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Gruss A.,Montpellier University | Gruss A.,University of Miami | Gruss A.,Southeast Fisheries Science Center
Aquatic Living Resources | Year: 2015

Marine protected areas (MPAs) are increasingly being considered and used for the management of fisheries targeting mobile fish populations. Here, the recent modelling literature on MPA effects for mobile fish populations and their fisheries is reviewed. Modelling studies conducted since 2011 have filled a considerable number of knowledge gaps on the impacts of MPAs for species exhibiting home-range behaviour, nomadic movements or behavioural polymorphism, and on the effects of "targeted MPAs", which aim to protect relatively small areas where migratory fishes spend an inordinate fraction of time or are highly vulnerable to fishing (e.g., nursery or spawning zones). Also, in recent years, two studies investigated the consequences of MPAs targeting highly migratory (tuna-like) fish populations for the first time in the history of MPA modelling. Recent modelling studies found that MPAs aimed at protecting mobile species may have positive conservation eff ects under a relatively wide range of situations, but may generate long-term fisheries benefits only under a very limited set of conditions. In particular, MPAs were not found to be beneficial for the fisheries targeting highly migratory populations. Strategies producing both conservation and fisheries benefits were identified, which depend on fish movement patterns and numerous aspects of fish life history and fisheries dynamics. However, in view of the diversity of fish movement patterns in MPA systems and current dynamics in resource management, it is clear that additional modelling work is needed to fully understand how protected areas aff ect mobile fish populations and their fisheries and to be able to implement pertinent MPAs. In particular, future modelling studies should systematically assess the effects of MPAs in relation to other management tools to find strategies that are most eff ective in meeting management objectives, and explore the impacts of "dynamic" MPAs that follow highly migratory fish populations in space and time. © EDP Sciences, IFREMER, IRD 2015. Source

Gruss A.,IRD Montpellier | Gruss A.,University of Miami | Gruss A.,Southeast Fisheries Science Center | Robinson J.,Seychelles Fishing Authority | And 4 more authors.
ICES Journal of Marine Science | Year: 2014

There is a global trend in the depletion of transient reef fish spawning aggregations ("FSAs"), making them a primary target for management with marine protected areas (MPAs). Here, we review the observed and likely effectiveness of FSAMPAs, discuss how future studies could fill knowledge gaps, and provide recommendations for MPA design based on species' life history and behaviour, enforcement potential, and management goals. Modelling studies indicate that FSA MPAs can increase spawning-stock biomass and normalize sex ratio in protogynous fish populations, unless fishing mortality remains high outside protected FSA sites and spawning times. In the field, observations of no change or continued decline in spawning biomass are more common than population recovery. When empirical studies suggest that FSA MPAs may not benefit fish productivity or recovery, extenuating factors such as insufficient time since MPA creation, poor or lack of enforcement, inadequate design, and poorly defined management objectives are generally blamed rather than failure of the MPA concept. Results from both the empirical and modelling literature indicate that FSA MPAs may not improve exploitable biomass and fisheries yields; however, investigations are currently too limited to draw conclusions on this point. To implement effective FSA MPAs, additional modelling work, long-term monitoring programmes at FSA sites, and collections of fisheries-dependent data are required, with greater attention paid to the design and enforcement of area closures. We recommend a harmonized, adaptive approach that combines FSA MPA design with additional management measures to achieve explicitly stated objectives. Conservation objectives and, therefore, an overall reduction in mortality rates should be targeted first. Fisheries objectives build on conservation objectives, in that they require an overall reduction in mortality rates while maintaining sufficient access to exploitable biomass. Communication among researchers, regulatory agencies, park authorities, and fishers will be paramount for effective action, along with significant funds for implementation and enforcement. © International Council for the Exploration of the Sea 2014. All rights reserved. Source

Gruss A.,Southeast Fisheries Science Center | Gruss A.,University of Miami | Drexler M.,University of South Florida | Ainsworth C.H.,University of South Florida
Fisheries Research | Year: 2014

