ICES Journal of Marine Science: Journal du Conseil

Rothschild, Brian J.

doi: 10.1093/icesjms/fsv027pmid: N/A

AbstractIn this essay, I review six decades of my career in marine science and fisheries, considering the ideas that came and went in the period as “food for thought”. I describe my inspirations and successes, and my disappointments and failures. My activities were both administrative and research-oriented. As regards the former, I was part of major changes in ocean policy and new ocean research programmes that gave me a unique perspective. For example, I was responsible for the implementation of the US extended jurisdiction in fisheries under National Oceanic and Atmospheric Administration. Also I conceived and led the creation of the Global Ocean Ecosystem Dynamics Programme (GLOBEC) and guided it in many international contexts, including its integration with the International Geosphere Biosphere Programme (IGBP). From a research standpoint, my efforts leading up to GLOBEC strongly influenced the introduction of ocean physics into biological oceanography. This led me into plankton dynamics, food signals, small-scale turbulence and physical forcing, even into the stochastic geometry of the plankton. My life-long interest in the dynamics of marine fish populations was strongly influenced by the seminal thinkers in fisheries and my research explored population regulation processes as well as practical applications of statistics and operations research to fisheries management. In my last academic post, I became founding Dean of the School for Marine Science and Technology (SMAST) at the University of Massachusetts. This position required integrating administrative and research (both pure and applied) perspectives to create an institution of academic excellence which was at the same time actively responsive to issues arising in our local, nationally prominent fisheries. I end the essay with a consideration of “what has changed”.

Thorson, James T.; Minto, Cóilín

doi: 10.1093/icesjms/fsu213pmid: N/A

AbstractFisheries biology encompasses a tremendous diversity of research questions, methods, and models. Many sub-fields use observational or experimental data to make inference about biological characteristics that are not directly observed (called “latent states”), such as heritability of phenotypic traits, habitat suitability, and population densities to name a few. Latent states will generally cause model residuals to be correlated, violating the assumption of statistical independence made in many statistical modelling approaches. In this exposition, we argue that mixed-effect modelling (i) is an important and generic solution to non-independence caused by latent states; (ii) provides a unifying framework for disparate statistical methods such as time-series, spatial, and individual-based models; and (iii) is increasingly practical to implement and customize for problem-specific models. We proceed by summarizing the distinctions between fixed and random effects, reviewing a generic approach for parameter estimation, and distinguishing general categories of non-linear mixed-effect models. We then provide four worked examples, including state-space, spatial, individual-level variability, and quantitative genetics applications (with working code for each), while providing comparison with conventional fixed-effect implementations. We conclude by summarizing directions for future research in this important framework for modelling and statistical analysis in fisheries biology.

Woods, Pamela J.; Holland, Daniel S.; Marteinsdóttir, Guðrún; Punt, André E.

doi: 10.1093/icesjms/fsv001pmid: N/A

AbstractImplementation of single-species catch limits in multispecies individual quota systems is problematic because it may incentivize discarding behaviour when quotas for some species limit catch of jointly caught species. Since discarding may reduce economic benefits and bias stock assessments, mechanisms that reduce incentives to discard can be beneficial. However, these mechanisms may be detrimental in the long term if they also pose a risk of stock depletion, which can occur if they enable catch to persistently exceed the total allowable catch (TAC). This study uses a bioeconomic model to analyse potential negative consequences of species quota transformation provisions, using the Icelandic individual transferable quota system as a case study. These provisions allow quota of one species to be transformed into quota of another species at specified rates related to relative market value. The system reduces the degree that the TAC of any particular species constrains catch of other species. However, it also allows catches of some species to exceed TACs, possibly leading to stock depletion. We explore how these provisions may affect long-term sustainability of individual species and profitability of the fishery as a whole. We focus on the extreme case of perfect targeting (i.e. full control of catch composition) to increase intuition on the potential for adverse effects of this system. Various combinations of species profitability are examined to determine attributes of species that lead to greater vulnerability, as well as interactions in species utilization. Consequences of changing harvest control rules are explored, and information needed to monitor for unintended consequences of such a system in practice are discussed. Although the species transformation system is designed to increase economic efficiency, our results show that it could lead to depletion in some cases, and may make it difficult to achieve optimal management goals.

Wang, Na; Wang, You-Gan; Courtney, Anthony J.; O'Neill, Michael F.

