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Story by Mark Hume with Photographs by Nick Didlick
“The flow of energy and nutrients back upstream via the Pacific salmon and the ability of the watershed to retain them, in large measure, determines the productivity of the entire watershed,” states the report, which for the first time synthesizes all the research data linking salmon with wildlife species. The study states that 138 species of birds, mammals, amphibians, and reptiles feed on salmon - and that the decomposing carcasses of spawned salmon are vital to the survival of juvenile fish. The report, Pacific Salmon and Wildlife: Ecological Contexts, Relationships, and Implications for Management, highlights the importance of salmon as “an ecological process vector,” carrying nutrients from the ocean to inland waterways. Without sufficient amounts of those nutrients, salmon and trout populations spiral downwards, affecting the health of everything from stonefly nymphs to grizzly bears. The study calls for a dramatic change to the fisheries management strategy currently popular in both Canada and the U.S., arguing that the approach, known as Maximum Sustained Yield, doesn’t adequately seed watersheds with salmon carcasses. One researcher estimates that “ only 3 percent of the marine-derived biomass once delivered by anadromous salmon to the rivers of Puget Sound, the Washington Coast, Columbia River, and the Oregon Coast is currently reaching those streams.” Hatcheries, once thought the answer to declining stocks, are blamed for significantly reducing the amount of salmon carcass nutrients in aquatic food webs. Numerous studies have underscored the importance of the nutrients transported to streams by spawning salmon. Nitrogen and carbon contained in rainbow trout residing in a southeast Alaska stream was derived almost entirely from the large numbers of pink salmon which spawned at the site,” states the report. “Juvenile coho salmon, cutthroat trout and steelhead in a tributary of the Snoqualmie River, Washington, obtained as much as 40% of the carbon and nitrogen in their muscle tissue from the carcasses of coho salmon. . .(and research) found a relationship between the proportion of marine-derived nitrogen in insects and the density of spawning sockeye salmon in tributaries of the Stuart River in interior British Columbia.” At the Keogh River, on northern Vancouver Island, and in some Washington State streams, researchers have recently demonstrated the importance of nutrients to the growth and survival of young salmon.
On the Keogh, fertilizer has been added to the river to replace the nutrients lost when the salmon run crashed. Salmon fry there are bigger and more plentiful; stonefly and Mayfly hatches are more abundant, and resident trout have grown larger. The report cites a study in Washington that demonstrates the same thing in a different way and concludes that managing for maximum sustained yield can have a deadening effect on a watershed. Managing at the MSY level may have the effect of substantially reducing the delivery of marine-derived nutrients to freshwater habitats,” states the report.
Coho at the enriched site grew twice as fast as fish at the site without carcasses and achieved a body size nearly 50% greater by early winter. Body size of juvenile salmon has been positively correlated with overwinter survival in freshwater. Increased smolt size provides a survival advantage. . . Therefore, if harvest of fish causes a reduction in the nutrient delivery to the stream sufficient to impact growth, survival will be negatively impacted. This impact will decrease recruitment to the next generation of spawners, further depleting the nutrient capital of the system and potentially further depressing survival. The effect is a progressive downward shift.” The report was compiled as part of a project known as Wildlife-Habitat Relationships in Oregon and Washington. The Washington Department of Fish and Wildlife and the Northwest Institute are the lead organizations in the project. David H. Johnson and Thomas A. O’Neil were the executive managers . The report is authored by some 14 scientists and supported by more than 30 organizations including native groups, government agencies, industry and conservation organizations. |
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The crucial role of salmon in a massive ecosystem that links more than four million square kilometers of ocean habitat to the watersheds of the Pacific Northwest is detailed in a comprehensive new report issued by government agencies in two U.S. states.
The decreased availability of carcasses has been shown to impact the growth rate of juvenile fishes. Artificially increasing availability of marine-derived materials by adding the carcasses of hatchery-spawned coho salmon to a small stream in southwestern Washington accelerated growth of juvenile coho salmon in this system relative to a nearby stream reach with low availability of carcasses. 
