A 500-year context for the recent surge in sockeye salmon (Oncorhynchus nerka) abundance in the Alagnak River, Alaska
Schindler DE, Leavitt PR, Johnson SP, Brock CS. 2006. A 500-year context for the recent surge in sockeye salmon (Oncorhynchus nerka) abundance in the Alagnak River, Alaska. Canadian Journal of Fisheries and Aquatic Sciences. 63:1439-1444
Returns of sockeye salmon (Oncorhynchus nerka) to the Alagnak River in Bristol Bay, Alaska, during the last 3 years were unprecedented in the last five decades. Enumerated run sizes averaged about 1 million fish from 1955 to 2002 but surged unexpectedly to average 5.4 million fish in 2003-2005. These huge returns currently pose a challenge to management of Bristol Bay sockeye for several resions, including that it is unclear whether the recen surge is abundance is a new phenomenon or if iti has arisen as part of interdecadal population variability. To answer this question we used changes in lake sedimentary -15N coupled with an isotope-mixing model to estimate historical abundances of sockeye salmon populations in this ecosystem. Our analyses show that periods of high salmon abundance have occurred every ~100 years during the last five centries, interspersed by prolonged periods of substantially lower abundance. We suggest that the recent high returns are an expression of the long-term variability that is characteristic of this stock and will be a relatively transient phenomenon.