doi: 10.1093/icesjms/fsu216pmid: N/A

AbstractDeriving an estimate of optimal fishing effort or even an approximate estimate is very valuable for managing fisheries with multiple target species. The most challenging task associated with this is allocating effort to individual species when only the total effort is recorded. Spatial information on the distribution of each species within a fishery can be used to justify the allocations, but often such information is not available. To determine the long-term overall effort required to achieve maximum sustainable yield (MSY) and maximum economic yield (MEY), we consider three methods for allocating effort: (i) optimal allocation, which optimally allocates effort among target species; (ii) fixed proportions, which chooses proportions based on past catch data; and (iii) economic allocation, which splits effort based on the expected catch value of each species. Determining the overall fishing effort required to achieve these management objectives is a maximizing problem subject to constraints due to economic and social considerations. We illustrated the approaches using a case study of the Moreton Bay Prawn Trawl Fishery in Queensland (Australia). The results were consistent across the three methods. Importantly, our analysis demonstrated the optimal total effort was very sensitive to daily fishing costs—the effort ranged from 9500–11 500 to 6000–7000, 4000 and 2500 boat-days, using daily cost estimates of $0, $500, $750, and $950, respectively. The zero daily cost corresponds to the MSY, while a daily cost of $750 most closely represents the actual present fishing cost. Given the recent debate on which costs should be factored into the analyses for deriving MEY, our findings highlight the importance of including an appropriate cost function for practical management advice. The approaches developed here could be applied to other multispecies fisheries where only aggregated fishing effort data are recorded, as the literature on this type of modelling is sparse.

Fay, Gavin; Link, Jason S.; Large, Scott I.; Gamble, Robert J.

doi: 10.1093/icesjms/fsu214pmid: N/A

AbstractSuccessful implementation of Ecosystem-Based Fisheries Management (EBFM) requires appropriate action as informed by reference points in an ecosystem context. Thresholds in the response of ecological indicators to system drivers have been suggested as reference points for EBFM, though the management performance of these indicators and possible values for their reference points have not been widely evaluated. We used Management Strategy Evaluation to test the performance of control rules that used ecological indicators to adjust the advice from single-species stock assessments, using the Georges Bank finfish fishery as a case study. We compare the performance of control rules that used ecological indicators to that of single-species FMSY control rules when the system dynamics were governed by the same multispecies population model. Control rules that used indicator-based reference points were able to perform better against catch and biodiversity objectives than when harvests were based on single-species advice alone. Indicators and values for reference points associated with good performance varied depending on the management objective. We quantified tradeoffs between total catch, biodiversity, and interannual variability in catch, noting that it was possible in some instances to achieve higher than average biodiversity while maintaining high catches using indicator-based control rules. While improved performance was noted using ecological indicators, outcomes were variable, and the gains in performance obtained may be similar to alternative methods of implementing precaution in single-species fishery control rules.

Thorson, James T.; Shelton, Andrew O.; Ward, Eric J.; Skaug, Hans J.

doi: 10.1093/icesjms/fsu243pmid: N/A

AbstractIndices of abundance are the bedrock for stock assessments or empirical management procedures used to manage fishery catches for fish populations worldwide, and are generally obtained by processing catch-rate data. Recent research suggests that geostatistical models can explain a substantial portion of variability in catch rates via the location of samples (i.e. whether located in high- or low-density habitats), and thus use available catch-rate data more efficiently than conventional “design-based” or stratified estimators. However, the generality of this conclusion is currently unknown because geostatistical models are computationally challenging to simulation-test and have not previously been evaluated using multiple species. We develop a new maximum likelihood estimator for geostatistical index standardization, which uses recent improvements in estimation for Gaussian random fields. We apply the model to data for 28 groundfish species off the U.S. West Coast and compare results to a previous “stratified” index standardization model, which accounts for spatial variation using post-stratification of available data. This demonstrates that the stratified model generates a relative index with 60% larger estimation intervals than the geostatistical model. We also apply both models to simulated data and demonstrate (i) that the geostatistical model has well-calibrated confidence intervals (they include the true value at approximately the nominal rate), (ii) that neither model on average under- or overestimates changes in abundance, and (iii) that the geostatistical model has on average 20% lower estimation errors than a stratified model. We therefore conclude that the geostatistical model uses survey data more efficiently than the stratified model, and therefore provides a more cost-efficient treatment for historical and ongoing fish sampling data.

Bell, Richard J.; Richardson, David E.; Hare, Jonathan A.; Lynch, Patrick D.; Fratantoni, Paula S.

doi: 10.1093/icesjms/fsu217pmid: N/A

AbstractClimate change and fishing can have major impacts on the distribution of natural marine resources. Climate change alters the distribution of suitable habitat, forcing organisms to shift their range or attempt to survive under suboptimal conditions. Fishing reduces the abundance of marine populations and truncates their age structure leading to range contractions or shifts. Along the east coast of the United States, there have been major changes in fish populations due to the impacts of fishing and subsequent regulations, as well as changes in the climate. Black sea bass, scup, summer flounder, and winter flounder are important commercial and recreational species, which utilize inshore and offshore waters on the northeast shelf. We examined the distributions of the four species with the Northeast Fisheries Science Center trawl surveys to determine if the along-shelf centres of biomass had changed over time and if the changes were attributed to changes in temperature or fishing pressure through changes in abundance and length structure. Black sea bass, scup, and summer flounder exhibited significant poleward shifts in distributions in at least one season while the Southern New England/Mid-Atlantic Bight stock of winter flounder did not shift. Generalized additive modelling indicated that the changes in the centres of biomass for black sea bass and scup in spring were related to climate, while the change in the distribution of summer flounder was largely attributed to a decrease in fishing pressure and an expansion of the length–age structure. While the changes in ocean temperatures will have major impacts on the distribution of marine taxa, the effects of fishing can be of equivalent magnitude and on a more immediate time scale. It is important for management to take all factors into consideration when developing regulations for natural marine resources.

