Impacts of stocking trout on resident fish and benthic macroinvertebrates in streams in Northeastern PA

Background/Question/Methods Fish stocking programs are commonly used to increase the abundance of game fish in streams, but the impacts of stocking on the stream community are under studied.  Rainbow trout, brown trout, and brook trout are stocked in streams throughout the northeastern US, sometimes several times per year with more than one species.  We studied 6 pairs of streams in northeastern PA; each pair included 1 stocked and 1 nearby non stocked stream with similar physical and chemical characteristics.  We used kicknets to sample benthic macroinvertebrates in late spring of 2009.  We electroshocked 5 stream pairs over the summer of 2009 to sample the resident fish assemblage.

Results/Conclusions Our results indicate that there were no differences in the density or family richness of macroinvertebrates, but family diversity was higher in non stocked streams.  Results of ordination analyses suggest that macroinvertebrate assemblages are affected by location in the landscape (pairs are similar) and the presence of stocked fish. Fish biomass was marginally higher in non stocked streams, and we identified differences in size distributions of some species. Against a background of considerable variation among streams, our study measured differences in macroinvertebrate and fish assemblages that appear to be related to trout stocking.  This and other studies support the need for further research related to impacts of widespread stocking practices.