Date of Award
Master of Science
After steep declines due to overharvest and habitat loss, North American river otter (Lontra canadensis) populations have been increasing in most of the U.S. Radiotelemetry is an essential tool for understanding river otter habitat use, survival rates, and sources of mortality, which is important for successfully managing these growing populations. Surgically implanting radiotransmitters is standard for river otters, but strict requirements for the handling and transport of DEA-scheduled drugs for sedation, and the lack of accessible surgery suites, can limit researchers. My objectives were to: (1) develop a non-scheduled drug combination to sedate river otters and surgically implant intra-abdominal transmitters in a field setting, (2) determine survival rates and causes of mortality for river otters, and (3) quantify fourth order habitat selection at river otter daytime resting sites. During 2018-2020, I surgically implanted 24 river otters with transmitters in southern Illinois and monitored them via radiotelemetry to determine survival and causes of mortality. The effectiveness of the drug combination of Dexmedetomidine and Nalbuphine for chemically immobilizing river otters was tested to determine the appropriate dosage. I used homing to track river otters to 132 daytime resting sites where I described the structure used, closest water type, and distance to water; for 51 of these resting sites I also measured understory cover, overstory cover, distance to water, and presence of river otter and beaver sign. These 51 sites were paired with 1-4 random riparian locations, where I measured the same habitat variables. I then modeled habitat selection of daytime resting sites using conditional logistic regression. A combination of 0.06 mg dexmedetomidine/kg and 1.2 mg nalbuphine/kg injected intramuscularly followed by a 10-15 min induction period was sufficient to chemically immobilize river otters enough for further sedation with 1-4% isoflurane gas. Surgery in the field was successful, with only 2 sedation-related mortalities recorded. Estimated river otter survival was 0.84 ± 0.09 with no difference between males (0.83 ± 0.11) and females (0.86 ± 0.13) ( = 0, P = 0.900) and or between protected areas (0.80 ± 0.10) and harvested areas (0.83 ± 0.15) ( = 0.3, P = 0.600). Four river otters died (2 harvest, 2 unknown causes) during my study. Daytime rest sites were located in non-enclosed vegetation (n = 54) as well as enclosed sites, such as bank dens (n = 39), beaver lodges (n = 33), and wood piles (n = 6). River otters selected for greater understory cover at all sites, though enclosed sites had less understory cover than non-enclosed sites (all P ≤ 0.001). The top habitat selection model included the parameters understory cover and the beaver sign but did not include canopy cover. My study offers a novel way to sedate river otters without DEA-scheduled drugs, updates information about river otter survival, and provides new information on fourth order habitat selection at daytime resting sites.
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