ABSTRACT The demand for marine resources is increasing, and an increasing number of fish stocks are fully or overexploited. To turn this downward projection around, states need to strengthen the effectiveness, equity and implementation of fisheries management measures. One important component that often determines the performance of fisheries management is the capacity of the participating parties. Despite the increased global awareness regarding the need for enhanced capacity support, many coastal developing states still lack the skills and tools to implement conservation and management measures effectively. In this paper, we highlight some of the current issues in capacity building, looking at the individual, national and regional levels. We argue that capacity is a core determinant of equity and effectiveness in fisheries governance. Furthermore, we describe the potential of complementary mechanisms to provide capacity support. Specifically, we focus on the climate change regime and the Agreement on Biodiversity Beyond National Jurisdiction. Unless coastal developing states have the sustained scientific, legal, technical, institutional and financial capacity to participate meaningfully in regional fisheries management organisations, the adoption of conservation and management measures will not necessarily translate into effective or equitable outcomes.
ABSTRACT Human activity has altered nearly all ecosystems on Earth, contributing to substantial biodiversity loss across taxonomic, genetic and functional dimensions, from the intraspecific to the ecosystem scale. Yet some components of biodiversity remain hidden or underappreciated, including behavioural diversity. Behaviour is often among the earliest whole‐organism responses to environmental change, and diversity in behaviour can occur within individuals, among individuals, among populations and across communities and ecosystems. This variation may influence growth, survival, reproduction, ecological interactions and responses to anthropogenic pressures, although its effects on population stability and resilience are likely context‐, scale‐ and component‐dependent. In this review, we examine behavioural diversity in fishes, defined here as variation in behavioural traits across levels of biological organisation, from individuals to ecosystems. Our review has two complementary aims. First, we provide a conceptual overview of behavioural diversity, clarify how it differs from related constructs such as personality, plasticity, and behavioural syndromes, and summarise the evolutionary, ontogenetic, ecological, stochastic and anthropogenic processes that generate or erode it. Second, we evaluate why behavioural diversity matters for fish ecology, fisheries management, aquaculture, restoration and conservation. We conclude by identifying key research needs, including improved quantification, stronger empirical links between behavioural diversity and ecological outcomes, and the development of management approaches sensitive to behavioural diversity. More explicit consideration of behavioural diversity should improve our ability to predict fish behavioural diversity responses and to design conservation and management measures that account for variation rather than only average behavioural responses.
ABSTRACT Zoonotic parasites are an increasingly recognised challenge for seafood safety. Anisakid nematodes currently represent the most significant fish‐borne parasitic threat in Atlantic wild fisheries. Recent regional surveys and global syntheses suggest significant increases in the prevalence and intensity of anisakid infections across multiple commercially important fish species, raising concerns for public health, marketability and consumer confidence. At the same time, the growing popularity of raw and lightly processed seafood has increased human exposure to anisakids, potentially amplifying infection risk independently of ecological changes in parasite abundance. Here, we synthesise current knowledge on anisakid parasitism in Atlantic fish and critically examine the interacting mechanisms that may be driving these trends. We highlight the roles of climate‐driven ecosystem change, recovery and redistribution of marine mammal definitive hosts, shifts in fish host ecology, evolving fishing and post‐capture handling practices, changing seafood consumption patterns, and major advances in parasite detection and diagnostics. While improved surveillance has undoubtedly increased reporting, converging evidence suggests that changes in host–parasite dynamics are also occurring. We further discuss practical mitigation options across the seafood value chain, from onboard handling and processing to retail, food service and consumer awareness, emphasising the need for coordinated, risk‐based approaches. Collectively, these developments challenge the long‐standing perception of wild fish, especially when consumed raw or lightly processed, as inherently safe, underscoring the importance of integrating ecological insight, consumer behaviour, technological innovation and public‐health guidance to ensure sustainable fisheries and safe seafood consumption.
