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Age estimates are essential for fisheries assessment and management, but deepwater (>200 m) fishes are often difficult to age using traditional techniques. Therefore, age-predictive epigenetic clocks were developed for a model deepwater reef fish, blackbelly rosefish Helicolenus dactylopterus, using two tissue types (fin clips and muscle; n = 61 individuals; 9−60 years) and Δ14C-validated consensus age estimates. The influence of biological information (length and sex) on epigenetic clock accuracy, and the potential for developing a multi-tissue clock, were also assessed. Bisulfite-converted restriction site-associated DNA sequencing (bsRADseq) was used to identify CpG sites (cytosines followed by guanines) exhibiting age-correlated DNA methylation, and epigenetic clocks showed strong agreement (R2 > 0.98) between predicted and consensus ages. Including length and sex data enhanced accuracy and precision (R2 > 0.99; mean absolute error < 1 year). Age-associated CpG sites were identified across tissues, but a multi-tissue clock performed poorly relative to single-tissue clocks. Overall, results demonstrate that accurate and precise epigenetic clocks can be developed for deepwater fishes, and the inclusion of biological information may enhance clock accuracy and precision. [ABSTRACT FROM AUTHOR]

Habitat models often rely on data with incomplete or patchy survey coverage, making it necessary to project observed habitat relationships into unsampled areas. Model transferability is often assumed, rarely tested, and may result in uninformed management recommendations if not validated. In the eastern Gulf of Maine, data from the federal trawl survey has historically been used to identify suitable habitat for juvenile Atlantic cod (Gadus morhua), despite mainly sampling in offshore waters. This study evaluated the spatial transferability of a habitat suitability index model by projecting offshore habitat relationships inshore and comparing them to models built using two inshore surveys. Due to rare warm-water exposure in offshore waters, the federal survey model was unable to identify suitable habitat in the warmer, shallower areas that the inshore surveys identified, suggesting that offshore models are not transferable inshore for juvenile cod in the eastern Gulf of Maine. The results of this study have implications for fisheries worldwide and suggest that incorrectly assuming model transferability could pose a significant hurdle for effective conservation and management. [ABSTRACT FROM AUTHOR]

Evaluating the efficacy of the use of Trojan male brook trout with two Y chromosomes (MYY) requires a better understanding of reproductive performance. We measured the reproductive performance of hatchery age-0 and age-1 MYY brook trout compared to hatchery XY males using laboratory crosses. Offspring of XY males had higher survival than offspring of age-1 MYY 1-day post-fertilization, but not offspring of age-0 MYY. We found no detectable differences in survival from eyed-egg to the juvenile-fry stage. However, size-at-age differed, where offspring of age-0 MYY were 3.6% smaller in length and 25.2% smaller in weight than those of XY males. For crosses fertilized by both MYY and XY males, we found that a significantly higher proportion of offspring within families were sired by MYY versus XY males. These results show, under controlled conditions, evidence for possible fitness advantage for MYY under sperm competition, but a possible fitness disadvantage associated with early growth of their offspring. Overall, our results hold promise for the use of MYY brook trout to serve as an effective eradication tool. [ABSTRACT FROM AUTHOR]

Accurate and precise estimates of survey abundance indices are essential inputs for stock assessment models and are important for the successful conservation and management of fisheries stocks. Since abundance indices can be standardized in various different ways, from conventional design-based approaches to model-based approaches, it is essential to compare the efficiency of those approaches and quantify the consequences for stock assessments. In this study, we focus on an important commercial stock of witch flounder (Glyptocephalus cynoglossus) in NAFO 3N+3O divisions. We first compare the survey indices standardized by design-based and model-based approaches, and find that a model-based estimator provides more precise estimates of survey indices than design-based approach for this stock. We then apply a widely used age-structured statistical catch-at-length (ACL) assessment model to the standardized catch-at-length survey indices from both approaches to estimate the age-based population dynamics for this stock. We conclude that the ACL model fit to model-based indices performed better than the same model fit to design-based indices. [ABSTRACT FROM AUTHOR]

The proportion of mature fish at length is one of the most important population attributes when evaluating reproductive potential for fish stock assessment purposes. Bias in maturity ogive parameters can lead to fishery management decisions based on misspecified biological reference points. These parameters can vary spatially and temporally, and this variability should be understood and included in the assessment models. However, integrating this variability becomes challenging when specific spatial-dependent ogives cannot be used in the stock assessment model. Hence, this study proposes a novel use of a multivariate response Bayesian regression model, employing an integrated nested Laplace approximation to estimate a single global maturity ogive using data from various spatial areas. This model explicitly accounts for differences in the sampling process and combines information from different areas to estimate shared maturity ogive parameters using joint-likelihood procedures. The model is applied to the European hake stock in ICES (International Council for the Exploration of the Sea) Divisions 27.8.c and 27.9.a, serving as a practical guide. In this model, we have considered different predictors to handle the relationship between the probability of being mature and the length and year covariates. Our results suggest that the logistic formulation correctly captures the relationship between the probability of being mature and length. For year variability, including a year factor covariate or year random effect in the predictor model produces similar values of goodness of fit measures. [ABSTRACT FROM AUTHOR]

Fish that undertake juvenile migration pass through habitats that vary in mortality risk. The ability to identify regions of persistently low survival would improve fishery management. We conducted a field study combined with predictive modeling of survival in downstream migrating juvenile sea lamprey using a new micro-acoustic telemetry tag designed for implantation into small, slender-bodied fishes. Detection data were collected from eight receivers placed across a coastal riverine–wetland–lake complex. Juvenile sea lamprey initiated downstream movement near nautical twilight, stopped frequently, and were more likely to move during high river discharge. Estimated survival was highest in the riverine reach, declined through the river–wetland complex, and dropped precipitously in the drowned rivermouth lake. However, the high transmission rate and resulting short battery life of the microtransmitters (as configured) likely resulted in missed detections in the lower reaches. Simulation analyses suggested survival estimation could be improved by increasing the number of tagged lamprey and staggering release locations. We offer practical recommendations for the use of this new transmitter in field studies with small anguilliform fish. [ABSTRACT FROM AUTHOR]

