Assess Salmonids in the Asotin Creek Watershed: 2004 Annual Report

The Asotin Creek watershed is located in southeast Washington and is a tributary of the Snake River. Originating in the Blue Mountains, Asotin Creek is a historically productive subbasin for steelhead trout (Oncorhynchus mykiss) and spring Chinook salmon (O. tshawytscha). Many habitat restoration projects, aimed at recovering ESA listed salmonids, have been completed in the subbasin. The Asotin Creek assessment project addresses RPA 180 for population status monitoring. Plans for an adult salmonid trap were completed during the project year. During a short 2004 juvenile trapping season, a 1.52 m rotary migrant trap was operated just below Headgate Dam, at rkm 13.2. Mean trap efficiency was 20.5% for steelhead and 45.7% for Chinook salmon. Of the 8,028 juvenile steelhead captured, 42.0% were parr, 56% were transitional smolts and 2% were fully-smolted juveniles. The estimated population of juvenile steelhead emigrating at rkm 13.2 was 43,457 individuals. One female kelt that we captured was a repeat spawner. In addition, 600 yearling Chinook salmon, 1,273 subyearling Chinook salmon and 4 bull trout were captured. Substantially more emigrating parr and transitionally-smolted juvenile steelhead were captured than expected. This suggests that the Asotin Creek subbasin may be a nursery of the Lower Snake River steelhead ESU. Juvenile steelhead from the subbasin may emigrate from the Asotin Creek subbasin and complete their rearing in the mainstem Snake River or other tributary. This information provides a new perspective on the classification and emigration patterns of juvenile steelhead in Asotin Creek, which may be an important factor in overall survival estimates and management alternatives for the Asotin Creek steelhead population.