Abstract

Populations of invasive silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis), collectively known as “Asian carp,” are growing rapidly in Illinois and may make up a large fraction of available prey for river otters (Lontra canadensis) in larger waterbodies. Our goals were to assess the frequency of Asian carp in otter diets and compare the frequency of occurrence of prey groups (fish, crayfish, and amphibians) in otter diets between land cover types and seasons. We searched for Asian carp otoliths and pharyngeal teeth, as well as parts of other fishes, crayfish, and amphibians in 155 otter scats collected from 43 stream sites in central and southern Illinois during January-April 2013 and 2014. Consistent with previous studies, fish and crayfish were primary prey items for otters, followed by amphibians. Frequency of occurrence of crayfish increased from January-February to March-April, but frequency of occurrence of the other prey types remained similar between those periods. Land cover type did not seem to influence frequency of occurrence of prey types. Asian carp pharyngeal teeth and otoliths occurred in four (2.6%) scat samples, two from sites were Asian carp were not previously confirmed to be present. This is the first direct confirmation of Asian carp in the diet of wild river otters. Otoliths and pharyngeal teeth provided effective structures for identifying fish species in otter diet.

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