cushing 1975) between larvae and their food resources alone. More complex fundamental triad (Bakun 1996(Bakun , 1998 and riverscape recruitment (Humphries et al. 2020) mechanisms may better predict riverine larval fish productivity. ...
Executive summary:
The Daly River has been identified as an exemplar of the potential future water demand in the region (Douglas et al. 2011). The Daly River catchment in the Northern Territory (NT) supports highly significant environmental, economic and Indigenous cultural values (Jackson 2006; Hermoso et al. 2018). The river contains a highly diverse aquatic fauna, including two nationally threatened elasmobranchs, eight of the nine freshwater turtle species in the NT and over 90 species of fish within its freshwaters (Pusey et al. 2020). The river also supports important recreational and commercial fisheries and provides significant cultural value to its Indigenous people (Jackson 2006; Hermoso et al. 2018).
Agricultural, forestry and mining development in the Daly catchment has been increasing over recent years, with concomitant increases in demand for its water resources. Future development has the potential to place increased pressure on the river system through direct impacts caused by water extraction and from indirect impacts arising from native vegetation clearing and land-use activities. The NT Water Allocation Planning Framework allocates at least 80% of river flow or aquifer in the Top End region at any time as environmental water. This precautionary approach occurs in the absence of science for more discrete environmental flow targets to be set, and currently provides a high level of protection for environmental values and security for water licence holders. However, recent assessments have found that some aquifers in the Daly catchment are over-allocated, and that further quantification of the environmental water requirements is urgently needed to support sustainable management (Northern Territory Government 2019a,b).
This research project aimed to collate existing knowledge and develop new knowledge on critical flow-ecology relationships and risk-based scenario models for key environmental assets in the Daly River. Initial project scoping and design of the proposed research was conducted in strong collaboration with NT Government water policy staff and Traditional Owners, who provided critical guidance on the project’s direction and emphasis. The project was divided into nine linked objectives, and incorporated elements from two PhD theses.
This report presents the research approach and outcomes from each of these objectives in separate sections, and provides key findings and a range of key environmental flow considerations for the Daly and Katherine rivers. Where possible, the flow considerations have been developed to be specific to reaches and discharge thresholds. In other cases, flow considerations are more general statements. These environmental flow considerations are intended to provide further insight for review of environmental flow rules in the catchment.
... SSB). Traditional self-regenerating models (Beverton et al. 1984) combine yield and SSB per recruit with a stock-recruitment relationship (SRR), which relates the abundance of spawners with subsequent recruitment (Ricker 1954;Beverton and Holt 1957;Cushing 1975;Shepherd 1982). Two SRR models are the most commonly used: the Beverton-Holt model, where recruitment increases asymptotically, and the Table 3 Models used to assess spawner-recruit systems and their productivity and recruitment assumptions. ...
Understanding the processes that drive reproductive success in marine fish stocks is critical to effective fisheries management. These processes can be difficult to investigate, especially in age‐structured populations, because they occur at transgenerational scales. Reproductive success is often attributed to a small portion of the adult population (<0.01%) and thought to be driven primarily by random external factors, consistent with the concept of sweepstake reproductive success (SRS). A competing concept, the reproductive resilience paradigm, posits that fishes have evolved complex spawner‐recruit systems to achieve lifetime reproductive success and maintain population stability within highly variable environments. Here, we examine these two concepts. First, we analyse the popular sport fish red drum ( Sciaenops ocellatus , Sciaenidae), drawing on genetic and reproductive data to estimate a plausible range for the ratio of effective population size () to adult abundance () and to infer variance in lifetime reproductive success (). Then, we synthesize available data and infer for two other fishes that have ratios reportedly >0.10, the southern bluefin tuna ( Thunnus maccoyii , Scombridae) and the silver seabream ( Chrysophrys auratus , Sparidae). Although commonly regarded as an SRS species, red drum did not meet the SRS criterion. Overdispersed values were inferred for all three species, with those for red drum and silver seabream being dependent upon population‐closure assumptions. Results are presented within the conceptual framework of reproductive resilience, considering the roles of random extrinsic forces versus evolved traits to achieve lifetime reproductive success and population stability in high and variable mortality environments.
... This flatness in the yield per recruit curve is considered an artifact of the model itself as it assumes that the recruitment is constant regardless of the value of the fishing effort (F). According to the analysis of Cushing (1968Cushing ( & 1980 for this model, it can be suggested that as F increases, fewer numbers of P. lividus remain in the sea, while greater numbers of individuals below the commercialization size (5 cm) are caught. At the same time, the average weight of the P. lividus declines with the increased value of F, meaning that each P. lividus has less chance to put on weight. ...
... critical period, growth-mortality, individual characteristics, larval physiology, predation, recruitment endpoint Cushing (1975) was the first to recognize the close relationship between growth rate and mortality rate and the existence of an integrated process determining recruitment outcome. He proposed that the growth rate to mortality rate ratio could be used as a metric to characterize year-class success. ...
Early life survival is critical to successful replenishment of fish populations, and hypotheses developed under the Growth-Survival Paradigm (GSP) have guided investigations of controlling processes. The GSP postulates that recruitment depends on growth and mortality rates during early life stages, as well as their duration, after which the mortality declines substantially. The GSP predicts a shift in the frequency distribution of growth histories with age towards faster growth rates relative to the initial population because slow-growing individuals are subject to high mortality (via starvation and predation). However, mortality data compiled from 387 cases published in 153 studies (1971-2022) showed that the GSP was only supported in 56% of cases. Selection against slow growth occurred in two-thirds of field studies, leaving a non-negligible fraction of cases showing either an absence of or inverse growth-selective survival, suggesting the growth-survival relationship is more complex than currently considered within the GSP framework. Stochastic simulations allowed us to assess the influence of key intrinsic and extrinsic factors on the characteristics of surviving larvae and identify knowledge gaps on the drivers of variability in growth-selective survival. We suggest caution when interpreting patterns of growth selection because changes in variance and autocorrelation of individual growth rates among cohorts can invalidate fundamental GSP assumptions. We argue that breakthroughs in recruitment research require a comprehensive, population-specific characterization of the role of predation and intrinsic factors in driving variability in the distribution and autocorrelation of larval growth rates, and of the life stage corresponding to the endpoint of pre-recruited life.
... Dichas bases refieren específicamente a flotas de bandera extranjera, y contienen datos de embarcaciones en faena de pesca, representados mediante puntos, a una resolución espacial de 0.10 grados, del 03 de enero de 2012 hasta el 31 de diciembre de 2020, pero no incluyen datos de captura de especies. La alta cantidad de datos disponibles permite realizar cruces con bases de variables ambientales para explorar la influencia del medio en la dinámica de ese esfuerzo (Afonso-Dias et al., 2004;Cushing, 1975;Kroodsma et al., 2018;Natale et al., 2015;Torres Palenzuela et al., 2004). ...
Introduction: Until today, the fishing effort by foreign fleets in the Costa Rican Pacific has not been analyzed.
Objective: To determine the spatial distribution of the fishing effort of those fleets, variables that shape that
distribution, and if they interact with management figures and highly fragile ecosystems.
Methods: Using fishing effort data from 2012 to 2020, obtained from Global Fishing Watch, an Index of Fishing
Effort (IEP) was calculated to apply geospatial and multivariate statistics, as well as multiple regression models.
A grid with 55 905 cells of 0.10 degrees was used to apply Hot Spot Analysis, and another grid with 24 176
cell-year-month analysis units of 0.25 degrees was used to apply a Linear Regression Model.