Despite great promise for understanding the impacts and extent of climate change and extreme weather events on aquatic animals, their species, and ecological communities, it is surprising that electronic tagging and tracking tools, like biotelemetry and biologging, have not been extensively used to understand climate change or develop and evaluate potential interventions that may help adapt to its impacts. In this review, we provide an overview of methodologies and study designs that leverage available electronic tracking tools to investigate aspects of climate change and extreme weather events in aquatic ecosystems. Key interventions to protect aquatic life from the impacts of climate change, including habitat restoration, protected areas, conservation translocations, mitigations against interactive effects of climate change, and simulation of future scenarios, can all be greatly facilitated by using electronic tagging and tracking. We anticipate that adopting animal tracking to identify phenotypes, species, or ecosystems that are vulnerable or resilient to climate change will help in applying management interventions such as fisheries management, habitat restoration, invasive species control, or enhancement measures that prevent extinction and strengthen the resilience of communities against the most damaging effects of climate change. Given the scalability and increasing accessibility of animal tracking tools for researchers, tracking individual organisms will hopefully also facilitate research into effective solutions and interventions against the most extreme and acute impacts on species, populations, and ecosystems. [ABSTRACT FROM AUTHOR]

Ecological models are used to understand where fishing vessels operate, improving fisheries management success. The ideal free distribution (IFD) predicts equalization of catch across locations in response to distributions of fish and competing vessels. We applied the IFD as a null model to investigate the movement and catch per vessel (CPUE) of the sockeye salmon drift gillnet fleet in Bristol Bay, AK, from 1980 to 2019. The IFD prediction of equal CPUE across areas was not supported, so we explored violations of two assumptions of the theory. We categorized each vessel according to its mobility, highlighting the "free to move" assumption, and found that when we removed nonmobile vessels, some districts had fewer vessels than predicted from their high CPUE. We examined the "equal competitive ability" assumption by calculating the average CPUE, relative to success of other vessels. The underutilization of profitable districts persisted. Overall, the fleet underused high CPUE areas when considering differences in mobility and relative fishing success, indicating that unmeasured safety concerns, travel costs, knowledge of fishing grounds, or other factors could be preventing an IFD. [ABSTRACT FROM AUTHOR]

Accounting for marine stocks spatiotemporal complexity has become one of the most pressing improvements that should be added to the new generation of stock assessment. Disentangling persistent and dynamic population subcomponents and understanding their main drivers of variation are still stock-specific challenges. Here, we hypothesized that the spatiotemporal variability of density in two adjacent fish stocks is associated with spatially structured environmental processes across multiple spatiotemporal scales. To test this, we applied a generalized empirical orthogonal function and dynamic factor analysis to fishery-independent and -dependent data of red mullet, a highly commercial species, in the Western Mediterranean Sea. Areas with persistent and dynamic high aggregations were detected for both stock units. A large-scale climatic index and local open-ocean convection were associated with both stocks, while other variables exhibited stock-specific effects. We also revealed spatially structured density dynamics within the examined management units. This suggests a metapopulation structure and supports the future implementation of a spatial stock assessment. Considering the common—generally unrealistic—assumptions of panmictic structure and absence of connectivity with neighbouring stock units, our methodology can be applied to other species and systems with putative spatial complexity to inform more accurate population dynamics and structure. [ABSTRACT FROM AUTHOR]

Similar to many freshwater ecosystems, the Laurentian Great Lakes of North America have undergone numerous anthropogenic stressors resulting in considerable loss of biodiversity and habitat. Among Great Lakes fishes, the coregonine sub-family has endured the most extensive declines, including extinction of several species (Coregonus johannae, C. alpenae, and C. kiyi orientalis) and at least 10 instances of local extirpations of other species (C. nigripinnis, C. reighardi, C. zenithicus, C. hoyi, and C. artedi) across all 5 lakes, much of which occurred prior to the 1960s owing to overfishing, interactions with non-indigenous species, and habitat loss. Despite these declines, no federal-, provincial-, or state-mandated actions were ever implemented to conserve coregonine diversity, potentially because so much of the coregonine declines occurred prior to the enactment of federal conservation legislation. Possible explanations for inaction since enactment of that legislation include insufficient data on biological vulnerability or threats, unresolved taxonomy, and limited support from the fishery management agencies and their stakeholders prior to the 2000s. In recent decades, however, several fishery management agencies have undertaken efforts to re-introduce coregonine diversity. These efforts helped lead to development of a science-based framework to restore coregonines that was universally endorsed by fishery managers representing eight U.S. states, four U.S. tribal organizations, and the province of ON, Canada, in May 2018. The basin-wide framework is based on principles of conservation biology and adaptive management. We describe details of its key steps, including planning, restoring, and evaluating, while also describing recent implementation efforts to develop methods, improve available resources, and enhance coordination across the basin. Although our paper describes a regional effort to restore native coregonines, our adaptive-management approach could be used by other multi-agency stakeholders seeking to conserve or restore native fishes. [ABSTRACT FROM AUTHOR]

Despite the importance of recruitment for population dynamics and assessing stock status, limited information exists on the relative influence of various ecosystem and demographic factors on the recruitment dynamics of marine fishes. We develop a statistical framework to identify the ecosystem and demographic factors influencing the recruitment of marine fishes and facilitate improved predictions of recruitment. We demonstrate the approach by examining the relative influence of ecosystem and demographic factors on the recruitment of southern Gulf of St. Lawrence spring- and fall-spawning Atlantic herring (Clupea harengus) stocks, highlighting the benefit of considering multiple factors to better understand recruitment trends. We found that different combinations of biological and physical ecosystem factors along with demographic factors had a significant influence on the recruitment and recruitment rate of spring- and fall-spawning herring. The study emphasizes the value of considering ecosystem characteristics when examining recruitment, provides a framework for researchers to investigate and model recruitment of other fish populations, and supports the continued development and implementation of ecosystem-based fisheries management approaches for species, such as Atlantic herring. [ABSTRACT FROM AUTHOR]

