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Welcome to the interactive web schedule for the 2019 Midwest Fish & Wildlife Conference! The schedule is subject to change (as of November 7, 2018). Please check back for updates. To return to the main Conference website, go to: www.midwestfw.org.

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Tuesday, January 29 • 11:20am - 11:40am
(WILDLIFE: MAMMALS) Using Stable Isotope Analysis to Evaluate the Diet of the North American River Otter Throughout Ohio

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AUTHORS: Sara Adamczak, The Ohio State University; Anne Wiley, The University of Akron; Mažeika Sullivan, The Ohio State University; Stanley Gehrt, The Ohio State University

ABSTRACT: The North American river otter (Lontra canadensis) is an apex riverine predator that is adapted to hunting in the water. This lifestyle results in a diet focused on aquatic and semi-aquatic species.  We sought to determine river otter diet composition and trophic level using stable isotope analysis. Understanding diet and trophic level provides insight into how river otters might influence community dynamics and potentially reveal important prey species for river otters in various riverine systems. We collected tissue, whisker and nail samples collected from 108 river otters across Ohio during 2017-2018. We used these samples to estimate the ratios d<sup>15</sup>N and d<sup>13</sup>C, comparing river otter values to those of potential prey items. The d<sup>15</sup>N measurements serve as indicators of a consumer's trophic level, whereas d<sup>13</sup>C values are used to determine carbon sources in a trophic network. Our preliminary analyses revealed a higher d<sup>15</sup>N for males (mean = 14.58) than females (mean = 13.97), suggesting that male otters tend to feed at a slightly higher trophic level than female river otters. The trophic level of juvenile river otters (15N = 14.02) was the same as adults (= 2 years old; d<sup>15</sup>N = 14.01); possibly a result of juveniles mostly feeding from their mothers until weaning. Yearling river otters (1-2 years old) appeared to feed at a higher trophic level than adults. This age difference may be a result of younger individuals feeding at multiple trophic levels compared to adults. The feeding habits of younger individuals, and consequently their trophic level, will often change over time. Perch, sunfish, and crayfish were found the preferred prey species across all otter age classes. These results support the idea of stable isotopes as a useful tool when examining river otter ecology, providing insight on river otter dietary sources, as well as their trophic positioning.

Tuesday January 29, 2019 11:20am - 11:40am
VETERANS MEETING ROOM A/B