Arctic Science Journeys
Radio Script
1996

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Growing Up a Salmon
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"We've got predators, anything from as small as a quarter-pound dolly varden going after them to whales. We've seen whales catch a school of our fry that's swimming along the beach and they'll turn over on their side and actually filter feed them right off the beach almost. Just about all the fish eating birds will get their share of them, and pretty much any fish out there will go after our fry at one time or another."

While numerous species feast on young salmon, until recently biologists thought that large adult pollock -- the most abundant predator in the sound -- ate most of the fry released each spring. But new research has discovered that adult pollock sometimes switch to even easier prey.

The easier prey are billions of tiny crustaceans called copepods that rise to the surface to feed on algae blooms in the sound. Though only the size of a grain of rice, each copepod is packed with protein. Ted Cooney is a fisheries oceanographer at the University of Alaska Fairbanks.

"The copepods and the salmon are appearing at about the same time. And large predatory fish like pollock which normally one would think would key immediately on the small fish seem to feed efficiently on copepods. And we think they do this by filter feeding the copepods on their gill rakers essentially opening their mouths and swimming slowly through patches of these little animals. When all this is going on the pollock aren't paying attention to the salmon fry."

Although the feast is short lived, millions of young salmon get a much needed boost. They'll need it too, because within weeks the copepods will disappear and the opportunistic pollock will return to eating young salmon. Fishermen have suggested removing adult pollock from the sound to help more young salmon survive. But Ted Cooney isn't so sure wiping out the pollock would work.

"Because large pollock feed on, among other things, their own young, removing a lot of larger pollock, the survival of the younger fish would increase and you might end up with more pollock in the system than you actually started with."

Cooney's research is part of a long-term study of how salmon grow and survive in Prince William Sound. The work is part of a larger Sound Ecosystem Assessment program funded with money from the Exxon Valdez oil spill settlement.

For Arctic Science Journeys, this is Debra Damron.