Results: The data reveals the fishing activity of international fleets associated with four types of fishing gear,
and a wide coverage of a high IEP by two fleets throughout the nine years analyzed. The IEP is primarily
associated with location and varies by month and year. There is also relative evidence that its influenced by the
concentration of oxygen and nitrates.
Conclusions: International fleets come into direct conflict with officially defined zones for national fleets and
disrespect protected oceanic areas and a declared non-fishing zone to protect marine resources in the Costa
Rican Pacific. Their activities in the Dome may affect a national yellowfin tuna fishery.
... Coupled with limiting food resources (Cushing, 1975), seasonally colder water temperatures can have sublethal (e.g., stunted growth) and lethal effects on fishes (Brown et al., 2011;Hurst, 2007;Shuter et al., 2012). Periodically, winter stress syndrome can be amplified by cold-shock stress. ...
Colder water temperatures are generally regarded as a stressful period for fishes (i.e., winter stress syndrome), which can be exacerbated by cold‐shock stress associated with major arctic freezes. Although cold‐shock stress and mass mortalities are well documented for coastal marine fishes, few studies report the effects of winter stress or cold‐shock stress on inland fishes. The purposes of this study were to describe patterns in inland fish mortalities associated with winter stress syndrome and with cold‐shock stress in Texas as a regional example of inland fish mortalities associated with colder water temperatures. Using fish mortality reports (1969–2021) recorded by state agency biologists, colder water temperature mortalities occurred in 66% (N = 35) of the years, with greatest percentages of the reports occurring during three major arctic freezes in 1981, 1983 and 2021. The majority of reports were from urbanized counties (79%) and from lentic habitats (56%). Seventeen taxa and 1,021,217 individuals were estimated to be killed during the 53s years. Numbers of inland fish mortalities were greater during major arctic freeze years than non‐major arctic freeze years, attributed primarily to mortalities of non‐native fishes (e.g., blue tilapia Oreochromis aureus, suckermouth catfish Hypostomus plecostomus). Numbers of native fish mortalities, primarily clupeids and catostomids, were not different between major arctic freeze years and non‐major arctic freezes. The 43,000 inland fish mortalities reported during major arctic freeze years are in stark contrast to the 35 million coastal marine fish mortalities. Proposed mechanisms to explain cold‐shock mortalities in coastal waters (e.g., species within the northern extent of their range, lack of access to deeper water) are similar in inland waters, yet inland waters do not have the same level of mortalities. Consequently, the disparities between mortalities in coastal and inland waters are not readily discernable at this time.
... The general rationale for using empirical models to forecast abundance as a function of environmental conditions is clear: recruitment is affected by oceanographic parameters such as temperature, nutrient concentrations and primary production (Cushing 1975;Fogarty 1989), and in annual species (including many cephalopods) the fished stock consists entirely of new recruits of the year. However, such models can be (and often are) constructed with no detailed understanding of the underlying mechanisms, and several authors have urged caution because of the risk of spurious correlations (e.g. ...
WGCEPH worked on six Terms of Reference. These involved reporting on the status of stocks; reviewing advances in stock identification, assessment for fisheries management and for the Marine Strategy Framework Directive (MSFD), including some exploratory stock assessments; reviewing impacts of human activities on cephalopods; developing identification guides and recommendations for fishery data collection; describing the value chain and evaluating market drivers; and reviewing advances in research on environmental tolerance of cephalopods.
ToR A is supported by an annual data call for fishery and survey data. During 2019–2021, compared to 1990–2020, cuttlefish remained the most important cephalopod group in terms of weight landed along the European North Atlantic coast, while loliginid squid overtook octopus as the second most important group. Short-finned squid remained the least important group in landings although their relative importance was almost double in 2019–2022 compared to 1992–2020. Total cephalopod landings have been fairly stable since 1992.
Cuttlefish landings are towards the low end of the recent range, part of a general downward trend since 2004. Loliginid squid landings in 2019 were close to the maximum seen during the last 20 years but totals for 2020 and 2021 were lower. Annual ommastrephid squid landings are more variable than those of the other two groups and close to the maximum seen during 1992–2021. Octopod landings have generally declined since 2002 but the amount landed in 2021 was higher than in the previous four years.
Under ToR B we illustrate that the combination of genetic analysis and statolith shape analysis is a promising method to provide some stock structure information for L. forbsii. With the summary of cephalopod assessments, we could illustrate that many cephalopod species could already be included into the MSFD. We further provide material from two reviews in preparation, covering stock assessment methods and challenges faced for cephalopod fisheries management. Finally, we summarise trends in abundance indices, noting evidence of recent declines in cuttlefish and some octopuses of the genus Eledone.
Under ToR C, we describe progress on the reviews of (i) anthropogenic impacts on cephalopods and (ii) life history and ecology. In relation to life history, new information on Eledone cirrhosa from Portugal is included.
Under ToR D we provide an update on identification guides, discuss best practice in fishery data collection in relation to maturity determination and sampling intensity for fishery monitoring. Among others, we recommend i) to include the sampling of cephalopods in any fishery that (a) targets cephalopods, (b) targets both cephalopods and demersal fishes or (c) takes cephalopods as an important bycatch, ii) Size-distribution sampling, iii) the use of standardized sampling protocols, iv) an increased sampling effort in cephalopod.
Work under ToR E on value chains and market drivers, in conjunction with the Cephs & Chefs INTERREG project, has resulted in two papers being submitted. Abstracts of these are in the report.
Finally, progress under ToR F on environmental tolerance limits of cephalopods and climate envelope models is discussed, noting the need to continue this work during the next cycle.
... In order to reach sustainable harvest practices, fisheries scientists have attempted for over a century to effectively and accurately predict the abundance of upcoming year classes entering a fishery, that is, recruitment (Hjort, 1914;Walters & Collie, 1988;Myers, 1998). This body of work has been highly focused on identifying the critical stage for recruitment determination (Cushing, 1975), including the vulnerable larval stage from internal (yolk-sac) to external feeding (first 20-30 d of life for North Sea (NS) herring larvae, Denis et al., 2016), as newly-hatched larvae experience a change in growth, predation, starvation, and survival trade-offs (Myers, 1998;Yúfera and Darias, 2007). However, research on recruitment processes is challenging due to the high number and variability of potential drivers of recruitment with relatively low explanatory power (Hjort, 1914;Walters and Collie, 1988;Myers, 1998;Rice and Browman, 2015). ...
Sustainable fishery practices require accurate predictions of fish recruitment—the abundance of a new year class entering a fishery. A key driver of recruitment is the impact predator-prey dynamics experienced during early life stages has on their survival at later stages, as in the Match-Mismatch Hypothesis (MMH). MMH states that predator survival depends on the match (or mismatch) between the timing of predator feeding and that of prey availability. This study aims to understand how predator-prey spatio-temporal overlap explains the variation in a pelagic fish population. We explore the predator-prey overlap between each pair of three trophic levels in the North Sea (NS) from 1982–2017: herring (Clupea harengus) larvae, zooplankton (Temora longicornis, Oithona sp.,Pseudocalanus spp., and Acartia spp.), and a phytoplankton index. We found that MMH explained 23% of recruitment (1-year-old) of NS autumn-spawning (NSAS) herring, performed similarly (21–26%) when using different trophic levels, and that there was a spatial pattern in both the overlap and the negative relationship between the overlap and recruitment, similar to the variation of habitat use of NS herring. Our results characterize how the MMH, including spatial variability, plays in controlling herring recruitment, while also considering unexplained variation for future study.
