Benjamin P. Sandford

NOAA NWFSC Pasco Field Station, 3305 E. Commerce St, Pasco, WA 99301

Sockeye salmon from Idaho’s Snake River basin were listed as endangered under the Endangered Species Act in 1991 and have partially recovered, though significant challenges remain. For example, although record returns occurred for this population, particularly in 2015 and even 2023, low river flows and high water temperatures substantially impacted adult upstream survival, particularly for fish barge-transported as juveniles from Snake River dams to below Bonneville Dam (BON).

Idaho Fish and Game in collaboration with NOAA Fisheries and other agencies implemented a study to assess effects of rearing strategy, release protocol, and migration route on survival of both juvenile sockeye migrating downstream and adults migrating upstream. To assess efficacy of the US Army COE barge strategy to avoid dam-related mortality, we used detection information from individual fish tagged with Passive Integrated Transponder tags.  Using 2009-2023 hatchery sockeye data, we found (1) juvenile survival from Redfish Lake, ID to Lower Granite Dam (LGR) ranged 15-71%; (2) juveniles subsequently transported to below Bonneville Dam (BON) had higher, more variable, ocean survival than did non-transported fish migrating in-river; (3) upstream adult survival from BON to LGR was highly variable, ranging 4% to 76%. Furthermore, adults barge-transported as juveniles averaged 43% survival, compared to 58% for non-transported fish; (4) taken together, total survival from LGR back to LGR for transported fish was similar to non-transported fish; and (5) there was indication of interactive greater negative effects for juvenile-transported sockeye related to warmer water temperatures during adult migration.

These results suggest greater scrutiny regarding effects of juvenile transportation on population dynamics of this at-risk salmon population.