Environmental Studies Program


Date of this Version



Environmental Studies Undergraduate Student Thesis, University of Nebraska-Lincoln, 2020.


Copyright 2020 Alexandrea Otto


Understanding prey preference in Eurasian otters, Lutra lutra, is important to provide greater insight into aquatic predator-prey relationships which will inform conservation efforts. Identifying the composition of an organism’s diet is one of the primary steps in understanding an organism and developing effective conservation strategies. This study expands upon basic identification of consumed items to estimate size of fish eaten by Eurasian otters to provide information on the diet of these important aquatic predators. Many studies on the Eurasian otter have considered diet from river systems, yet less is known of their diet in marine systems. The goal of my study was to provide greater insight on the diet of Eurasian otters in marine/coastal environments. The objectives were to conduct a qualitative assessment on items consumed and to conduct a quantitative analysis on fish species eaten. I first hypothesized that otters consume a wide variety of prey items I predicted fish to be the most frequently consumed prey item. Secondly, I hypothesized otters will select larger and slower fish species. I predicted the length and age estimations will suggest adult fish are being eaten more. I also predicted slower fish species will be selected more than other species I identified consumed items by assessing items in spraints. I photographed fish otoliths under scope magnification to outline the otolith shape for species identification. Finally, I performed fish total length on total otolith length regressions to estimate size and age. The Eurasian otter spraints in Galicia (Northwest region of Spain) reveal a majority of spraint parts originating from marine rather than freshwater fish and prey. This study identified cephalopods as prey items for the first time and majority of fish selected where in the family Gobiidae. Investigating diet in this novel environment has allowed further insight into the flexibility of otter foraging and how their diet reflects their environment, which has important conservation implications for this threatened species in this study area.