Holistic approaches for invasive species management: Exploring biotic resistance of European green crab (Carcinus maenas) via river otter (Lontra canadensis) diet

Establishment of the European green crab (Carcinus maenas) on the west coast United States has led to concerns regarding loss of eelgrass beds and influence on marine communities. To begin examining whether predators can potentially buffer green crab expansion, I studied river otter (Lontra canadensis) diet from scat remains and estimated green crab abundance from removal trapping efforts. River otter scats on the Wa’atch and Tsoo-Yess rivers, Washington, USA, were collected during August-September 2018 and April-September 2019. Hard remains of prey were reported as percent frequency of occurrence, and green crab prey were compared to monthly catch-per-unit-effort (CPUE). Scats collected from the Tsoo-Yess River contained no green crab, perhaps due to the relatively low abundance of green crab compared to other crustacean and fish prey. River otters consumed green crab in the Wa’atch River, but its low occurrence in their diet (0.7-5.2%) suggests that they were not an important prey source. However, I hypothesize that if green crab numbers increase there will be a subsequent increase in consumption by river otters and, as such, suggest documenting the population status of green crabs in both rivers, and conducting additional predator-prey diet studies to gauge the potential for long-term biotic resistance of green crab populations