The role of ecotype‐environment interactions in intraspecific trophic niche partitioning subsequent to stocking

Worldwide, stocking of fish represents a valuable tool for conservation andmaintenance of species exploited by recreational fishing. Releases of hatchery-reared fish aremore and more recognized to have numerous demographic, ecological, and genetic impacts onwild populations. However, consequences on intraspecific trophic relationships have rarelybeen investigated. In this study, we assessed the impacts of supplementation stocking andresulting introgressive hybridization on the trophic niches occupied by stocked, local, andhybrid lake trout (Salvelinus namaycush) within populations of piscivorous and planktivorousecotypes stocked from a wild piscivorous source population. We compared trophic niches usingstable isotope analysis (d13C andd15N) and trophic position among the three genetic origins.Putative genetic effects were tested with phenotype–genotype association of“life history”ecological traits (body size, growth rate, condition index, and trophic niche) and genotypes(RADseq SNP markers) using redundant discriminant analysis (RDA). Results showed thatsympatry resulting from the stocking of contrasting ecotypes is a risk factor for niche parti-tioning. Planktivorous populations are more susceptible to niche partitioning, by competitiveexclusion of the local fish from a littoral niche to an alternative pelagic/profundal niche.Observed niche partitioning is probably a manifestation of competitive interactions betweenecotypes. Our results emphasize that ecotypic variation should be considered for more efficientmanagement and conservation practices and in order to mitigate negative impact ofsupplementation stocking