River Otter Feeding Habits in Wisconsin, U.S.A.: Evidence of Microbead Contamination

Abstract. The ability of an animal to acquire enough food to meet its caloric needs is key to its survival and fitness. Understanding the composition of that animal's diet is a crucial element to consider when assessing the species' health and overall role in its ecosystem. We conducted a dietary study of Northern River Otter (Lontra canadensis) at 18 sites across 12 different watersheds in Wisconsin, U.S.A., from summer 2017 through winter 2018. We report the frequency of prey remains found in river otter scats (n = 190) collected at these sites. Fish of any kind appeared in 86% (n = 163) of all scat samples, while crayfish (Cambaridae) were the most commonly occurring individual prey item, appearing in 62% (n = 117) of all scat samples. The second most common prey groups were the bottom feeder fish (Catostomidae and Cyprinidae) group and the panfish (Centrarchidae) group, which both occurred in 45% of all scats. While identifying prey species, we found small, spherical objects that did not appear to be of biological origin in 48% (n = 92) of all scats. After testing the objects using multiple approaches, we confirmed the objects as microbeads, defined as small beads of plastic composition no larger than 5mm in size. This is the first recorded observation of plastic microbeads associated with river otters in North America, and may indicate bioaccumulation of these objects in inland waterways.