Interacting effects of density and temperature on growth of wild and hatchery young-of-the-year anadromous brown trout (Salmo trutta L.)

Stocking can affect population density but may influence fish growth responses to changes in environmental conditions. In a multi-year field experiment, we investigated the interactive effects of density and temperature on the growth of young-of-the-year anadromous brown trout in streams stocked with wild-origin hatchery-reared brown trout. Fish origin was the predominant factor influencing growth rate, thereby highlighting the importance of discriminating between wild and hatchery-reared individuals. Growth was positively related to temperature (degree-days) and negatively related to density, with the growth response to temperature modulated by density. Temperature had a more pronounced effect on juvenile growth at low density than at high density. The reduced growth response to temperature caused by density could reduce population resilience and should be considered in management and conservation strategies.