Historical Records Reveal Changes to the Migration Timing and Abundance of Winter Steelhead in Olympic Peninsula Rivers, Washington State, USA

Abstract

We analyzed multiple historical data sources (circa 1948–1960) to estimate migration timing and abundance of Olympic Peninsula winter steelhead Oncorhynchus mykiss in the Quillayute, Hoh, Queets, and Quinault rivers, Washington, to provide context for contemporary (circa 1980–2017) population trends. Contemporary wild winter steelhead migrations peak 1–2 months later than historical migrations, and migration timing breadth has contracted by up to 26 d (a 37% reduction of the interquartile range of the migration timing distribution). Migration timing changes coincide with an era of peak industrial forestry and introductions of early migrating hatchery winter steelhead stocks. We estimate that contemporary mean wild winter steelhead abundance has declined by 55% across populations compared to circa 1948–1960 historical means, with 1920s records suggesting declines of up to 77% in the Queets River. Migration timing shifts and the magnitude of population declines are not evident in modern fisheries monitoring records, which began around 1980. Our results demonstrate how modest extensions of the period of record (e.g., 30 years) increase the power to identify population changes that are not readily apparent from contemporary fisheries monitoring programs. Historical fisheries data can help managers to avoid the shifting baseline syndrome and provide important reference points for rebuilding population diversity and abundance.