Stocking practices shape the taxonomic and functional diversity of fish communities in gravel pit lakes

Freshwater fishes are widely stocked to enhance existing stocks and create new fishery opportunities, but quantification of ecological effects of stocking on recipient communities is still limited. Here, we quantified recent stocking practices in geographically close gravel pit lakes with contrasting history and management, and measured effects of stocking on fish community structure (taxonomic and functional diversity and body-size structure). Between 2011 and 2017, 50% of managers stocked fish into gravel pit lakes at least once. However, stocking density (1.6 kg.year(-1).ha(-1) to 907 kg.year(-1).ha(-1)), stocking diversity, and species stocked (from rainbow trout-dominated to cyprinid-dominated) were highly variable. Stocking intensity and choice of stocked species were primarily driven by management objectives and lake size. Stocking intensity was associated with changes in the recipient fish community, with an increase in taxonomic and functional richness and nonlinear changes in community size spectrum. Our findings demonstrate that recent stocking practices can modulate ecological dynamics of fish communities in gravel pit lakes with important consequences on functional characteristics that should be incorporated into management practices.