Lost Habitat Nurtured Salmonby Joe Rojas-Burke
The Oregonian, September 29, 2003
Dams and dikes wiped out the fishes' lower Columbia River nursery, says a study that has implications for fish restoration
A vast network of marshes and side channels along the lower Columbia River once sheltered and fed hordes of young salmon preparing for life at sea.
Nearly two-thirds of the swampy habitat has disappeared, according to a new study that is one of the first to calculate the impact of a century's worth of diking and dam-building on the river's lowest freshwater reach.
The findings by environmental researchers at Oregon Health & Science University highlight the immense challenge facing agencies and conservation groups trying to restore pivotal habitats for endangered salmon. Hundreds of dikes have converted the broad floodplain into privately owned farm and pastureland. Massive upriver dams protect entire cities and towns from flooding.
Habitat loss is one of the leading causes of the Pacific salmon crisis. Although Columbia Basin salmon populations have rebounded in recent years, numbers remain a fraction of the historic abundance, and a dozen groups are listed as threatened or endangered.
"What we have done is clarify what the tradeoffs are. Society has to make the value judgments," said David Jay, an associate professor at OHSU's OGI School of Science and Engineering.
He co-authored the study with graduate student Tobias Kukulka, now at the University of Rhode Island. The work was published last week in the Journal of Geophysical Research -- Oceans.
For decades, conservation efforts largely ignored the lower river and estuary, regarding them as a mere conduit for passing fish. That view has drastically changed during the past five years, as studies have revealed how marshes along the lower river and estuary serve as a vital nurseries where young salmon gain size and strength before facing the rigors of adult life in the open ocean.
A place of food and shelter "These shallow water habitats do lots of things," said Dan Bottom, a biologist with the National Marine Fisheries Service who is leading estuary studies in the Columbia and other rivers.
The slow-moving, tea-colored waters of marshes support an abundant food chain of plankton, insects and crustaceans. Shaded pools and side channels also offer hiding places from predators and main river flood torrents.
Chinook salmon, in particular, make extensive use of such habitat, Bottom said. Some chinook linger in lower-river side channels and marshes for as long as four months, he said.
Kukulka and Jay focused on a 25-mile stretch of the lower Columbia. Their work, funded by the U.S. Army Corps of Engineers and the National Marine Fisheries Service, shows how it may be possible to focus restoration efforts to get the most from limited dollars.
The researchers developed a mathematical model, run on a computer, to represent the chaotic interaction of ocean tides and shifting river flows. The program makes it possible to estimate how high the river would rise -- and how much land would be inundated -- if there were no dikes or dams during the spring freshet, the massive surge of runoff from melting snow in the mountains.
55 dams hold back water Now 55 dams, built to generate power and control flooding, hold back enough water to reduce the Columbia's peak spring flows nearly in half. If no dikes had been built, the dams alone would eliminate about 29 percent of the lower river marshes and channels historically available for salmon during May, June and July, the researchers concluded.
Dikes alone would take water from about 52 percent of the habitat, their model estimated. Together, dikes and dams have eliminated about 62 percent of the shallow water habitat, or about 6,900 acres.
"It is a little shocking how big the changes have been," Jay said. But he found reassurance in the result that diking is a bigger contributor than dam operations.
"There are probably areas where dikes can over time be removed at lower cost than altering flow-management," he said. Releasing more water for habitat would be costly because it would leave less water for power generation in the summer.
But dike removal could meet strong local resistance.
A fear of a lost tax base "It's the kind of thing communities fear -- the idea of land coming out of production and the loss of tax base," said Ian Sinks, a biologist with the Columbia Land Trust. The Vancouver-based nonprofit has purchased hundreds of acres along the lower Columbia for the creation of havens for threatened salmon, Columbian white-tailed deer and other wildlife. To reassure residents around Grays River, Sinks said, the tax-exempt land trust has agreed to keep paying property taxes on recently acquired acres.
Bottom, the federal biologist, said the new computer model is helping to fill a glaring gap in knowledge of salmon habitat needs in the lower river. Government and private groups have begun buying former wetlands and funding restoration projects, but the effort lacks a coordinated plan to prioritize and focus limited dollars, Bottom said.
"What you are seeing right now is a lot of ad hoc stuff," he said. "No one has developed a good snapshot of what the opportunities are, what habitats are most important to try to restore."
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