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Apex Predators in the Central Pacific: An Ecosystem Approach

The current levels of mortality owing to fisheries are unlike anything in the long evolutionary history of exploited species and, therefore, that fisheries are a powerful ecological force. <br/>Understanding fishery effects as causes of perturbation offers important lessons about the ecological processes that regulate structure and function of pelagic ecosystems. <br/> The previous project, Apex Predators in Pelagic Ecosystems, focused on trophic interactions in the central north Pacific (CNP) ecosystem based on modeling analyses at three scales: bioenergetics of individual fish species, predator-prey interactions and ecosystem models. The ecological effects of <br/>long-line fisheries for tunas, billfishes and sharks has been a consistent theme in all three areas of model development. The major lessons were that: 1. Characterizing trophic ontogeny was a key component to building effective models for this system of strongly overlapping use of prey resources and intra-guild predation, and 2. Fisheries have become and continue as the main cause of change in trophic structure of the CNP. This project will support continuation and expansion of the first project. Dr. Kitchell and collaborators will develop models that can evaluate the role of fishery effects in food web dynamics, expand that to include interactions with large-scale environmental effects such as those due to ENSO, PDO, and/or climate change dynamics and use the consequent models as a basis for evaluating resource management policies that can change ecosystem structure and function. Three major objectives will be pursued: <br/> Experimental Approach to Modeling. They have developed a model of trophic interactions and <br/>fishery effects for the central north Pacific (CNP) based, in part, on merging population-scale data with food web information and the history of fishery development. An ecological analogue exists in the central south Pacific (CSP) where fishery development occurred at a later time. The researchers will use the CNP approach to develop a CSP model, then conduct the equivalent of an independent, replicate analysis of the <br/>trophic changes owing to fishery development. Merging these models creates a single tool that allows evaluation of local effects expressed in a large-scale context. Characterizing fisheries as the equivalent of <br/>new predators allows an evaluation of .strong interactions in food webs and the complex feedback mechanisms that emerge from fishery effects. <br/> Modeling to Include Environmental Drivers. They will implement environmental forcing due to <br/>ENSO, PDO and/or global change effects expressed in our models of the CNP, CSP and a similar model <br/>of the eastern tropical Pacific (ETP) developed through collaboration sponsored by the National Center <br/>for Ecological Analysis and Synthesis (NCEAS). The investigators will use statistical approaches that evaluate anomalies in the population data as the basis for differentiating effects of the fisheries from those of the <br/>environmental forcing that alters primary production rates and its expression in production of higher <br/>trophic levels. <br/> Bycatch and Ecological Interactions. Major conservation issues revolve around bycatch of <br/>threatened or endangered turtles, birds, sharks and billfishes in these pelagic ecosystems. Dr, Kitchell and co-workers will use a "scenarios" approach to simulation of alternative management actions, the likely responses of changes in fishery exploitation processes, their consequent ecological changes and their socioeconomic <br/>consequences. The basic Ecosim model now includes the capacity to evaluate the latter using inputs of <br/>fish prices plus weighting for goals based on employment, conservation and/or ecosystem management.

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