Evaluating Dynamics of Food Availability for Lesser Scaup at Pools 13 and 19 of the Mississippi River

The lesser scaup (Aythya affinis; hereafter, scaup) is an omnivorous diving duck that is a species of conservation concern in the Midwest. Since the 1970s, the continental scaup population has declined, with numbers well below the 6.3 million goal set by the North American Waterfowl Management Plan. Several factors have been implicated in the scaup decline, including decreased food availability at migratory stopover sites in the upper Midwest. Navigational Pools 13 and 19 of the Upper Mississippi River System (UMRS) are crucial refueling sites for migratory waterfowl, especially diving ducks, prior to reaching higher latitudes where food shortages have been documented. Unlike other navigational pools of the UMRS, few aquatic invertebrate and vegetation evaluations have been conducted on Pool 19. Our ongoing research seeks to create a spatiotemporal habitat assessment of Pools 13 and 19. We evaluated potential foraging biomass and habitat conditions at 50 stratified random sites on each Pool in 2019 and 2020. While beds of submersed aquatic vegetation were abundant on Pool 13, few were found on Pool 19. Mean scaup food biomass from 2019 samples was largely dependent on the presence of gastropods and bivalves (Pool 19 Summer = 388.1 kg/ha ± 104.5 [SE]; Pool 19 Fall = 398.9 kg/ha ± 107.8 [SE]; Pool 13 = 1,133.8 kg/ha ± 284.8 [SE] ). Scaup food found on Pool 19 did not differ seasonally in 2019 (p = 0.714), and biomass from seeds was minimal in both study areas.