ABSTRACT Aquaculture is now the fastest growing food sector and may be a promising solution to increasing seafood demands. Yet, carnivorous aquaculture species such as salmon and seabass continue to rely on fishmeal and fish oil (FMFO), which are derived largely from pelagic fish that are sometimes key to the food security of some coastal nations. This reliance on wild‐caught resources fuels debates around the ethics, sustainability and socio‐economic impacts of transforming edible fish into feed. Despite growing concerns, traceability and transparency around the origin and composition of FMFO is limited, leaving feed ingredients largely invisible to customers, consumers and policymakers. We argue that this opacity erodes trust and hinders informed debate and conversation around the growth of aquaculture, its sustainability, and ethical concerns regarding just and equitable food systems. Here, we highlight how DNA metabarcoding of commercial feed samples offers a promising transparency tool by revealing a wide diversity of species, far beyond what labels disclose. If aquaculture is to demonstrate that it supports global food security, this blind spot around fish feed will need to be addressed urgently. Increased transparency on FMFO sourcing and composition could rebuild public trust, empower producers, consumers and regulators, and safeguard the livelihoods of coastal communities by ensuring a just pathway to aquaculture production.
ABSTRACT Satellite‐based vessel‐tracking technologies have ushered in a new era for monitoring fishing activity at scale. By combining artificial intelligence (AI) methods with remotely‐sensed data, researchers can now detect, classify and analyse fishing behaviour across vast and previously unobservable ocean regions. Technological advancements in vessel tracking are rapidly reshaping fisheries science and management, enabling new insights into fleet behaviour and its effects on marine ecosystems. This review synthesizes the state of the science in AI‐enabled vessel tracking and highlights its transformative potential across four core domains: stock assessment and catch reconstruction, effort controls, spatial management, and monitoring, control, and surveillance. We explore how satellite‐based vessel‐tracking data complement legacy systems such as logbooks and observers, while also unlocking new capabilities to track ‘dark vessels’ that are not publicly observable by other means. We also identify key scientific and institutional challenges that are priorities for advancing the scientific frontier, including: filling data gaps for small‐scale fleets, resolving uncertainty in behavioural inference and vessel identities for dark fleets, integrating catch and effort reporting, expanding real‐time decision support, designing cutting‐edge policy instruments to manage fisheries and developing shared standards for algorithm transparency and validation. As the field matures, we propose a forward‐looking agenda to ensure that fleet tracking delivers on its promise to enhance transparency, support real‐time decision‐making and drive more inclusive, science‐based ocean governance.
ABSTRACT In Neotropical river systems, dams promote profound physical and biological changes by disrupting longitudinal connectivity, altering flow regimes, and modifying nutrient and energy pathways. These transformations have the potential to reshape the trophic organization of fish assemblages. Here, we conducted a systematic review and multilevel meta‐analysis to evaluate the effects of river impoundment on species richness within trophic guilds across upstream (control), reservoir, and downstream (intervention) river stretches. Following the PRISMA guidelines, we screened 2428 records from four scientific databases and grey literature, of which 26 studies met the eligibility criteria for quantitative synthesis. Overall, no consistent differences in trophic guild richness were detected between upstream reference stretches and reservoir or downstream stretches. However, meta‐regression analyses showed that latitude explained variation in trophic guild richness within reservoir stretches, whereas reservoir area was the only significant predictor in downstream stretches. Although significant residual heterogeneity remained, these results indicate that trophic responses to river impoundment are strongly context dependent and influenced by environmental conditions operating at different spatial scales. Overall, our findings indicate that river impoundment does not consistently alter trophic guild richness across Neotropical river systems but instead promotes context‐dependent ecological responses, providing new insights into the functional organization of fish assemblages and supporting conservation and management strategies for dammed rivers.
Ocean acidification (OA) remains a major and underexplored threat to marine fishes, particularly regarding reproductive physiology and early life stages (ELS). Although research over the past 15 years has documented diverse OA effects, substantial knowledge gaps persist. Most studies focussed on a limited set of species from North America and Europe, leaving broad uncertainty across phylogenetic groups, geographic regions and multi-stressor conditions. In adult fish, especially females, elevated pCO2 can shift energy allocation to prioritise reproductive output at the expense of egg or clutch size. While adult and juvenile fish have well-developed acid-base balancing systems, embryos and larvae possess only rudimentary mechanisms, making them more vulnerable to OA. This article stresses the importance of understanding these physiological and mechanistic responses to predict the future of fish stocks and ecosystem health as OA intensifies due to ongoing CO2 emissions. Our results highlight that OA responses in fish are highly variable and often specific to life stage and species, with acute and sometimes stage-specific effects not fully documented. Lastly, our recommendations on targeted research and funding are necessary to address the remaining knowledge gaps, including broadening taxonomic and geographic sampling, exploring multi-stressor scenarios and improving understanding of the downstream effects of OA on fish reproduction and development. Maintaining robust fish populations is vital for food security, employment and ecosystem functioning, making continued investigation into OA's impacts a scientific and societal priority.
