Whirling Disease Confirmed On The San Juan River in New Mexico

On January 12, 2000 the New Mexico Department of Game and Fish confirmed what many have suspected for years: Whirling Disease is present in the San Juan River tailwater. In late December, rainbow trout were collected from various locations on the river beginning in the Catch and Release water directly below Navajo Dam and ending several miles down river at the Rainbow Lodge below the Aztec Bridge. Rainbow trout in each of the areas sampled tested positive for Whirling Disease.

While the discovery was unpleasant, it was not unexpected. Whirling Disease has been spreading South at an alarming rate for the past several years. In fact, two major tributaries to the San Juan river, the Animas River and Los Pinos River, were also known to be infected with Whirling Disease prior to discovery on the San Juan. Further, the Parkview state hatchery along with 2 other New Mexico hatcheries have tested positive for Whirling Disease. The San Juan is stocked periodically with rainbow trout from the Parkview hatchery.

Rainbow and cutthroat trout infected with Whirling Disease at an early age often develop deformed spines and/or blackened tails. Spinal deformation is caused by the disease attacking the cartilage in a young trout as it is developing. The result is a fish that is deformed and often swims in circles or "whirls". These deformed fish have a hard time feeding and are much more susceptible to predators. Consequently, the mortality rate in Whirling Disease infected fish is very high.

Whirling Disease is most damaging to rainbow and cutthroat trout during the first several months of life. After that, trout are more likely to survive the disease but will remain carriers of the spores that spread the disease. Whirling Disease can be devastating to rivers that rely on natural reproduction. This was the case on the famous Madison River in Montana where 90% of the rainbow trout population died out over the period of a few years as a result of Whirling Disease. However, natural reproduction on the San Juan is very limited. The magnificent San Juan fishery is maintained by periodic stocking of trout 3" fingerlings. These 3" fingerlings are old enough to survive the disease. According to the New Mexico Department of Game and fish, there will be little impact on the quality of the San Juan fishery because of Whirling Disease.

The biggest impact of Whirling Disease in New Mexico will be to any lakes, streams, or rivers where natural reproduction is counted on to support the fishery. Among the highest concerns is the impact to recent efforts to reintroduce the Rio Grande Cutthroat trout in New Mexico. A native trout of New Mexico, the Rio Grande Cutthroat was once on the endangered species list. Studies have shown the mortality rate for Whirling Disease infected Rio Grande Cutthroat to be among the highest of all species of trout.

Brown trout are resistant to Whirling Disease so the impact on the brown trout population is negligible. However, brown trout are able to carry and spread the disease. Humans cannot contract whirling disease so fish that are carriers of the disease are safe to eat. However, there are some precautions that we as fisherman can take to help prevent the spread of this disease. Please visit the links below for more details on Whirling Disease and how fisherman can help: 

NM Game & Fish Information on Whirling Disease

National Partnership on the Management of Wild and Native Cold Water Fisheries: Whirling Disease Initiative 

This article was compiled by Mike Mora using details presented at a recent NM Trout meeting. Special thanks to: