Demographic and Reproductive Characteristics of Reintroduced Northern River Otters in Kentucky: Implications for Population Growth

Abstract

Reproductive parameters and estimates of population size of northern river otters (Lontra canadensis) are poorly documented in southeastern United States. We examined the current population status of river otters in Kentucky, reintroduced in 1991 to 1994, by deriving demographic and reproductive characteristics from necropsies of river otter carcasses collected during harvests in Nov. through Feb., 2006–2009. We derived age distribution, sex ratio, pregnancy rate, and litter size of river otters and used these data to model future population growth of river otters in Kentucky. Data indicate 35.7% of female river otters in the yearling age class showed evidence of reproductive activity. The pregnancy rate (0.72) and average litter size [3.14 ± 1.46(sd)] of adult females was high compared with values reported for established populations of river otters elsewhere in eastern North America; consistent with an expanding and successfully recolonizing population. The population age distribution was skewed toward young age classes, with sex ratio of juvenile animals (1.58∶1.0) significantly favoring males. Models demonstrated the most plausible population growth estimates when using a 5% additive mortality factor, with extinction a possibility at lower published annual survivorship rates (below 0.73). Our data support a conservative harvest rate for sustained long-term management of river otters in Kentucky, especially for the eastern mountain region.