Bottom-tow gear fisheries (trawls and dredges) produce similar to 24 million mt of harvest annually, representing a globally important animal-sourced food system. While many are currently sustainably managed, growing concern over the potential for ecosystem impacts from bottom-tow gears has increased pressure to improve these fisheries. We assembled an international working group of > 30 contributors, including fishing industry participants, managers, non-governmental ocean conservation organization representatives, and scientists to synthesize obstacles to bottom-tow fisheries sustainability and to develop expert-based recommendations to operationalize sustainability advancements moving forward. We identified 30 key gaps impeding bottom-towed fisheries sustainability spanning 6 core challenge areas including: seafloor disturbance, bycatch and discards, management design and implementation, fishing operations, cross-sector conflicts, and public perception and communication. We generated 28 priority recommendations to address bottom-tow fisheries sustainability obstacles with themes including: addressing data gaps, advancing mechanistic understanding and modelling tools, strengthening management processes, and improving knowledge sharing and communication. Cross-disciplinary and diverse system experience among fisheries and marine ecosystem stakeholders will be critical for operationalizing bottom-tow fisheries sustainability advancements. As the global human population approaches 10 bn in the next 30 years, ensuring sustainable wild capture fisheries is an imperative for feeding the world. Outputs from this synthesis serve as a resource for fishing and marine ecosystem stakeholders to identify key challenge areas and associated entry points for solutions-oriented efforts to improve the sustainability of bottom-tow fisheries.
Automatic and accurate estimation of fish sizes from images is essential for many monitoring, fisheries management, stock assessment and conservation efforts. However, current methods often rely on physical reference objects or stereo-camera systems that are not always available. This paper explores the advancements, applications and challenges of automated fish body-size estimation from images, using artificial intelligence (AI) and machine learning (ML) methods. We first introduce key concepts in AI and ML for a non-specialised audience and review existing literature on models used for fish size estimation. We identify key barriers such as a lack of high quality and publicly available datasets, image variability, scattered efforts and the challenges of model generalisation across diverse species. Then we present a novel framework for size estimation from monocular (non-stereo) images without a specified reference object, using a dataset from an angling app. Our approach utilises an efficient, pretrained deep learning-based feature extraction tool integrated with an automated regression pipeline. Our findings demonstrate a promising pathway for size estimation in images without a reference object, with most estimated fish lengths within 10% of their true length. Future research and collaborative efforts should focus on diversifying and sharing training data and integrating metadata. To this end, we created a user-friendly online application, where the community can test the model performance and contribute photos. Finally, it is essential to rigorously test and refine the robustness of current models in real-world fisheries applications and to adopt standardised, comparable metrics for evaluating fish size estimation models across studies.
Steepness, a parameter derived from the stock-recruit relationship, is widely used in fishery stock assessments to scale the productivity of a population. Steepness is a highly influential parameter, but it is often unknown a priori and is typically difficult to estimate. Attempts to statistically estimate steepness, either within stock assessments or through meta-analyses, can lead to implausible results. We move beyond steepness as a statistical concept to emphasize that steepness is determined by life history traits and the early life survival of offspring of a population. We return to the original derivation of the Beverton-Holt stock-recruit relationship, and model recruitment to the population as a function of total egg production, rather than using spawning biomass as a proxy. We then demonstrate how to calculate steepness based on biology through a case study of rockfishes (Sebastes spp., Scorpaenidae) in the California Current, where steepness has been notoriously difficult to estimate. We leverage a wealth of reproductive ecology and early life history information (empirical data and associated life history parameters) to compute steepness values for four species of rockfishes, in order to illustrate how steepness varies by species based on differences in their life histories. We also show the sensitivity of steepness to the different life history traits. We conclude that steepness of a stock-recruit relationship is a real biological parameter and can be meaningfully informed with life history parameters including early life survival.
