Shot Ingestion in Scaup on the Lower Great Lakes After Nontoxic Shot Regulations in Canada

Abstract

Use of lead shot for waterfowl hunting was banned in the United States in 1991 to reduce the incidence of lead toxicosis in waterfowl. In 1999 Canada implemented a similar ban. The lower Great Lakes (LGL) are important migratory areas for greater (Aythya marila) and lesser scaup (A. affinis). Prior to the implementation of the Canadian ban, 11% and 8% of greater and lesser scaup harvested in the LGL, respectively, had ingested lead shot. We collected greater and lesser scaup on the Canadian side of lakes Erie, Ontario, and St. Clair during autumn 1999 and spring 2000 to determine if lead shot ingestion declined 1 year after the ban in Canada. There were no intraspecific (lake, season, sex, or age) or interspecific differences in proportion of birds containing ingested shot. Overall, only 0.6% of birds (n = 4 of 722) contained lead shot and only 3.1% contained nontoxic shot. The low frequency of toxic relative to nontoxic shot ingestion suggests that shot may quickly become inaccessible to scaup on lacustrine areas of the Great Lakes. Thus, the risk of lead toxicosis to scaup migrating through the LGL appears low at this time. Pre- and postban differences in overall ingestion frequencies (8–11% vs. 3.7%) suggests that preban numbers may have been biased (elevated) because lead shot ingestion can increase harvest susceptibility. However, recent scaup dietary shifts may also have contributed to overall declines in shot consumption. Low postban lead shot ingestion may also be indicative of high hunter compliance with nontoxic shot regulations in Canada.