... The variability in primary production influenced the fishery production which has a strong link between phytoplankton and fisheries variability [3,8] . There are several previous studies which indicated that nitrogen-limitation is a widespread phenomenon in tropical coastal waters of Bay of Bengal [47,22,34] . ...
Phytoplankton assemblages in the south eastern coastal area of the Bay of Bengal, Bangladesh was studied from surface water for a period of 12 months (July 2020 to June 2021) in relation to environmental variables like, water temperature, pH, dissolved oxygen, salinity, conductivity, transparency, rainfall, TDS and nutrient contents-including nitrate, nitrite, phosphate and silicate. A total of 137 phytoplankton species were identified whereas, 115 species of diatoms from 44 genera, 15 species of dinoflagellates from 8 genera, 2 species of green algae from 2 genera, 4 species of cyanobacteria from 3 genera and 1 species of silicoflagellate were identified. The highest phytoplankton abundance was found at Shaplapur about 12245 cells/l and the lowest at Saint Martin's Island about 1250 cells/l. Phytoplankton showed complete dominance of diatom genera namely Asterionella japonica & Thalassionema nitzschiodes in post-monsoon and Odontella rhombus in pre-monsoon. Other frequently occurring diatoms were Coscinodiscus perforatus, Actinocyclus normanii, Thalassiothrix fraunfeldii, Ditylum brightwelli, Rhizosolenia alata, Chaetoceros affinis, Thalassionema nitzschoides etc. respectively. Species diversity was observed to be maximum in post-monsoon (67 species) followed by pre-monsoon (42 species) and monsoon season (28 species). The average annual environmental variables values among the stations were salinity (27.09±2.27 PSU); water temperature (27.22±0.40 ºC); DO (4.78±0.15 mg/l); TDS (21.33±1.93 g/l); Conductivity (41.40±3.49 mS/cm); Transparency (3.09±2.02 ft); Rainfall (87±0.00 mm); NO3-N (0.38±0.07 mg/l); PO4-P (0.07±0.01 mg/l); SiO4 (0.06±0.01 mg/l) respectively. Correlation studies of phytoplankton composition to physicochemical variables indicated significant negative relation with water temperature, salinity and pH but positive relation with nitrate, nitrite, silicate and phosphate of the water body. Nitrate was found to be the limiting factors for phytoplankton growth during pre-monsoon periods whereas, the role of silicate and phosphate remained insignificant in these perspectives.
... Traditionally, recruitment studies have focused on the effect of bottom-up factors on pre-recruit life stages, that is the impact of abiotic factors placing limits on primary production that propagate to higher trophic levels leading to resource limitation. Prey availability and hydrography (i.e., water currents) were first highlighted as the major factors contributing to larval survival (Hjort 1914;Cushing 1975;Iles and Sinclair 1982). Also, the potential role of maternal effects (i.e., body fat) on offspring fitness was introduced by these early studies (Hjort 1914), a mechanism that we now understand better (Hixon et al. 2014). ...
Understanding the drivers behind fluctuations in fish populations remains a key objective in fishery science. Our predictive capacity to explain these fluctuations is still relatively low, due to the amalgam of interacting bottom-up and top-down factors, which vary across time and space among and within populations. Gaining a mechanistic understanding of these recruitment drivers requires a holistic approach, combining field, experimental and modelling efforts. Here, we use the Western Baltic Spring-Spawning (WBSS) herring ( Clupea harengus ) to exemplify the power of this holistic approach and the high complexity of the recruitment drivers (and their interactions). Since the early 2000s, low recruitment levels have promoted intense research on this stock. Our literature synthesis suggests that the major drivers are habitat compression of the spawning beds (due to eutrophication and coastal modification mainly) and warming, which indirectly leads to changes in spawning phenology, prey abundance and predation pressure. Other factors include increased intensity of extreme climate events and new predators in the system. Four main knowledge gaps were identified related to life-cycle migration and habitat use, population structure and demographics, life-stage specific impact of multi-stressors, and predator–prey interactions. Specific research topics within these areas are proposed, as well as the priority to support a sustainable management of the stock. Given that the Baltic Sea is severely impacted by warming, eutrophication and altered precipitation, WBSS herring could be a harbinger of potential effects of changing environmental drivers to the recruitment of small pelagic fishes in other coastal areas in the world.
Graphical abstract
... These reference points could be interpreted as the level of stock biomass at which recruitment is impaired, or where there is recruitment overfishing. Recruitment overfishing occurs when a population has been fished down to a point where spawning biomass is so low that recruitment decreases substantially (Cushing, 1975;Sissenwine and Shepherd, 1987). Estimation of biomass limit reference points varies a lot regionally, and the estimation method impacts the level and the associated uncertainty of the reference point (Deurs et al., 2021). ...
The International Council for the Exploration of the Sea (ICES) has provided scientific stock advice based on reference points to manage fisheries in the North Atlantic Ocean and adjacent seas for decades. ICES advice integrates the precautionary approach with the objective of achieving maximum sustainable yield. Here, we examine ICES reference point evolution over the last 25 yr and provide a comprehensive empirical review of current ICES reference points for data-rich stocks (Category 1; 79 stocks). The consistency of reference point estimation with the ICES guidelines is evaluated. We demonstrate: (1) how the framework has evolved over time in an intergovernmental setting, (2) that multiple precautionary components and sources of stochasticity are included, (3) that the relationship and historical context of stock size and recruitment are crucial for non-proxy reference points, (4) that reference points are reviewed frequently, taking into account fluctuations and multiple sources of variability, (5) that there are occasional inconsistencies with the guidelines, and (6) that more comprehensive and clearer documentation is needed. Simplifying the stock-recruit typology and developing quantitative criteria would assist with this critically important classification. We recommend a well-documented, transparent, and reproducible framework, and periodic syntheses comparing applications across all stocks.
... Such species often respond to specific environmental cues that enable them to optimize their reproductive success. For example, many temperate fishes initiate reproduction in response to changes in water temperature, and this may lead to reproductive phenologies that improve food availability for their offspring (i.e. the 'Match-Mismatch hypothesis' of Cushing 1975). However, in tropical marine environments with less seasonal variation, many coral reef fishes spawn continuously throughout the year (exhibiting 'extreme iteroparity', Philippi and Seger 1989;Warner 1998;Wilbur and Rudolf 2006;Shima et al. 2018). ...
Pelagic eggs and larvae of many coral reef fishes will encounter a dynamic and risky environment as they disperse between the reef and offshore habitats. Life-history theory predicts that spawning adults should synchronize their reproductive effort with specific environmental conditions that facilitate offspring survival. Favourable conditions for reproduction may be determined by local environmental conditions at the spawning site, or signalled by larger-scale environmental cues, such as the lunar cycle. Multiple cues may interact in complex ways to cause additional variation in spawning intensity. We evaluated a set of environmental variables that potentially determine temporal and spatial variation in spawning patterns of a highly iteroparous fish, the sixbar wrasse ( Thalassoma hardwicke ). Specifically, we monitored focal territories of terminal-phase males over a 5-month period, quantified spawning activities, and evaluated a hierarchical set of predictive models using a model selection approach (AICc). Temporal variation in spawning (and population densities at the spawning site) was most strongly associated with the lunar cycle and maximal around the new moon. Local hydrodynamic conditions and other environmental variables observable at the spawning site were less strongly correlated with temporal variation in spawning. Territory proximity to the reef edge was a strong predictor of spatial variation in spawning intensity; territories closest to the reef edge experienced more spawning. These observations suggest that females make predictable decisions about where and when they spawn. Females appear to recognize strong, persistent spatial gradients in spawning habitat quality, and primarily vary their spawning effort in accordance with a large-scale environmental cue (the lunar cycle).
