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Alternative title

River otter diet in the lower Wa'atch and Tsoo-Yess river estuaries

Date Permissions Signed


Date of Award

Spring 2021

Document Type

Masters Thesis

Department or Program Affiliation


Degree Name

Master of Science (MS)



First Advisor

Acevedo-Gutiérrez, Alejandro, 1964-

Second Advisor

Akmajian, Adrianne M. (Adrianne Monet)

Third Advisor

Miner, Benjamin G., 1972-


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.




river otter, lontra canadensis, european green crab, carcinus maenas, diet, biotic resistance, frequency of occurrence, Makah Bay, Wa'atch River, Tsoo-Yess River


Western Washington University

OCLC Number


Subject – LCSH

Introduced freshwater organisms--Washington (State); Carcinus maenas--Biological control--Washington (State); Eelgrass--Loss--Washington (State); North American river otter--Food--Washington (State)

Geographic Coverage

Washington (State)




masters theses




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