Cedar River Salmon
Scientists learn first-hand how salmon colonize once-inaccessible habitat
In 2003, when the City of Seattle installed a fish ladder at its Landsburg Dam facility on the Cedar River, it opened a wealth of opportunities for coho and chinook salmon — and for Washington Sea Grant-funded researcher Thomas Quinn.
Landsburg Dam was originally intended to divert drinking water for Seattle residents. However, since its construction in 1900, the dam effectively excluded any migrating salmon from 21 miles of river and its tributaries in the upper Cedar River watershed, southeast of Seattle.
By today’s understanding, this was not a good thing. In recent years, resource managers have become increasingly aware of the importance of salmon spawning habitat in Washington and elsewhere in the Pacific Northwest.
“Pacific salmon are by far the most valuable commercial resource of the fisheries of the eastern North Pacific, with a landed value of $390 million over the past 10 years,” says Quinn, a professor at the UW’s School of Aquatic & Fishery Sciences.
“However, the fish have lost about 40 percent of their range and have declined markedly in abundance at the southern end of their distribution. They are in such jeopardy that one or more runs of all the species except pink salmon have been listed under the federal Endangered Species Act.”
In collaboration with Seattle Public Utilities, the Muckleshoot Tribe, Washington Department of Fish and Wildlife and the National Marine Fisheries Service, Quinn and his research team are learning first-hand how salmon make use of previously inaccessible spawning habitat. This information will be extremely helpful, Quinn says, for planning any future dam alteration or removal projects. It will also provide insights into the ways with which salmon have historically colonized newly opened waterways under natural conditions.
Installing a fish ladder at the dam was an important step, according to Quinn. However, it didn’t automatically ensure the success of salmon runs in the upper Cedar River watershed.
“We had to address several nagging questions,” Quinn admits. “What if the fish don’t establish themselves in the habitat we’ve now provided them access to? And if they do, are we actually reducing the overall densities of salmon returning to other parts of the watershed?”
Quinn got what he describes as a “build it and they will come” answer to his first question. Within days of the fish ladder’s opening in September 2003, the first adult chinook salmon entered the ladder’s holding area. Here, Seattle Public Utilities biologists used nets to gently prod the fish into what is known as a pescalator — a giant, turning screw-like device inside a translucent tube. The pescalator carried these first fish and subsequent arrivals up the tube, to be released at the top.
During this step, Quinn made sure that data were gathered on the species, size and sex of each returning fish. A small piece of fin, about the size of a pencil eraser, was also snipped from each fish’s dorsal fin. The fin tissue samples would later be used for DNA testing, with which scientists could establish the identities and trace the parental lines of subsequent returning fish.
Other salmon were fitted with radio-tracking devices that Quinn’s assistant, UW doctoral student Joseph Anderson, could use to keep tabs on the movements of individual fish as they moved upstream, searching for suitable spawning sites. Wearing dive masks and dry suits, Anderson and others conducted “snorkel surveys” to locate juvenile salmon born in the watershed. Some of these fish were also individually tagged. Subsequent studies of these fish have shown that juveniles move upstream as well as downstream — a finding that may add to our understanding of the dynamics of colonization by generation after generation of adult salmon. Quinn theorizes that the returning salmon may be encouraged by the presence of juvenile fish to exploit previously unexploited parts of the watershed.
To date, the research team has gathered data on hundreds of returning chinook and coho salmon. Interpretation of this information may tell us how salmon select breeding habitats in areas where they were not already imprinted as juveniles and whether predation on adult or juvenile fish might prevent populations from becoming established.
“Will the newly established habitat continue to attract stray salmon?” says Quinn. “Will returning adults in the next generation use the specific breeding habitat where they were spawned or will they spread out and colonize other parts of the upper watershed? How will the genetic structure of the new populations evolve, given the number of founders, variation in reproductive success and continued straying?”
Quinn saves the most fundamental question for last. Will the salmon establish self-sustaining populations that increase the total production from the river system? Only time — and further Sea Grant-funded research — will tell.
Spring 2007
Contact David G. Gordon, Science Writer for Washington Sea Grant, for further information.