Survival of Age‐0 Hatchery Summer‐Run Chinook Salmon is Enhanced by Early Release

Abstract

Subyearling (age-0) hatchery summer-run Chinook Salmon Oncorhynchus tshawytscha have been released into the Columbia River in mid-June from Wells Fish Hatchery, Washington, since 1993, but release-to-adult survival (SAR) under this strategy has been low. I used paired releases of four broods of coded-wiretagged age-0 Chinook Salmon released in mid-May (early release [ER] group) and mid-June (late release [LR] group) to evaluate whether advancing the release date could improve SAR. Additionally, passive integrated transponder tags implanted in a subsample of each release group were used to estimate emigration rate and release-to-McNary Dam survival of juvenile fish. Mean migration rate from release to McNary Dam was significantly faster for LR fish than for ER fish. No among-year difference in mean survival from release to McNary Dam was observed between ER and LR groups, although differences were observed within years. Mean overall SAR was significantly greater for ER fish than for LR fish. These results suggest that altering the release date of age-0 Chinook Salmon at Wells Hatchery would enhance return survival.

Size and timing of hatchery releases influence juvenile-to-adult survival rates of British Columbia Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon

“…Our multi-hatchery model results found that survival rates are expected to increase for releases of sub-yearling Chinook salmon from early May to early-June, yearling Chinook salmon from mid-April to early May, and yearling coho salmon from mid-May to mid-June, which is consistent with other studies (Mathews and Ishida 1989;Duffy and Beauchamp 2011;Snow 2016). Sub-yearling or "ocean-type" Chinook salmon are the most common life history in BC, generally entering the marine environment within 3 months after emergence from the gravel (i.e., less than 1-year of freshwater residency) and returning to spawn in between August and October (Groot and Margolis 1991).…”