How stock of origin affects performance of individuals across a meta-ecosystem: An example from sockeye salmon

Background/Question/Methods

Across landscapes, different habitats will vary in productivity in space and time and, if these habitats are connected, individuals can exploit their changes in productivity.  However, if there are multiple populations of the same species on the landscape these migrations can lead to population interactions that vary in space and time with habitat productivity.  There may also be within-population differences in performance between individuals that migrate and those that do not. Population structure can be cryptic, so assessing both the distribution of and interactions between populations on the landscape can be challenging.  Genetic tools provide a useful alternative to time-intensive tagging studies for salmonids because of their high population differentiation at relatively fine spatial scales.  Furthermore, there is strong interest in managing these species to maintain population diversity.  We explored the rearing habitat use and body condition of juvenile sockeye salmon in an Alaska Peninsula watershed using single-nucleotide polymorphisms (SNPs).  This watershed contains two connected lakes with very different thermal and productivity regimes during the growing season. 

Results/Conclusions

The upstream lake population consistently had emigrants of similar length but lower body condition than residents.  In the downstream habitat, the proportion of upstream emigrants varied among years (17-40%).  Their body condition relative to downstream residents was higher for smaller fish and lower for larger fish.  Natal lake residents showed large differences in body condition, with the upstream lake producing much higher condition fish than the downstream lake.  Differences in the duration of freshwater rearing are known between these populations, however, we do not yet know if there is within population diversity associated with upstream residents and emigrants.  Furthermore, the relative productivity of these lakes is strongly dependent on their thermal characteristics which are very responsive to changes in climate.  Assessing sockeye salmon freshwater productivity under future change will require an understanding of both the drivers of habitat productivity and the ability of populations to take advantage of habitat connectivity.