The Effect of Dreissenid Mussels on the Strength of Density Dependent Growth and Recruitment of Lake Whitefish in Lake Huron

Density dependence is a form of ecological feedback that can play an important role in a population, impacting the relationship between population density and individual growth and altering the recruitment process. The strength of density dependence can shape population dynamics and a population’s response to harvest. For the present study, we evaluated the strength of density dependent growth and survival of lake whitefish in one of the largest lakes in the world, Lake Huron.

Lake whitefish support a significant commercial fishery in the Laurentian Great Lakes, and are the most harvested fish species in Lake Huron. Despite the economic importance of this population however, density-dependent growth and stock-recruitment relationships have not been described for lake whitefish in Lake Huron.  We focused on lake whitefish in southern Lake Huron and evaluated the relationship between population density and two factors: (1) individual growth and (2) the number of young juveniles recruited to the population.

We found evidence that while both growth and recruitment decreased over the entire study period (1985 to 2009), relationships between these factors and density appear to have changed in the years just after the invasion of dreissenid mussels. Prior to dreissenid invasion, growth decreased with increasing abundance; however, this trend did not continue after the dreissenid invasion. Furthermore, while a positive trend was observed between growth and cumulative growing degree days before dreissenid establishment, growth decreased with increasing cumulative growing degree days after dreissenids became established.

Stock-recruitment relationships also changed in recent years. Predictions from a statistical catch-at-age stock assessment model found little variance in adult abundance but highly variable recruitment in years following dreissenid establishment. Additionally, increasing annual growing degree days negatively impacted recruitment for the post-invasion time period but had little effect prior to that.  Taken together, our results support existing claims that availability of high quality food sources has likely become a primary limiting factor for lake whitefish in the Great Lakes following the establishment of dreissenid mussels, and that this has impacted the strength of important ecological feedbacks.