Is protecting isolated populations enough? On the role of Yellowstone National Park in the recovery of river otters in the Rocky Mountains

Ben-David, Merav
By the early 1900’s, river otters ( Lontra canadensis ) were extirpated from most freshwater systems in western North America due to overharvest and pollution. Remnant populations survived in the greater Yellowstone region, largely due to the establishment of Yellowstone National Park in 1872. Despite improvement to water quality following the Clean Water Act of 1972 and limits on harvest since the mid-1950s, river otter populations showed limited recovery in the Rocky Mountain region. Reintroduction efforts in several states (Colorado, Utah, Nebraska, and South Dakota), led to the successful establishment of river otter populations. Nonetheless, otter recovery in many Wyoming watersheds has not yet occurred.  In this project we conducted a formal survey of otters across the state using camera traps and non-invasive genetic sampling. Our preliminary results show that the Yellowstone population was the source of at least two independent expansion events; one into the Shoshone River and another to the Snake. From there otters colonized the Upper Wind River. We also found that river otters in the Green River are genetically distinct, and that population may be an expansion of the reintroduced animals in Utah. Similarly, otters from Colorado seem to expand into the headwaters of the Platte River. The ability of overland dispersal by otters contrast with their limited spread into the Big Horn and lower Platte Rivers. In future work we intend to model the dynamics of otter expansion and the role of barriers (e.g., dams and large reservoirs) and water flow in an effort to better understand the current distribution of otters in Wyoming.
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river otters,AMK Ranch,Yellowstone National Park,Rocky Mountains
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