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Estimating HistoricalSockeyeSalmonAbundanceUsingStableIsotopesandNitrogenBudgetsofCentralIdaho Lakes
Department: Biology
Specimen Elements
Unknown to Unknown
Rachel Brinkley
Idaho State University
City: Pocatello
Idaho's sockeye salmon (Oncorhynchus nerka) have been decimated due to factors in (e.g. harvest) and out (e.g. hydropower development) of basin. Extensive management efforts have been aimed at restoring these populations following years of very low spawner returns. However, limited understanding regarding the historical escapement, pre-dam SAR’s, and the historical contribution of MDN emphasizes a need for a frame of reference to inform current and future restoration and management activities. Anadromous salmon have a high proportion of stable isotope 15N:14N relative to other nitrogen sources. As such, the analysis of sediment δ15N is an effective means of constructing historical population estimates. By using temporal shifts in δ15N as determined by sediment cores integrated into lake nitrogen budgets, we quantified historical abundance of spawning sockeye salmon for a suite of Idaho lakes. Our results suggest that current restoration objectives may be as low as 5% of sockeye that historically utilized this watershed for spawning. Initial declines in escapement were on the order of 80% over 10 years following the construction of a downstream dam. Historical smolt-to-adult returns(6-11%)may be higher than previously derived estimates (4%), and the nutrient subsidy via spawning sockeye historically may have contributed as much as 16% of the nitrogen input to the system. Key Words: Snake River Sockeye, sediment core, historical escapement, recovery goals, sockeye management, Snake River Dams, smolt-to-adult survival, marine derived nutrients

Estimating HistoricalSockeyeSalmonAbundanceUsingStableIsotopesandNitrogenBudgetsofCentralIdaho Lakes

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