Effects of regulate lake levels on muskrats in Voyageurs National Park, Minnesota
Thurber JM and Peterson RO. 1988. Effects of regulate lake levels on muskrats in Voyageurs National Park, Minnesota. Research/Resources Management Report. MWR-9. Research and Science Division, Midwest Regional Office, National Park Service, U.S. Department of the Interior. Omaha, Nebraska
Muskrats ( Ondatra zibethicus ) were studied as part of a comprehensive project by the National Park Service to determine effects of current water management programs on the aquatic biota of Voyageurs National Park. Water levels in Rainy Lake (minimal drawdown) are fairly stable with average fluctuations of one meter annually. Namakan Reservoir (significant drawdown) experiences fluctuations averaging 2.7 meters annually with high water through summer and early fall and a winter drawdown. Muskrat habitat and population characteristics in the two water regimes were compared from 1985-1987. Radiotelemetry was used to assess differences in mortality and long distance dispersal (1984-1987). Standard body measurements did not differ between areas. Significantly greater muskrat density was indicated in the minimal drawdown area for spring 1986 sign survey, fall 1986 trapnight success and house counts for 1985-86 and 1986-87. All other density estimates indicate greater numbers in the minimal drawdown area, although findings were not statistically significant. Overwinter survival of radioed muskrats was very low in both areas, especially during freeze-up in early winter. Impacts on muskrats would be reduced if a fluctuation schedule was implemented that has a more natural amplitude, a partial drawdown of about 1 m in early fall, and a further drawdown occurring over a short time in winter similar to that now occurring in Rainy Lake. This would allow time for muskrat houses to be constructed in deeper water, keep food shortage time to a minimum, and thus decrease above-ice foraging time and exposure to predators.
- Type
- Published Report
- Authors
- Thurber, J; Peterson, R
- Date of Issue
- 1988-07
- Publisher
- Research and Science Division, Midwest Regional Office, National Park Service, U.S. Department of the Interior
- Units
- VOYA , WRD
- Keywords
- Animal Studies, Clemson, Habiatat Suitability, Mammals, Water Level, Water Quantity, Wildlife habitat improvement, Wildlife Monitoring