Radio Script
1999

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Dead Salmon Still Migrate
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STORY: On a cool summer day somewhere in Southeast Alaska, a marten prowls the shore looking for an easy meal. Its efforts are soon rewarded with a spawned-out pink salmon. Dragging the salmon up the bank and into the woods, the marten finds shelter under an upturned tree and begins feasting on its catch. It would appear the migration of this salmon has come to an end. But as ecologist Merav Ben-David of the University of Alaska Fairbanks has learned, the migration has in one sense only just begun.

BEN-DAVID: "The rest of the carcass, what's left over, decomposes and the nitrogen is released into the soil. Plants pick that nitrogen up. And that's what I found. I found evidence of marine-derived nitrogen in plants up to 1,000 meters away from the stream, in sites of carnivore activity."

Nitrogen is an element essential to the growth of plants and animals. In research described recently in the journal Nature, Merav Ben-David traced the migration of nitrogen from decaying salmon into the ecosystem. She was at first surprised to find in plants and trees high levels of Nitrogen 15--a type of nitrogen more commonly found in ocean food webs. She didn't have to look far to see how it got there.

BEN-DAVID: "You put in the river otters, the mink and the marten and suddenly you have a system of transporting the nutrients much further from the stream than otherwise."

With each salmon containing about 74 grams of nitrogen, the tens of millions of salmon that die each summer in Alaska leave behind a lot of nitrogen. Exactly how all that nitrogen gets used, and which plants and trees rely on it the most, is the subject of future research.

For now, Merav Ben-David says her research underscores the importance of both salmon and predators to a healthy ecosystem. Take either out of the picture, and the system begins to fall apart.

OUTRO: For Arctic Science Journeys, this is Doug Schneider, reporting from Fairbanks, Alaska.