NORTHERN RIVER OTTER POPULATION ASSESSMENT AND CONNECTIVITY IN WESTERN MONTANA

Darin Edward Newton, The University of Montana

Abstract

Northern river otters (Lontra canadensis) are elusive and difficult to monitor, and little is known about their movement patterns or how populations are structured on the landscape. Otters are sensitive to degradation of aquatic systems, mostly due to loss of prey. This is evident in the Upper Clark Fork River (UCFR), Montana, which has been polluted from decades of mining activity. My objectives for this project were to determine otter population substructuring and connectivity in western Montana and Idaho, and produce a habitat assessment and population estimate for otters in the UCFR. I used genotypic data from otter tissue samples collected in Montana and Idaho to determine otter population structuring and connectivity. I found no evidence that otter movements are restricted to streams, and there appears to be movements between otter populations in MT and ID over a mountain range. Pair-wise FST values were highest between ID and MT rivers, but were still within the range shown in otter populations with no physical barriers. Four possible first generation migrants were detected, with two of those migrants between ID and MT. Least-cost path analyses revealed that genetic distances between pairs of otter samples were more correlated with Euclidean distances than stream distances. I characterized vegetation at 310 random locations and 35 otter latrine sites along the UCFR. Random sites were characterized by low overstory and understory cover, and tended to have ground cover dominated by grass, shrub, and dirt/sand. Latrine sites were located in areas with significantly higher bank heights and medium levels of understory cover. Latrine sites also tended to be located near beaver activity more than random sites. In addition to the habitat assessment, I non-invasively collected hair and scat samples for use in genetic population estimates. I was able to genotype 11 scat and hair samples, for a total of 8 individuals. I was unable to calculate a population estimate because of low sample size. It is not recommended to use non-invasive sampling measures to estimate population until other genetic markers (e.g. SNPS) are developed for otters that can utilize low-quality DNA from otter scat. Otters can be found in multiple aquatic habitat types, and my habitat analyses reveal little to guide restoration in the river. Therefore, otters may not be an appropriate tool to guide restoration efforts on the UCFR. However, continuing to monitor otter latrine sites can be an effective way to track ecological responses to restoration.