Twenty-six years ago, in response to regionally devastating fisheries collapses in Canada, Hutchings et al. asked "Is scientific inquiry incompatible with government information control?" Now, a quarter-century later, we review how government science advice continues to be influenced by non-science interests, particularly those with a financial stake in the outcome of the advice. We use the example of salmon aquaculture in British Columbia, Canada, to demonstrate how science advice from Fisheries and Oceans Canada (DFO) can fail to be impartial, evidence-based, transparent, and independently reviewed—four widely implemented standards of robust science advice. Consequently, DFO's policies are not always supported by the best available science. These observations are particularly important in the context of DFO having struggled to sustainably manage Canada's marine resources, creating socio-economic uncertainty and putting the country's international reputation at risk as it lags behind its peers. We conclude by reiterating Hutchings et al.'s unheeded recommendation for a truly independent fisheries-science advisory body in Canada to be enshrined in the decision-making process. [ABSTRACT FROM AUTHOR]

For many of the world's fisheries, harvest control rules (HCRs) are the main tools for supporting decision-making. We previously clarified the optimal shape of the HCR to achieve multiple fisheries management objectives (maximising average catch, reducing variation in yields, and avoiding stock collapse) and ensure robustness to estimation errors in biomass by numerically estimating the optimal values of the 21 biological reference points (BRPs) comprised in the HCR. However, for actual management, a simple but comprehensive functional form to emulate the optimal HCR is desirable, as numerical HCR optimisation with many BRPs is time-consuming. Here, we introduced three objective utility functions (U1–U3) representing HCR performance for composite management objectives: mean–variance utility functions, where the performance indicator for variation in yields is the standard deviation (U1) or the annual average variance (U2) of yields, and the constant relative risk aversion utility function (U3). We derived two equations to emulate the optimal HCRs with three adjusting parameters corresponding to the management objectives and different magnitudes of estimation errors. These equations will help stakeholders discuss desired management strategies by showing expected catch and risk by adjusting the parameter values. [ABSTRACT FROM AUTHOR]

Length limits are often used in recreational fisheries management to prevent overharvest and manipulate fish size distributions. These regulations are ideally customized to meet water-specific stock dynamics and fishery objectives. However, in districts with numerous discrete waters, fisheries are commonly managed with a universal regional regulation. Evaluating alternative regional length limits requires consideration of management objectives that may not be important at the single-system level but that emerge as relevant at the regional scale, such as uniformity of regional harvest, diversity of average catch sizes, and opportunity to harvest. We developed a flexible tool for evaluating regional length limits. The tool joins the well-established Beverton–Holt yield-per-recruit model with elements of decision-support methods. The model quantifies regional management objectives as utility functions that are weighted and summed into a single value used to evaluate alternative length limits. The flexibility of the tool stems from its capacity to consider a mixture of stock parameters and associated uncertainty to evaluate multiple length limits, weighting an array of regional fishery objectives quantified by various performance metrics. This adjustability affords flexibility to consider a diversity of options that can stimulate innovation in setting regional length limits. We demonstrate the model by evaluating varying length limits on fishery objectives related to the management of hypothetical yellow perch (Perca flavescens) populations and real black crappie (Pomoxis nigromaculatus) populations. [ABSTRACT FROM AUTHOR]

Implementation of precautionary approach (PA) management systems has generally proven to be a betterment over historic management practices in sustainable use of fisheries resources. However, PA management systems can minimize the application of holistic assessment advice. Single-indicator approaches, typically featuring a measure of stock biomass or abundance, have emerged as dominant in developing methods for PA frameworks. This often leads to advice generated from these frameworks being applied within narrowly focused decision-making pathways and can minimize management application of important ancillary factors. We argue this outcome is counter to the intent of PA management systems and that multi-indicator PA frameworks are a better approach. In this analysis, we detail the multi-indicator PA system development for demonstrative case studies focused on three lucrative fisheries resources in Newfoundland & Labrador, highlighting how multi-indicator PAs are potentially a better approach for the management of stocks with a contrasting range of ecological roles, socioeconomic importance, and data quality. The work is intended to generate a discussion on how PA frameworks should evolve to best suit management purposes. [ABSTRACT FROM AUTHOR]

A limit reference point (LRP) is defined as a level of biomass to be avoided with high probability, which should be selected to protect fish stocks from "serious harm". We present an evidence-based approach for diagnosing serious harm and apply it to the selection of LRPs for five Pacific herring (Clupea pallasii) stocks in British Columbia (BC). Natural mortality (M) is estimated to be time varying and has increased more than it declined over the past three decades, which presents a challenge for estimation of equilibrium reference points based on maximum sustainable yield. We present a semi-empirical approach for developing LRPs, which examines surplus production in relation to spawning biomass to determine whether there is evidence for low productivity, low biomass (LP-LB) states consistent with serious harm. Three stocks showed evidence of persistent LP-LB states that resulted in periods of fishery closures. Based on these results, an LRP of 30% of unfished spawning biomass (0.3B0) was recommended and adopted for management of all five major stocks of BC Pacific herring. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) monitoring methods have played a significant role in improving fisheries management decisions. Yet, their impact to date has been rather limited in Canada, where eDNA sampling and analyses are only beginning to be used to inform management and conservation decisions, practices, and policies. Studies investigating hurdles to the incorporation of eDNA evidence into fisheries management decisions generally focus on technical challenges (i.e., risks of false-positive and false-negative detections). We set out to identify challenges that eDNA researchers and conservation practitioners must overcome to fully unlock the benefits of eDNA sampling for fish management in the Canadian context. We discuss aspects of the broad and heterogeneous geography, preponderance of regions located far from densely populated areas, complex political landscape, and cultural diversity of Canada that may complicate the design of reliable eDNA monitoring tools or restrict their use if not adequately addressed. To advocate for the wider use of eDNA sampling, we outline a number of action items that would facilitate the broad adoption of eDNA sampling as a monitoring tool at the Canadian scale. [ABSTRACT FROM AUTHOR]

As climate change disrupts fisheries, scientists are interested in fisheries projections under climate change scenarios. However, projections that account for spatial oceanographic gradients use increased variable selection power and output high spatial resolution climate data are needed to improve strategic fisheries management. This study uses the least absolute squares and selection operator, a regularization technique, and improved, climate change projections from phase 6 of the Couple Model Intercomparison Project to relate Atlantic surfclam, Spisula solidissima solidissima, recruitment to climate variables. Results show a longitudinal gradient in New York State waters where western recruitment displays a negative relationship with sea surface temperature and eastern recruitment displays a negative relationship with eastward spring wind intensity. Models project that recruitment in 2050 will decrease 100% in western waters and remain sporadic, but high, in eastern waters. This study provides insight regarding surfclam responses to climate change and considerations (methodological and statistical) for improved climate-based fisheries projections. [ABSTRACT FROM AUTHOR]

