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600 Capitol Way North, Olympia, WA 98501-1091

This document is provided for archival purposes only.
Archived documents do not reflect current WDFW regulations or policy and may contain factual inaccuracies.

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September 27, 2001
Contact: Pete Hahn, (360) 902-2431

WDFW hones Puget Sound chinook salmon management

Capturing, Marking, and Releasing Green River Chinook Salmon

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AUBURN - The Washington Department of Fish and Wildlife (WDFW) is fine-tuning its management of federally protected Puget Sound chinook salmon through a combination of high-tech science and low-tech grunt work.

WDFW biologists are capturing, marking and releasing some Green River chinook salmon as the fish make their way upriver to the spawning grounds. Crews later doing surveys of the spawning areas soon will look for the marked fish to assess the accuracy of chinook population estimation methods.

Green River chinook are one of several Puget Sound-area chinook stocks that presently are being intensely studied to estimate chinook populations and to assess various methods used to make those estimates, said Pete Hahn, a WDFW biometrician in charge of the study.

"It's important to have the most accurate, up-to-date information possible in fisheries management, particularly when we're dealing with a federally protected species," Hahn said. "We need good population estimates to meet the obligations of the U.S.-Canadian Pacific Salmon Treaty, and the data we have on individual chinook population estimates in Puget Sound ranges from fair to very good."

The WDFW crew is using a 200-foot-long, soft-meshed beach seine net to safely capture fish in a stretch of the Green River near Auburn. Crews collect data, including sex, size, and any marks such as a missing adipose fin to determine wild or hatchery origin.

The fish, listed under the Endangered Species Act in 1999, are safely released back into the river, but not before each fish has a small hole punched into the bony plate covering the gill. State and tribal fisheries crews will be surveying the Green River's spawning areas – all the way to Howard Hanson Dam in the Cascade Foothills. The crews will be inspecting carcasses and identifying the number of marked and unmarked fish.

Hahn said the data collected by survey teams will allow WDFW to make a "mark-recapture" population estimate. This estimate of the population size will be compared to three different estimates made from counting spawning nests, known as "redds." Crews count redds from the air by helicopter and by floating the spawning grounds in rafts.

The chinook data collection project is expected to provide biologists with other important information, Hahn said, including the number and proportion of hatchery-origin chinook that spawn naturally in areas outside Soos Creek, a tributary to the Green and site of a state salmon hatchery.

"We hope this effort gives us a more accurate picture of the physical distribution of chinook spawning grounds, as well as the overall age composition of each gender of natural and hatchery-origin spawners," he said.

About 2 percent of the fish caught in the beach seines are fitted with small radio transmitters, inserted into the gut. The transmitters send out a constant signal that WDFW staff track as the fish move upstream to spawn.

"The primary purpose of using radio transmitters is to determine if the beach seining and subsequent handling of the fish is leading to additional mortality," Hahn said. "If an unusually high number of the radio-tagged fish die before they spawn, then we may have to modify the way we capture and mark returning chinook and it will allow us to correct our population estimates. It's also important that this effort to improve our knowledge base doesn't harm chinook spawning."

Hahn said that so far only two of the radio-tagged fish have died before spawning, leading him to believe that the project, which is being funded by the National Marine Fisheries Service to improve spawning population data, is having a minimal impact on the returning fish run and that the population estimate will be accurate.

Hahn noted that research crews have seen a number of illegal fishers in the lower Green River and Soos Creek, which are generally closed to all fishing in September and October to protect chinook stocks. Chinook retention is prohibited throughout the Green River system. Anglers can check the "Fishing in Washington" regulation pamphlet for information regarding fishing seasons.