Radio Script
2000

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Sockeye Salmon Diets
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INTRO: Soon after a salmon is born, it leaves freshwater for life in the open ocean. Exactly what salmon do out there in the big blue sea remains largely a mystery to scientists. But as Doug Schneider reports in this week's Arctic Science Journeys Radio, one scientist has gained some answers by studying what salmon eat as they migrate home to spawn.

STORY: Sifting through a salmon's cut-open stomach isn't glamorous work, but heck, somebody has to do it.

MCINTOSH: "There's definitely a learning curve to it."

That someone is Bruce McIntosh, a fisheries master's degree student at the University of Alaska Fairbanks.

McIntosh studied the feeding habits of sockeye salmon that migrate home to spawn in Alaska. Sockeye salmon are one of five salmon species native to the state.

MCINTOSH: "It's been pretty much always taken for granted that once the salmon enter freshwater that they stop feeding. But what we don't know is whether they feed to a maximum until they enter the freshwater? Is there any kind of form to that behavior?"

To find out, McIntosh spent the last two summers poking around inside the stomachs of thousands of sockeye salmon. He looked at salmon caught near spawning grounds on the south end of Alaska's Kodiak Island. He also studied salmon caught in Shelikof Strait, a wide ocean channel north of the island, used by salmon migrating to spawning areas hundreds of miles away.

McIntosh made some interesting and potentially important discoveries as he examined the two groups of salmon. He found, for example, that salmon caught near Kodiak island ate less as they got closer to their spawning grounds. Conversely, sockeye salmon in Shelikof Strait showed no sign of slowing their feeding.

MCINTOSH: "They're moving through on to other places. That's why we're interested in these fish, as a migrating fish that are still actively feeding when it's that far from its natal stream. They haven't started the urge to spawn, that instinctual behavior. It's not apparent for spawning but they continue to put on growth and beef up energy before spawning."

What they ate was also of interest to McIntosh. He expected to find partially digested remains of small fish, but instead he found zooplankton, tiny crustaceans more commonly thought to be prey for juvenile salmon.

MCINTOSH: "A lot of crab larvae. Some terapods, which are essentially snails, and some euphausids and cumaceans, which tend to be bottom dwellers but can also come up to the surface. It was mostly the small zooplankton that seemed to be dominant in a lot of the fish we looked at."

That sockeye salmon feed voraciously as they migrate home makes sense when you consider the tasks that lie ahead for salmon.

MCINTOSH: "Generally it's just considered that size make you more fit--and the fact that once the salmon hit freshwater they stop feeding so they're not taking energy in anymore. So it's just a straight expenditure of energy. You're not only looking at physical size to get around barriers, currents, and obstacles. A lot of the energy is being partitioned off into the development of eggs and sperm."

McIntosh's study is important because scientists don't fully understand how salmon survive at sea. His findings also point out the importance of Alaska's nearshore marine environment to salmon returning home to spawn. That information could help managers protect salmon against things like oil spills. McIntosh's study was funded by UAF's Coastal Marine Institute, the U.S. Minerals Management Service, and the Alaska Department of Fish and Game.

OUTRO: This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program and the University of Alaska Fairbanks. I'm Doug Schneider.

For more information about sockeye salmon, visit these web pages:

Alaska Department of Fish and Game Wildlife Notebook

ADF&G Home page

Thanks to the following individual for help preparing this script:

Bruce McIntosh
University of Alaska Fairbanks
School of Fisheries and Ocean Sciences
Coastal Marine Institute
Fairbanks, Alaska 99775-7220
Ph: 907-474-7931
Email: fsbcm1@uaf.edu