Bottom-towed fishing gears produce significant amounts of seafood globally but can result in seafloor habitat damage. Spatial closures provide an important option for mitigating benthic impacts, but their performance as a fisheries management policy depends on numerous factors, including how fish respond to habitat quality changes. Spatial fisheries management has largely focused on marine protected areas with static locations, overlooking dynamic spatial closures that change through time. To investigate the performance of dynamic closures, we develop a spatial fishery model with fishing-induced habitat damage, where habitat quality can affect both fish productivity and movement. We find that dynamic spatial closures often achieve greater harvest and habitat protection than fixed marine protected areas or conventional nonspatial maximum sustainable yield management, especially under strong habitat–stock interactions. Determining optimal dynamic spatial closures may require considerable information, but we find that simple policies of fixed-schedule rotating closures also perform well. Dynamic spatial closures have received less attention as fisheries management tools, and our results demonstrate their potential value for addressing both harvest and habitat impacts from fishing. [ABSTRACT FROM AUTHOR]

Consideration of economic outcomes is commonplace in most fisheries management systems globally, although only a few jurisdictions have adopted an economic objective as the primary target for fisheries management. Such an objective has been adopted for Australia's federally managed fisheries, with maximum economic yield (MEY) identified as the primary management objective. Correspondingly, target reference points defined in terms of biomass (i.e., BMEY) are used in harvest control rules. In the absence of explicit BMEY estimates, proxy estimates based on maximum sustainable yield (i.e., BMSY) are used. Identifying BMEY in multi-species fisheries is complicated as most stock assessments are undertaken at the individual species level, but economic activity occurs across species. This is further complicated when different fishing activities using different fishing gears and targeting practices (i.e., métiers) are present in a fishery. We employ an age-structured bioeconomic model to estimate BMEY for key species in a multi-species, multi-métier fishery. We find that optimal biomass levels are substantially higher than those assumed under the current proxy-based system, and that the economic targets are sensitive to prices and fishing costs, both of which change over time. [ABSTRACT FROM AUTHOR]

Fishers commonly disagree with stock assessment results, particularly when a stock declines and strict harvest controls become necessary. Such regulations alter fisher perceptions of stock dynamics, contributing to a divergence in perspectives. Some assessments have inconsistent terminal year values (retrospective patterns) which fuel distrust in scientific advice. When assessment and fishery perspectives disagree, independent surveys can help identify biases and interpret discrepancies. We examine fishery trends and assessment results for Atlantic cod in the Gulf of Maine, a stock which has declined for decades. Trends were compared to a scientific industry cooperative trawl survey and a telephone survey of fisher perceptions. Trawl survey results generally corroborate the assessment perspective on population scale and decline, yet suggest a different view of the age structure. Fisher perceptions were at odds with the assessment and trawl survey and likely resulted from regulations that altered fisher behavior, causing catch rates to increase while the stock declined. Divergent perspectives may be an unavoidable consequence of fishery management, yet acknowledging the underlying mechanisms might help avoid future conflict. [ABSTRACT FROM AUTHOR]

Fisheries are complex social–ecological systems, meaning that the achievement of 'sustainable' fisheries demands a multifaceted approach, involving ecological, economic, social, and institutional dimensions. Addressing these diverse concerns requires the collection and synthesis of new sources of information by science-advising bodies and the engagement of multiple knowledge types from rightsholders and stakeholders. The 'modernized' (2019) Fisheries Act in Canada allows for a diverse range of considerations to form the basis of fisheries management decisions, including knowledge from community or industry groups, but it remains unclear where and when such information is available, how this information is prioritized, who contributes to information-gathering processes, and what the management consequences of information use might be. The present study uses a selection of science-advising documents and briefing notes for decision makers to explore the information and priorities informing fisheries management decisions in Atlantic Canada, with a focus on how rightsholders and stakeholders contribute to the process. These findings can inform efforts to adopt an inclusive and participatory approach to evidence-based decision making to achieve sustainable fisheries, in the broadest sense of the word. [ABSTRACT FROM AUTHOR]

The giant red sea cucumber (Apostichopus californicus) fishery in BC, Canada, is considered sustainable by managers but not by many harvesters. In 1997, the Kitasoo/Xai'xais First Nation began experimental fishing areas (EFAs) at Tolmie Channel and Laredo Inlet to test the effects of different exploitation rates on sea cucumber populations and determine what harvest levels are sustainable. These EFAs were annually surveyed by dive transects and subsequently harvested from 1998 to 2018. Bayesian surplus production models developed in 2011 indicated that the fishery was sustainable, after which the fishery changed from annual to 3-year rotational harvests. Here, we develop updated models to estimate the sustainability of the fishery using all currently available EFA data, including direct estimates of unfished biomass. Our models suggest that the fishery is likely to persist for 175 years at the current harvest rate annually or rotationally, though such long-term projections are likely inaccurate. We present methodology to generate scientific advice for the process of determining a maximum sustainable exploitation rate in the form of crash rate analysis. [ABSTRACT FROM AUTHOR]

Biological reference points for fishery management depend on estimates of current stock status relative to unfished biomass (depletion). The ratio of fish density outside to inside a marine reserve, the density ratio, could serve as a proxy for depletion for data-poor management. However, transient dynamics associated with time lags in returning to the unfished state following reserve implementation make that proxy inaccurate on short time scales. We assessed density ratio management rules using an age-structured, spatially explicit model of four US west coast nearshore fishes following reserve implementation, with scenarios encompassing sampling error, recruitment variability, and uncertainty in natural mortality. In deterministic simulations, management incorporating time lags generally resulted in a higher mean and lower variability in biomass over 20 years, but lower mean yield compared to management that did not. However, when stochastic recruitment was included, differences among simulations due to stochasticity were much greater than any difference in performance between management strategies. Nonetheless, in certain cases, accounting for time lags could help avoid unwarranted increases in harvest effort after reserve implementation. [ABSTRACT FROM AUTHOR]

