Seasonal foraging and piscivory by sympatric wild and hatchery-reared steelhead from an integrated hatchery program

Abstract

We compared the diet of hatchery-reared steelhead produced from an integrated hatchery program as emigrating spring smolts and non-migrating hatchery residuals to their sympatric wild counterparts. Our results suggest that there is a potential for hatchery fish to affect wild steelhead populations due to dietary overlap and subyearling salmonid predation; however, relative ecological risk did not increase as steelhead delayed or forwent emigration. Predation by hatchery smolts was related to release timing, but not experience with native fish. Diet composition appears to be more strongly affected by seasonal and yearly differences in prey abundance and presence rather than differences in rearing environments. Hatchery and wild steelhead showed small but important foraging differences. Hatchery smolts did not consume as many salmonids as wild fish and hatchery residuals showed relatively stronger surface oriented feeding behavior than wild parr. Because most hatchery smolts emigrated shortly after release and the overall number of residuals in the study creek was low, we speculate that in this case there is low dietary and predatory-based risk of hatchery steelhead in Abernathy Creek negatively impacting wild salmonids.