Predicting consumer biomass, size-structure, production, catch potential, responses to fishing and associated uncertainties in the world's marine ecosystems

Existing estimates of fish and consumer biomass in the world’s oceans are disparate. This creates uncertainty about the roles of fish and other consumers in biogeochemical cycles and ecosystem processes, the extent of human and environmental impacts and fishery potential. We develop and use a size-based macroecological model to assess the effects of parameter uncertainty on predicted consumer biomass, production and distribution. Resulting uncertainty is large (e.g. median global biomass 4.9 billion tonnes for consumers weighing 1 g to 1000 kg; 50% uncertainty intervals of 2 to 10.4 billion tonnes; 90% uncertainty intervals of 0.3 to 26.1 billion tonnes) and driven primarily by uncertainty in trophic transfer efficiency and its relationship with predator-prey body mass ratios. Even the upper uncertainty intervals for global predictions of consumer biomass demonstrate the remarkable scarcity of marine consumers, with less than one part in 30 million by volume of the global oceans comprising tissue of macroscopic animals. Thus the apparently high densities of marine life seen in surface and coastal waters and frequently visited abundance hotspots will likely give many in society a false impression of the abundance of marine animals. Unexploited baseline biomass predictions from the simple macroecological model were used to calibrate a more complex size- and trait-based model to estimate fisheries yield and impacts. Yields are highly dependent on baseline biomass and fisheries selectivity. Predicted global sustainable fisheries yield increases ≈4 fold when smaller individuals (< 20 cm from species of maximum mass < 1kg) are targeted in all oceans, but the predicted yields would rarely be accessible in practice and this fishing strategy leads to the collapse of larger species if fishing mortality rates on different size classes cannot be decoupled. Our analyses show that models with minimal parameter demands that are based on a few established ecological principles can support equitable analysis and comparison of diverse ecosystems. The analyses provide insights into the effects of parameter uncertainty on global biomass and production estimates, which have yet to be achieved with complex models, and will therefore help to highlight priorities for future research and data collection. However, the focus on simple model structures and global processes means that non-phytoplankton primary production and several groups, structures and processes of ecological and conservation interest are not represented. Consequently, our simple models become increasingly less useful than more complex alternatives when addressing questions about food web structure and function, biodiversity, resilience and human impacts at smaller scales and for areas closer to coasts

Risky business: the combined effects of fishing and changes in primary productivity on fish communities

There is an increasing need to understand ecosystem responses to multiple stressors in that such complex responses depend not only on species-level responses, but also on species interactions and ecosystem structure. In this study, we used a multi-model ecosystem simulation approach to explore the combined effects of fishing and primary productivity on different components of the food-web across a suite of ecosystems and a range of model types. Simulations were carried out under different levels of primary productivity and various fishing scenarios. In addition to exploring synergistic, additive or antagonistic combined effects of multiple stressors, we included a fourth category “dampened”, which refers to less negative or less positive impacts compared to additive ones, and in contrast to previous studies, we explicitly considered the direction (positive or negative) of the combined effects. We focused on two specific combined effects (negative synergism and positive dampened) associated with the risk of resultant lower fish biomass than expected under additive effects. Through a meta-analysis of the multi-models' simulation results, we found that (i) the risk of negative synergism was generally higher for low-trophic-level (LTL) taxa, implying that following an increase of fishing pressure on a given LTL stock, the subsequent decrease of biomass under low primary productivity would be larger than expected under additive effects and (ii) the risk of positive dampened effects was generally higher for high-trophic-level (HTL) taxa, implying that given a management measure aimed at reducing the impact of fishing on HTL stocks, the subsequent rebuilding of these stocks would be slower than expected. Our approach to categorizing and exploring cumulative effects can be applied to evaluate other community properties, and provide guidance for fisheries management

Ecological indicators to capture the effects of fishing on biodiversityand conservation status of marine ecosystems

