Abundance and Age Structure of Skagit River Steelhead Smolts: 2012 Annual Report

During the first year of the study we were able to successfully capture, tag and release sufficient numbers of steelhead (Oncorhynchus mykiss) smolt to estimate abundance from each of three tributary trapping locations (Table 1). An interesting finding was that trapping locations further upstream or at higher elevation (Bacon and Illabot creeks) had earlier median catch dates than the lower tributary (Finney Creek). Matching this trend was the mainstem trap where steelhead catch had the latest median catch date (Table 1). Also the higher elevation and colder water tributaries of Illabot and Bacon creeks had more age-4- and age-3 smolts than Finney Creek and the mainstem trap. Steelhead smolt population age structure was different in each sampled tributary (Table 6). A total of 1,096 steelhead smolts were PIT-tagged in the three upstream tributaries.

Table 1.Steelhead smolt abundance from Skagit River tributaries and mainstem trap.

We captured 431 steelhead at the mainstem trap, but only one was a recapture of a smolt tagged in the three upstream tributaries. Due to an insufficient number of recaptures, we were unable to estimate total Skagit basin steelhead smolt abundance.