Pécuchet, Laurène; Nielsen, J. Rasmus; Christensen, Asbjørn

doi: 10.1093/icesjms/fsu220pmid: N/A

AbstractWhile the impact of environmental forcing on recruitment variability in marine populations remains largely elusive, studies spanning large spatial areas and many stocks are able to identify patterns common to different regions and species. In this study, we investigate the effects of the environment on the residuals of a Ricker stock–recruitment (SR) model, used as a proxy of prerecruits' survival, of 18 assessed stocks in the Baltic and North Seas. A probabilistic principal components (PCs) analysis permits the identification of groups of stocks with shared variability in the prerecruits' survival, most notably a group of pelagics in the Baltic Sea and a group composed of gadoids and herring in the North Sea. The first two PCs generally grouped the stocks according to their localizations: the North Sea, the Kattegat–Western Baltic, and the Baltic Sea. This suggests the importance of the local environmental variability on the recruitment strength. Hence, the prerecruits' survival variability is studied according to geographically disaggregated and potentially impacting abiotic or biotic variables. Time series (1990–2009) of nine environmental variables consistent with the spawning locations and season for each stock were extracted from a physical–biogeochemical model to evaluate their ability to explain the survival of prerecruits. Environmental variables explained >70% of the survival variability for eight stocks. The variables water current, salinity, temperature, and biomass of other fish stocks are regularly significant in the models. This study shows the importance of the local environment on the dynamics of SR. The results provide evidence of the necessity of including environmental variables in stock assessment for a realistic and efficient management of fisheries.

Émond, Kim; Sainte-Marie, Bernard; Galbraith, Peter S.; Bêty, Joël

doi: 10.1093/icesjms/fsu240pmid: N/A

AbstractMany snow crab fisheries have fluctuated widely over time in a quasi-cyclic way due to highly variable recruitment. The causes of this variability are still debated. Bottom-up processes related to climate variability may strongly affect growth and survival during early life, whereas top-down predator effects may be a major source of juvenile mortality. Moreover, intrinsic density-dependent processes, which have received much less attention, are hypothetically responsible for the cycles in recruitment. This study explored how climate, larval production, intercohort cannibalism and groundfish predation may have affected recruitment of early juvenile snow crab in the northwest Gulf of St Lawrence (eastern Canada) over a period of 23 years. Abundance of early juvenile snow crabs (2.5–22.9 mm in carapace width), representing the first 3 years of benthic life, came from an annual trawl survey and was used to determine cohort strength. Analyses revealed a cyclic pattern in abundance of 0+ crabs that may arise from cohort resonant effects. This pattern consisted of three recruitment pulses but was reduced to two pulses by age 2+, while the interannual variability of cohort strength was dampened. This reconfiguration of the earliest recruitment pattern was dictated primarily by bottom water temperature and cannibalism, which progressively overruled the pre-settlement factors of larval production and surface water temperature that best explained abundance of 0+ crabs. The results strongly suggest that bottom-up and density-dependent processes prevail over top-down control in setting the long-term trends and higher-frequency oscillations of snow crab early recruitment patterns.

Essington, Timothy E.; Baskett, Marissa L.; Sanchirico, James N.; Walters, Carl

doi: 10.1093/icesjms/fsu242pmid: N/A

AbstractEcosystem-based fisheries management seeks to consider trade-offs among management objectives for interacting species, such as those that arise through predator–prey linkages. In particular, fisheries-targeting forage fish (small and abundant pelagic fish) might have a detrimental effect on fisheries-targeting predators that consume them. However, complexities in ecological interactions might dampen, negate, or even reverse this trade-off, because small pelagic fish can be important predators on egg stages of piscivorous fish. Further, the strength of this trade-off might depend on the extent to which piscivorous fish targeted by fisheries regulate forage species productivity. Here, we developed a novel delay-differential bioeconomic model of predator–prey and fishing dynamics to quantify how much egg predation or weak top-town control affects the strength of trade-off between forage and piscivore fisheries, and to measure how ecological interactions dictate policies that maximize steady-state profits. We parameterized the model based on ecological and economic data from the North Sea Atlantic cod (Gadus morhua) and Atlantic herring (Clupea harengus). The optimal policy was very sensitive to the ecological interactions (either egg predation or weak top-down control of forage by predators) at relatively low forage prices but was less sensitive at high forage fish prices. However, the optimal equilibrium harvest rates on forage and piscivores were not substantially different from what might be derived through analyses that did not consider species interactions. Applying the optimal multispecies policy would produce substantial losses (>25%) in profits in the piscivore fishery, and the extent of loss was sensitive to ecological scenarios. While our equilibrium analysis is informative, a dynamic analysis under similar ecological scenarios is necessary to reveal the full economic and ecological benefits of applying ecosystem-based fishery management policies to predator–prey fishery systems.