Caring for Cutthroat

Student's research helps managers protect struggling trout species

A westslope cutthroat trout (Photo by Aubree Benson) 

Her brown eyes glued to the microscope , Kellie Carim deftly pokes at the half-millimeter-wide bone under the lens with tweezers. It comes into view, a foot wide, on the computer monitor to her right. With practiced smoothness, she twists the knobs, adjusts the light, snaps a photo, files it on the computer and is on to the next sample.

UM graduate student Kellie Carim studies bones that reveal the ages and life histories of trout.It’s her way of fighting for a native species.

Carim is a doctoral candidate working in UM researcher Lisa Eby’s fish lab. The tiny bones she so vigilantly documents are called otoliths, and they have each been removed from the inner ear of a wild westslope cutthroat trout. Otoliths can be read like the rings of trees, giving insight to the fish’s age and life story.

This is Carim’s contribution to this struggling species — measuring little bones cut from inside their skulls.

"There is an intrinsic value in native species," Carim says. "Every native species has the right to live and persist within its native range."

Westslope cutthroat trout, as their name implies, are primarily found on the western slope of the northern Rocky Mountains. The fish are painted with a palette ranging from golden yellow to pumpkin orange, with spots heavily concentrated toward the tail and along the evergreen back, with hints of pink here and there. All feature the signature "cutthroat" — a prominent red slash under each jawbone. Because of land use and hybridization with non-native rainbow trout, populations have diminished to only 5 percent of their native range.

Carim herself is a non-native of sorts. Growing up in St. Paul, Minn., she always loved the outdoors, but not necessarily trout.

"I was never really interested in fish until I came here," Carim says. "It was more that trout in Montana are really good species for asking the types of research questions that I like to ask."

But after three years at UM, these fish stole her heart.

"For a long time I kind of thought maybe I would not continue in aquatic stuff," Carim says. "But now with how much fun this has all been, I am going to continue down this road."

That excites the local fisheries biology community, as her research sheds an important light on facets of westslope conservation practices.

The westslope cutthroat is a candidate for listing under the Endangered Species Act. Petitions have been filed three times, most recently in 2003. Though well-adapted to their pristine natural environs, westslope populations do not deal well with human encroachment. Because of their strict reliance on cold, clean water and interconnected habitats, they are considered an indicator species — the proverbial canary in the coal mine. When conditions for the fish sour, westslope populations nosedive. Pollution, mining, logging, erosion, ranching and grazing all have taken a heavy toll.

Before 1889, westslope cutthroat overlapped slightly on the western edge of their range with Columbia River redband trout, a native subspecies of rainbow trout. In the years to come, hatchery-created and propagated rainbow trout were introduced into nearly every suitable environment within the westslope’s native range.

In the late 1800s, rainbows were considered the perfect fish. Hardy, fast-growing, hard-fighting and good-tasting, some managers imagined them as the ideal replacement for the more fragile native trout species that were probably headed for extinction anyway. This attitude created many problems, but perhaps nowhere more than the west slope of the Rockies.

Introductions of brown trout, lake trout, brook trout and kokanee salmon all took some toll, but beyond the competition for food and space, rainbow trout present an even more subversive problem: hybridization.

’Bows and ’cutts are so genetically similar that they can interbreed and produce fertile offspring — a rare feat, biologically speaking. And they do so quite extensively. Hybridization in this situation is the norm rather than the exception.

Robb Leary, a conservation geneticist for Montana Fish, Wildlife and Parks, estimates that pure strains of westslope account for less than 10 percent of the overall population. The rest are, to varying degrees, hybrid individuals with rainbow genes.

"Essentially all the larger bodies of water that would have supported large populations are all gone," Leary says, meaning they have been inundated with non-native species. "Most of your non-hybridized westslope are restricted to small tributary streams in places with natural or anthropogenic barriers."

Behind these barriers, Montana fisheries managers put all of their hope.

The common practice for isolating pure strains of cutthroat, Leary says, is to locate a stream with a natural obstacle such as a waterfall or simply build an impassible dam or culvert. Managers carefully measure and apply a chemical called rotenone to the selected stream, which exterminates all fish in that section. Then they bring in pure-strain westslope.

This practice has succeeded not only with westslope but with the many imperiled cutthroat subspecies across the West. However, the solution is not without problems.

"Isolation is a pretty drastic conservation strategy," says Fish, Wildlife and Parks Fisheries Biologist Matt Boyer. "You are saying that if you don’t take that measure, you are going to lose the population and you are willing to take on the risks of isolation."

Genetic diversity is a surrogate for long-term health, the ability of a population to adapt to changing environmental conditions. Without the possibility for influx of genetic material from neighboring populations, the fish can suffer the perils of inbreeding depression. Carim wants to know how the practice may affect the survival of this species.

"My research uses conservation genetics and population biology to weigh trade-offs in management," Carim says. "Specifically, I look at factors contributing to inbreeding and lack of genetic diversity in small populations of trout."

To do this, Carim extracts DNA from westslope fins using chemical compounds and a centrifuge. Then she sequences the genes to see whether each base pair codes for either one or two traits. This is important because if too many pairs in too many individuals are homozygous — both coding for the same trait — genetic diversity is low.

"Some of my populations are nearly all homozygous," Carim says. "At that point they have lost a lot of genetic diversity compared to other populations. That means there’s a very high potential for inbreeding depression."

After examining otoliths, she can infer information such as growth rate and adult survival in a population. These vital rates, along with information on levels of genetic diversity, allow her to gain a better understanding of the overall viability of the population.

By correlating stream length — a measure of the amount of habitat available to an isolated population — to the level of genetic variability, she can make recommendations to managers such as Leary and Boyer for current and future projects.

"She gave us indication that, to some extent in some of these small isolated populations, you actually might want to consider going in and introducing fish from other sources to break down inbreeding," Leary says. "That is probably the most important thing she is looking at. They get so inbred that it starts to adversely affect their viability."

Carim examines the growth rings on a cutthroat otolith bone, which reveals the age and even size of the fish.Efforts like these may bring westslope cutthroat back from the brink of extinction, but no one thinks the fight is over — or ever will be.

"Part of me thinks you have to maintain optimism in the field of conservation biology to stay sane," Carim says. "But honestly, when you look at the bigger picture and what’s predicted to change with climate change, cutthroat trout don’t really stand that much of a chance."

With the predictions for the next 100 years, Carim expects that westslope will disappear from even more of their historic range, which she describes as "a fraction of a fraction."

Like others in her field, she puts on a smile and goes about her work anyway. Fly-fishermen bring major revenue to the state of Montana, so research that can be applied to preserving their quarry is usually well-supported.

"Cutthroat have a charismatic value to the public in Montana," Carim says. "Forty years ago, many people could have cared less what they were catching, whether it was a brown trout or a rainbow trout, but to catch a cutthroat trout now has a much greater value than it used to."     

 By Sam Lungren

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