Management of marine species often relies on biological reference points (BRPs): threshold and target indicators that trigger management actions. These BRPs are usually based on the biology of the species and rarely consider environmental effects. Under climate change, this is problematic as many biological/physiological relationships are assumed temporally static. This spurious assumption can lead to inaccurate management practices. To combat this problem, recent research highlights the importance of developing temporally dynamic BRPs. This paper sees the development of a dynamic BRP calculator to inform management of levels of spawning biomass necessary to sustain the desired future levels of recruitment given forecasted climate scenarios. We test this calculator on American lobster (Homarus americanus) of the Gulf of Maine and Georges Bank. Results for lobster indicate a temperature-driven, but complex, spawning biomass/recruitment relationship. Increased warming scenarios appear to yield overall higher recruitment per spawning biomass and dynamic BRPs calculated under these scenarios reveal that smaller population levels can sustain management-desired recruitment levels. This study highlights the importance of developing dynamic BRPs for fisheries management in a changing environment. [ABSTRACT FROM AUTHOR]

Arctic fishes are threatened by climatic change and other anthropogenic stressors, yet information on how such changes impact survival remains scarce. Acoustic telemetry has become valuable for studying aspects of fish ecology, including survival, which is invaluable in understanding potential responses to changing conditions. In Cambridge Bay, NU, we have been using acoustic telemetry to study movements and habitat use of the culturally and commercially important Arctic char (Salvelinus alpinus). Here, we combine acoustic telemetry data and Bayesian multistate mark–recapture models to study the survival of Arctic char from 2014 to 2018 in the region in freshwater and marine/estuarine habitats. We found that survival probabilities were high (>0.87) and models considering two environments (freshwater and marine) perform better than those considering three (including estuarine habitats). Furthermore, the survival in fresh water was higher than survival in marine/estuary environments. Overall, the results of this study further our understanding of important demographic parameters (i.e., survival) for Arctic char in the region, which will be useful in refining fishery management plans for the largest commercial fishery for this species in Canada. [ABSTRACT FROM AUTHOR]

Forage fish form a critical trophic link in marine ecosystems, and yet, for many species, there is limited information available. As nations move from single species stock assessments to ecosystem approaches to fisheries management (EAFMs), more information on forage fish will be required. In this study, 50 years of scientific literature were systematically mapped for 11 forage fish species in Canada's Arctic, Atlantic, and Pacific oceans. The objectives were to identify (1) knowledge clusters and gaps and (2) the pressures studied in relation to forage fish outcomes. Of the 2897 articles mapped, the majority studied adults and the distribution, productivity, growth, and life history of commercially fished species. Knowledge gaps were identified for forage fish: (1) that were noncommercially exploited; (2) egg and larval life history stages of most species and juveniles of noncommercial species; (3) diets of most species; (4) migration and performance for all species and survival of noncommercial species; and (5) the effects of some pressures (e.g., large-scale climate pressures). Addressing these knowledge gaps would improve the application of EAFMs. [ABSTRACT FROM AUTHOR]

Redfish (Sebastes spp.) in the Northwest Atlantic (NWA) extend from Baffin Island in the north to the Gulf of Maine in the south. The two most abundant species are Sebastes mentella and Sebastes fasciatus, which are morphometrically similar and difficult to visually distinguish. Redfish are long-lived, slow-growing, late-maturing, tend to produce large year classes episodically, and have complex population structure. Intraspecific genetic groups are abundant in the NWA. They are often semipelagic and patchily distributed, which makes them difficult to survey. These are all characteristics that cause difficulties for stock assessment and for sustainable fisheries management. This was the focus of The Ocean Frontier Institute Northwest Atlantic Redfish Symposium in 2018. In this paper, we synthesize the information known about NWA redfish. To improve the scientific basis for sustainable harvest strategies, key research recommendations involve (1) improved biological sampling including species and ecotype; (2) developing integrated stock assessment models; (3) developing harvest strategies with management reference points that are appropriate for redfish; (4) improving fishing technology and practices to avoid capture of small nonmarketable redfish and other species. [ABSTRACT FROM AUTHOR]

Trophic interactions are drivers of ecosystem change and stability, yet are often excluded from fishery assessment models, despite their potential capacity to improve estimates of species dynamics and future fishery sustainability. In Lake Ontario, recreational salmonine fisheries, including Chinook salmon (Oncorhynchus tshawytscha) and lake trout (Salvelinus namaycush), depend on a single prey species, alewife (Alosa pseudoharengus). To accommodate strong trophic interactions among species, we developed a multispecies statistical catch-at-age assessment (MSCAA) model that links the dynamics of the salmonine fisheries and alewife via prey consumption and predator growth. We found that prey availability had declined since 2015 due to decreased alewife recruitment and increased Chinook salmon biomass, leading to higher alewife mortality rates and lower predator growth rates. Forward projections of predator–prey dynamics suggest that Chinook salmon stocking reductions may improve the probability for alewife population growth, but could be counteracted by increased natural Chinook salmon recruitment. Combined with predator- and prey-monitoring efforts, multispecies assessments show promise as models of intermediate complexity to support a transition to ecosystem-based approaches to fisheries management. [ABSTRACT FROM AUTHOR]

Growth is a key component of population dynamics and, thus, fisheries management, yet drivers of its variations are often poorly understood. Using individual data collected over 80 years, we explored how environmental drivers affect growth in a major population of Atlantic herring (Clupea harengus). The results confirm that intrinsic factors (age and maturation) determine growth to a large degree but also that extrinsic factors such as temperature have some influence. While the role of intrinsic factors was independent of time series length, the importance of extrinsic drivers varies strongly with the analysed time period. It remains unclear whether this is caused by data inconsistencies back in time, spurious correlations appearing in shorter time series, shifts in population dynamics, or dynamic interactions between variables that cannot be determined with current data. Generally, environmental effects on growth became less clear and relevant with increasing time series length. What drives variation in growth may therefore change over time, potentially due to impacts such as fishing or climate change. It also underlines that seemingly clear correlations can break down or change their sign over time; hence, caution is advised when interpreting results from time series of 20–40 years. [ABSTRACT FROM AUTHOR]

