Variations in reproduction and age structure in the North American river otter in North Carolina, USA

Historically, the North American river otter (Lontra canadensis; otter) was distributed across North Carolina, USA, but populations were decimated by the early 1900s. Otter trapping was prohibited in 1938, reopened in 1947, and gradually expanded until it was opened statewide in 2005. Between 1986 and 1992, the North Carolina Wildlife Resources Commission and Great Smoky Mountains National Park released 404 otters to restore populations in western North Carolina. Our objective was to determine if the age structure and reproductive rates of otters throughout North Carolina shifted from 1978 to 2018 between remnant and reintroduced populations. During the 1978-1980 (period 1; Coastal Plain) and the 2009-2013 and 2014-2016 (period 2; statewide) trapping seasons, we collected 1,439 otter carcasses from licensed trappers, fur buyers, and wildlife damage control agents throughout the 3 Furbearer Management Units (FMUs) and 14 river basins in North Carolina. We conducted necropsies, used cementum annuli of the lower canine for age analysis, and counted corpora lutea and fetuses for fecundity estimates. Age distributions for all otters were skewed toward the younger age classes and did not differ between collection periods. During period 1, adults in the Coastal Plain had higher corpora lutea counts than during period 2, whereas Coastal Plain yearlings and juveniles had higher numbers of corpora lutea during period 2. During period 2, corpora lutea counts differed among FMUs; counts in the Mountain FMU (x = 2.56) were higher than in the Coastal Plain FMU (x = 1.62) or the Piedmont FMU (x = 1.91). Within the Coastal Plain FMU and pooling all age classes, fecundity increased by 45% from period 1 to period 2. Adult fecundity in the Coastal Plain FMU declined 16% from period 1 to period 2, while juveniles and yearlings began reproducing between the periods, indicating that reproduction has shifted to younger age classes between 1978 and 2018.