A comparison of sockeye salmon (Oncorhynchus nerka) in two climate regimes in the north Pacific Ocean using stable carbon and nitrogren isotope ratios

Abstract

This study explores how the climate shift in the late 1970's impacted sockeye salmon feeding. Stable isotope ratios (¹³C and ¹⁵N) of recent muscle and scale tissues from five mature salmon species are highly correlated (R²=0.96 and 0.91, respectively), validating the use of archived scales for retrospective analysis. These data suggest a trophic separation by species with chinook occupying the highest level, followed by coho with some degree of overlap among sockeye, pink and chum at the lowest level. Archived scales from four different sockeye stocks from Kodiak Island and Southeast region were analyzed over the last 34 years to investigate changes relative to the 1976-1977 Climate Regime Shift. Most stocks show no statistical differences before and after the regime shift in either isotope. Despite recorded differences in sockeye abundance and size between these two regimes, these data suggest only minor changes in prey items.