Whirling Disease And Montana's Prized Spring Creeks

Ryen Anderson, Montana State University Graduate Student

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In Montana, wild trout are a treasure, a commodity, and a priority. After the discovery of whirling disease in the Madison River in 1994, all of Montana’s wild trout appeared to be threatened. Since then, however, much has been discovered about the distribution of whirling disease, how and why it affects trout, and environmental conditions that may trigger the disease.

Interestingly, the accumulation of this knowledge ironically prompted concerns that another Montana treasure, one that provides ideal habitat for wild trout, also could provide the ultimate habitat for whirling disease to thrive.

The suspect happened to be Montana’s prized spring creeks.

In Montana there are more than 100 spring creeks, and most of them are located in the southwest corner of the state. All are unique in terms of their size—they range from 30 feet long to 30 miles long--but they share a similar characteristic: groundwater bubbles up at the source and within the entire spring creek system. This upwelling of groundwater keeps spring creeks at a uniform temperature, maintains their steady flows and contributes to their nutrient-rich waters. Such a productive and perpetual environment is important to wild trout that depend on abundant aquatic vegetation, prolific hatches and year round spawning opportunities.

Some feared these same trout friendly characteristics could promote whirling disease by providing similarly ideal environmental conditions to support the whirling disease parasite’s life cycle.

With the support of the Whirling Disease Foundation and Montana Fish, Wildlife & Parks, and six very committed landowner families, researchers took an in depth look at the pattern of whirling disease in spring creeks. The results we found were not only unexpected, but actually produced a positive spin on the whirling disease puzzle.

Our study took place on nine different spring creeks in eight different drainages. Some of the spring creeks we studied were located on public land, but most were on private land and nearly all offer world-famous wild trout fishing opportunities.

We used "sentinel cages" containing young-of-the-year rainbow trout to test for the prevalence of whirling disease in all nine spring creeks for 21 continuous months. We also set out to determine when the young wild trout eggs incubating within the gravels of these streams would be hatching, and how those newly hatched fish withstood possible high levels of whirling disease infections.

For those following the effects of whirling disease on wild trout in rivers and mountain-fed tributaries, the success of the parasite stems from its ability to peak at the same time young fish are most vulnerable to infection just days after hatching.

We expected similar findings in spring creeks but instead found a different and unique pattern.

We found that spring-spawning trout, such as rainbow and cutthroat, emerge when the whirling disease parasite is at its lowest levels in spring creeks. In addition, we found that the parasite’s peak abundance occurred in late fall and continued through the winter months.

While we’re not yet sure why the whirling disease parasite peaks in fall and winter opposed to spring and summer, it’s welcome good news. It appears that Montana’s unwavering spring creek systems not only provide idyllic trout habitat, but also may offer relief from a disease plaguing a Montana treasure.