RECONSTRUCTING SALMON ABUNDANCE IN RIVERS: AN INITIAL DENDROCHRONOLOGICAL EVALUATION

Abstract

Decision-makers concerned with salmon or their stream habitats are faced with many persistent, difficult questions including: how large and variable were these populations before European settlement? Here, we examine the feasibility of reconstructing salmon abundance using links between marine nutrients carried upstream by Pacific salmon (Oncorhynchus spp.) and growth of dominant riparian trees in two Alaskan systems. We employ standard dendrochronology methods and regression models to quantify relationships between annual tree-ring growth, salmon escapement, and the climate pattern that affects oceanic production of Northeast Pacific salmon stocks, the Pacific Decadal Oscillation (PDO). We find that known, annual salmon escapement is significantly related to tree-ring growth at two sites in the Pacific coastal rainforest (PCRF) (r2 = 0.23, P < 0.05 at each site), but not at two sites in the boreal forest. We then use relationships established at PCRF sites to reconstruct preliminary salmon spawning abundances to 1820 A.D. The PDO was not correlated with local 19-yr salmon escapement records and could not be used in re- constructions. Reconstructions compare favorably to southeastern Alaska fisheries catch data from 1924 to 1994 (Pearson correlation = 0.301 (P = 0.02) and 0.401 (P < 0.01)). This study demonstrates the promise and utility of dendrochronology for reconstructing salmon returns to streams.