Density of lead and nontoxic shotshell pellets in gulf coast prairie ricelands

Abstract

Waterfowl ingest residual lead or nontoxic shotshell pellets while foraging for food in agricultural and other habitats. The Chenier Plain of Louisiana and Texas and the Texas Mid-Coast provide important habitats for wintering waterfowl, yet these regions are characterized by long traditions of waterfowl and other game-bird hunting, which potentially exposes waterfowl to historical lead pellets remaining in the environment. Recent evidence suggests that migrant and resident waterfowl within the Chenier Plain and Texas Mid-Coast regions continue to ingest lead pellets despite strict shotshell regulations. Thus, we randomly collected and radiographed soil cores (10-cm diameter and depth) from production and idled ricelands (n = 500 from each type) in the Chenier Plain (n = 760) and Texas Mid-Coast (n = 240) during November 2013 to estimate density of lead and nontoxic pellets in important waterfowl habitats of these regions. Across all regions and field types, we detected only one lead pellet and zero nontoxic pellets, despite 100% detection of known numbers of pellets in test samples. The single lead pellet was recovered from a production rice field in the Chenier Plain, yielding an estimated density of 1,019 lead pellets/ha (95% CI: 0-3,034) in this sampling region. Failure to detect lead pellets in other regions and nontoxic pellets across all regions precluded estimation but suggested pellet densities, ˂ 3,000 pellets/ha. We speculate that regular soil tillage of ricelands helps incorporate pellets into the soil, rendering all or most unavailable to our sampling and foraging by waterfowl. We recommend that future research estimate densities of lead pellets in areas where they may be concentrated (e.g., near permanent hunting blinds), where dove hunting is prevalent, and in other heavily hunted waterfowl habitats along the Gulf Coast (e.g., coastal marsh).