OLYMPIA--The Washington Department of Fish and Wildlife, the University of Washington and Northwest Indian Fisheries Commission are beginning a scientific study to determine why the number of adult coho salmon returning to central and southern parts of Puget Sound are declining.
Coho returns to northern Puget Sound rivers and the Columbia River have not shown the same downward trend.
The decline in some Puget Sound stocks has occurred even though Canada has drastically reduced its fisheries for Washington-bound coho and Washington has taken tough protective measures in the ocean and Puget Sound on behalf of its own wild coho stocks as well as those from British Columbia's Thompson River.
"For some reason fewer and fewer adults from southern Puget Sound coho runs are surviving at sea. We don't know why but we've got to find out," said Jeff Koenings, director of the Washington Department of Fish and Wildlife.
"We're also concerned that changes appear to be occurring in the south Sound's natural balance that may be affecting other animal and fish life." Koenings added.
In the Seattle-Bremerton area (Marine Area 10) coho returns have declined from more than 1 million in 1987 to less then 200,000 in recent years.
Koenings noted that 20 to 30 percent of the coho smolts produced in the mid- 1980's in the Deschutes River were either caught in fisheries or returned to spawn. In recent years only about 5 percent of the smolts produced by the river have survived to be harvested or spawn.
While south and central Sound coho stocks have been declining, WDFW scientists have found the numbers of marine mammals, dogfish, ling cod, gulls and some other species have increased while stocks of herring, rockfish, cod, pollock and whiting have decreased. There also may have been increases in harmful algae blooms but decreases in canopy kelp, which provides important habitat for many marine species.
Dr. Bob Francis, a University of Washington College Fisheries professor, said, "There seem to be a broad range of signals coming out of the south and central Sound that the entire ecosystem may have been altered in a significant fashion."
"We at the University of Washington are proposing to join in this effort with agency scientists to explore ecosystem responses, " he added.
"The collection of information put forth by WDFW employees should sound some alarms, it's clear that South Sound ecosystems have been changing in ways that are not good for wild and hatchery coho," commented Dr. Nathan Mantua, of the University of Washington Department of Atmospheric Sciences.
"Gathering information about the entire ecosystem seems critical to me, because it's also pretty clear that we can't effectively manage salmon without consideration of how salmon interact with other species and the always changing habitat in Puget Sound. I hope to lend a hand by investigating the impacts of climate variations in Puget Sound," Mantua added.
Billy Frank, chairman of the Northwest Indian Fisheries Commission, commented, "While coho returns to central and southern Puget Sound have declined steadily over the past decade, chum returns have actually been increasing. We need to investigate what has changed in the productivity of this region's ecosystem to allow one salmon species to thrive while another is declining. As co-managers of the salmon resource, the treaty Indian tribes in western Washington are committed to finding these answers."
Areas the scientists will investigate include:
- Trends in food sources available to fish in the south Sound.
- Effects of fisheries and hatchery programs as well as habitat trends
- Coho and chinook productivity trends
- Analyzing or re-analyzing scientific material, such as plankton samples, that have been collected in the past. Some of the materials never have been studied because of a lack of funding.