Arctic Grayling, scared to death: Are Brown Trout an impediment to Arctic Grayling reintroduction success in Michigan?

Abstract Introduction Arctic Grayling Thymallus arcticus were extirpated from Michigan in 1936. Their demise was likely caused by overfishing, habitat destruction from large-scale logging, and the introduction of Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta. Subsequently, Brook Trout and Brown Trout have become the dominant salmonid species in Michigan streams. Past attempts to restore Arctic Grayling to Michigan have been unsuccessful, perhaps due to competition with these now-resident salmonids. Objective To determine the impacts of competition between age-0 Arctic Grayling and age-0 Brook Trout and Brown Trout on Arctic Grayling growth and survival. Methods Competition trials were performed in experimental streams, lasting 2 months, across 3 years, with three treatment types: the control, 10 Arctic Grayling with 10 Arctic Grayling; the Brook Trout treatment, 10 Arctic Grayling with 10 Brook Trout; and the Brown Trout treatment, 10 Arctic Grayling with 10 Brown Trout. Results Brown Trout had a significant effect on Arctic Grayling growth and mortality, while Brook Trout had no effect on Arctic Grayling growth or mortality. Conclusion Age-0 Brown Trout negatively impacted growth, condition, and survival of age-0 Arctic Grayling, while the impacts of age-0 Brook Trout or conspecifics were negligible. This suggests reintroduction of Arctic Grayling may be more successful in streams with few or no Brown Trout.