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      Foraging Behavior and Success of a Mesopelagic Predator in the Northeast Pacific Ocean: Insights from a Data-Rich Species, the Northern Elephant Seal


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          The mesopelagic zone of the northeast Pacific Ocean is an important foraging habitat for many predators, yet few studies have addressed the factors driving basin-scale predator distributions or inter-annual variability in foraging and breeding success. Understanding these processes is critical to reveal how conditions at sea cascade to population-level effects. To begin addressing these challenging questions, we collected diving, tracking, foraging success, and natality data for 297 adult female northern elephant seal migrations from 2004 to 2010. During the longer post-molting migration, individual energy gain rates were significant predictors of pregnancy. At sea, seals focused their foraging effort along a narrow band corresponding to the boundary between the sub-arctic and sub-tropical gyres. In contrast to shallow-diving predators, elephant seals target the gyre-gyre boundary throughout the year rather than follow the southward winter migration of surface features, such as the Transition Zone Chlorophyll Front. We also assessed the impact of added transit costs by studying seals at a colony near the southern extent of the species’ range, 1,150 km to the south. A much larger proportion of seals foraged locally, implying plasticity in foraging strategies and possibly prey type. While these findings are derived from a single species, the results may provide insight to the foraging patterns of many other meso-pelagic predators in the northeast Pacific Ocean.

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          Pelagic marine predators face unprecedented challenges and uncertain futures. Overexploitation and climate variability impact the abundance and distribution of top predators in ocean ecosystems. Improved understanding of ecological patterns, evolutionary constraints and ecosystem function is critical for preventing extinctions, loss of biodiversity and disruption of ecosystem services. Recent advances in electronic tagging techniques have provided the capacity to observe the movements and long-distance migrations of animals in relation to ocean processes across a range of ecological scales. Tagging of Pacific Predators, a field programme of the Census of Marine Life, deployed 4,306 tags on 23 species in the North Pacific Ocean, resulting in a tracking data set of unprecedented scale and species diversity that covers 265,386 tracking days from 2000 to 2009. Here we report migration pathways, link ocean features to multispecies hotspots and illustrate niche partitioning within and among congener guilds. Our results indicate that the California Current large marine ecosystem and the North Pacific transition zone attract and retain a diverse assemblage of marine vertebrates. Within the California Current large marine ecosystem, several predator guilds seasonally undertake north-south migrations that may be driven by oceanic processes, species-specific thermal tolerances and shifts in prey distributions. We identify critical habitats across multinational boundaries and show that top predators exploit their environment in predictable ways, providing the foundation for spatial management of large marine ecosystems. ©2011 Macmillan Publishers Limited. All rights reserved
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            Recent studies document unprecedented declines in marine top predators that can initiate trophic cascades. Predicting the wider ecological consequences of these declines requires understanding how predators influence communities by inflicting mortality on prey and inducing behavioral modifications (risk effects). Both mechanisms are important in marine communities, and a sole focus on the effects of predator-inflicted mortality might severely underestimate the importance of predators. We outline direct and indirect consequences of marine predator declines and propose an integrated predictive framework that includes risk effects, which appear to be strongest for long-lived prey species and when resources are abundant. We conclude that marine predators should be managed for the maintenance of both density- and risk-driven ecological processes, and not demographic persistence alone.
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              Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.

                Author and article information

                Role: Editor
                PLoS One
                PLoS ONE
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                15 May 2012
                : 7
                : 5
                : e36728
                [1 ]Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, California, United States of America
                [2 ]Department of Biology, Sonoma State University, Rohnert Park, California, United States of America
                [3 ]Centro de Investigación en Alimentación y Desarrollo A.C., Unidad Guaymas, Guaymas, Sonora, México
                [4 ]National Marine Mammal Laboratory, Alaska Fisheries Science Center/National Marine Fisheries Service/National Oceanic and Atmospheric Administration, Seattle, Washington, United States of America
                [5 ]Scripps Institute of Oceanography/University of California San Diego, La Jolla, California, United States of America
                [6 ]Marine Mammal Commission, Bethesda, Maryland, United States of America
                [7 ]Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, California, United States of America
                [8 ]Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan
                University of California Davis, United States of America
                Author notes

                Conceived and designed the experiments: PWR DPC DEC JPGR JLH SES. Performed the experiments: PWR DPC DEC JPGR CDC MAF CG KTG JLH LAH CEK JLM SMM BIM SHP SES NMT SVA KY. Analyzed the data: PWR DEC CG JLH SHP SES. Contributed reagents/materials/analysis tools: DPC DEC JPGR. Wrote the paper: PWR DPC DEC JPGR MAF CG KTG JLH CEK JLM SMM BIM SHP SES NMT SVA.

                Robinson et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                : 1 November 2011
                : 5 April 2012
                Page count
                Pages: 12
                Research Article
                Behavioral Ecology
                Conservation Science
                Population Ecology
                Marine Biology
                Fisheries Science
                Marine Conservation
                Marine Ecology
                Population Biology
                Population Dynamics
                Population Ecology



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