Pacific Salmon Environmental and Life History Models: Advancing Science for Sustainable Salmon in the Future
Long-term Perspectives on Salmon Abundance: Evidence from Lake Sediments and Tree Rings
Deanne Drake, Robert J. Naiman, Bruce Finney, and Irene Gregory-Eaves
Abstract.—Here we review developments in paleoecological reconstruction of Pacific salmon abundance and discuss the new management context and implications provided by the reconstructions. Currently, two approaches are yielding long term reconstructions of salmon abundance over the last hundreds to thousands of years. First, in sockeye salmon Oncorhynchus nerka nursery lakes, the abundance of adult salmon is reflected in chemical and biological characteristics of lake sediments. These indicators have been used to reconstruct patterns of salmon abundance over 2,500 years and are compared at several points by archeological data. Second, emerging techniques using riparian tree-ring-growth have produced sub-decadal resolution reconstructions of stream-spawning sockeye, Chinook O. tshawytscha, pink O. gorbuscha, and chum O. keta salmon populations over the last 150–350 years. Paleoecological reconstructions provide important insights into salmon abundance and their variability prior to European settlement of western North America. For example, sediment-based reconstructions show periods of naturally low sockeye salmon abundance at ~A.D. 1800 and from ~A.D. 0–700 in Alaskan lakes, and tree-ring based reconstructions show river-specific patterns in abundance with cycles of 21–68 years in duration. Both types of reconstruction also suggest relatively rapid, natural “recovery” of salmon populations after periods of low abundance. As additional reconstructions become available and a more synthetic understanding of them is developed, paleoecological reconstructions will allow better evaluation of management paradigms (e.g., the long-term fidelity of Pacific Decadal Oscillation cycles and regional salmon abundance) as well as identification of additional patterns that cannot be extracted from limited historical data sets. Paleoecological perspectives play a potentially important role in changing societal expectations of salmon resources by recognizing natural variations in abundance. Such expectations, if tempered by acknowledging natural changes in salmon productivity, can be incorporated into flexible models, management and restoration strategies.