River Otter (\u3ci\u3eLontra canadensis\u3c/i\u3e) Distribution and Habitat Suitability in Nebraska

River otters (Lontra Canadensis) were extirpated in Nebraska by the early 1900’s, but in 1986, the Nebraska Game and Parks Commission (NGPC) began reintroduction efforts. Following reintroductions, the otter was listed as a tier-1 at-risk species in Nebraska. With increasing otter populations, NGPC is evaluating a de-listing plan. In order to inform de-listing efforts, I surveyed Nebraska’s rivers documenting otter sign and used modeling techniques to estimate otter distribution and habitat suitability. Otter sign surveys were conducted on the navigable rivers of Nebraska. Occupancy modeling techniques were used to examine patterns in otter detections. The best model incorporated distance to the nearest otter release site, beaver occupancy, and flow rate. The Niobrara, Elkhorn, and Platte rivers and the southern Loup River system were the areas most supported as areas likely to have otters. Data collected by NGPC were used to examine patterns among historical otter records. Maximum entropy (maxent) modeling identified the Platte, northern Elkhorn, southern Loup River system, and sections of the Niobrara as areas most likely occupied. Maxent habitat suitability modeling identified the Platte, eastern Niobrara, southern Elkhorn, and southern Loup River system as areas with preferred otter habitat. The distance to a release site and flow rate had the strongest impact on model fit. Results were consistent with estimates prepared by NGPC, and spatial correspondence between occupancy estimation methods was high. Future efforts to translocate or reintroduce more otters should focus on areas with high habitat suitability and areas with high occupancy estimates but few occurrence records. Advisor: Craig Alle

River Otter Distribution in Nebraska

The river otter (Lontra canadensis) was extirpated from Nebraska, USA, in the early 1900s and reintroduced starting in 1986. Information is needed regarding the distribution of river otters in Nebraska before decisions can be made regarding its conservation status. Understanding distribution of a species is critically important for effective management. We investigated river otter distribution in Nebraska with occupancy modeling and maximum entropy (Maxent) modeling using 190 otter sign observations on Nebraska’s navigable rivers and 380 historical otter records from November 1977 to April 2014. Both methods identified the Platte River, Elkhorn River, central and eastern Niobrara River, and southern Loup River system as core areas within the distribution of otters in Nebraska. The Maxent model provided more liberal estimates of site occupancy and identified some smaller rivers as being within the distribution of otters in Nebraska, which were not identified using occupancy modeling. We recommend that multiple data sets and analysis methods be used to estimate species distribution because this allows for the broadest geographical coverage and decreases the likelihood of overlooking areas with fewer animal records. If further reintroduction efforts or translocation efforts are to take place in the future, we recommend focusing on areas with high modeled occupancy but few historical and survey records

River Otter Distribution in Nebraska

The river otter (Lontra canadensis) was extirpated from Nebraska, USA, in the early 1900s and reintroduced starting in 1986. Information is needed regarding the distribution of river otters in Nebraska before decisions can be made regarding its conservation status. Understanding distribution of a species is critically important for effective management. We investigated river otter distribution in Nebraska with occupancy modeling and maximum entropy (Maxent) modeling using 190 otter sign observations on Nebraska’s navigable rivers and 380 historical otter records from November 1977 to April 2014. Both methods identified the Platte River, Elkhorn River, central and eastern Niobrara River, and southern Loup River system as core areas within the distribution of otters in Nebraska. The Maxent model provided more liberal estimates of site occupancy and identified some smaller rivers as being within the distribution of otters in Nebraska, which were not identified using occupancy modeling. We recommend that multiple data sets and analysis methods be used to estimate species distribution because this allows for the broadest geographical coverage and decreases the likelihood of overlooking areas with fewer animal records. If further reintroduction efforts or translocation efforts are to take place in the future, we recommend focusing on areas with high modeled occupancy but few historical and survey records