Evaluating the Performance of Snake Basin Supplementation Hatcheries Against Expectations, and Revising Operations in an AM Loop

Chinook salmon escapement levels to the Snake River basin are well below conservation and management thresholds and goals.  Hatchery supplementation is one type of management action being used to increase escapement, supporting integrated harvest and conservation goals.  Great uncertainty exists about the risks and benefits of supplementation actions.   We have developed Monitoring and Evaluation (M&E) plans to guide adaptive management decisions related to hatchery supplementation programs.  These M&E plans established management assumptions which are tested by quantifiable means. If any of the assumptions are proven to be false, adaptive management options are developed. Testing assumption validity uses comparisons between: 1) hatchery product (treatment) and pre-established program targets, 2) treatment and natural-origin con-specifics, and 3) treatment vs. treatment.  Four examples demonstrating the connection between management assumption, monitoring and evaluation results, and adaptive management response will be presented.  Example 1 (Imnaha River Summer Chinook Salmon) - Spatial distribution of hatchery-origin spawners resulting from acclimated smolt release was demonstrated to differ from natural-origin spawner distribution.  Splitting the smolt release into an acclimated (existing release site midway through spawning area) and direct release (near upper end of spawning area) is being considered. Example 2 (Lostine River Spring Chinook Salmon) – Post-release survival of juveniles acclimated and released during two different periods showed higher survival for the later release group.  Acclimation periods were adjusted to enable a later release date, resulting in higher survival rates. Example 3 (Snake River Fall  Chinook Salmon) – Release of hatchery production at a life stage (sub-yearling smolt) historically expressed by the natural population resulted in insufficient adult returns to buffer demographic collapse of the population. Life stage at release was changed to a yearling smolt to increase survival rates. This change did increase in numbers of returning adults, however, it has also changed another life history trait (age-at-return).  Adaptive management options are now being developed to address the shift in age-at-return. Example 4 (Grande Ronde Basin Spring Chinook Captive Broodstock) -  Assessment of captive broodstock rearing in two different environments demonstrated that fish reared in freshwater had higher survival and fecundity over those reared in saltwater.  Although some rearing continued in saltwater due to hatchery rearing space constraints, freshwater rearing was maximized.