Whirling Disease and Native Cutthroat Trout of the Yellowstone Lake Ecosystem

Koel, Todd; Mahony, Daniel; Kinnan, Kendra; Rasmussen, Charlotte; Hudson, Crystal; Murcia, Silvia; Kerans, Billie

Whirling disease, caused by the exotic parasite Myxobolus cerebralis, is responsible for severe declines in wild trout populations in the Intermountain West (Bartholomew and Reno 2002). In Colorado (Nehring and Walker 1996) and other states where infection has been severe, whirling disease has had a significant negative economic impact on the recreational fishing industry. In Montana, the number of wild rainbow trout (Oncorhynchus mykiss) in the Madison River declined 70–90% after the introduction of M. cerebralis (Vincent 1996). The parasite has spread to many other drainages in the western part of the state, resulting in population-level effects (E. R. Vincent, personal communication). The parasite was first documented in Wyoming waters in 1988 and has spread to at least seven river drainages there. In Yellowstone National Park (YNP), examination of wild trout for whirling disease began in earnest in 1995 through the U.S. Fish and Wildlife Service’s Wild Fish Health Survey. Myxobolus cerebralis was first detected in the park in 1998 in native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvierii)collected from Yellowstone Lake. The Yellowstone cutthroat trout is considered a keystone species in the Greater Yellowstone Ecosystem. It provides a significant source of protein for the grizzly bear (Ursus arctos) during the spring and midsummer (Reinhart and Mattson 1990; Gunther 1995). The diet of the threatened bald eagle (Haliaeetus leucocephalus) in the park consists of about 25% fish (Swenson et al. 1986). Many other avian and terrestrial species in the Yellowstone Lake ecosystem use Yellowstone cutthroat trout as an energy source (Schullery and Varley 1995).

Whirling Disease and Native Cutthroat Trout of the Yellowstone Lake Ecosystem

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