... The size of the juvenile fish reflects growth (in addition to variable spawning and hatching times) and is one aspect of the recruitment variability 'puzzle'. Interaction between growth rate and mortality is implied in the 'growth-mortality' hypothesis (Beverton and Holt 1957, Cushing 1975, Anderson 1988, Houde 2009). Since the duration in a segment of larval development is inversely related to growth rate, the accumulated mortality from the impact of size-selective predators also varies inversely with growth rate. ...
Young-of-the-year (0-group) fish in the Barents Sea have been investigated in an annual joint Norwegian-Russian pelagic trawl survey in autumn, using a standardized procedure since 1980. We use a conceptual framework of ‘upstream’ spawning areas and ‘downstream’ nursery areas, recorded as 0-group distribution in the Barents Sea, to address spatial (geographical) and temporal (1980–2017) variation in 0-group length. Four boreal species (cod Gadus morhua, haddock Melanogrammus aeglefinus, herring Clupea harengus, and deepwater redfish Sebastes mentella) tended to have smaller 0-group individuals in the northern and eastern parts of the Barents Sea, with the largest individuals found in the central part where they were also most abundant. We interpret this to reflect slower growth as the ‘fore-runners’ of the seasonal cohort of juveniles are transported into colder waters (through lateral mixing). The Arctic species (capelin Mallotus villosus and polar cod Boreogadus saida) showed a different pattern with increasing 0-group length with increasing distance away from the spawning areas, seen most clearly for capelin. The longer juveniles in northern areas are probably older and stemming from early spawning.
There was temporal covariation in 0-group length between the six species over the 38-year time series, with highest correlation between cod and haddock. The covariation reflected similar fluctuations in four decadal ‘waves’, with maxima in 0-group length in the early/mid 1980s, 1990s, 2000s, and 2010s. There was a high degree of spatial consistency in the temporal patterns of variation in 0-group length, with synchronous variations in different geographical areas. There were also increasing linear trends over the time series for cod, haddock, and polar cod, which represented increase of about 20%, 40%, and 15% of the initial length for the three species, respectively. The fluctuations and trends in 0-group length were positively correlated with seawater temperature, which suggests a strong effect of climate variability and warming (by 1.5–2.0 °C since 1980) on 0-group length. The clear differences among the species, and the limited fraction of variance explained by temperature, suggest that other factors such as food play additional roles. Zooplankton biomass integrated over the water column had low explanatory power, but this may reflect intrinsic limitations in the data (e.g., depth-integrated, end of season) in providing an adequate representation of feeding conditions, rather than suggesting that food was not important.
... For more than a century, it has been accepted that the survival and growth of early life stages form a bottleneck for marine fish recruitment (Cushing, 1975(Cushing, , 1990Iles and Sinclair 1982;Houde 2008). However, gaining a mechanistic understanding of the factors and processes driving fluctuations in year class success is still a major challenge in fisheries science. ...
The role of small prey (< 200 µm) in larval marine fish nutrition is largely understudied. Here, we explore the contribution of protozooplankton (PZP 20–200 µm) to larval fish diets, compared to metazoan microzooplankton (MZP 55–200 µm). More specifically, we tested whether the contribution of PZP increased during the low productivity season and decreased as larvae grow. We used North Sea autumn spawning herring (Clupea harengus) as a case study, as it is a key species with high commercial and ecological importance. In autumn and winter, the potential PZP and MZP prey was dominated by cells < 50 µm (mainly Gymnodiniales, Pronoctiluca pelagica,Tripos spp. and Strombidium spp.), while copepod nauplii and copepodites where more abundant in autumn than in winter. Based on their trophic enrichment (∆15 N), larvae preferentially grazed on small MZP < 50 µm rather than PZP both in autumn and winter. Larvae of different body size (range 8–14 mm standard length) fed at the same trophic level but on different prey (similar δ¹⁵N but different δ¹³C). Growth rates (based on RNA/DNA estimates) were similar in autumn and winter, suggesting that growth was not affected by station-specific differences in the composition of the prey field. Our results not only underscore the important role of MZP on larval herring diets both in autumn and wintertime, but also emphasize the limitations of bulk stable isotope analysis. Given the current low recruitment in North Sea herring, these results provide significant information for future monitoring approaches relevant to stock assessment of this species.
... This would have an impact on the species' population if it happened to multiple individuals in the same year or spawning cycle. Following Cushing's (1975) 'single process' principle, the longer the larvae stay in a stage of high mortality, then the more likely a higher overall population mortality will result. In a series of experiments on coral reef fish, Simpson et al. (2016b;vessel -70-125 dB re 1 µPa 2 Hz -1 ; 0-3,000 Hz) investigated the impacts of vessel noise on survival and found that in the presence of boat noise only 27 % of 39 larval fish managed to survive the observation period, compared to 79 % of 39 larval fish surviving in the control condition (p < 0.001 significance level reported). ...
The effects of noise on aquatic life is a topic of growing international concern. Underwater noise can impact both the physiology and behaviour of fish species on a wide-ranging scale, from minor changes and adaptations to major injury and death. Future mitigation of anthropogenic noise in the ocean is dependent on greater awareness of the effects of noise, the amount of risk, and degree of harm, likely to affect fish populations. Currently, there is a lack of incentive for
mitigation measures to be put in place. Knowledge and evidence of the impacts of anthropogenic noise on fish is rapidly increasing (Figure 1.2) but with over 32,000 species of fish of differing conservation and commercial importance, it is extremely difficult to decide where to focus research for maximum benefit (Hawkins et al., 2015). Predictions and assumptions about
potential impacts lack accuracy as variations in experimental equipment and techniques, lack of
agreed standards, different algorithms for analysis, ambiguous and interchangeable terminology,
and different quantities, units and metrics, all lead to incongruities (ISVR Consulting, 2004;
Barlow et al., 2014; Rogers et al., 2016). Often it is not possible to compare studies or make
generalisations (OSPAR, 2009; Wilcock et al., 2014). Here the aim is to aid the mitigation process by directing research priorities toward the most vulnerable fish species, and developing models and tools that allow for informed and cost-effective mitigation methods in a bid to reduce the effects of anthropogenic noise from marine traffic.
... Such programmed migratory and homing behaviour in fishes constitutes a pattern in which individuals spend their early life in a specific locality and subsequently return to this locality to spawn. This pattern, which describes the spawning and early life characteristics of GoR herring, resembles the well known "migration triangle" behaviour observed in many marine fishes (Cushing 1975;Secor 2015). We propose that a recruitment bottleneck in the GoR herring, may now be keyed to the evolved and fixed spawning behaviour of adults. ...
