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Fish stock productivity, and thereby sensitivity to harvesting, depends on physical (e.g. ocean climate) and biological (e.g. prey availability, competition and predation) processes in the ecosystem. The combined impacts of such ecosystem processes and fisheries have lead to stock collapses across the world. While traditional fisheries management focuses on harvest rates and stock biomass, incorporating the impacts of such ecosystem processes are one of the main pillars of the ecosystem approach to fisheries management (EAFM). Although EAFM has been formally adopted widely since the 1990s, little is currently known to what extent ecosystem drivers of fish stock productivity are actually implemented in fisheries management. Based on worldwide review of more than 1200 marine fish stocks, we found that such ecosystem drivers were implemented in the tactical management of only 24 stocks. Most of these cases were in the North Atlantic and north-east Pacific, where the scientific support is strong. However, the diversity of ecosystem drivers implemented, and in the approaches taken, suggests that implementation is largely a bottom-up process driven by a few dedicated experts. Our results demonstrate that tactical fisheries management is still predominantly single-species oriented taking little account of ecosystem processes, implicitly ignoring that fish stock production is dependent on the physical and biological conditions of the ecosystem. Thus, while the ecosystem approach is highlighted in policy, key aspects of it tend yet not to be implemented in actual fisheries management.

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There is growing interest in models of marine ecosystems that deal with the effects of climate change through the higher trophic levels. Such end-to-end models combine physicochemical oceanographic descriptors and organisms ranging from microbes to higher-trophic-level (HTL) organisms, including humans, in a single modeling framework. The demand for such approaches arises from the need for quantitative tools for ecosystem-based management, particularly models that can deal with bottom-up and top-down controls that operate simultaneously and vary in time and space and that are capable of handling the multiple impacts expected under climate change. End-to-end models are now feasible because of improvements in the component submodels and the availability of sufficient computing power. We discuss nine issues related to the development of end-to-end models. These issues relate to formulation of the zooplankton submodel, melding of multiple temporal and spatial scales, acclimation and adaptation, behavioral movement, software and technology, model coupling, skill assessment, and interdisciplinary challenges. We urge restraint in using end-to-end models in a true forecasting mode until we know more about their performance. End-to-end models will challenge the available data and our ability to analyze and interpret complicated models that generate complex behavior. End-to-end modeling is in its early developmental stages and thus presents an opportunity to establish an open-access, community-based approach supported by a suite of true interdisciplinary efforts

Highly resolved general circulation models (GCMs) now generate realistic flow fields, and have revealed how sensitive larval drift routes are to vertical positioning in the water column. Sensible representation of behavioural processes then becomes essential to generate reliable patterns of environmental exposure (growth and survival), larval drift trajectories and dispersal. Existing individual-based models involving larval fish allow individuals to vary only in their attributes such as spatial coordinates, and not in their inherited behavioural strategies or phenotypes. We illustrate the interaction between short-term behaviour and longer-term dispersal consequences applying a model of larval cod Gadus morhua drifting in a GCM, and show how variations in swimming behaviour influence growth and dispersal. We recommend a deep integration of oceanography and behavioural ecology. First, we need to understand the causes and survival value of behaviours of larval fish, framed in terms of behavioural ecology. Second, we need practices to address how drift and dispersal of offspring are generating spawning strategies (timing and location) of adults, using life history theory. Third, the relative importance of local growth and mortality versus the need to drift to particular areas depend strongly on the mobility of organisms at the time of settling, or the spatial fitnesslandscape. The field of 'individual-based ecology' provides sound methods to approach this interface between evolutionary theory and physical oceanography.

Petitgas, P., Secor, D. H., McQuinn, I., Huse, G., and Lo, N. 2010. Stock collapses and their recovery: mechanisms that establish and maintain life-cycle closure in space and time. – ICES Journal of Marine Science, 67: 1841–1848. Experience has established that the recovery of many collapsed stocks takes much longer than predicted by traditional fishery population models. We put forward the hypothesis that stock collapse is associated with disruption of the biological mechanisms that sustain life-cycle closure of intrapopulation contingents. Based on a review of case studies of nine marine fish stocks, we argue that stock collapses not only involve biomass loss, but also the loss of structural elements related to life-cycle diversity (contingents), as well as the breakdown of socially transmitted traditions (through a curtailed age range). Behavioural mechanisms associated with these structural elements could facilitate recovery of depleted populations. Migratory behaviour is argued to relate to phenotypic plasticity and the persistence of migration routes to social interactions. The case studies represent collapsed or depleted populations that recovered after a relatively short period (striped bass, capelin), after more than a decade (herring and sardine), or not at all (anchovy, cod). Contrasting the population dynamics from these stocks leads us to make a distinction between a depleted and a collapsed population, where, in addition to biomass depletion, the latter includes damage to contingent structure or space-use pattern. We also propose a mechanism to explain how lost habitats are recolonized.

Abstract:We evaluated the costs and benefits of long-distance horizontal migration by pelagic planktivores, Atlantic herring (Clupea harengus), blue whiting (Micromesistius poutassou), mackerel (Scomber scombrus), and capelin (Mallotus villosus) in the Norwegian and Barents seas using a numerical model and tested model predictions against field observations. Specifically, we considered (i) energetic costs as a function of body size, water currents, swimming speed, and distance, (ii) time costs as a function of speed and distance, and (iii) energetic gain in terms of differences in food intake between areas. The model demonstrates how body size restricts large-scale horizontal migration patterns. Model and field results suggest that the extent of migration will increase with increasing body length. The model predicts that long-distance migration costs may exceed energy intake for fish <20 cm, due to increased hydrodynamical drag with decreasing fish size. Field results suggest that migration distance is a function of length, weight, and age. Food abundance and distribution, current speed and direction, and differences in day length at boreal latitudes are believed to be the major driving forces influencing large-scale migration distance, direction, and timing in pelagic planktivores. Northwards latitudinal rather than longitudinal feeding migrations are explained by the improved feeding opportunities with increased day lengths.Résumé : Nous avons évalué les coûts et les avantages de la migration horizontale à longue distance de poissons pélagiques planctivores, à savoir le hareng (Clupea harengus), le merlan bleu (Micromesistius poutassou), le maquereau (Scomber scombrus) et le capelan (Mallotus villosus), dans la mer de Norvège et la mer de Barents. Nous avons comparé les prévisions obtenues d'un modèle numérique et d'un modèle fondé sur les observations aux valeurs observées sur le terrain. Plus précisément, nous avons examiné (i) les dépenses énergétiques en fonction de la taille, du courant, de la vitesse de nage et de la distance, (ii) les dépenses de temps en fonction de la vitesse et de la distance et (iii) le gain énergétique en fonction des écarts de la consommation alimentaire entre les zones. Le modèle montre comment la taille limite la migration horizontale à grande échelle. Le modèle et les résultats obtenus sur le terrain portent à croire que l'importance de la migration s'accroît avec la longueur du poisson. Selon le modèle, les coûts d'une migration sur une longue distance peuvent être supérieurs à l'énergie absorbée chez les poissons de moins de 20 cm de longueur, étant donné que la traînée hydrodynamique s'accroît à mesure que la taille du poisson décroît. Les résultats obtenus sur le terrain indiquent que la distance de migration est fonction de la longueur, du poids et de l'âge. L'abondance et la répartition de la nourriture, la vitesse et la direction du courant de même que la durée du jour, différente sous les latitudes boréales, semblent constituer les principales forces qui influent sur la...

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