Keystone Predators in the Central Pacific

Keystone Predators in the Central Pacific

James F. Kitchell, Christofer H. Boggs, Xi He, and Carl J. Walters

Keystone Predators in the Central PacificThis is part of Ecosystem Approaches for Fisheries Management
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We evaluated the potential of keystone predator effects among the guild of sharks, tunas, and billfishes at the apex of pelagic food webs in the central North Pacific ecosystem. The Ecopath approach was used as the basis for a dynamic model (Ecosim) that simulates the ecological effects of environmental change and/or fishery exploitation patterns. No single fish species of the highest trophic levels appears to have a profound and uniquely important role in the organization and structure of the central Pacific ecosystem. Instead: (1) The most important components among the guild of apex predators appear to be those such as yellowfin and skipjack tunas which have greater biomass than other apex predators, highly diverse diets, and rapid turnover rates. (2) Intraguild cannibalism and substantial diet overlap are common in these systems. The apparent complexity and importance of cannibalism invites more extensive data collection.(3) Simulated depletions of shark or tuna populations exhibit ecological changes similar to those observed when management or fishery exploitation effects are intense. (4) The ecological effects of longline fisheries are diffuse and diverse. If we are to affix a keystone predator label in this ecosystem, it is that due to fisheries exploitation.

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