Forecasting the number of individuals entering a fishery is critical for sustainable harvest and thereby management actions, but it remains challenging due to the considerable inter-annual variability and the complex nature of causal factors. This long-standing 'recruitment problem' has become even more urgent under ongoing climate change and the associated regime shifts overturning traditional predictive models. Leveraging the highly data-rich Northeast Arctic cod (Gadus morhua, Gadidae), this study proceeds beyond traditional data and method limitations. Such an initiative appears most timely because its recruitment (R), measured as number of 3-year-olds, is currently low and raising socio-economic concerns. We hypothesize a causal map and then apply Dynamic Structural Equation Model with sensitivity analyses to explore complex response patterns. The higher temperature exhibited a dual role: positive for spawning stock biomass (SSB) but negative for abundance of 1-year-olds (Age1) and R. Predation on postlarvae by northward-migrating Northeast Atlantic mackerel (Scomber scombrus, Scombridae), but not by herring (Clupea harengus, Clupeidae), appeared to influence Age1 negatively. As expected, fishing reduced SSB, whereas prey availability, represented by mesozooplankton biomass and stomach fullness, exerted a positive effect on Age1 and R. These suite of links remained robust, but shorter time series (< 30 years) may blur underlying patterns. Essentially, the low recruitment success (R/SSB) seen since 2010 (from the 2007 year class onwards) seems related to an overall poor situation for the 1-year-olds. Predictions give a less optimistic outlook and underline the high importance of maintaining today's advanced precautionary management strategies for this world's largest cod stock.
Public acceptability of fisheries policy remains a key challenge for successful governance, constraining the set of feasible management options. To many, public opinion seems mysterious-rarely aligned with scientific evidence, yet not random, as it is shaped by frames, narratives and social factors. Here, we examine public acceptance of governing a new fishery through a survey experiment conducted in 10 countries. As a case, we consider the mesopelagic zone, a largely untapped resource with high biomass and economic potential. However, mesopelagic fishing also entails ecological and social risks, including impacts on food webs, carbon sequestration and global equity. Acceptance varied substantially across countries. Support was lower in wealthier countries, such as Germany and the Netherlands, where respondents also favoured stricter regulation, and higher in Indonesia, Nigeria, the Philippines, and, to a lesser extent, Spain, where support for regulation was weaker. Different frames have different effects across countries. For example, emphasizing risks to food webs reduced acceptance in Argentina and Nigeria, while highlighting disproportionate burdens on the Global South further lowered support only in Nigeria. At the individual level, confidence in government and large companies increased support for mesopelagic fishing, whereas other demographic factors played smaller roles. These findings emphasize the role of equity concerns and localized public opinion in shaping policy for fisheries and highlight the context-dependent power of narrative framing.
Small pelagic fish (SPF) are critical to the trophodynamic structure and function of marine systems and support some of the most valuable and socially important fisheries worldwide. Their "boom and bust" population dynamics, shifts in distribution, and importance as forage resources for other fish stocks place unique challenges to assessing and managing SPF. In response to these challenges, an international working group was formed in 2019 to foster collaboration aimed at closing key knowledge gaps in the ecology and sustainable management of SPF. Here, that group reviews progress made over the last similar to 10 years and identifies priorities for the next stage of coordinated international collaboration. Key research needs include: (i) enhancing monitoring programs to capture shifts in SPF distribution and incorporating new technologies, from molecular tools and digital imaging to biophysical and ecological modelling, (ii) improving data sharing to better understand life-history bottlenecks and cross-regional population dynamics, (iii) advancing process-based studies on oceanic and trophodynamic interactions to clarify the ecological roles of SPF as both predators and prey, and (iv) conducting bioeconomic and risk analyses to assess the vulnerability of fishing-dependent human communities to environmental and fish population fluctuations. A key pathway forward involves integrating mechanistic ecological knowledge, ecosystem and bioeconomic modelling, and social-ecological frameworks into real-time, adaptive, and equitable management approaches. This integration will be essential for developing resilient, ecosystem-based fisheries management capable of anticipating tipping points, accommodating non-stationary population dynamics, and ensuring sustainability under future climate and socio-economic uncertainties.
