摘要: Monitoring vegetation and wildlife, and determining the effects of water levels on the ecosystem are identified strategies for the Environmental Management Technical Center's Long Term Resource Monitoring Program. As part of those... 展开 Monitoring vegetation and wildlife, and determining the effects of water levels on the ecosystem are identified strategies for the Environmental Management Technical Center's Long Term Resource Monitoring Program. As part of those strategies, we regressed harvest data for muskrats (Ondatra zibethicus) trapped in the 1990's, comprising 89% of the fur harvest by numbers, against water level fluctuations and aquatic vegetation on the Upper Mississippi River National Wildlife and Fish Refuge (Refuge). The Refuge extends 261 miles from north of Wabasha, Minnesota, to near Rock Island, Illinois, encompassing most of Pools 4 through 14. The Refuge covers nearly 200,000 acres of mostly open water, bottom land hardwoods, and aquatic vegetation. Recreational trapping has been allowed on the Refuge since 1939. During our six-year study period, for the 1990 and 1992 through 1996 seasons, we examined muskrat harvest data as reported on fur catch reports. We obtained daily water level data from the St. Paul District of the U. S. Army Corps of Engineers, who manage water levels on all pools within the Refuge in order to maintain a 9 ft navigation channel. Aquatic vegetation estimates were obtained from aerial photography taken during the late summer of 1989. 收起