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Dr. Clint Muhlfeld holding a rainbow trout X westslope cutthroat trout hybrid.

Q: Clint, first a general question. What do we lose when we lose native fish?

A: First let me say that native fisheries in North America have declined over the past century and many populations are in peril. Among the threats to them are habitat fragmentation and degradation, introductions of nonnative invasive species, and overfishing. Fortunately, in Montana, we have some intact ecosystems where native fish, such as the bull trout, the westslope cutthroat throat and the mountain whitefish, have prevailed for thousands of years. Bull trout and westslope cutthroat, for example, are broadly distributed and they are still abundant in some places.

In many cases, fisheries and resource managers are working to conserve native populations for the future. When we lose such native species, we lose the native biodiversity on the landscape. These and other native species are in a complex web of life where they are a critical link maintaining ecological processes and nutrient flow from aquatic to terrestrial systems. If you remove a link you put into motion the potential to unravel the structure, function and processes of aquatic ecosystems that have evolved over thousands and millions of years.

Westslope Cutthroat Trout.

The second thing we lose is part of the evolutionary history of native biota. Bull throat and cutthroat have been around for 14,000 years, surviving floods, fire and glaciations. When we lose natives, it’s often because of human activities, and basically that means an impaired watershed and links between aquatic and terrestrial communities. In the case of cutthroat trout, for example, they can be a major food source for eagles and bears. Westslope cutthroat are in less than 10% of the area they were in at the time of Lewis and Clark.

The third loss relates to a loss of our cultural heritage, our natural legacy. Many people value and enjoy native wildlife. One of the goals of management nowadays is to preserve species in the wild for future generations to enjoy and appreciate. Intact ecosystems have values far beyond monetary ones.

Q: Much of your recent research involves fish that are dear to many of us: the bull trout and the westslope cutthroat trout. How are the Glacier-area bull trout doing?

A: Not well. Many populations west of the Continental Divide are currently at high risk of extirpation. Although the Northern Rockies are recognized as a stronghold for them, populations have declined over the past 100 years primarily due to invasive species and habitat loss. Consequently, bull trout are listed as threatened under the Endangered Species Act. In the last 30 to 40 years, non-native lake trout, which likely came from Flathead Lake, have displaced bull trout as the dominant predator in many mountain lakes and streams in Glacier. Glacier National Park provided some of the largest populations of bull trout in the Columbia River system, representing about one third of the total natural (undammed) habitat left. There are 17 lakes west of the Continental Divide that contain native bull trout populations. Eleven of those now have lake trout. And those in which the bull trout are declining, some are on the brink of extinction. Of the remaining six lakes, one is at high risk and five are secure because they are above natural waterfalls, which prevent invasion of lake trout from downstream source populations.

The Upper Quartz Lake area is a lake system near Polebridge that contains a native fish assemblage, consisting of bull trout, westslope cutthroat and mountain whitefish. Recently, we found lake trout moving up this system. However, the native populations haven’t declined yet because lake trout have only recently invaded. We have begun a four year project to assess the feasibility of suppressing or eradicating the nonnative lake trout population, and we are working with the National Park Service to install a barrier below Middle Quartz Lake to prevent further invasion. The general approach is to use telemetry to track the lake trout to spawning areas and then remove them through netting. We may also electro-shock the lake trout eggs or use a pheromonal attractant to lure females and capture them that way.

We feel we have a good chance for success because we’ll have a barrier to new migration. And, Upper Quartz Lake is small so it’s easier to find the lake trout, which aren’t fully established yet and haven’t seeded all the habitats. Also, there are no Mysis (opossum) shrimp there. Lake trout love to eat them, but bull trout cannot access them and they directly compete for zooplankton, which are a key food source for bull trout juveniles. This work may help us learn how to help recover other greatly compromised populations.

A rainbow trout X westslope cutthroat trout hybrid with a high amount of nonnative rainbow introgression.

Q: We read that hybridization of rainbow and cutthroat trout is a problem – why is that?

A: Perhaps the greatest threat to native westslope cutthroat trout is hybridization with introduced rainbow trout. Although the upper Flathead River system is considered a regional stronghold, hybridization has recently spread upstream in the system, threatening the genetic integrity of pure populations. Genetically pure populations currently reside in the headwaters of the drainage, including the Bob Marshall and Scapegoat wildernesses, Glacier National Park, and the North Fork Flathead River in British Columbia, Canada. Where these populations are above barriers, they are mostly genetically pure. To thrive, they require cold water and connected streams, just like bull trout do. However, over the last 10 to 20 years, hybridization has increased in the upper system from downstream source populations of rainbow trout, most of which originally came from a private fish hatchery. These hybrids do better in warmer streams that have been degraded by land use.

We know that hybridization spreads upstream from sources in the valley bottoms and hybrids have much greater straying rates than rainbows. This means that instead of going back to mate in the stream where they were born, they tend to invade new streams. What makes matters worse is that the spread is being promoted by a few hybrid males that are reproductively fit. These males are the exception to the general pattern of a rapid decline in fitness with increasing levels of hybridization. However, despite heavy fitness penalties hybridization may also still spread because hybrids produce more hybrids and compound the problem. Conservation of native cutthroat trout requires a two-pronged approach. First, we work to maintain and improve suitable habitats throughout the system, and second, we need to control and eliminate hybrid sources in downstream areas. If downstream hybrid sources persist, the final outcome for the westslope cutthroat does not look good- we will lose the genetic combinations and resultant adaptations that have enabled the cutthroat to survive for thousands of years.

Q: What are your summer research plans?

A: First let me say that perhaps the greatest threat to aquatic ecosystems in southeast British Columbia and northwest Montana is the threat of open pit coal mining and coal-bed methane drilling in Canada at the headwaters of the Flathead and Elk rivers. This summer I am working on an international team of scientists to assess impact of gas and development in these areas on water quality, aquatic habitat, and fish and wildlife populations. To date, every cutthroat population that we have genetically tested in the British Columbia portion of the system is genetically pure; and the highest density of bull trout redds (spawning nests) are immediately downstream of the proposed open-pit coal mine and coal-bed methane wells in the headwaters. These bull trout are migrating over 200 kilometers to complete their life cycle, indicating these areas are critical for the persistence of transboundary populations in Canada and the United States. With a permit from the British Columbia Ministry of Environment and support from Glacier Park, the University of Montana, Montana state agencies and the Ktunaxa First Nation Tribe, we are doing what we can to garner the science necessary to prove that area’s critical importance to these species. The genetic threats to the bull trout and cutthroat have come from the bottom up. This is a situation where the entire system could unravel from the top down if these proposed activities in the headwaters are allowed.

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