Eared grebe diet on Great Salt Lake, Utah, and competition with the commercial harvest of brine shrimp cysts

Abstract

AbstractInteractions between wildlife and commercial harvest industries need to be understood to manage resources for all users. About 1.5 million eared grebes (Podiceps nigricollis), half the North American population, stage on Utah's Great Salt Lake (GSL) each fall. A $56 million commercial harvest industry also operates during fall when the harvest of brine shrimp (Artemia franciscana) cysts occurs. Eared grebes and commercial harvest both utilize brine shrimp cysts creating a potentially adverse relationship. We assessed the diet of eared grebes to determine the extent to which they are dependent on brine shrimp and their cysts. We collected individual birds to measure diets and examine changes in body condition of staging eared grebes. Cysts were consumed by 40% of collected eared grebes and made up >75% of aggregate biomass of stomach samples. Despite the high occurrence of cysts in stomach samples, cysts were not the primary food item of eared grebes. Cysts were held in the stomach for longer periods by feather mass, so esophagus samples were a better indicator of diet. Adult brine shrimp were the primary food collected from the esophagus from October until December. After cold water temperatures caused a die‐off of adult brine shrimp, cysts became more prevalent in the diet of eared grebes. Concomitantly, eared grebe body weights decreased as their diet shifted to brine shrimp cysts. Current monitoring and management of commercial harvest are sufficient to maintain yearly populations of adult brine shrimp to sustain eared grebes populations. © 2013 The Wildlife Society.