Northern Prairie Wildlife Research Center
Estimated breeding population sizes of canvasbacks (Aythya valisineria) ranged from 742,400 to 353,700 during 1955-1992 (Caithamer et al. 1992, J. Dubovsky, U. S. Fish and Wildl. Serv., Migr. Bird Manage. Off., Laurel, Md., unpubl. data). Hunting of canvasbacks was periodically restricted or prohibited during these years because the population size was below minimum thresholds that the U. S. Fish and Wildlife Service (USFWS) had established (U.S. Dep. Inter. 1983, Anderson 1989). During this study, hunting of canvasbacks was prohibited during the waterfowl season (30-day length, daily bag limit of 3 ducks) in the Central, Mississippi, and Atlantic flyways.
Concern over loss of canvasbacks on the Upper Mississippi River National Wildlife and Fish Refuge heightened during the 1989 waterfowl season when state and federal law-enforcement personnel reported unusually high numbers of canvasbacks in areas open to hunting and many canvasbacks dead from gunshots.
Wildcelery (Vallisneria americana) traditionally has been a large proportion of the diet of canvasbacks while they staged on the Upper Mississippi River (Korschgen et al. 1988, Korschgen 1989). The density and distribution of wildcelery in Lake Onalaska, a portion of Navigation Pool 7, have been declining since 1989. During 1978-88, an estimated 1,214-1,416 ha of wildcelery were in Lake Onalaska. During 1989-1992, there were less than 40 ha; similar declines in other navigation pools of the Upper Mississippi River also have been documented (C. E. Korschgen, Natl. Biol. Serv., La Crosse, Wis., unpubl. data). Coincident with the decline in wildcelery canvasbacks spent more time in shallow, backwater marshes away from open-water areas that were closed to hunting; many shallow backwater marshes were open to hunting.
|Information signs were posted at landings as reminders to waterfowl hunters. Photo by J.M. Nissen, 1990.|
Personnel of the USFWS, Wisconsin Department of Natural Resources, Minnesota Department of Natural Resources, University of Wisconsin--La Crosse County Extension Services, Ducks Unlimited, and concerned waterfowlers made a concerted effort to reduce canvasback mortality in Navigation Pool 7 of the Upper Mississippi River during the 1990-1992 waterfowl-hunting seasons. They implemented an educational program to increase hunter awareness of the problems faced by canvasbacks on the Upper Mississippi River and coupled it with rigorous law enforcement. In 1990, managers were prepared to close waterfowl hunting areas if canvasback mortality was found to be excessive or law enforcement was no longer a deterrent. The first need was to quantify the effect of local hunting on canvasbacks. Our objectives were to quantify attempts by hunters to shoot canvasbacks, recommend methods to reduce the illegal kill of canvasbacks, and provide a database for future evaluation of management practices.