Despite over a century of fisheries research focused on identifying environment-recruitment relationships, robust and long-standing relationships remain elusive, and the prevalence of ephemeral relationships has raised doubts about their utility for explaining recruitment. However, what if these relationships are shadows of other life-history processes? To explore this question, we simulated populations where the environment affects natural mortality, a life-history process often assumed to be constant, to determine whether spurious environment-recruitment relationships arise. Specifically, we produced a series of simulations in which the environment affects only one life-history process, while estimation models were misspecified with respect to which process was environmentally driven. Our simulations show that misspecified models consistently produce false detections of environmental effects on recruitment when the environment affects only natural mortality. These results indicate that previously identified environment-recruitment relationships that later broke down may have been artifacts of environmental effects acting on other life-history processes that were assumed to be constant. Focusing exclusively on recruitment may therefore obscure the true pathways through which environmental variability influences population dynamics. Ultimately, sound scientific advice in the face of marine ecosystem complexity requires hypothesis driven model comparisons and transparent model assumptions.
The consequences of mis-managing vulnerable stocks (i.e., those with low productivity and high susceptibility to depletion) are high and potentially permanent. To support sustainable fisheries management, stock assessments can be improved by increasing the quantity and quality of fishery-independent survey (i.e., survey) data. Social and economic value typically determine sampling priorities, but high value stocks are not necessarily at the highest risk for depletion. So, we modified the Productivity-Susceptibility Analysis, a data-limited fishery assessment tool, to identify which stocks are most vulnerable to unpredicted stock depletion (due to overfishing, environmental stressors, or mis-management from unknown or mis-specified stock status). We examined the vulnerability of 426 fish stocks or species within stock complexes that NOAA Fisheries assessed from 2005 to 2024 (excluding highly migratory and salmon stocks). We then examined patterns of vulnerability by taxonomy, area and survey method. The most vulnerable stocks were demersal teleosts (e.g., Psychrolutids, Macrourids, Scorpaenids). On average, the Caribbean Sea, West Coast and Pacific Islands contained the most highly vulnerable un-sampled stocks. Visual surveys in Alaska sampled the most vulnerable stocks on average, followed by bottom trawl surveys in Alaska. Across all areas, bottom trawl surveys provided stock assessment information for nearly twice as many stocks as any other survey method on average. Data limitations can lead to large buffers around catch limits and whether highly vulnerable stocks are subject to directed fisheries or are constraining 'choke' stocks in others, considering stock vulnerability alongside social and economic value may lead to better fishery management outcomes.
Acoustic communication is now recognised as a widespread and functionally important component of fish behaviour. However, its evolutionary interpretation remains fragmented, as different types of acoustic signals are not interpreted with the same level of confidence. In particular, sounds recorded under disturbance or from hand-held individuals are widely used in comparative studies but remain debated in evolutionary contexts. Here, we re-examine these limitations by reviewing empirical, mechanistic and behavioural evidence across a wide range of teleost taxa. We show that interspecific acoustic differences are not restricted to reproductive contexts and that sounds obtained under disturbance can reflect intrinsic species-level properties of neural control, musculature and sound-producing structures. At the same time, we highlight that acoustic species specificity has not been demonstrated as a general rule across fishes, nor does sound alone constitute a universal prezygotic barrier. By integrating behavioural context, sound-production mechanisms and recording methodologies, this review provides a framework to interpret acoustic variation in an evolutionary context and clarifies the scope, limits and evolutionary relevance of different acoustic datasets.
Rapid changes in marine ecosystems highlight the need to account for time-varying productivity in stock assessments used to support fisheries management. Common approaches incorporate annual variation or regressing processes such as recruitment, natural mortality, or growth on environmental variables. While the latter represents a step toward biological realism, it often fails to account for interactions among variables and may yield biased inferences when key drivers are correlated or unmeasured. We introduce a novel framework, Structural Causal Enhanced Stock Assessment Modelling (SCEAM), which integrates a Dynamic Structural Equation Model (DSEM) into a state-space stock assessment method. SCEAM encompasses and extends the full range of existing time-varying approaches within a single framework, enabling direct comparison among them. We applied SCEAM to walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska to improve recruitment forecasting, comparing three causal models of increasing complexity to recruitment modelled as random deviations around a mean, a first order autoregressive process, or regressed on a single variable. We found that a causal model with intermediate complexity best balanced fit, parsimony, and predictive skill. This configuration reduced unexplained variance of recruitment by 69% and improved one-year-ahead forecasts. Key variables included juvenile body condition and juvenile and larval catch rates. Our study represents the first application of a structural causal model embedded within a fisheries population model. SCEAM offers a unified, hypothesis-driven approach for integrating multiple non-independent variables. We therefore propose that SCEAM serve as a general scientific and statistical framework for conducting next-generation ecosystem- and climate-linked fisheries stock assessments.