Exogenous anomalies induced by contemporary climate change may severely impact
dynamics of early life stages of fish. Here, we modelled how growth rate and
abundance of postflexion larvae, and recruitment of Baltic spring-spawning herring (
Clupea harengus membra s) in the Pärnu Bay, Gulf of Riga (GoR) may respond to
shifting climate variables. Higher larval growth rates were aligned with later seasonal
emergence of yolk-sac larvae, while lower abundance of postflexion larvae occurred in
years of earlier seasonal seawater warming. Cooler temperatures (<16 °C) in spring
expanded the optimal thermal window for first-feeding herring larvae, attributable to the
absence of early seasonal water temperature warming. Higher recruitment levels
emerged in years of seasonally delayed warming and were associated with a higher
abundance of postflexion larvae. In recent decades, the trend towards earlier warming
of the Baltic Sea in spring threatens to create a bottleneck to the successful recruitment of
herring. The existing paradigm that abundant Baltic herring year-classes occur only in
the years following mild winters no longer stands as environmental conditions undergo
rapid change. The relative contribution of Pärnu Bay larval nursery areas to recruitment
has diminished as the suitable thermal window has been dramatically reduced in
recent decades. Evolving thermal dynamics in the GoR have developed relatively
recently and in future present a bottleneck for herring production.
... However, the effect of temperature is less critical at age-0 than for the other juvenile stages. This result suggests that different ecological processes, as the timing between the fish spawning and the onset of annual primary production, might influence the survival of age-0 (Cushing, 1975 (Pauly & Cheung, 2018). It emphasizes the importance of the older age classes to keep a stock of marine fish in a good state, robust to climate change (Anderson et al., 2008) and to maintain ecological interactions functioning (Dell et al., 2014). ...
Climate change and harvesting can affect the ecosystems' functioning by altering the population dynamics and interactions among species. Knowing how species interact is essential for better understanding potentially unintended consequences of harvest on multiple species in ecosystems. I analyzed how stage-specific interactions between two harvested competitors, the haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua), living in the Barents Sea affect the outcome of changes in the harvest of the two species. Using state-space models that account for observation errors and stochasticity in the population dynamics, I run different harvesting scenarios and track population-level responses of both species. The increasing temperature elevated the number of larvae of haddock but did not significantly influence the older age-classes. The nature of the interactions between both species shifted from predator-prey to competition around age-2 to -3. Increased cod fishing mortality, which led to decreasing abundance of cod, was associated with an increasing overall abundance of haddock, which suggests compensatory dynamics of both species. From a stage-specific approach, I show that a change in the abundance in one species may propagate to other species, threatening the exploited species' recovery. Thus, this study demonstrates that considering interactions among life history stages of harvested species is essential to enhance species' co-existence in harvested ecosystems. The approach developed in this study steps forward the analyses of effects of harvest and climate in multi-species systems by considering the comprehension of complex ecological processes to facilitate the sustainable use of natural resources.
... By contrast in sandy substrates, sediment erosion and overlay disturbs frequently the surface layers and stimulates the benthic infauna to recede into the deeper layers (Zwarts and Wanink, 1993), where it is inaccessible for small fishes. Small juvenile fish eat more in relation to their body weight than large adult fish, they have less energy reserves, and thus sufficient food resources are more important for them as for larger adult fish (Cushing, 1975). Therefore, in relation to the potential risks ( Friese et al., 2020a; Chapter 3) small fish have higher potential benefits from using the salt-marsh creeks than adults would have. ...
... This prediction was based on Asch (2015) who found a trend for earlier spawning in 18 of 43 species between 1951 and 2008. Because zooplankton phenology did not change during this period, she discussed the potential for increased larval mortality under climate change if spawning did not overlap with zooplankton prey productivity (Asch, 2015;Cushing, 1975). Subsequent to Asch (2015), incidents of altered phenology have been documented in phytoplankton (Chivers et al., 2020;Salgado-Hernanz et al., 2019), crustaceans (Emond et al., 2020), and fish (Lombardo et al., 2020) in various locations around the world. ...
The 2014-2016 Northeast Pacific marine heatwave (MHW) induced the warmest 3-year period on record in the California Current Ecosystem. We tested whether lar-val fish assemblage structure, phenology, and diversity dynamics were comparable to past warming events from 1951 to 2013. First, we hypothesized, based on past observations of biological effect of warming, that mesopelagic species with southern distributions relative to southern California and Pacific sardine Sardinops sagax (a coastal pelagic species) would increase during the MHW while northern mesopelagics and northern anchovy Engraulis mordax (coastal pelagic) abundances would decline. Similar to past warming, southern mesopelagics increased and northern mesopelag-ics decreased. Unexpectedly, however, a common southern mesopelagic, Mexican lampfish Triphoturus mexicanus, was approximately three times more abundant than the previous annual high. Furthermore, whereas sardine abundance did not increase, larval anchovy abundance rose to near-record highs in summer 2016. Second, we hypothesized that fishes would spawn earlier during the MHW. Fishes did not spawn in an earlier season within a year, but five of six southern mesopelagic taxa spawned earlier than typical within winter and spring. Third, we predicted that species richness would increase moderately due to an influx of southern and exodus of northern species. Richness, however, was very high in all seasons and the highest ever during the summer as multiple species with primarily southern distributions were recorded spawning for the first time in southern California. The richness of northern species was also unexpectedly high during the MHW. Northern species likely persisted in the study area because in addition to the warm water, pockets of cold water were consistently present. If, as predicted, conditions similar to the MHW become more common as oceans warm, this unique and largely unexpected combination of fishes may reflect future biological conditions.
... A standard NPZ model has five transfer functions, each with countless possible functional forms (see Franks, 2002 for a nice review). The NPZ framework has also been extended to include the effects of bacteria and detritus, and is similar to the multicomponent systems used in the current generation of global climate models (Aumont et al., 2015;Cushing, 1975;Fasham et al., 1990). However, a more complex biogeochemical model is not necessarily a better one for developing process-based understanding (Franks, 2002;Turner et al., 2014). ...
The distribution of oceanic biogeochemical tracers is fundamentally tied to physical dynamics at and below the mesoscale. Since global climate models rarely resolve those scales, turbulent transport is parameterized in terms of the large‐scale gradients in the mean tracer distribution and the physical fields. Here, we demonstrate that this form of the eddy flux is not necessarily appropriate for reactive tracers, such as nutrients and phytoplankton. In an idealized nutrient‐phytoplankton system, we show that the eddy flux of one tracer should depend on the gradients of itself and the other. For certain parameter regimes, incorporating cross‐diffusion can significantly improve the representation of both phytoplankton and nutrient eddy fluxes. We also show that the efficacy of eddy diffusion parameterizations requires timescale separation between the flow and reactions. This result has ramifications for parameterizing subgrid scale biogeochemistry in more complex ocean models since many biological processes have comparable timescales to submesoscale motions.
... Moreover, there was apparently no follow-up to this idea. This is possibly because of the dominance of the belief that the ratio of mean length at first maturity (L m ) to asymptotic length (L ∞ ), earlier labelled "reproductive load" by Cushing (1975), is a "Beverton and Holt invariant" or even "invariant" (Charnov, 1993). ...
The standard response to the question “why do fish reach first maturity when they do” is that, at some point (or age), they perceive environmental stimuli, which are converted via the pituitary and the hypothalamus into triggers for a hormonal cascade leading to gonadal maturation and the release of gametes. Yet, the question rarely asked is why fully formed young fish do not respond to the environmental stimuli that the adults react to by maturing and spawning. This question requires an answer, from ichthyologists and/or physiologists, e.g., in the form of a heuristic that individual fish can use, even if the explanation provided here (elaborating on a causal mechanism for the juvenile-to-adult proposed by the author in 1984) should be considered inadequate.
