(www.interscience.wiley.com). DOI: 10.1002/rra.746 SIMULATING EFFECTS OF HYDRO-DAM ALTERATION ON THERMAL

Hydroelectric dams may affect anadromous fish survival and recruitment by limiting access to upstream habitats and adversely affecting quality of downstream habitats. In the Manistee River, a tributary to Lake Michigan, two hydroelectric dams poten-tially limit recruitment of anadromous rainbow trout (steelhead) by increasing tailrace water temperatures to levels that signifi-cantly reduce survival of young-of-year (YOY) fish. The objectives of this study were to determine whether proposed restoration scenarios (dam removals or a bottom withdrawal retrofit) would alter the Manistee River thermal regime and, con-sequently, improve wild steelhead survival and recruitment. Physical process models were used to predict Manistee River ther-mal regimes following each dam alteration scenario. Empirical relationships were derived from historical field surveys to quantify the effect of temperature on YOY production and potential recruitment of Manistee River steelhead. Both dam altera-tion scenarios lowered summer temperatures and increased steelhead recruitment by between 59 % and 129%, but total recruit-ments were still low compared to other Great Lakes tributaries. Considering only temperature effects, bottom withdrawal provides the greatest promise for increasing natural steelhead recruitment by decreasing the likelihood of year-class failures in the warmest summers. Results of this study may allow managers to evaluate mitigation alternatives for Manistee River dams during future relicensing negotiations, and illustrate the utility of physical process temperature models in groundwater-fed riv