Bioaccumulation of environmental toxicants in aquatic ecosystems presents a significant ecological challenge including potential implications for fish reproduction and population dynamics. Through this meta-analysis, we investigated how elevated mercury (Hg) and polychlorinated biphenyls (PCBs)-two prevalent and problematic contaminants-in large, and presumably old fish, affect toxicant concentrations in their eggs and subsequent offspring success. We synthesized published data to analyse: (1) the association between maternal size and egg toxicant loads, (2) the relationship between maternal muscle toxicant concentrations and egg toxicant loads and (3) the impact of egg toxicant loads on offspring hatching success, mortality and growth. Our results revealed that maternal size was strongly, positively associated with egg toxicant concentrations, with Hg showing an effect size nearly double that of PCBs. Similarly, toxicant concentrations in maternal muscle tissues were strongly, positively associated with egg concentrations for both contaminants. Additionally, elevated egg toxicant loads were associated with decreased hatching success and increased offspring mortality, whereas impacts on growth rates varied by toxicant, highlighting negative impacts on early life stages. These findings have important implications for fisheries management, particularly regarding the protection of 'big old fat fecund female fish' (BOFFFFs). Although BOFFFFs typically produce numerous eggs, our study shows these benefits may be offset by increased toxicant transfer to offspring in contaminated systems. Management strategies should consider the reproductive benefits of BOFFFFs and the potential disadvantages of maternal toxicant transfer when establishing conservation priorities, especially in historically or currently contaminated systems or populations more susceptible to bioaccumulation.
Central to ecosystem-based fisheries management is ensuring the sustainability of bycatch and byproduct species. However, the sustainability of these species is difficult to assess as the lack of information limits the use of traditional stock assessment methods. We demonstrate, using a complex multi-species fisheries exemplar, the efficient assessment of large numbers of diverse species, using a modified Sustainability Assessment for Fishing Effects (SAFE) approach. Applying this technique to 256 teleost and elasmobranch species caught in Australia's Northern Territory Demersal and Timor Reef Fisheries, we first applied an initial screening assessment to identify at-risk species followed by a secondary SAFE assessment for a more detailed evaluation. To enhance the precision of the secondary assessment, we incorporated species distribution modelling and refined fishing footprint estimates through spatial analysis of trawl paths, from vessel monitoring system data. Additionally, we integrated Monte Carlo simulations into the SAFE process to quantify uncertainties in fishing footprint and capture efficiency parameters. The conservative criteria applied in the initial screening process assessed 208 species as low-risk, with the remaining 48 species evaluated through our modified secondary SAFE approach. These 48 species were also subsequently classified as low-risk. Our approach adds steps to the SAFE process but enables us to efficiently assess large numbers of diverse species and thereby allows resources to be allocated to those species most at-risk. This adaptable approach is readily modifiable for application in other fisheries, including those with no or limited effort and catch data.
Introductions of species outside their native range, such as pink salmon (Oncorhynchus gorbuscha) in the Laurentian Great Lakes, can serve as unplanned experiments that provide new insights into ecological adaptation. We synthesize available information on the understudied Great Lakes pink salmon invasion and highlight how this case can inform research and management related to expansions and invasions of this species in the Pacific, Arctic and North Atlantic Oceans. Accidentally introduced to Lake Superior in 1956, pink salmon quickly spread to all five Great Lakes, displaying unexpected behaviours and life history plasticity. This invasion history demonstrates a remarkable ability of pink salmon to establish from a small founder population, colonize large areas, produce explosive year classes to rapidly increase in abundance, and complete a full life cycle entirely in freshwater. One of the most striking changes is a shift from their rigid 2-year Pacific life cycle to a variable maturation age ranging from 1 to 4 years, likely influenced by prey availability as well as temperature and other environmental factors. We discuss implications for expansions elsewhere and outline five research themes necessary for understanding pink salmon dynamics in the Great Lakes with broader relevance for managing the species everywhere: (1) What drives rapid changes in abundance? (2) How do temperature extremes influence their ecology? (3) What causes departures from the 2-year life cycle? (4) How important is it for the phenology of life history events to match new habitats? (5) What guides pelagic movements and straying in new habitats?
