Contrasting Ecology Shapes Juvenile Lake-Type and Riverine Sockeye Salmon

Abstract

Here we compare the body shape of juvenile (age-0) sockeye salmon Oncorhynchus nerka that rear in lakes (lake type) with that of those that rear in rivers (riverine) and relate rearing habitat to morphology and ecology. The two habitats present different swimming challenges with respect to water flow, foraging strategy, habitat complexity, and predation level. We present morphological data from three riverine and three lake-type populations in southwest Alaska. Using multivariate analyses conducted via geometric morphometrics, we determine population- and habitat-specific body shape. As predicted, riverine sockeye salmon have a more robust body shape, whereas lake-type sockeye salmon have a more streamlined body shape. In particular, we found differences in caudal peduncle depth (riverine deeper), eye size (riverine larger), and overall body depth (riverine deeper). One lake-type population did not follow the predicted pattern, exhibiting an overall exaggerated riverine body shape. Differences between the habitats in terms of predation, complexity, and foraging ecology are probably drivers of these differences. Allometry differed between life history types, suggesting that there are habitat-specific developmental differences.