Determinants and Dynamics of Production Rates of Stream-Dwelling Salmonids: The Importance of Intrinsic Factors

Based on published and unpublished long-term data sets covering a wide range in size, growth, density, and production rates reported for resident, sea-migratory, and lake-migratory stream-dwelling salmonid populations, we examined, revisited, and summarized cohort and annual production rates and turnover ratios at a global scale, including most of the production rates variability reported worldwide, within the range 0.01–45 g m−2 year. Major highlights include strong recruitment-dependent cohort production rates and density-dependent annual production rates. Moreover, when combining a heterogeneous suit of slow-growing, high-density and fast-growing, low-density populations, we observed striking trade-offs along a continuum of recruitment, growth, and production rates: lowest recruitment is strongly related to highest growth and lowest production rates, whereas, at the opposite extreme, highest recruitment is related to lowest growth and highest production until an asymptotic value upon which production rates remain constant. In addition, asymptotic recruitment-dependent cohort and density-dependent annual turnover rates suggest a maximum cohort production-to-biomass ratio = 6 and annual production-to-biomass ratio = 2. Previous assessments of discharge-dependent recruitment relationships in combination with the patterns elucidated here revealed dramatic year-to-year variations in recruitment and cohort production rates, implying that annual production rates only maximize over several successive favorable years for recruitment, a most unlikely event. These processes suggest that annual production rates appear to have a maximum limit at approximately 40–45 g m−2 year across stream-dwelling salmonid populations. All patterns highlighted here are summarized in simple linear and nonlinear models that may be steadily applied to a variety of predictive purposes.