Changes to the Productivity and Trophic Structure of a Sockeye Salmon Rearing Lake in British Columbia

Abstract

In the 1990s, the returns of sockeye salmon Oncorhynchus nerka to Long Lake in Smith Inlet, British Columbia, declined substantially. In 1997 the commercial fishery was closed, and it will not be reopened until the population shows signs of sustained recovery. We examined paleolimnological and geochemical variables from a sediment core extracted from Long Lake in 2002. The nitrogen isotope concentration (δ¹⁵N), which is associated with salmon production, declined to unprecedented levels in the 20th century. Sodium and other alkali elements have also decreased at a generally accelerating pace since the mid-19th century, and there are indications that the headwater glacier has receded apace. Accompanying these trends were notable changes in proxies for lake ecology, including the size and abundance of planktonic invertebrates. The timing and behavior of these unprecedented changes in the sedimentary record point to potential impacts from both commercial fishing and climate change.