Environmental and phenological variability: Match-mismatch effects of lake conditions and entry timing on sockeye salmon survival and growth

Background/Question/Methods

Survival of an organism can depend on multiple seasonally-fluctuating features, including suitability of thermal dynamics and availability of food resources. The fitness of a consumer depends on spatial and temporal overlap with prey production, and a modification in life history timing of either prey or consumer might confer a trophic decoupling and loss of ecological function. This has been observed in primary consumers across systems, but the strength of mismatch effects is less clear for secondary consumers. The potential for mismatches might be especially pronounced in organisms that change habitats, such as sockeye salmon (Oncorhynchus nerka), which move from natal streams to a freshwater lake where they rear for up to two years before moving to sea. This project compared growth and survival from fry to smolt stage for sockeye salmon with different lake entry dates. Multivariate time series models were used to test the hypothesis that the most successful entry times correspond to favorable lake conditions with respect to zooplankton blooms and location and onset of lake thermocline, and that a change in either fish entry time or seasonal lake dynamics can have negative effects on fish growth and survival. 

Results/Conclusions

Across years, fish entering the lake system later in the season encountered higher productivity and warmer water temperatures, and experienced higher average rates of growth and survival. However, lake conditions vary on the order of weeks from year to year, and the optimal date for lake entry was found to be not static across time and up to a month apart between years. In addition, the relative effect of zooplankton abundance or water temperature in predicting sockeye salmon performance varied interannually, and zooplankton dynamics was found to be a better predictor by integrating across temperature and productivity. These results suggest that maintaining a wide window of lake entry times preserves the biological variability in this life history event that is necessary to succeed in an unstable environment. Interactions between phenology and a varying environment can be especially complex for organisms that occupy multiple habitats or feed on multiple prey types, and the effects of manipulated life history timing via management, loss of intraspecific diversity, or environmental change requires examination of the temporal variability of both an organism and its environment.