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Too Many Sharks
2002 AAAS Annual Meeting - Science in a Connected World
Not Enough Sea Lions, Too Many Sharks: Global Warming Signal?
Saturday, February 16, 2002 8:45 a.m. - 10:15 a.m.
Coordinators: Bruce Wright, Conservation Science Institute; Vincent Gallucci, University of Washington
Ecosystems in the North Pacific are experiencing significant changes, measured by changes in patterns of abundance and presence of many marine animals. These patterns include increases in salmon, decreases in forage fishes, and declines in three pinniped species: Steller sea lions, harbor seals, and northern fur seals. Simultaneously, two shark species: Pacific sleeper sharks and salmon sharks appear to experiencing population explosions.
The focus of this symposium is upon pinniped and shark population dynamics and possible predator-prey interactions. A change in the sub-arctic climate regime may be involved in this interaction. It is likely that such interactions are endemic. However, a change in climate may work differentially to the sharks' benefit by intensifying the number of successful predation events and expanding their population sizes.
Photo of large Pacific sleeper sharks on the deck of a trawl vessel.
Pinnipeds and sharks are both K-selected species, at the top of the food chain, and living 25-50 years. Therefore, changes in shark or sea lion survival may not be observed for many years. Examination of tropical ecosystem food webs reveals that sharks occupy a wide range of niches, classified according to habitat (reef, oceanic, coastal, etc.) and depth stratification, much of which is temperature mediated. In the Alaskan system, the two shark species are also depth stratified and habitat specific. It is suggested that the regime shift in the North Pacific Ocean is affecting habitats, making the ecosystem less favorable for pinnipeds and more favorable for sharks. This is reflected by increased juvenile survival for the sharks and decreases in pinniped populations.
Session 1, Shark Abundance Changes, Salmon Sharks and Pacific Sleeper Sharks, will be presented by Bruce Wright of the Conservation Science Institute
Session 2, Pinniped Abundance Changes: Endangered Sea Lions, will be presented by Thomas R. Loughlin of the National Marine Mammal Lab.
Session 3, Sharks, Pinnipeds, and Ecosystem Dynamics, will be presented by Vincent Gallucci of the University of Washington.
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