Steelhead Trout Production Studies at Sitkoh Creek, Alaska, 2003–2009, and 2009 Final Report

Alaska Department of Fish and Game, Fishery Data Series No. 12-82, Anchorage

The need for life history information on steelhead Oncorhynchus mykiss in Southeast Alaska prompted a multi-year study whereby steelhead adults and smolts were counted through a weir on Sitkoh Creek each spring from April-June, 2003–2009. The ultimate goal of this project was to estimate demographic parameters necessary for describing spawner-recruit relationships such as the number of steelhead smolt produced per spawner. This information could be combined at some later date with data from a habitat-based carrying capacity project to estimate escapement targets. This report summarizes the final year (2009) of the Sitkoh Creek production project and provides comparison to previous years (2003–2008). An immigrant-emigrant weir was operated each spring from 2003 to 2009. In 2009, a total of 402 adult steelhead were counted through the weir, compared to an average for 2003–2008 of 543. The Chapman estimate for the 2009 escapement was 408 (Bayesian SE = 1.1). First-time spawners identified by their previously implanted passive integrated transponder tags comprised 65% of the adult escapement in 2009, which was corroborated by scale ages. The remaining escapement was comprised of repeat spawners, strays, or fish that were not previously sampled. Approximately 88% of the kelts survived spawning during 2009 and were successfully passed downstream through the weir, the highest kelt survival during the entire study period. During 2009, 893 steelhead smolt, 2,610 sea-run cutthroat trout, and 20,372 sea-run Dolly Varden emigrated downstream. Of the total number of emigrant steelhead smolt, 153 were scale sampled. An estimated 40% of the 2009 smolts were age-3-freshwater fish, and 51% were age-4-freshwater fish.