Coming at the issue from both the beginning with the rapid spread of commercial whaling after WWII, and the end, with drastic declines of kelp forests today, Springer, Estes and their six co-authors present a domino theory of major ecosystem impacts and restructuring.

It started with the capture of hundreds of thousands of great whales from the North Pacific Ocean from 1946 to 1979. The paper's eight authors argue that this removal of prey forced some killer whales to seek alternative sources of food. Beginning with harbor seals (populations collapsed early 70's - early 80's) then fur seals (mid 70's - mid 80's), sea lions (late 70's - 90 's) and finally sea otters (90's - today), the killer whales targeted populations of small, coastal marine mammals.

The authors surmise that killer whales may have preferred harbor seals and fur seals to sea lions because of the higher nutritional value of harbor seals and because seals are less aggressive and easier to catch.

As the pinnipeds became comparatively rare, some killer whales expanded their diet to include the calorically least profitable mammals - the sea otters - with rippling ecosystem effects. By the late 1990's low numbers of sea otters allowed an explosion of sea urchins and decimation of the kelp forests due to the sea urchins' over grazing.

"The point of this story is not to vilify whaling and exonerate overfishing," says Estes. "In principle we think that when any species is exploited to excess - be it pollock, halibut or whales - it may trigger a broad and devastating 'domino effect,' and the ecosystem impacts are significant."

Estes had already shown that killer whale predation had a significant impact on sea otter populations, but the question remained as to whether they could really account for the other declines. To see if it was possible
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Contact: Jessica Brown
jbrown@seaweb.org
202-497-8375
SeaWeb
22-Sep-2003