Blood Lead Concentrations and Ingested Shot in Ring-necked Ducks at Catahoula Lake, Louisiana

We analyzed blood lead concentrations and prevalences of ingested lead and steel shot in 93 ring-necked ducks (Aythya collaris) at Catahoula Lake, Louisiana. Blood lead concentrations were higher for immatures than for adults, but did not differ between sexes or between randomly collected and hunter-shot birds. Blood lead concentrations were elevated (> 0.20 ppm) in 18 of 31 immatures (58%) and 13 of 61 adults (21%), and were toxic (> 0.50 ppm) in 11 immatures (35%) and 5 adults (8%). Prevalences of ingested lead shot were higher for immatures (7 of 32 birds, 22%) than for adults (3 of 61 birds, 5%), but did not differ between sexes or collection methods. Prevalences of ingested steel shot did not differ between sexes, but were higher for hunter shot (10 of 39 birds, 26%) than for randomly collected birds (2 of 54 birds, 4%), and tended to be higher for immatures (8 of 32 birds, 25%) than for adults (4 of 61 birds, 7%). We recommend continued monitoring of lead exposure in ring-necked ducks at Catahoula Lake to evaluate management techniques used there to reduce lead poisoning. Proc. Annu. Conf. Southeast. Assoc. Fish and Wildl. Agencies 47:292-298 Waterfowl mortality associated with ingestion of lead shot has been documented throughout the United States and in several other countries (Sanderson and Bellrose 1986, Pain 1992). Sublethal physiological effects of lead poisoning in waterfowl also have been described (e.g., Mautino and Bell 1986, Hohman et al. 1990a, Havera et al. 1992, Samuel et al. 1992). Although lead shot currently is prohibited for waterfowl hunting in the United States, shot deposited in prior seasons can remain available to foraging birds for many years in some habitats (Mudge 1984, Anderson 1986, Pain 1991). Monitoring of lead exposure is necessary to determine the effectiveness of nontoxic shot regulations or other management techniques used to reduce lead poisoning of waterfowl (Havera et al. 1992). 'Present address: U.S. Fish and Wildlife Service, San Luis National Wildlife Refuge Complex, Box 2176, Los Banos, CA 93635. 1993 Proc. Annu. Conf. SEAFWA Ring-necked Duck Lead Exposure 293 Most investigators have relied on prevalences of ingested lead shot in gizzards of hunter-shot birds to assess lead exposure in waterfowl (Anderson and Havera 1985). However, this technique has been questioned because birds with ingested lead shot may be more vulnerable to hunting and thus may be more likely to be included in gizzard surveys than are birds without ingested shot (Samuel et al. 1992). Moreover, prevalence of ingested lead shot in gizzards is less sensitive for detecting lead exposure than are blood analysis techniques (Anderson and Havera 1985). Catahoula Lake has been a popular waterfowl hunting area since at least the turn of the century and is one of the most intensively hunted areas in Louisiana (Wills 1965). The density of lead shot in sediments of Catahoula Lake is extremely high, exceeding most other major waterfowl staging areas in the United States (Hohman et al. 1990a). Consequently, lead poisoning of waterfowl has been a recurring problem at Catahoula Lake (Yancey 1953, Wills and Glasgow 1964, Smith 1981, Zwank et al. 1985, Hohman et al. 1990a). Use of lead shot was prohibited on 90% of the lake in fall 1987 and on the entire lake in fall 1988. Despite conversion to nontoxic shot, an estimated 10,000 ducks died of lead poisoning at Catahoula Lake during fall and winter 1989-90 (R. Helm, pers. commun.). A recent experiment indicated that deep tillage is a viable management option for reducing availability of lead shot to foraging waterfowl on the lake (Peters and Afton 1993b). Our objectives were to: (1) estimate lead exposure of ring-necked ducks at Catahoula Lake following conversion to nontoxic shot but before deep-tillage treatments; (2) compare blood lead concentration and prevalence of ingested shot in the same sample of birds; and (3) investigate the effects of sex, age, and collection method (random vs. hunter shot) on lead exposure estimates. Financial support for our study was provided by Regions 4 and 8 of the U.S. Fish and Wildlife Service, Placid Oil Company, Ducks Unlimited Inc. through the Institute for Wetland and Waterfowl Research, National Rifle Association, a Rockefeller Scholarship, the Louisiana Department of Wildlife and Fisheries (LDWF), the Louisiana Cooperative Fish and Wildlife Research Unit, and the Graduate School and School of Forestry, Wildlife and Fisheries at Louisiana State University. We thank K. Richardson and D. Cubanski for assistance in data collection and T. Eberhardt of the Minnesota Department of Natural Resources for loaning equipment. S. Wood of the Illinois Natural History Survey conducted the blood lead analysis, and R. Pace III gave helpful advice on our statistical analysis. We thank numerous personnel of the LDWF for their cooperation and support, especially B. Crain for assistance in collecting birds. We also appreciate assistance provided by W. Tradewell and personnel of Saline Wildlife Management Area and E. Sipco and personnel of Catahoula National Wildlife Refuge (NWR). F. Bryan, R. Chabreck, J. Emnnger, S. Havera, R. Helm, R. Pace III, and V. Wright made helpful suggestions for improving the manuscript.