Hatchery chum salmon straying in Southeast Alaska, 2011

Alaska Department of Fish and Game, Fishery Data Series No. 12-45, Anchorage.

In 2011, we collected otoliths from chum salmon at wild stock index streams in the Northern Southeast Inside Subregion (NSEI) of Southeast Alaska to estimate the overall proportion of stray hatchery fish in the escapement index for the subregion. Sixteen of 63 index streams were randomly selected for sampling and collections of otoliths at each stream were designed to be representative of the entire escapement. Samples of greater than 50 fish were obtained from 14 of 16 streams and hatchery fish were detected in 12 of those streams. The overall estimated proportion of hatchery fish in the NSEI escapement index in 2011 was 9.8% (95% CI=8.9%–10.7%), which was lower than the 2010 estimate of 13.5%, and the difference was statistically significant. We observed considerable year-to-year variation in the proportion of hatchery fish in five of eight streams that had been sampled in prior years. The proportion of hatchery strays in all samples collected from 2008 to 2011 decreased as distance from release sites increased and the proportions were generally highest at streams located within 50 km of the nearest hatchery release site. Modification of summer chum salmon escapement indices to account for the proportions of hatchery strays observed during our studies would result in little or no change to current escapement goals due to the method used to establish goals. Information on hatchery chum salmon straying will be considered in future assessments of wild chum salmon stocks.