Detailed project information for Study Plan Number 03035

Branch :	Southern Appalachian Field Branch
Study Plan Number :	03035
Study Title :	Effects of River Otter Reintroduction on Muskrat and Mussel Populations at Mammoth Cave National Park
Starting Date :	05/01/2002
Completion Date :	12/31/2008
Principal Investigator(s) :	Clark, Joe
Primary PI :	Clark, Joe
Telephone Number :	(865) 974-4790
Email Address :	jclark1@usgs.gov
SIS Number :
Primary Program Element :
Second Program Element :
Status :	Active
Abstract :	BACKGROUND The Green River drainage has long been recognized for its mussel diversity. At least 72 species of mussels historically occurred within the Green River drainage in and around Mammoth Cave National Park (MACA), Kentucky, but this number has been reduced to approximately 53 species today (Cicerello 1999). Although Hardison and Layzer (2001) argued that mussel recruitment was poor on that section of the Green River because of altered flow regimes, more recent surveys have revealed significant recruitment (Layzer et al. 2001). However, whether these highly variable recruitment rates are adequate for population sustainability still is not known. Muskrats (Ondatra zibethicus) have been shown to be significant predators of certain species and size classes of mussels and clams (Neves and Odom 1989, Hanson et al. 1989, Jokela and Mutikainen 1995, Tyrrell and Hornbach 1998). Researchers that have studied mussels in the Green River have reported finding large feeding sites or ‘middens’ of mussel shell fragments cached by muskrats (J. Layzer, USGS, personal communication). These middens are among the best places to look for evidence of the 4 endangered species of mussels known to inhabit the area. Working in the nearby North Fork Holston River in Virginia and Tennessee, Neves and Odom (1989) reported that muskrat predation on mussels is probably retarding mussel recovery, and likely is contributing to further declines of endangered mussel populations throughout the Tennessee River drainage. Although the demographic effects of muskrat predation on mussel beds in the Green River are unknown, large amounts of shell fragments have been found and, given the uncertainty about recruitment and the declining diversity in the Green River, such predation could be important. River otters (Lutra canadensis) have been successfully reintroduced to a number of states including Missouri, Pennsylvania, and Indiana (Erickson et al. 1984, Serfass et al. 1993, Johnson and Berkley 1999). Such a reintroduction is proposed for MACA. Anecdotal observations elsewhere suggest that the reintroduction of river otters dramatically reduces muskrat populations, which, in turn, may reduce the number of mussels consumed by the muskrats. However, whether such an interspecific relationship between otters and muskrats exists and its mechanism (e.g., predation, displacement, competitive exclusion) has not been determined. Although otters are not known to predate significantly upon muskrats (Wilson 1952), studies based on scat analyses could be biased toward those food items that are more easily identified (e.g., scales, exoskeletons). Therefore, it is important to determine the effects that the reintroduction of river otters will have on muskrats and, in turn, the mussels that inhabit the Green River. OBJECTIVES To develop monitoring techniques for river otters and muskrats and to use them to evaluate the effects that otter reintroduction has on muskrat and mussel populations over time. HYPOTHESIS TO BE TESTED River otter reintroduction will have a negative effect on muskrat populations and, in the longer term, will result in a decrease in muskrat predation on mussels.
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