Populations of the eastern oyster (Crassostrea virginica) have experienced declines from overfishing and disease throughout much of its US range, though development of maximum sustainable yield (MSY) management criteria has been elusive. This is due in part to the discordance between oyster spawning stock and recruits, as the classic stock–recruitment model does not account for the requirement of shell substrate on which recruits settle. This issue was recently addressed with the development of a surface area–recruitment model, which is herein incorporated into a simulation analysis to estimate MSY-based reference points for C. virginica in the Delaware Bay. Simulations demonstrate that at low natural mortality, fishing mortality (F) may be sustainable at values between 10% and 15%; however, if disease or other mortality-enhancing processes occur, the margin of error in fishing is small and may quickly lead to population and reef collapse, emphasizing a precautionary F < 10%. The MSY-based reference points generated here provide rebuilding goals for the oyster fishery and reef management on fished and unfished reefs and the framework from which shell-planting can be incorporated and optimized in the future. [ABSTRACT FROM AUTHOR]

Given the global collapse of most oyster fisheries, we explored the conditions under which the interaction of oysters and fishers can lead to multiple system equilibria and how those conditions might affect management strategies and recovery efforts. Using simple, but plausible, models of oyster fisheries, we identified tipping points, multiple equilibria, and hysteresis under a wide range of realistic model parameterizations. In collapsed systems with hysteresis, recovery of the system will require far less harvest than that which precipitated the collapse, and recovery times can be on decadal scales. We also derived optimal, non-equilibrium, state-dependent fishing policies and found that these policies can perform well, but are accompanied by high variation in the allowable harvest. Critically, these optimal policies also require constant monitoring of system state and frequent control of fishing effort. Finally, we examined habitat-enhancement scenarios that mimic proposed and ongoing restoration programs. We found that these efforts can increase the number of fishers the system can support and reduce otherwise long recovery times in collapsed systems. [ABSTRACT FROM AUTHOR]

Fisheries discards have become a source of concern for the perennation of marine resources. To reduce discards, the European Union adopted a Landing Obligation under the reform of its Common Fisheries Policy. However, food web consequences of reducing discards remain uncertain since their degree and pathway of reintegration are understudied. We used multi-marker DNA metabarcoding of gut contents and an ecological network approach to quantify marine fauna reliance on discarded fish and functional importance of discard consumers in coastal fishing grounds. We show that potential discard consumption is widespread across fish and invertebrates, but particularly important for decapods, which were also pinpointed as functionally important. Potential discard consumption may represent up to 66% of all interactions involving fish prey in the reconstructed network. We highlight that discard reliance may be more important than previously assessed in some fishing areas and support functionally important taxa. While reducing discarding remains a conservation priority, it is crucial to understand discards reintegration in marine food webs to anticipate changes in the context of an ecosystem approach to fisheries management. [ABSTRACT FROM AUTHOR]

Multispecies fisheries, particularly those that routinely adapt the timing, location, and methods of fishing to prioritize fishery targets, present a challenge to traditional single-species management approaches. Efforts to develop robust management for multispecies fisheries require an understanding of how priorities drive the network of interactions between catch of different species, especially given the added challenges presented by climate change. Using 35 years of landings data from a southern California recreational fishery, we leveraged empirical dynamic modelling methods to construct causal interaction networks among the main species targeted by the fishery. We found strong evidence for dependencies among species landings time series driven by apparent hierarchical catch preference within the fishery. In addition, by parsing the landings time series into anomalously cool, normal, and anomalously warm regimes (the last reflecting ocean temperatures anticipated by 2040), we found that network complexity was highest during warm periods. Our findings suggest that as ocean temperatures continue to rise, so too will the risk of unintended consequences from single-species management in this multispecies fishery. [ABSTRACT FROM AUTHOR]

Environmental temperature directly controls the rate at which ectotherms grow and develop. The growing degree-day metric (GDD, °C·day) scales time by temperature to create a thermal time scale relevant to ectothermic organisms. Here we assess the ability of GDD to model size-at-age and duration-to-moult in 15 datasets (9 size-at-age, 6 duration-to-moult) comprising 7 species of lobsters and crabs. We applied generalized linear models to assess the ability of GDD vs. "calendar" time to explain growth and development observations within and across trials. Best-fit models included GDD with fewer parameters in 6 of 9 size-at-age and 5 of 6 duration-to-moult datasets and a better fit to the data in 6 of 9 size-at-age datasets. Our results show that the individual growth of lobster and crab species can be modelled using thermal time models. Such models can be used to identify thermal tolerance limits, predict growth under varying temperature conditions and disentangle temperature effects from those of other factors affecting individual growth and development, resulting in improved growth models for field conditions including fisheries management. [ABSTRACT FROM AUTHOR]

Emerging evidence suggests that zooplankton production is affected by physiological and nutritional constraints due to climate change and eutrophication, which in turn could have broad implications for food-web dynamics and fisheries production. In this study, we developed a resource-based zooplankton production dynamics model that causally links freshwater cladoceran and copepod daily production-to-biomass (P/B) ratios with water temperature, phytoplankton biomass and community composition, and zooplankton feeding selectivity. This model was used to evaluate constraints on zooplankton growth under four hypothetical scenarios: involving natural plankton community seasonal succession; lake fertilization to enhance fisheries production; eutrophication; and climatic warming. Our novel modeling approach predicts zooplankton production is strongly dependent on seasonal variation in resource availability and quality, which results in more complex zooplankton dynamics than predicted by simpler temperature-dependent models. For mesotrophic and hypereutrophic lakes, our study suggests that the ultimate control over zooplankton P/B ratios shifts from physiological control during colder periods to strong resource control during warmer periods. Our resource-based model provides important insights into the nature of biophysical control of zooplankton under a changing climate that has crucial implications for food web energy transfer and fisheries production. [ABSTRACT FROM AUTHOR]

