Challenges for Diadromous Fishes in a Dynamic Global Environment

Tracking Sockeye Salmon Population Dynamics from Lake Sediment Cores: A Review and Synthesis

Irene Gregory-Eaves, Daniel T. Selbie, Jon N. Sweetman, Bruce P. Finney, and John P. Smol


Abstract.—Pacific salmon Oncorhynchus spp. play a central role in coastal ecosystems that rim the North Pacific Ocean. Given the ecological, cultural, and economic importance of Pacific salmon, there is great interest in defining the magnitude and frequency of change in these fish stocks. Fisheries scientists, through analyzing harvest records, have demonstrated pronounced salmon production variability. The causes underlying such marked fluctuations are currently debated. Collating harvest records across a broad geographic range over the past ~80 years, fisheries scientists have advanced a plausible argument that climate-induced oceanographic changes explain a significant fraction of the variation in salmon catch records. However, without data that predate the introduction of large-scale human interventions (e.g., commercial harvesting, dams, hatchery releases), it is difficult to isolate the role of climate in shaping fish stock dynamics. Within the past decade, however, we have developed a paleolimnological approach for tracking past sockeye salmon Oncorhynchus nerka population abundances, and numerous papers have applied this approach to infer changes in these fish over the past hundreds to thousands of years. Here, we provide an overview of the approach and a synthesis of the work that has been conducted in this field to date. It is clear that numerous sockeye salmon populations have undergone pronounced changes, even prior to human interventions. Furthermore, tracking salmon populations over millennial timescales with paleolimnology has revealed modes of change that were previously never imagined possible. Such long-term perspectives indicate that sockeye salmon is a resilient fish species. We note, however, that when natural environmental changes are compounded by intense human impacts, populations have been particularly susceptible to extirpation.