Changes to a Brown Trout Population after Introducing Steelhead in a Michigan Stream

Abstract

We evaluated the effects of steelhead Oncorhynchus mykiss (migratory Rainbow Trout) introduction on the population dynamics of resident Brown Trout Salmo trutta from 1995 to 2008 in a small, low-gradient trout stream. Data on Brown Trout population density, survival, and growth were collected from the treatment section in Hunt Creek, Michigan, where adult steelhead were stocked each spring during 1998–2003, as well as from two reference stream reaches. The presence of steelhead had no apparent effect on the density of age-0 Brown Trout, but the mean density of all age-1 and older (age-1+) Brown Trout year-classes that interacted with juvenile steelhead of the same age was 46% lower than the density of age-1+ year-classes that did not interact with juvenile steelhead of the same age. No differences in density of age-1+ Brown Trout were detected in reference sections between the periods of steelhead presence or absence in the treatment section. Lower annual survival rates for year-classes of age-0 Brown Trout that interacted with steelhead in the Hunt Creek treatment section were the primary reason that density of age-1+ Brown Trout fell to nearly half the levels that existed before steelhead were introduced or after most steelhead had emigrated from the stream. Although our case study showed that the introduction of steelhead into a small, low-gradient stream resulted in lower densities of resident Brown Trout, upstream passage of steelhead into streams with high-quality habitat also offers tremendous potential to increase wild production of juvenile steelhead, thereby reducing fisheries managers’ reliance on hatchery-reared fish for stocking the Great Lakes.

Received August 16, 2013; accepted January 2, 2014

ACKNOWLEDGMENTS

Many personnel of the MDNR Fisheries Division and university students provided assistance with this study. Special thanks to T. Adams, who coordinated field sampling, assisted with data summarization, and estimated age from thousands of trout scales. We thank the many biologists and technicians who assisted with field sampling, including those from the MDNR Northern Lake Huron and Central Lake Michigan fisheries management units and the MDNR Alpena and Charlevoix fisheries research stations. We are also grateful to D. Hayes at Michigan State University for statistical consultation and advice. J. Kocik and two anonymous reviewers provided helpful comments that greatly improved this manuscript. Financial support for this study was provided by the Federal Aid in Sport Fish Restoration Fund (Study 654, Project F-80-R, Michigan) and the MDNR Fish and Game fund.