IndiSeas (“Indicators for the Seas”) is a collaborative international working group that was established in2005 to evaluate the status of exploited marine ecosystems using a suite of indicators in a comparative framework. An initial shortlist of seven ecological indicators was selected to quantify the effects of fishing on the broader ecosystem using several criteria (i.e., ecological meaning, sensitivity to fishing, data avail-ability, management objectives and public awareness). The suite comprised: (i) the inverse coefficient of variation of total biomass of surveyed species, (ii) mean fish length in the surveyed community, (iii)mean maximum life span of surveyed fish species, (iv) proportion of predatory fish in the surveyed community, (v) proportion of under and moderately exploited stocks, (vi) total biomass of surveyed species,and (vii) mean trophic level of the landed catch. In line with the Nagoya Strategic Plan of the Convention on Biological Diversity (2011–2020), we extended this suite to emphasize the broader biodiversity and conservation risks in exploited marine ecosystems. We selected a subset of indicators from a list of empirically based candidate biodiversity indicators initially established based on ecological significance to complement the original IndiSeas indicators. The additional selected indicators were: (viii) mean intrinsic vulnerability index of the fish landed catch, (ix) proportion of non-declining exploited species in the surveyed community, (x) catch-based marine trophic index, and (xi) mean trophic level of the surveyed community. Despite the lack of data in some ecosystems, we also selected (xii) mean trophic level of the modelled community, and (xiii) proportion of discards in the fishery as extra indicators. These additional indicators were examined, along with the initial set of IndiSeas ecological indicators, to evaluate whether adding new biodiversity indicators provided useful additional information to refine our under-standing of the status evaluation of 29 exploited marine ecosystems. We used state and trend analyses,and we performed correlation, redundancy and multivariate tests. Existing developments in ecosystem-based fisheries management have largely focused on exploited species. Our study, using mostly fisheries independent survey-based indicators, highlights that biodiversity and conservation-based indicators are complementary to ecological indicators of fishing pressure. Thus, they should be used to provide additional information to evaluate the overall impact of fishing on exploited marine ecosystems

Ecological indicators to capture the effects of fishing on biodiversityand conservation status of marine ecosystems

IndiSeas (“Indicators for the Seas”) is a collaborative international working group that was established in2005 to evaluate the status of exploited marine ecosystems using a suite of indicators in a comparative framework. An initial shortlist of seven ecological indicators was selected to quantify the effects of fishing on the broader ecosystem using several criteria (i.e., ecological meaning, sensitivity to fishing, data avail-ability, management objectives and public awareness). The suite comprised: (i) the inverse coefficient of variation of total biomass of surveyed species, (ii) mean fish length in the surveyed community, (iii)mean maximum life span of surveyed fish species, (iv) proportion of predatory fish in the surveyed community, (v) proportion of under and moderately exploited stocks, (vi) total biomass of surveyed species,and (vii) mean trophic level of the landed catch. In line with the Nagoya Strategic Plan of the Convention on Biological Diversity (2011–2020), we extended this suite to emphasize the broader biodiversity and conservation risks in exploited marine ecosystems. We selected a subset of indicators from a list of empirically based candidate biodiversity indicators initially established based on ecological significance to complement the original IndiSeas indicators. The additional selected indicators were: (viii) mean intrinsic vulnerability index of the fish landed catch, (ix) proportion of non-declining exploited species in the surveyed community, (x) catch-based marine trophic index, and (xi) mean trophic level of the surveyed community. Despite the lack of data in some ecosystems, we also selected (xii) mean trophic level of the modelled community, and (xiii) proportion of discards in the fishery as extra indicators. These additional indicators were examined, along with the initial set of IndiSeas ecological indicators, to evaluate whether adding new biodiversity indicators provided useful additional information to refine our under-standing of the status evaluation of 29 exploited marine ecosystems. We used state and trend analyses,and we performed correlation, redundancy and multivariate tests. Existing developments in ecosystem-based fisheries management have largely focused on exploited species. Our study, using mostly fisheries independent survey-based indicators, highlights that biodiversity and conservation-based indicators are complementary to ecological indicators of fishing pressure. Thus, they should be used to provide additional information to evaluate the overall impact of fishing on exploited marine ecosystems

Evaluating changes in marine communities that provide ecosystem services through comparative assessments of community indicators

