Collapse of seals, sea lions & sea otters in North Pacific triggered by overfishing of gr...( for a change in killer whale feeding be...)

for a change in killer whale feeding behavior to have a significant impact on seals and sea lions, co-authors Dan Doak and Terrie Williams modeled the nutritional requirements of killer whales, the nutritional value of sea lions and otters, and the number of deaths necessary to explain the documented declines of marine mammals in the Aleutian Islands. They found that a dietary shift by less than 1% of the estimated 3,888 killer whales across the region would have been enough to drive the observed declines. The inability of sea otters, seals and sea lions to sustain increased mortality from redirected killer whale predation makes sense based on their much smaller aggregate biomass compared with the great whales. "After five years of examining this problem, I don't see any fatal inconsistencies with our hypothesis," says Estes.

Many scientists have difficulty believing that predation could play such an important role in the structure of marine food webs, but the authors show that the timing of events; information on the abundance, diet and foraging behavior of both predators and prey; and feasibility analyses based on demographic and energetic modeling, are all consistent with this hypothesis. Dr. Robert Paine, of the University of Washington agrees, "It's a plausible and unifying explanation for the sequential collapse. In a multiple causation world, this is likely one of the main causes."

Traditionally, little attention has been paid to the role of predation in structuring open ocean ecosystems (i.e. top down effects). For the last 30 years most scientists have focused on bottom up influences such as changes in the physical oceanic environment and food shortages. These researchers are convinced that the power of predation is much greater than previously realized if animals are forced to switch food sources, the ripple effects through an ecosystem can be profound.

One of the most striking implications of this work is the complex interconnect
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Contact: Jessica Brown
jbrown@seaweb.org
202-497-8375
SeaWeb
22-Sep-2003

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