Lake Washington Sockeye Smolt Collection: 2012 Annual Report

A major portion of the Lake Washington sockeye population is produced in the Cedar River. Sockeye were introduced into the Cedar River basin from the Baker River (Skagit basin) between 1917 and 1945 and were naturalized in the system by the 1960's (Kolb 1971). Today, sockeye production from the Cedar River includes both natural and hatchery-origin portions. Hatchery-origin sockeye are reared at Washington Department of Fish and Wildlife's (WDFW) Cedar River Sockeye Hatchery. Brood stock for this program is collected from sockeye returns to the Cedar River. The purpose of this hatchery program is to mitigate for loss of sockeye salmon spawning habitat above Landsburg Dam, which was built in 1901, blocking anadromous fish migrations, in order to provide a majority of Seattle's water supply. A fish passage facility at Landsburg Dam began operation in 2003 and allows coho and Chinook salmon, but not sockeye, access to spawning and rearing habitat above Landsburg Dam.

The Cedar River sockeye population has been well monitored at both the adult and emergent fry stages of their life cycle. Adults return to the river to spawn in September, and the numbers of adult spawners have been monitored by local, state, and tribal entities since 1967. Between January and May of each year, natural-origin sockeye emerge from the gravel and migrate downstream to Lake Washington. Production and survival of sockeye fry has been monitored by WDFW since the 1992 outmigration (1991 brood year). Production of natural-origin sockeye fry is estimated by expanding catch in an inclined-plane trap positioned near the river mouth (Seiler and Kishomoto 1996; Kiyohara and Zimmerman 2012).

Beginning in 1992, hatchery sockeye fry have been released into the Cedar River. Hatchery-origin sockeye have been released as both fed and un-fed fry over the natural outmigration period. Hatchery releases are classified into three release categories: (early, middle, and late) and have occurred at different locations in the watershed. The purpose of these multiple release strategies has been to evaluate which rearing and release strategy maximizes survival while minimizing impacts to natural-origin sockeye. Survival of natural and hatchery-origin sockeye is studied at two subsequent points of their life history - smolts leaving the lake and adult spawners returning to the river. The proportions of natural and hatchery-origin sockeye at the fry, smolt, and adult life stages, provide a measure of relative survival through the lake and marine environment and test the assumption that hatchery and natural-origin sockeye experience similar conditions during their predominantly one year of rearing in Lake Washington and one to four years of rearing in the ocean.

Natural and hatchery-origin sockeye in Lake Washington have no external marks that identify their origin. The small body size of released hatchery sockeye fry prohibits marking tools such as adipose clips and coded-wire tags typically used as external marks for other hatchery releases in Washington State. Therefore, Lake Washington hatchery sockeye fry receive a thermally-induced otolith mark (Volk et al 1990). This mark is detected if the fish is lethally sampled and the otolith is removed and processed. Thermal marking is applied in different patterns in order to specify release date, location, and other characteristics of the fry (e.g., feeding period).

In 2004, WDFW began collection of sockeye smolts from Lake Union and Lake Washington. Collections occur in the month of May, which represents the sockeye outmigration period. Otoliths were retrieved from up to 1,000 sockeye smolts with the goal of better understanding relative survival between lake entry and lake emigration of natural-and hatchery-origin sockeye, as well as among the different hatchery release strategies (Schroder et al 2009). Fish were also examined for viral pathogens at the WDFW Pathology Lab for indicators of potential epidemics present in the smolt population.

This report describes the 2012 collection of sockeye smolts in lakes Union and Washington as they began their migration to the sea. Results of the otolith analysis will be presented in a separate report prepared by WDFW's Otolith Lab.