Fisheries provide critical provisioning services, especially given increasing human population. Understanding where marine communities are declining provides an indication of ecosystems of concern and highlights potential conflicts between seafood provisioning from wild fisheries and other ecosystem services. Here we use the nonparametric statistic, Kendall[U+05F3]s tau, to assess trends in biomass of exploited marine species across a range of ecosystems. The proportion of 'Non-Declining Exploited Species' (NDES) is compared among ecosystems and to three community-level indicators that provide a gauge of the ability of a marine ecosystem to function both in provisioning and as a regulating service: survey-based mean trophic level, proportion of predatory fish, and mean life span. In some ecosystems, NDES corresponds to states and temporal trajectories of the community indicators, indicating deteriorating conditions in both the exploited community and in the overall community. However differences illustrate the necessity of using multiple ecological indicators to reflect the state of the ecosystem. For each ecosystem, we discuss patterns in NDES with respect to the community-level indicators and present results in the context of ecosystem-specific drivers. We conclude that using NDES requires context-specific supporting information in order to provide guidance within a management framework.We would like to thank the IndiSeas Working Group, endorsed by IOC-UNESCO (www.ioc-unesco.org) and the European Network of Excellence Euroceans (www.eur-oceans.eu). KMK was supported by Conservation International and the Sea Around Us project, a collaboration between The University of British Columbia and The Pew Charitable Trusts. MC was partially supported by the EC Marie Curie CIG grant to BIOWEB and the Spanish Research Program Ramon y Cajal. LJS was supported through the South African Research Chair Initiative, funded through the South African Department of Science and Technology (DST) and administered by the South African National Research Foundation (NRF). YJS and MTT were supported by the French project EMIBIOS (FRB, contract no. APP-SCEN-2010-II). LJS and YS were also funded by the European collaborative project MEECE – Marine Ecosystem Evolution in a Changing Environment – (FP7, Contract no. 212085). CPL was supported by Defra project MF1228 (From Physics to Fisheries) and DEVOTES (DEVelopment of innovative Tools for understanding marine biodiversity and assessing good Environmental Status) funded by EU FP7 (grant Agreement no. 308392), www.devotes-project.eu. GIvdM was partially supported by the Norwegian Nature Index programme and the Institute of Marine Research, Norway. HO was funded was funded by the Estonian Ministry of Education and Research (grant SF0180005s10). MAT was funded by a predoctoral FPI fellowship from the Spanish Institute of Oceanography (IEO). MJJJ was supported by the EC Marie Curie IOF Grant, PIOF-GA-2013-628116. We acknowledge all those who conducted surveys to collect the data used in this study.Peer reviewe

An end-to-end coupled model ROMS-N2P2Z2D2-OSMOSE of the southern Benguela foodweb: parameterisation, calibration and pattern-oriented validation

In order to better understand ecosystem functioning under simultaneous pressures (e.g. both climate change and fishing pressures), integrated modelling approaches are advocated. We developed an end-to-end model of the southern Benguela ecosystem by coupling the high trophic level model OSMOSE with a biophysical model (ROMS-N2P2Z2D2). OSMOSE is a spatial, multispecies, individual-based model simulating the whole life cycle of fish with fish schools interacting through opportunistic and size-based predation. It is linked to the biogeochemical model through the predation process; plankton groups are food for fish and fish apply a predation mortality on plankton. Here we describe the two-way coupling between the models and follow a pattern-oriented modelling approach to validate the simulations. At the individual level, model outputs are consistent with observed diets for several species from small pelagic fish to top predatory fish, although biases emerge from underestimation of macrozooplankton and lack of vertical structure. At the population level, the seasonality of the size structure is similar between the model and data. At the community level, the modelled trophic structure is consistent with the knowledge available for this ecosystem. The structure of the foodweb is an emergent property of the model, showing trophic links between species, their strength and the strong connectivity observed. We also highlight the capacity of this model for tracking indicators at various hierarchical levels.Keywords: individual-based model, model validation, pattern-oriented modelling, trophic interactions, two-way couplingAfrican Journal of Marine Science 2014, 36(1): 11–2

L'halieutique ou l'exploitation des ressources vivantes aquatiques : une science protéiforme

National audienceL’Association Française d’Halieutique réunit environ 200 scientifiques français de divers organismes d’enseignement supérieur et de recherche, de diverses disciplines, tous intéressés par l’halieutique (la science de la pêche, mais aussi des ressources aquatiques exploitées, des écosystèmes qui les supportent et des systèmes d’exploitation). Tous les deux ans, l’association organise un colloque scientifique de trois jours. Le dernier a eu lieu en juillet 2015 à Montpellier; l’occasion de faire un point sur les grandes tendances et les grands défis auxquels fait face la communauté. Cet article repose en grande partie sur les présentations faites au cours de ce colloque et qui sont consultables en ligne (http://association-francaise-halieutique.fr/conferences/)