Spatial ecosystem models, such as OSMOSE, have become integral tools in achieving ecosystem-based management for their ability to thoroughly describe predator-prey dynamics in a spatially explicit context. Distribution maps, which define the initial spatial allocation of functional groups abundance, can have a large effect on the predator-prey dynamics that spatially explicit ecosystem models simulate. Here, we introduce the delta GAM approach we developed to be able to produce distribution maps for an OSMOSE model of the West Florida Shelf (Gulf of Mexico), OSMOSE-WFS. This delta GAM approach predicts the spatial distribution of different life stages of the multiple functional groups represented in OSMOSE-WFS ('life-stage groups') at different seasons, over the entire Gulf of Mexico (GOM) shelf including areas where abundance estimates do not exist, using different research survey datasets and regional environmental and habitat features. Our delta GAM approach consists of fitting two independent models, a binomial GAM and a quasi-Poisson GAM, whose predictions are then combined using the delta method to yield spatial abundance estimates. To validate delta GAMs, bootstraps are used and Spearman's correlation coefficients (Spearman's ρ's) between predicted and observed abundance values are estimated and tested to be significantly different from zero. We use pink shrimp (Farfantepenaeus duorarum) to demonstrate our delta GAM approach by predicting the summer distribution of this species over the GOM shelf and the West Florida Shelf. Predictions of the delta GAM reflect existing empirical research related to pink shrimp habitat preferences and predictions of a negative binomial GAM previously designed for the GOM. We find that using a delta rather than a negative binomial GAM saves significant computation time at the expense of a slight reduction in GAM performance. A positive and highly significant Spearman's ρ between observed and predicted abundance values indicates that our delta GAM can reliably be used to predict pink shrimp spatial distribution. Spearman's ρ was also positive and highly significant in every life-stage group represented in OSMOSE-WFS and season, though often low. Therefore, delta GAMs fitted for the different life-stage groups and seasons correctly predict qualitative differences between low- and high-abundance areas and are deemed appropriate for generating distribution maps for OSMOSE-WFS. The delta GAM approach we developed is a simple, convenient method to create distribution maps to be fed into spatially explicit ecosystem models, where wide spatial and taxonomic coverage is desired while benefits of high precision estimates are lost at run-time. © 2014. Source

Donahue M.J.,Hawaii Institute of Marine Biology | Karnauskas M.,Southeast Fisheries Science Center | Toews C.,University of Puget Sound | Paris C.B.,University of Miami
PLoS ONE | Year: 2015

Many species of reef fishes form large spawning aggregations that are highly predictable in space and time. Prior research has suggested that aggregating fish derive fitness benefits not just from mating at high density but, also, from oceanographic features of the spatial locations where aggregations occur. Using a probabilistic biophysical model of larval dispersal coupled to a fine resolution hydrodynamic model of the Florida Straits, we develop a stochastic landscape of larval fitness. Tracking virtual larvae from release to settlement and incorporating changes in larval behavior through ontogeny, we found that larval success was sensitive to the timing of spawning. Indeed, propagules released during the observed spawning period had higher larval success rates than those released outside the observed spawning period. In contrast, larval success rates were relatively insensitive to the spatial position of the release site. In addition, minimum (rather than mean) larval survival was maximized during the observed spawning period, indicating a reproductive strategy that minimizes the probability of recruitment failure. Given this landscape of larval fitness, we take an inverse optimization approach to define a biological objective function that reflects a tradeoff between the mean and variance of larval success in a temporally variable environment. Using this objective function, we suggest that the length of the spawning period can provide insight into the tradeoff between reproductive risk and reward. © 2015, Public Library of Science. All rights reserved. This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Source

Long W.C.,National Oceanic and Atmospheric Administration | Van Sant S.B.,National Oceanic and Atmospheric Administration | Van Sant S.B.,Southeast Fisheries Science Center | Haaga J.A.,National Oceanic and Atmospheric Administration
Journal of Experimental Marine Biology and Ecology | Year: 2015

Since the 1970s, dominance of the shallow water Pribilof Islands king crab populations has shifted from blue king crab (. Paralithodes platypus) to red king crab (. Paralithodes camtschaticus), potentially influenced by interactions at the juvenile stage. In laboratory experiments, we determined whether habitat and temperature could mediate competitive and predatory interactions between juveniles of both species. We examined how density and predator presence affect habitat choice by red and blue king crabs. Further experiments determined how temperature and habitat affect predation by year-1 red king crab on year-0 blue king crab. Finally, long-term interaction experiments examined how habitat and density affected growth, survival, and intra-guild interactions between red and blue king crab. Red king crabs had a greater affinity for complex habitat than blue king crabs and the presence of predators increased preference for complex habitat for both species. Predation on year-0 blue king crabs by year-1 red king crabs was lower in complex habitats and at colder temperatures. When reared alone, red king crab survival was higher at low densities and in complex habitats. When reared with blue king crab, survival of red king crab was higher in complex habitats and in the presence of blue king crab. Blue king crab survival was substantially lower in the presence of red king crabs regardless of habitat. In both rearing experiments, differences in changes in crab size appeared to be driven by mortality rates and size-selective predation. This demonstrates that interactions between juvenile red and blue king crabs are primarily driven by intra-guild predation and not competition for resources. These results, suggest that juvenile red king crabs have an advantage over blue king crabs which could lower productivity of the Pribilof Islands blue king crab stock since the former became dominant in that system. © 2014. Source

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