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... Oct.91 October 1991 respectively. Cushing (1975) suggested that, the variation in tinling, intensity and duration of phytoplankton cycles are mostly related to change in production ratio (compensation rate/depth ofnlixing) which is in tum largely dependent on seasonal variations in light and wind actions. The production ratio increases in spring with increasing temperature, since incident radiation increased and wind speed tended to decrease reducing mixing. ...
... Fish spawning timing in temperate regions is often cyclical to allow for the synchronous occurrence of early life stages and environmental conditions conducive to their growth (i.e. temporal overlap with seasonal zooplankton blooms) in order to improve the probability of offspring survival (Cushing, 1975(Cushing, , 1990Kristiansen et al., 2011). Since recruitment variability is the outcome of multiple complex trophodynamic and physical processes that act on the early life stages of fishes (Houde, 2008), a match between fish spawning and zooplankton blooms does not guarantee high recruitment. ...
Spawning timing in fish is generally cyclical in temperate regions in order to increase the probability of matching larval occurrence with ideal environmental conditions. The capelin stock in Northwest Atlantic Fisheries Organization Divisions 2J3KL collapsed in 1990 – 91 and has not recovered. This collapse was concomitant with collapses in groundfish stocks and cold oceanographic conditions. Using citizen science data, newspaper archives, gray and primary literature, and monitoring data, a century of capelin beach spawning times were compiled. Capelin beach spawning has been persistently 3 weeks later since the stock collapse. To identify potential predictors of capelin spawning timing, an exploratory analysis was conducted using environmental and biological variables and a period factor that categorized a year as either pre-collapse (1990 and earlier) or post-collapse (post-1990) in a step-wise multiple regression model. Spawning timing was predicted to be delayed in the post-collapse period when there were negative anomalies in the Newfoundland and Labrador Climate Index and summer (June-August) North Atlantic Oscillation, and when there was a decrease in mean length of the spawning population. The production of weak year-classes is predicted when spawning is delayed, suggesting that late spawning is severely inhibiting the recovery of the stock.
... Successful reproduction and recruitment of riverine fishes are commonly thought to be influenced by a river's hydrological regime (Bailly et al., 2008;Humphries et al., 2020;Junk et al., 1989;Poff et al., 1997;Welcomme & Halls, 2001). Indeed, reproductive strategies of fishes are the result of long-term evolution in response to natural flow regimes (Lytle & Poff, 2004), and variation in the timing of larval production and the match or mismatch with suitable rearing conditions is commonly thought to determine the success of subsequent recruitment (Cushing, 1975;Humphries et al., 2013;Tricklebank et al., 1992). ...
• Setting ecologically based water-extraction rules requires an understanding of the relationships between hydrology and the completion of aquatic organism life cycles. Successful reproduction of riverine fishes has been linked to hydrological variation across diverse climatic regions. However, the reproductive ecology for many species in wet–dry tropical northern Australia is poorly understood, and consequently there is little knowledge on how temporal (seasonal) and spatial hydrological variation influences fish reproduction in this region.
• This study aimed to quantify the hydrology-related reproductive ecologies of freshwater fish across the wet–dry seasonal cycle and between differing hydrological classes in a northern Australian river (Daly River, Northern Territory) subject to increasing interest in water extraction. Sampling of larval and juvenile fish was undertaken over 1 year at eight sites classified into perennial and intermittent flow types. Fish spawning phenologies were developed and spatial–temporal dynamics in larval fish assemblages were investigated using model-based multivariate and univariate analyses.
• Spawning occurred in all hydrological seasons, with low-flow dry season periods identified as important for many fish taxa. For a different fish assemblage, spawning mostly occurred during high-flow wet season periods. Larval assemblages in the wet season were more diverse than in the dry and wet–dry seasons. Perennial sites maintained higher diversity than intermittent sites year-round; however, larvae were more abundant in intermittent sites for some taxa. Spatial and temporal differences in larval assemblages were largely explained by variation in the occurrence and relative abundance of three aseasonally spawning taxa (Craterocephalus spp., Melanotaenia spp. and Ambassis spp.) and the largely wet-period spawning of Terapontidae spp.
• These results add to growing evidence of variation in spawning phenologies among fish species and the use of multiple hydrological phases for aseasonal reproduction. The diverse range of hydrological conditions used for spawning and rearing, and the differences between hydrological river classes among taxa, suggests that water-extraction and environmental flow rules should aim to maintain hydrological conditions catchment-wide during both low and high-flow periods to reduce the risk of impacting fish reproduction. In particular, the results suggest that if perennially flowing sites began to flow intermittently, such as through over-extraction of water or due to climate change, less diverse fish assemblages may result.
• This study expands our understanding of the relationships between hydrology and the reproductive ecology of freshwater fish in wet–dry tropical climates and may inform future ecologically based approaches to setting water-extraction rules.
... Species such as E. encrasicolus, G. niger, A. presbyter, Parablennius pilicornis and P. gattorugine spawn during warmer months, which was confirmed by the high occurrence of larvae during these seasons, while other species can be classified as autumn spawners: S. pilchardus, A. tobianus, C. mustela and T. luscus. The strong link with other zooplanktonic groups, which are an abundant source of food for fish larvae, are most probably related with the synchrony between the life cycle of prey and predators (Cushing, 1975). In this study, high abundances of Cladocera and Cnidaria coincide with higher abundances of S. solea and E. encrasicolus in the coastal area. ...
The present study describes the larval and juvenile fish fauna of an estuary and its adjacent coastal area (Mondego estuary, Northwest coast of Portugal) and evaluates their function as nurseries for marine fish. For this, larvae and juveniles were sampled in both systems. The temporal and spatial patterns of the ichthyoplankton community were described for each system and related to the influence of environmental factors. Additionally, the recruitment pattern was evaluated based on the composition of juveniles. Results show a seasonal variation of larval density and community structure between and within systems, indicating a degree of segregation according to their ecological functional classification. Temperature was the most important environmental factor structuring the communities. The juvenile recruitment patterns observed show a different nursery function of the estuary and coastal area for early life stages of different species, reinforcing the need to integrate larval and juvenile stages to better understand fish life cycles and the connectivity between systems.
... Fishes of the Haemulidae family have an essential ecological role in energy fixation for the reef communities and they also are one of the largest prey of larger species, such as groupers and snappers (Cushing, 1975;Darcy, 1983). Worldwide, a total of 133 species in 18 genera are recognized (Nelson et al., 2016). ...
White grunt (Haemulon plumierii) has gained relevance as an alternative resource to fisheries off the northern coast of the Yucatán Peninsula, however, knowledge of its biology in the region is scarce. Thus, in order to explore the reproductive biology of H. plumierii, a total of 355 specimens were caught with a hand line and bait, from September 2015 to November 2016 to conduct histological analysis of the gonads. The sample was represented by 233 males and 122 females, differing from the 1:1 sex ratio (1 female per 2.1 males). The reproductive season occurred from February to August with a maximum peak in May. The 50% maturity size (L 50) was estimated at 15.15 and 15.22 cm TL for males and females, respectively. The batch fecundity ranged from 9,363 to 42,371 eggs per batch, with an average of 26,558 eggs. Several reproductive biology features were observed in H. plumierii, such as spring spawning seasonality, length at sexual maturity, asynchronous oocyte development with an indeterminate fecundity, and batch spawning. This kind of information can guide proposals for further sustainable fishery management measures that may guarantee the continuity of this economically important species in the region.