Euphausiids are a keystone species in marine food webs of the Northeast Pacific Ocean, important for forage fish, commercial fish species and marine predators such as seabirds and whales. Ecosystem-based fisheries management relies on realistic lower-trophic-level information for forecasting under future changing climate scenarios. We synthesised information from quantitative modelling studies analysing the relationship between euphausiids and their environment for two species of euphausiids that dominate assemblages in this region — Euphausia pacifica and Thysanoessa spinifera. Studies analysed suggest that variables reflecting the physical and biological environment in situ, features reflecting the geomorphic marine landscape, and large-scale climate indices all significantly affect euphausiid biomass and distribution. Temperature was the most tested predictor variable in the euphausiid models reviewed; however, it was significant in fewer models than other variables tested. We review and compare model structures, predictor variable selection and temporal lag phases to develop recommendations for species distribution modelling of euphausiids in the Northeast Pacific Ocean. We believe the results from this review will be applicable globally across regions with similar climates where euphausiids are numerous and can be adapted for different species and environments. [ABSTRACT FROM AUTHOR]

Identifying changes in fish growth is important for accurate scientific advice used for fisheries management, because environmental change is affecting fish growth and size-at-age is a critical component of contemporary stock assessment methods. Growth-increment biochronologies are time series of growth-increments derived from hard parts of marine organisms that may reveal dynamics of somatic fish growth. Here we use time series of otolith increments of two fish stocks to fit and compare a biologically derived growth model and a generalized statistical model. Both models produced similar trajectories of annual growth trends, but the biologically based one was more precise and predicted smaller interannual fluctuations than the statistical model. The biologically based model strongly indicated covariance between anabolic and catabolic rates among individuals. Otolith size-at-age did not closely match fish length-at-age, and consequently the growth model could not accurately hindcast observed fish length-at-age. For these reasons, fitted growth dynamics from otolith biochronologies may best suited to identify growth rate fluctuations, understand past drivers of growth dynamics, and improve ecological forecast in the face of rapid environmental change. [ABSTRACT FROM AUTHOR]

Translational ecology defines a collaborative effort among scientists and stakeholders to rapidly translate environmental problems into action. This approach can be applied in a fisheries management context when information needed to inform regulations is unavailable, yet conservation concerns exist. Our research uses a translational ecology framework to assess the stock status and develop research priorities for the crevalle jack (Caranx hippos) in the Florida Keys, USA, a currently unregulated species. Interview data that compiled expert fishing guide knowledge were used to develop hypotheses tested using existing fisheries-dependent datasets to check for agreement among sources and assess the consistency of observed patterns. Six hypotheses were developed concerning the status and trends of the crevalle jack population in the Florida Keys, and four of these hypotheses received clear support, with agreement between guide observations and one or more of the fisheries-dependent datasets. The results of our study outline an effective translational ecology approach for recreational fisheries management designed to rapidly recognize potential management needs as identified by fishing guides, which allows for actionable science and proactive management. [ABSTRACT FROM AUTHOR]

Excess bycatch of marine species during commercial fishing trips is a challenging problem in fishery management worldwide. The aims of this paper are twofold: to introduce methods and provide a practical guide for spatiotemporal modelling of bycatch data, as well as to apply these methods and present a thorough examination of Greenland shark (Somniosus microcephalus) bycatch weight in a Canadian Arctic fishery. We introduce the spatially explicit two-part model and offer a step by step guide for applying the model to any form of bycatch data, from data cleaning, exploratory data analysis, variable and model selection, model checking, to results interpretation. We address various problems encountered in decision making and suggest that researchers proceed cautiously and always keep in mind the aims of the analysis when fitting a spatiotemporal model. Results identified spatiotemporal hotspots and indicated month and gear type were key drivers of high bycatch. The importance of onboard observers in providing robust bycatch data was also evident. These findings will help to inform conservation strategies and management decisions, such as limiting access to spatial hotspots, seasonal closures and gear restrictions. [ABSTRACT FROM AUTHOR]

Understanding the space use of fishes in early life stages provides information that can contribute to effective fisheries management; however, it can be difficult to track fish in shallow, densely vegetated areas. Using acoustic telemetry, 60 subadult yellow perch (Perca flavescens) were tagged and monitored in a vegetated area of the Detroit River (May–November 2018). Variable detection range from submerged aquatic vegetation (SAV) was incorporated in estimates by applying a spatiotemporal correction to aid with interpretation of seasonal changes in activity space. Although subadult yellow perch were commonly detected in the array, demonstrating the importance of SAV habitat (mean detection residency index: 0.85), 60% of individuals were not detected following August, the period with highest activity space estimates, likely due to seasonal movements and predation. Individuals were more commonly detected during the daylight hours compared to night, but activity peaked at crepuscular periods. This study provided spatial information about the often-overlooked early life history of yellow perch, increasing the ecological information available for a species of management and conservation interest in the Great Lakes. [ABSTRACT FROM AUTHOR]

Understanding the factors underlying species establishment is critical for the management of invasive fishes, yet the roles of propagule pressure and environmental factors are infrequently quantified in joint models. We estimated the establishment likelihood of the invasive black carp (Mylopharyngodon piceus) by examining the relative influence of propagule pressure (introduction size and age structure) and environmental factors (temperature-driven young-of-year [YOY] overwinter survival, adult survival, age at maturity, and longevity). Simulations demonstrated that both propagule pressure and environmental factors can act as non-linear bottlenecks to establishment. When the model was applied to 12 Great Lakes tributaries and nearshore areas, black carp establishment was probable with sufficient propagules and under most environmental conditions (median p = 0.21–0.73, 0.70–1.00, and 0.46–0.97 for 100 pairs of age 4, age 9, and age 16 fish, respectively), except for YOY (p < 0.01). Our analysis is one of the few studies to examine the relative role of propagule pressure and environmental conditions on establishment, indicating that both factors can lead to establishment failure independently or concurrently within an ecosystem. [ABSTRACT FROM AUTHOR]

A correction is presented to the article discussing R.D. Moore's critiques of a forestry-related study on salmonid habitat, particularly emphasizing the challenges and considerations related to spatial comparisons, riparian harvest impact on stream temperature.

