Vosbigian, R.A., L. Wendling, T. Copeland, and M.R. Falcy. 2024. Cycles in adult steelhead (Oncorhynchus mykiss) length suggest interspecific competition in the Pacific Ocean. Canadian Journal of Fisheries and Aquatic Sciences.
Abstract
The growth rate of fish often reflects environmental conditions. We describe a previously undocumented two-year cycle in the lengths of adult steelhead (Oncorhynchus mykiss). This cycle is present in multiple stocks in the Snake River Basin and in both sexes for individuals spending two years in the ocean. Steelhead lengths were significantly correlated with a well-known two-year cycle of abundance of Pink Salmon (O. gorbuscha) in the Pacific Ocean. The lengths of adult steelhead that spent two or three years in the ocean exhibit negative associations with the abundance of Pink Salmon originating from the Kamchatka Peninsula in Russia. Negative associations exist between all ages of steelhead and Pink Salmon originating from North America. We suggest that competition for gonatid squid, a primary component of steelhead diet, can explain the decreased growth of steelhead in years when Pink Salmon are more abundant. Collectively, our results suggest transmission of ecological interactions from Russia to North America that is consistent with interspecific density dependence in the Pacific Ocean.