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Canvasback Mortality from Illegal Hunting on the Upper Mississippi River

Discussion


Concerns about the illegal kill of canvasbacks on the Upper Mississippi River are not new. Perry and Geissler (1980) reported that incidence of embedded shot in immature canvasbacks they captured on the Mississippi River in 1975 and 1976 was greater than anticipated for a species that was protected under season closures during migration to wintering areas. Eight percent of immature and 26% of adult canvasbacks captured near La Crosse, Wisconsin, contained embedded shot. The authors concluded that the shot were probably from illegal hunting and that increased education and law enforcement were warranted. Hochbaum and Caldwell (1977) believed the inability of hunters to identify canvasbacks contributed to non-compliance with restrictions and bag limits for canvasbacks at Delta Marsh, Manitoba.

Education of hunters and law enforcement were immediately increased when canvasback harvest increased along the Upper Mississippi River in 1989. During 3 years, education focused on waterfowler awareness of the current status of canvasbacks, the importance of Pool 7 as a resource for canvasbacks, and improvement of hunter identification of canvasbacks. Federal and state law enforcement officers, management personnel, and local waterfowlers joined forces to educate hunters on canvasback identification through leaflets, videos, information signs, a short-range-radio broadcast at 1 boat landing, media interviews, and waterfowl identification and information workshops. Most waterfowlers seemed aware of the problem because nearly all hunters polled at Lake Onalaska landings were aware of the canvasback situation on the river in the La Crosse area. Although it was not possible to directly determine whether education improved hunter identification of waterfowl, many hunters that used the various videotapes or participated in the workshops commented that they wanted to improve their skills, and this program provided them with the resources to do so.

GIF -- Picture of hunters
Waterfowl hunters were able to obtain waterfowl identification booklets and other information at boat landings during contacts with bag checkers. Photo by R. A. Nissen, 1991.

The Migratory Bird Management Office estimated an annual canvasback kill of 140-800 (GIF -- Mean symbol = 402 SE = 116) birds in the Mississippi Flyway during closure years 1987-1991 (Waterfowl Harvest Surv. Sect., Migr. Bird Manag. Off., USFWS, unpubl. data). Our estimates suggest that about 128-166 canvasbacks were killed/year (not including crippling loss) in the Lake Onalaska study area alone during 1991-1992. Total canvasback kill during closures may be higher than currently estimated on a flyway or national basis.

This study and a study by Haramis et al. (1993) illustrate the vulnerability of canvasbacks to hunting, even under the protection of a closed hunting season. During law enforcement and routine refuge activities in 1991 and 1992, 22 canvasback carcasses were recovered on the Upper Mississippi River National Wildlife and Fish Refuge on Navigation Pools 7 and 8. Among these were 4 after-hatching-year males, 4 after-hatching-year females, 9 hatching-year males, and 5 hatching-year females (C. E. Korschgen, Natl. Biol. Serv., unpubl. data). Although the actual age- and sex-composition of canvasbacks using the Upper Mississippi River National Wildlife and Fish Refuge is unknown, we believe a disproportionate number of hatching-year birds may have been killed by hunters.

The quantity and quality of available habitat are important to future canvasback management on the river. This was evident during the 1989-1991 duck hunting seasons when canvasbacks fed on alternative foods in shallow marsh habitat because wildcelery tubers were not available in traditional areas. Because wildcelery was unavailable, fewer canvasbacks concentrated on Pool 7 and remained there for less time than previous years. A different response was evident in 1992 when invertebrates such as sphaeriid clams and chironomid larvae were abundant and localized beds of sago pondweed (Potamogeton pectinatus) and wildcelery plants (C. E. Korschgen, Natl. Biol. Serv., unpubl. data) were available on the river. Canvasbacks peaked at nearly 50,000 on Lake Onalaska in late October 1992. Furthermore, canvasbacks used Pool 7 for an extended period from mid-October to early December. Although nearly 3 times as many canvasbacks were present in 1992 as in 1991, the encounter rate was considerably lower in 1992. Canvasbacks may have returned to traditional open water areas and avoided shallow marsh habitat that was open to hunting.


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