Detecting Compensatory Growth in Juvenile Atlantic Salmon: The Role of Life History

Compensatory growth (CG) is an intriguing phenomenon that has long interested fish ecologists.  Although it has been well studied in laboratory environments, few studies have observed its presence in a natural environment, and therefore, the functional role of compensatory growth is still somewhat ambiguous. In Atlantic salmon (Salmo salar, L.), manipulative studies have suggested life history decisions can influence the expression of CG.  In this study we use observational data from both the laboratory and the field to study the interaction between life history and the presence and strength of CG in immature juvenile Atlantic salmon.  Because we could not always assign individuals to a life history group we used piecewise quantile regression to analyze regression plots when there might be a mix of the two life history groups.  We found that life history-dependent compensatory growth was evident in the laboratory and field depending on the season analyzed.  Our results indicate that life history and season can be important determinants of CG responses and can lead to the maintenance of two growth strategies: 1) accelerating growth to reach an adequate size before migration or 2) delaying growth and remaining in the stream for another year before migration.