Cooperative Fish and Wildlife Research Units Program: Minnesota
Education, Research and Technical Assistance for Managing Our Natural Resources

French, W. E., B. Vondracek, L. C. Ferrington, Jr., J. Finlay, and D. J. Dieterman. online. Winter feeding, growth and condition of brown trout Salmo trutta in a groundwater-dominated stream. To be submitted to Fisheries Management and Ecology


Winter can be a stressful period for stream trout populations. Groundwater may moderate water temperature and reduce the negative impacts of winter but few studies have examined food webs supporting trout under winter conditions. We used diet, stable isotope analysis, and mark-recapture to examine winter feeding, growth, and condition of brown trout Salmo trutta in a groundwater-dominated stream. Growth occurred during the winter season and was greater for fish < 150mm (mean = 4.1 mg/g/day) than for those 151 - 276mm (mean = 1.0 mg/g/day). Overall condition from early winter to late winter did not vary for fish < 150mm (Mean Wr = 89.5) and increased for those 151 - 276mm (Mean Wr = 85.8 early, 89.4 late). Although composition varied both temporally and by individual, brown trout diets were dominated by aquatic invertebrates; primarily Isopods, Dipterans, and Trichopterans. Stable isotope analysis supported the observations of dominant prey taxa observed in stomach contents, and suggested trout may have used a combination of allochthonous- and autochthonous-derived resources. We found that trout likely benefited from the thermal regime and increased prey abundance present in this groundwater-dominated stream during winter.