Effective management of freshwater fish habitat is essential to supporting healthy aquatic ecosystems and sustainable fisheries. In Canada, recent changes to the Fisheries Act enhanced the protection of fish habitat, but application of those provisions relies on sound scientific evidence. We employed collaborative research prioritization methods to identify scientific research questions that, if addressed, would significantly advance the management of freshwater fish habitat in Canada. This list was generated by a diverse group of freshwater fish experts, including substantial contributions from practitioners who administer provisions of the Fisheries Act. The research questions generated in this study identify priority topics for future research, while highlighting issues that could be addressed with different funding models. As a result, this study should support evidence-based management of Canada's aquatic resources by identifying scientific knowledge gaps faced by practitioners, and suggesting mechanisms to address them. Given the important contribution of Canadian freshwater systems to global ecosystem values, and the similar scientific challenges facing fish habitat managers in other jurisdictions, this study is likely to have broad applicability. [ABSTRACT FROM AUTHOR]

Management of protected species is difficult when objectives include the recovery of both predator and its prey. Ideally, identifying trade-offs between competing objectives involves evaluating management alternatives with a quantitative model that integrates information on both species, but data are often limited. We used new predator diet data and simulation modeling to update our understanding of seal predation on juvenile Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) in the Puget Sound. Under prey size assumptions used by previous studies, estimates suggest predation could be a significant source of mortality for Chinook salmon (mean: 37% of ocean age-0 juveniles), but varied considerably among years (range of median estimates: 22%–49%). However, when we estimated prey size from otoliths recovered from seal scats, the impact (numbers of fish consumed) decreased by 71%. Predation on coho salmon was estimated to be relatively low under both scenarios (6%–8% of ocean age-0 juveniles) with a 21% decrease in consumption using otolith-derived prey size. Our analysis highlights the importance of updating model inputs and re-evaluating assumptions of multi-species models used for ecosystem-based fisheries management. [ABSTRACT FROM AUTHOR]

Acoustic telemetry systems technology is useful for studying fish movement patterns and habitat use; however, the data generated from omnidirectional acoustic receivers are prone to large observation errors because the tagged animal can be anywhere in the detection range of the receiver. In this study, we used the Bayesian state space modeling (SSM) approach and different smoothing methods including kernel smoothing and cross-validated local polynomial regression to reconstruct fish movement paths of walleye (Sander vitreus) using data obtained from a telemetry receiver grid in Lake Winnipeg, Manitoba, Canada. Using the SSM approach, we obtained more realistic movement paths, compared with the smoothing methods. In addition, we have highlighted the advantages of the SSM approach to estimate undetected movement paths, over simple smoothing techniques, by comparing ecological metrics such as path length and tortuosity between different reconstruction approaches. Reconstructed paths could be useful in making effective fishery management decisions on Lake Winnipeg in the future by providing information on how walleye move and distribute in Lake Winnipeg over space and time. [ABSTRACT FROM AUTHOR]

Despite decades of commercial harvest of bigmouth buffalo (Ictiobus cyprinellus) from Jamestown Reservoir, North Dakota, and the recent rapid growth of sport bowfishing that targets this species, there is a lack of biological information on this native catostomid. At present, no-limit recreational and commercial harvest of bigmouth buffalo occurs in North Dakota, with no harvest-reporting for recreational take. A long-lived life history was recently documented for this species, with a life-span exceeding 100 years. At Jamestown Reservoir, bigmouth buffalo were aged to 58 years of age, with onset of sexual maturity 10 years for females. Evidence for episodic recruitment over a 60-year period was in 1962–1979, 1993–2011, and 2017, with recruitment success more likely during non-drought periods. Annual commercial harvest data from this reservoir indicate bigmouth buffalo have declined significantly over the past 30 years, most precipitously since 2010 during the bowfishing era. The demographic patterns, episodic recruitment, and harvest changes observed in this population are relevant for informing management of bigmouth buffalo and other long-lived freshwater fishes. [ABSTRACT FROM AUTHOR]

Determination of population structure and stock identification is a general problem in fisheries assessment and management. Pacific salmon fishery management regimes are evolving to require higher resolution of stock composition on increasingly smaller reporting units. For Chinook salmon (Oncorhynchus tshawytscha), a stock identification baseline comprised of some 125 198 individuals from 369 populations ranging from Russia to California was employed for genetic stock identification (GSI). GSI analysis based on variation at up to 547 single nucleotide polymorphisms (SNPs) was demonstrated to provide accurate estimates of stock composition for 68 conservation units (CUs) in British Columbia, 23 reporting groups in the United States, and one reporting group in Russia. In many instances, accurate population-specific estimates of stock composition within a CU were possible in fishery samples, as well as identifying individuals to some specific populations. A genetics-based assessment system provides an opportunity for conservation-based management of Canadian Chinook salmon. [ABSTRACT FROM AUTHOR]

Human-driven environmental change underlies recent changes in water clarity in many of the world's great lakes, yet our understanding of the consequences of these changes on the fish and fisheries they support remains incomplete. Herein, we offer a framework to organize current knowledge, guide future research, and help fisheries managers understand how water clarity can affect their valued populations. Emphasizing Laurentian Great Lakes findings where possible, we describe how changing water clarity can directly affect fish populations and communities by altering exposure to ultraviolet radiation, foraging success, predation risk, reproductive behavior, or territoriality. We also discuss how changing water clarity can affect fisheries harvest and assessment through effects on fisher behavior and sampling efficiency (i.e., catchability). Finally, we discuss whether changing water clarity can affect understudied aspects of fishery performance, including economic and community benefits. We conclude by identifying generalized predictions and discuss their implications for priority research questions for the Laurentian Great Lakes. Even though the motivation for this work was regional, the breadth of the review and generality of the framework are readily transferable to other freshwater and marine habitats. [ABSTRACT FROM AUTHOR]

Impacts of Karenia brevis red tide blooms have been an increasing cause of concern for fisheries management in the Gulf of Mexico (Gulf). The 2019 Gulf red grouper (Epinephelus morio) stock assessment was confronted with the challenges of quantifying and parameterizing red tides during both historical and projection time periods. Red tide mortality was estimated for each age class in the model solely in 2005 and 2014 during severe events. Given the considerable uncertainty surrounding the 2018 red tide and its substantial implications on the status of the population, several projection scenarios were evaluated. Under the assumption of no 2018 red tide mortality, near-term catches were projected to nearly double, a predicted outcome that appeared to be in contrast with recent record low catches and fishing industry perceptions of major stock depletion. In the event that the 2018 red tide caused mortality, but was not accounted for in projections, the recommended catch levels would lead to high probabilities of overfishing and potentially stock collapse. Collectively, these results highlight how consideration of uncertainty in projections can help avoid unintended consequences. [ABSTRACT FROM AUTHOR]