The need for a protean fisheries science to address the degradation of exploited aquatic ecosystems

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASAREThe symposium was organized with the financial support of Ifremer, IRD, Agrocampus Ouest and la Region Languedoc-Roussillon. We would like to thank all speakers, and especially the invited speakers (A. Bertand, V. Maris, B. Planque, F. Bonhomme, P. Freon, A. Avadi and B. Ioos), the Aquarium Mare Nostrum (Montpellier, France) staff for hosting this symposium, and all persons involved in the organization, with special thanks to Catherine Le Penven. Finally, we are very grateful to D. Caitriona Carter for her help in writing this article, and to D. Verena Trenkel and an anonymous referee for their valuable suggestions and comments when revising this paper.International audienceIn this introductory paper we highlight key questions that were discussed during the symposium on "Status, functioning and shifts in marine ecosystems" organized by the Association Française d'Halieutique) (French Association for Fisheries Sciences) (Montpellier, France, July 2015). This symposium illustrated that fisheries science is now working at multiple scales, on all dimensions of socio-ecosystems (ecological, political, sociological, economical...), with a great diversity of approaches and taking into account different levels of complexity while acknowledging diverse sources of uncertainty. We argue that we should go one step further and call for a protean fisheries science to address the deteriorated states of aquatic ecosystems caused by anthropogenic pressures. Protean science is constantly evolving to meet emerging issues, while improving its coherence and integration capacity in its complexity. This science must be nourished by multiple approaches and be capable of addressing all organizational scales, from individual fish or fishermen up to the entire ecosystem, include society, its economy and the services it derives from aquatic systems. Such a protean science is required to address the complexity of ecosystem functioning and of the impacts of anthropogenic pressures

Emergence of negative trophic level-size relationships from a size-based, individual-based multispecies fish model

Modeling the mechanisms underlying trophic interactions between individuals allows the food web structure to emerge from local interactions, which constitutes a prerequisite for assessing how marine ecosystems respond to various anthropogenic pressures. Using a multispecies spatially explicit individual-based model, the emergence of trophic patterns was explored in the eastern English Channel ecosystem, where pelagic-benthic trophic coupling was recently studied empirically. The OSMOSE model was applied to this ecosystem by explicitly representing the life cycle of 13 fish species and one squid group, forced by pelagic and benthic prey fields that are variable over time and space. A matrix defining possible accessibilities between life stages was added to the model to link benthic and pelagic communities through overlap of vertical distribution. After optimizing some parameters of the model to represent the average state of the fish community during the 2000-2009 period, the simulated trophic structure was explored and compared to empirical data. The simulated and stable-isotope-derived trophic levels of fish were in relatively good agreement. Intraspecific variability of the trophic level is high in the five stable-isotope datasets but is well encompassed by the model. Despite the hypothesis of opportunistic size-based predation, the simulation showed a decreasing trend of trophic level with size for four benthic species, a pattern observed empirically for a different set of species in the ecosystem. Model exploration showed that this emerging pattern varies spatially and is both explained by the spatial variability of prey availability and by the independence of trophic and size structures of benthic invertebrates. The combination of individual-based models, stomach contents and intrinsic tracers, such as stable isotopes, appears to be a promising tool to better understand the causes of observed trophic patterns

Plasticity of trophic interactions in fish assemblages results in temporal stability of benthic-pelagic couplings

This study addresses the temporal variability of couplings between pelagic and benthic habitats for fish assemblages at five periods in a shallow epicontinental sea, the Eastern English Channel (EEC). Organic matter fluxes fueling fish assemblages and the relative contribution of their different sources were assessed using stable isotope analysis and associated isotopic functional metrics. Couplings between benthic and pelagic realms appeared to be a permanent feature in the EEC, potentially favored by shallow depth and driven by the combination of two trophic processes. First, trophic interactions exhibited plasticity and revealed resource partitioning. Second, changes in the composition of fish assemblages did not impact benthic-pelagic couplings, as most dominant species were generalists during at least one time period, allowing complete use of available resources. Examining both unweighted and biomass-weighted indices was complementary and permitted a better understanding of trophic interactions and energy fluxes