Population Survey for River Otters in the Rocky Mountain National Park

Ben-David, Merav; Herreman, Jason; Boyd, Jessica

Recently, reintroduction of river otters (Lontra canadensis) to the Grand Canyon was suggested. This, however, could result in the genetic swamping of endangered L. c. sonora in adjacent watersheds. A quantitative spatial model evaluating the potential of natural recolonization of the Grand Canyon by otters assumes dispersal of animals from a viable source population in the upper reaches of the Colorado River. We initiated population surveys of river otters in the Rocky Mountain National Park (RMNP) to identify latrine sites, monitor scat deposition as an index of population size, and evaluate seasonal changes in latrine use to determine preferred sampling periods. Our data indicated that use of latrines and latrine site selection by river otters in RMNP changed both seasonally and annually. A sharp decline in number of latrines per km of stream and the reduction in number of feces per site occurred in all years, suggesting that otter behavior changes seasonally (2001: spring - 2.4 sites/km of river, fall - 1.4 sites/km; 2002: spring - 2.3 sites/km of river, fall - 0.6 sites/km; 2003: spring - 2.86 sites/km of river, fall - 0.22 sites/km). While spring densities of latrines were comparable in all years, the fall densities were considerably lower (43%) in 2002 and dramatically lower (16%) in 2003. The number of feces per site, a measure of otter activity, declined through time and between spring and fall in all years (2001: spring - 10.4 feces per site, fall - 4.75; 2002: spring - 6.1 feces per site, fall - 1.9; 2003: spring - 4.4 feces per site, fall -0.8). Our observations of latrine site selection suggest that otter activity and seasonal abundance may be related to the hydrology of the Colorado River. If true, then occasional failure to detect otter sign should not be interpreted as localized extinction. Nonetheless, because of the high sensitivity of otters to environmental disturbance, monitoring should be continued on a regular bases. A winter survey scheduled for the end of February 2004 as well as continued surveys by the University of Wyoming Student Chapter of the Wildlife Society should provide insights into temporal changes in the abundance of otters in Rocky Mountain National Park.