Density Dependence and Resource Heterogeneity Interact in Determining Morphology: Evidence from Atlantic Salmon

Intraspecific competition in juvenile Atlantic salmon (Salmo salar) is driven by density dependant interactions due to the territorial nature of their foraging tactics. Competition for limited resources is strong but both aggressive territorial defense and systems of social cooperation reflecting a scramble type of competition have been observed in the wild. Size is an important determinant of dominance and fitness in fish and morphology is related to their ability to acquire and defend resources.  In this presentation, we show results of an experiment designed to test whether the spatial distribution of resources and the density of competitors interacted to determine individual growth and functional morphology. Differences in size and changes in morphology were contrasted before and after individuals experienced a particular combination of density (#of individuals) and type of spatial distribution of resources (clumped vs. dispersed). We also tested whether growth and morphology differed between two different strains of Atlantic salmon with very different life histories: one anadromous (LaHave) and one landlocked (Sebago). A trade-off may exist between growth and functional morphology that is dependent on fish density and the distribution of resources. This could have important implications on the management Atlantic Salmon in the wild and in captivity.