Prey Selection by Marine-Coastal River Otters (Lontra canadensis) in Newfoundland, Canada

Abstract

Previous studies have suggested that diets of river otters (Lontra canadensis) vary in response to seasonal shifts in prey availability, and that they select slowly moving fish of moderate size. To test these assumptions for marine-coastal river otters in Newfoundland, Canada, we reconstructed diets and estimated body length of important fish prey through analysis of otoliths and other hard parts recovered from scats collected in Bonavista and Placentia bays. Diet of otters in Bonavista Bay also was compared with the species and size composition of the nearshore fish community, as determined by concurrent beach-seine sampling. Diets were qualitatively similar but quantitatively different between bays. Otters consumed proportionally more cunner (Tautogolabrus adspersus) and stickleback (Gasterosteidae) in Placentia Bay, and more sculpin (Cottidae) and cod (Gadus )i n Bonavista Bay. Flounder (Pseudopleuronectes americanus) was important in both bays, based on biomass, because individual fish in the diet were large. Fish-community composition in Bonavista Bay varied seasonally, a pattern that was not reflected in the diet, suggesting active selection of fish prey by otters. Slow-swimming fish (sculpin, flounder, and ocean pout [Macrozoarces americanus]/rock gunnel [Pholis gunnellus]) were overrepresented in the diet, and fast-swimming species (cod and hake [Urophycis]) were underrepresented. Otters also selected larger individuals within taxa. The lower limits at which size classes were incorporated into diet varied across fish species, and may reflect species differences in detectability by otters due to camouflage and behavior.