Whirling Disease

Tests Show No Evidence That Whirling Disease Is Spreading In Maryland

Department of Natural Resources officials are continuing to monitor sites throughout the state for evidence of whirling disease, a parasitic infection that attacks trout. Results from recent tests found no evidence the disease is spreading.

Anglers are urged to continue the successful precautions to prevent spread of the disease such as cleaning boats and equipment thoroughly after fishing and not transporting live fish, insects, bait, or plant from one body of water to another.

Maryland Whirling Disease Test Results For 2007

Although whirling disease presence in Maryland was documented as early as 1995, it became a larger issue in early 2007 with the discovery of infected fish at the Bear Creek hatchery in the Youghiogheny River basin. This was the first documentation in Maryland outside of the North Branch Potomac River. While Maryland Department of Natural Resources had not found direct evidence of negative impacts to trout populations in the North Branch Potomac River associated with whirling disease, the occurrence outside of that basin demonstrated the potential for spread of this organism. Nationally, impacts of Myxobolus cerebralis have ranged from undetectable to devastating with the severity of each case difficult to predict. As a result Maryland Department of Natural Resources decided to take aggressive action to stem the spread to new waters of the state and to the extent possible to limit the ability of the organism to perpetuate itself within its current range.

Read the synopsis in full.

Read the Bear Creek Hatchery Plan for 2008.

Maryland Department of Natural Resources is Asking Anglers to Help Prevent the Spread of Whirling Disease

The department is asking anglers to take a number of precautions when fishing their favorite trout streams to help prevent the spread of whirling disease. Recent events at several State Hatchery facilities have illustrated that the parasite is still present in some waters and can be unknowingly spread to new areas.

Whirling Disease Letter Sized  Poster, Click for Printable VersionThe organism is known to exist in the North Branch of the Potomac River. So anglers should pay particular attention when moving from that stream to other areas. However the full distribution of whirling disease will not be known until the department completes its wild fish testing statewide. Anglers should follow the simple steps described below when fishing any waters that hold trout.

To reduce the likelihood of spreading the spores of the organism we are asking anglers:

  1. Do not to move fish from one stream to another
  2. Do not discard trout carcasses in streams, or on stream banks
  3. Please be sure to clean mud from boots and equipment before moving from one stream to another
  4. Drain water from boats and live wells and rinse mud from trailers and gear before leaving the fishing site. It is preferable to dry your boats bilge when possible.

The whirling disease parasite was introduced into the eastern US from Europe in the late 1950s and is currently known to exist in 24 states. It was first discovered in Maryland in 1995 in the North Branch Potomac River. Although the parasite is harmless to humans, it can enter the skeletal tissue of trout, producing severe damage to infected fish and causing them exhibit the erratic "whirling" swimming behavior for which the disease is named. The parasite can be fatal to trout and is particularly harmful to rainbow trout.

Trout production at state hatcheries was reduced by approximately 20% this year due to the discovery of the parasite known to cause whirling disease at two facilities in Garrett County. In order to reduce the possibility of its spread, all infected fish were destroyed. As a result, stocking rates will be reduced in all waters across the state for the 2007 season.

This brochure put out by Montana State University is full of information concerning the disease. Montana State University has also put out a concise Fact Sheet regarding whirling disease, please view and print the fact sheet, if possible please carry with you while fishing.​​

Advice To Anglers Regarding Felt Soles on Wading Boots And Preventing The Spread of Disease And Invasive Species

Research responding to concerns regarding the spread of diseases and invasive species has shown that felts on the bottom of wading shoes and boots are major culprits in the transfer of such problems. Research by Gates (2007) concluded that felt material retained 100% of whirling disease spores in material testing; and in 2006, participants of a special American Fisheries Society meeting on the invasive algae Didymosphenia agreed that "felt-soled waders are one of the highest risk vectors in the spread of 'didymo' on a global scale."

In light of these findings, Maryland Department of Natural Resources (DNR) strongly urges anglers to eliminate the use of felt-soled boots and waders. For some areas, traditional rubber boots, or those with studded bottoms may provide as much traction as felts. For challenging areas, manufacturers are now offering 'sticky-soled' alternatives, with traction treads like those found on all weather tires. These sticky-soled rubber boots provide good traction, are non-absorptive and easy to clean. Guides and anglers have reported that the studded versions of these boots work as well as felts. They may take a little getting used to, but they don't absorb water, are more lightweight and may, ultimately, make walking easier. These new boot materials effectively reduce the chance of spreading disease and invasive organisms. By removing dirt and debris from these new types of footwear with a scrub brush, you can effectively prevent transmission of these agents from one area to another. Please consider helping the Maryland Department of Natural Resources protect the resources of the state by trying out alternatives to felt bottom waders.

Literature Cited

Gates, K.K. 2007. Myxospore Detection in Soil and Angler Movement in Southwest Montana: Implications for Whirling Disease Transport. Montana State University Master's Thesis

Western Division American Fisheries Society. 2006. Special Session on Didymosphenia geminata