Decline of the dissolved oxygen in the ocean is a growing concern, as it may eventually lead to global anoxia, an elevated mortality of marine fauna and even a mass extinction. Deoxygenation of the ocean often results in the formation of oxygen minimum zones (OMZ): large domains where the abundance of oxygen is much lower than that in the surrounding ocean environment. Factors and processes resulting in the OMZ formation remain controversial. We consider a conceptual model of coupled plankton–oxygen dynamics that, apart from the plankton growth and the oxygen production by phytoplankton, also accounts for the difference in the timescales for phyto- and zooplankton (making it a “slow-fast system”) and for the implicit effect of upper trophic levels resulting in density dependent (nonlinear) zooplankton mortality. The model is investigated using a combination of analytical techniques and numerical simulations. The slow-fast system is decomposed into its slow and fast subsystems. The critical manifold of the slow-fast system and its stability is then studied by analyzing the bifurcation structure of the fast subsystem. We obtain the canard cycles of the slow-fast system for a range of parameter values. However, the system does not allow for persistent relaxation oscillations; instead, the blowup of the canard cycle results in plankton extinction and oxygen depletion. For the spatially explicit model, the earlier works in this direction did not take into account the density dependent mortality rate of the zooplankton, and thus could exhibit Turing pattern. However, the inclusion of the density dependent mortality into the system can lead to stationary Turing patterns. The dynamics of the system is then studied near the Turing bifurcation threshold. We further consider the effect of the self-movement of the zooplankton along with the turbulent mixing. We show that an initial non-uniform perturbation can lead to the formation of an OMZ, which then grows in size and spreads over space. For a sufficiently large timescale separation, the spread of the OMZ can result in global anoxia.
Abundance indices are essential data for the application of stock assessment models to obtain fish abundance estimates. Abundance indices have usually been derived from fishery-dependent data, yet the increase in fisheries-independent surveys is now offering new opportunities for these calculations. In this study, we explored the usefulness of ichthyoplankton indices derived from scientific surveys in estimating spawning biomass. In addition, we also investigated whether the strength of the year–class of the commercial cohort of Atlantic hake, as a determinant, could be defined at an early life stage. We used samples collected during the triennial mackerel and horse mackerel egg surveys (MEGS), which cover the hake spawning area in the Bay of Biscay. The biomass indices were determined as the abundance of eggs in the early development stage (stage 1) when transformed into egg production (EP) from 1995 to 2019 in the months of March and April—which is considered a period of high spawning activity for hake in this area. Additionally, we built a metric for larval abundance and converted larval length into age. This was in addition to constructing a pre-recruit year-class index (YCI) while using the EVHOE bottom trawl abundance database for hake for the period of 1997 to 2016. The results of regression analysis of egg production and spawning stock biomass indicate that both parameters are significantly correlated (r = 0.76). By connecting the abundance of eggs and larvae in the adjoining stages, we are able to identify two periods of high mortality associated with the transition from “yolk-sac-first” to “feeding larvae” and “late larvae-YCI10”, but we were unable to discover when the strength of the recruitment year–class is determined. As such, it appears that for the northern stock of hake, recruitment is established in the late juvenile stages.
Se presentan resultados del proyecto “Evaluación del stock desovante de anchoveta y sardina común entre las regiones de Valparaíso y Los Lagos, año 2021”, cuyo objetivo general fue evaluar el stock desovante de los recursos anchoveta y sardina común durante el período de máxima actividad reproductiva. Además, se entregan resultados de las condiciones oceanográficas durante el crucero como también aquellas que están asociadas con el proceso de desove.
American Shad Alosa sapidissima is an anadromous clupeid that once supported a robust fishery but has declined drastically throughout its native range due to overfishing, dam proliferation, and poor water quality. A hatchery program on the James River in Virginia was introduced in 1992 to support the recovery of stocks. Following a moratorium of the fishery enacted in 1994, a fisheries‐independent survey was initiated in 1998 to monitor the population recovery efforts and status of American Shad stocks in Virginia. This paper examined 22 years of monitoring data for the James River and determined the effect of hatchery inputs on the James River stock of American Shad. The spawning stock index increased from 2.57 in 1998 to a peak of 9.33 in 2003 but has generally been declining since and has been at very low levels in most recent years. The hatchery prevalence for female American Shad (i.e., the percentage of fish derived from the hatchery) ranged between 3.6% and 60.5%. Years with higher spawning stock index values were significantly correlated to higher percentages of hatchery fish returning to spawn. The stock–recruitment relationship was best explained by the Ricker model, which had the lowest residual standard error and Akaike information criterion value. A threshold level of hatchery‐released individuals (approximately 4 million larvae) was necessary to achieve the highest numbers of returning spawners, but stocking above 7 million larvae correlated with declining returns. Long‐term monitoring of the James River American Shad spawning population allowed for the critical examination of the contribution of hatchery individuals to the yearly spawning run and the relative success rate of each hatchery year‐class. From these data, we consider that the James River spawning stock of American Shad was dependent upon hatchery inputs, with ideal hatchery returns occurring during years of moderate levels of hatchery stocking.
It has been more than 100 years since fish were first described to move to deep waters as size increased, termed ‘Heincke's Law’. However, large‐scale studies on ontogenetic shifts are rare compared with increased reports of distributional changes in response to temperature, often confounded with the ontogenetic shifts. We fill this gap by examining the distribution of ten abundant groundfish species in three dimensions, depth, latitude and longitude, at 10‐cm size intervals within nine subregions of NE Pacific. Here, we utilized large, quality‐controlled datasets from random depth‐stratified, bottom trawl surveys consistently conducted during summer along the NE Pacific shelf from 1996 to 2015. Groundfish demonstrated complex ontogenetic movements in three dimensions across species, size class and subregion. In addition to the expected ontogenetic deepening, shoaling also occurred and some species demonstrated major ontogenetic shifts in longitude and/or latitude with limited changes in depth. Based on standardized ontogenetic shifts in three dimensions, our analyses show that there were significant differences in aggregate fish ontogenetic shifts between small (≤30 cm) and large (>30 cm) size groups. Small fish exhibited substantially larger ontogenetic shifts in depth than the large size group while both groups showed relatively small shifts in latitude and longitude. Our analyses strongly suggest that size structure and ontogenetic shifts should be included in the population distribution.
Les causes et la dynamique de l'uwpelling ivoiro-ghanéen ont été récemment étudiées. Cette zone soutient une pêcherie de petits poissons pélagiques dont le plus dominant est la Sardinella aurita (S. aurita). Le succès du recrutement des premiers stades de développement de S. aurita est conditionné par la circulation locale qui permet soit de rapprocher les œufs et les larves des nourriceries, ou soit de les disperser vers le large où ils sont soumis à des conditions environnementales et trophiques défavorables. Les mécanismes par lesquels les conditions environnementales agissent pour réguler le recrutement de la S. aurita restent mal compris dans la région Nord du Golfe de Guinée, en particulier l'interaction potentielle entre la dispersion, la croissance et la mortalité des larves.L’objectif principal de la thèse est d'étudier l'impact de la disponibilité en nourriture sur la croissance et la dispersion des larves de sardinelles en utilisant une approche de modélisation numérique qui permet d'intégrer les processus hydrodynamiques, biogéochimiques et biologiques fondamentaux. Les résultats ont montré que les zones côtières sont les plus favorables à la rétention à cause de la présence des tourbillons qui agissent comme des barrières empêchant les œufs et les larves d'être emportés vers le large. Les pontes importantes ont lieu pendant la petite (Février) et la grande (Août,) saison d'upwelling. Les profondeurs de rétention maximale sont les couches de surface (0-25 m) et de subsurface (25-50 m). Elles sont associées aux maximum de distribution des champs de proies simulés et à la diminution de l'intensité du Courant de Guinée en profondeur.
Most organisms reproduce seasonally, including most species of marine invertebrates that live across wide ranges in habitat, depth and environmental conditions. We asked: What ultimately selects for seasonal reproduction in benthic marine invertebrates with planktotrophic larvae (characteristic of ≥70% of marine invertebrates)? We hypothesized that seasonal variation in food available for the larvae ultimately selects for timing of adult reproduction. Testing this hypothesis requires a whole life cycle perspective and approach. Using a known proximate cue, daylength, we shifted gametogenesis in the laboratory by six months in a seasonally breeding temperate sea star, the Ochre Star Pisaster ochraceus (Brandt 1835). We were then able to induce spawning, fertilize gametes and culture resulting embryos in vitro to produce feeding larvae six months out of phase with natural photoperiod. We field‐reared these out‐of‐season larvae, similarly produced in‐season conspecifics and similar larvae of an aseasonally breeding asteroid, the Bat Star Patiria miniata (Brandt 1835) in mesh‐covered flow‐through containers that were deployed in seasonally contrasting oceanographic conditions reflecting different productivity regimes and larval food availability in spring and fall. Larval development and survival were similar between seasons: for example, planktonic larval duration was 48 d to first metamorphosis in spring vs. 45 d in fall for P. ochraceus. Hence, temporal variation in available phytoplankton may not be an ultimate selection factor acting on these larvae to regulate timing of seasonal reproduction in the adults. Alternatively, in this and other species of marine invertebrates, selection acting on early benthic juveniles or other life stages may determine the timing of adult reproduction.
Bighead Carp Hypothalmichthys nobilis and Silver Carp Hypothalmichthys moltrix (hereafter collectively referred to as Bigheaded Carp) have spread throughout the majority of the Mississippi River since the 1970s. The current northern invasion edge of Bigheaded Carp in the Upper Mississippi River (UMR) spans between Pools 14 and 20 because of limited passage at Lock and Dam (LD) 19. Mechanisms limiting adult Bigheaded Carp abundance above LD19 are unknown but may be due in part to lack of reproductive success influenced by adult abundance and environmental factors. Our objective was to investigate how relative adult biomass and river temperature and discharge affect maximum annual Bigheaded Carp larval production in the UMR using a Ricker stock-recruitment model. Adult Bigheaded Carp relative biomass (kg/h) was estimated annually with boat electrofishing and larvae were collected every 10 d between May and August 2014–2017 in Pools 14–20 in the UMR. Adult relative biomass ranged from 0.0 to 880.9 kg/h, whereas maximum annual larval densities ranged from 0.0 to 2,869.4 larvae/m3. After accounting for variability among pools and years, the most supported linear Ricker stock-recruitment model indicated the number of recruits per spawner decreased with increasing adult relative biomass and increased with mean discharge. Our results highlight the importance of adult biomass and river discharge conditions for reproduction of Bigheaded Carp along leading edges of invasion. Management strategies that aim to maintain low adult abundance where reproduction is not yet occurring could help limit population increases via reproduction, whereas reducing high adult biomass (e.g., commercial harvest, barriers) may result in greater Bigheaded Carp reproductive output in the UMR.
Anthropogenic perturbations and climate change have altered the zooplankton community structure in the Klang Strait during the past 30 years, in that the taxa of large-bodied crustaceans (Acartiidae, Calanidae, Pseudodiaptomidae) are being replaced by those of small-bodied crustaceans (Oithonidae, Ectinosomatidae), gelatinous jellyfish, and appendicularians. Since zooplankton constitutes the main larval food, we questioned: have bottom-up effects impacted larval fish feeding via the food chain? Larval fish that were sampled previously (1985–1986) and nearly three decades thereafter (2013–2014) were analysed for their dietary composition. Despite the dramatic replacements of zooplankton taxa due to escalating anthropogenic disturbances, the dominant copepod families, Paracalanidae, Oithonidae and Euterpinidae, remain the major prey for fish larvae. Dietary shifts in prey composition from before to after impact depend on the larval fish family and their ontogenetic stage. Dietary changes are observed in the Bregmacerotidae, Engraulidae, Gobiidae and Sciaenidae that opportunistically feed on the small-bodied copepods (oithonids and Parvocalanus crassirostris), whereas the Callionymidae, Clupeidae and Cynoglossidae naturally feed on these copepods even before these prey become numerically dominant with anthropogenic disturbance. There is no dietary shift in the Leiognathidae, exceptional in that they are specialists feeding mainly on detritus and polychaete larvae. Since the bottom-up effects are not comprehensive among fish families and dietary plasticity is evident, it is postulated that only the intolerant or non-adaptable larval species are adversely affected by the environmental perturbations.
Vendace is commonly assumed at low risk to recruitment overfishing. This assumption has been confirmed for boreal stocks but might not apply at lower latitudes. We evaluated the risk of recruitment overfishing at the southernmost extent of vendace populations by comparing fecundity, natural mortality, and fishing mortality of two stocks differing in growth with those of a population not subject to fishing. Although in one study lake vendace grew faster owing to high lake productivity and low stock density, and had substantially higher age-specific fecundity, intense harvest before first spawning negatively affected the stock's recruitment potential by reducing spawner abundance. In contrast, in the slow-growing stock, vendace entered the fishery after first spawning, and egg production per recruit was similar to that of the population not subject to fishing. We conclude that vendace stocks characterized by fast somatic growth may be at higher risk of recruitment overfishing, which can be reduced by protecting first-time spawners.
Atlantic salmon Salmo salar L. and brown trout Salmo trutta fario L. are species of high socio-economic and ecological value. Declining populations make them target species of fisheries management. This paper reviews the direct effects of deficient longitudinal connectivity, changes in discharge, high water temperatures, oxygen depletion, changes in water chemistry and increasing loads of fine sediment on the critical life stages of spawning, egg incubation and emergence. It further provides an overview about the basic autecological requirements of Atlantic salmon and brown trout and summarises important thresholds of physico-chemical tolerances. This collection of information provides important baselines for assessing historical, ongoing and new threats relevant for the management of both species in fresh waters. Critical early-life stages of both species are almost identical, creating synergies in conservation and restoration. Seaward-migrating forms are exposed to further stressors, but improving starting conditions can also greatly improve their resilience.
Hake, mackerel, horse mackerel, anchovy and sardine larvae were identified from samples of ichthyoplankton collected during eight surveys in the Bay of Biscay between 2000 and 2005. Comparative analyses were carried out to explore the early growth patterns of these species based on differences in body proportion and the interpretation of the otolith microstructure to estimate their age. Statistical differences in development rates were observed for different body proportions. On the one hand, the larvae of hake, mackerel and horse mackerel prioritise the growth of those parts of the body related to feeding (body weight, head and jaw), while those of anchovy and sardine prioritise those related to swimming (body length). We propose that these different strategies are adaptations to reduce larval mortality, each of them focusing on the main factor that controls it during the early stages: starvation and predation. These growth strategies are interpreted from an environmental perspective mainly related to the characteristics of the food and the abundance of predators in the environment in which the larvae develop during this vulnerable life stage.
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