Much has been learned about the spread of the parasite that causes whirling disease into Colorado’s lakes, reservoirs and larger rivers since the early 1990s. However, early in the 21st century, very little was known about the degree of spread of M. cerebralis into high elevation streams that are important habitats for Colorado’s three sub-species of native cutthroat trout.
To address this issue, a 5-year research project was initiated in 2003. During 2003 and 2004, salmonids from approximately 88 different streams and 116 sites were tested for evidence of infection. In 2003, trout from approximately 32 percent of the collection sites tested positive for M. cerebralis.
During 2004, trout from approximately 21 percent of the collection sites tested positive for the parasite. Most of the salmonids that tested positive were brook, brown or rainbow trout collected from sites downstream of but connected to streams and reaches considered cutthroat trout recovery zones.
As of July 2005, empirical evidence indicates that only one Rio Grande cutthroat trout population and one Colorado River cutthroat trout population may be at risk of extirpation due to infection by M. cerebralis.
This investigation is scheduled to continue through the summer and fall of 2007.