Stock specific high-seas distribution of maturing sockeye salmon in the
North Pacific
Abstract
The stock-specific distribution of maturing and adult salmon in the
Northeast (NE) Pacific has been a persistent information gap that has
prevented us from determining the ocean conditions experienced by
individual stocks. This continues to impede understanding of the role of
ocean conditions in stock-specific population dynamics. We assessed
scale archives for 17 sockeye salmon (Oncorhynchus nerka) stocks
covering the entire North Pacific, from the Columbia River to Kamchatka
Peninsula, to define salmon locations during their last growing season
before returning to their spawning grounds. We used the relationship
between δ13C in salmon scales and sea water temperature to estimate
salmon distribution based on correlation strength. Significant
correlations were found for 13 of the stocks allowing us to define
feeding grounds with confidence. Complementary information from δ15N,
historical tagging studies, and connectivity analysis were used to
further refine distribution estimates. Based on the estimated
distributions of the NE Pacific stocks, we suggest a sequence of steps
that could result in salmon marine distributions. This study is a first
step toward determining stock-specific distributions of salmon in the NE
Pacific, and provides a basis for the application of the approach to
other salmon scale archives. This information will improve our ability
to relate stock dynamics to ocean conditions, ultimately enabling
improved stock management. For example, our estimated distributions of
Bristol Bay and NE Pacific stocks demonstrated that they occupy
different areas with a number of the former being distributed in the
high productivity shelf waters of the Aleutian Islands and Bering Sea.
This may explain while these stocks seem to have responded differently
to changes in ocean conditions, and the long term trend of increased
productivity of Bristol Bay sockeye.