Evidence Linking Delayed Mortality of Snake River Salmon to Their Earlier Hydrosystem Experience

Abstract

The numbers of Snake River salmon and steelhead Oncorhynchus spp. have substantially declined since the completion of the Columbia River hydrosystem. We used analytical approaches to identify management options for halting the decline of these stocks, such as removal of Snake River dams and improvements to the existing hydrosystem. The benefits these actions are predicted to have in terms of salmon recovery hinge on whether the mortality that takes place in the estuary and early in their ocean residence is related to earlier hydrosystem experience during downstream migration. Evidence from the literature demonstrates numerous mechanisms that would explain this delayed mortality in relation to a fish's experience passing through the hydrosystem. Spatial and temporal comparisons of stock performance provide indirect evidence of delayed mortality and evidence that delayed mortality is linked to hydrosystem experience. Recent mark–recapture data also provide evidence of differences in delayed mortality by route of passage through the hydrosystem. The different types of evidence discussed here suggest that the delayed mortality of Snake River fish is related to the hydrosystem.

Assessment of PIT tag retention and post-tagging survival in metamorphosing juvenile sea lamprey

“…For example, PIT telemetry has been used to determine system-wide, reach-specific, and seasonal survival [24,25], temporal and spatial movement patterns [26], and timing of movement and survival relative to stream conditions and hydropower operations [27,28]. Ultimately, having the capability to monitor downstream movement in natural, open, stream channels can provide a better understanding of when and how sea lamprey outmigrate.…”

Effects of Passive Integrated Transponder Tags on Smolt‐to‐Adult Recruit Survival, Growth, and Behavior of Hatchery Spring Chinook Salmon

“…More sophisticated individual-based models for data analysis were also developed (Burnham et al 1987) and applied, using PIT tags, to monitor juvenile salmonid survival and migration timing in the Columbia River basin (Skalski et al 1998;Muir et al 2001;Budy et al 2002). More recently, PIT tags have been used to estimate adult salmonid survivals in the Columbia River (Berggren et al 2003(Berggren et al , 2005Williams et al 2005;Copeland et al 2007).…”

Comparative Survival Study (CSS) of PIT-Tagged Spring/Summer Chinook and Summer Steelhead : 2008 Annual Report.

“…This reduction in smolt viability is potentially due to the stress, injury, and disease exposure associated with the "collection" process (Budy et al 2002;Marmorek et al 2004). If the detrimental effects of the "collection" process can be substantially reduced, then there is an opportunity to substantially improve SARs for bypassed and transported salmonid smolts.…”