Can hatcheries help conserve the westslope cutthroat?

TrendspottersWhen FWP biologists count wildlife, they’re learning which direction populations are moving. By John Fraley

This story is featured in Montana Outdoors
March–April 2002

Yes, say fisheries biologists, but the big question is where and how

Westslope cutthroat trout have lived in post-glacial western Montana for thousands of years. During that entire time, the species has been able to survive catastrophic fires, massive floods, and severe droughts. But in the less than 200 years since Meriwether Lewis first described the subspecies, the cutthroat’s range has dwindled. The population decline is due to stream siltation, dams, overfishing, and competition from—and hybridization with—introduced nonnative fish such as brook trout.

Habitat protection and restoration are important components of a westslope cutthroat recovery program. But is there a role for state hatcheries in the restoration and conservation of westslope cutthroat? Historically, Montana Fish, Wildlife & Parks (FWP) trout hatcheries were primarily used to produce large numbers of fish that were then stocked wherever possible. But in recent years, trout hatcheries have increasingly become the source of fish used in restoration work. FWP has committed itself to conserving native westslope cutthroat, and biologists are now discussing when and where to use hatcheries and hatchery-reared cutthroat as part of that effort.

The first brood fish
Despite its name, the westslope cutthroat is native to both sides of the Continental Divide. A cutthroat subspecies also found in Idaho, Washington, Oregon, and western Canada, the westslope lives in Montana’s Kootenai, Flathead, and Clark Fork watersheds and in the headwaters of the Missouri and Saskatchewan rivers. The populations in greatest danger of disappearing are those east of the divide, where they are today confined mainly to headwater reaches.

Efforts to increase numbers of this native species, especially in mountain lakes, began in 1952 when FWP first established a westslope cutthroat hatchery brood stock. (Brood stock are the fish held in a hatchery to produce eggs and young fish that are reared and then stocked.) That winter, three FWP employees flew into Big Prairie airfield in the Bob Marshall Wilderness. From there, they snowshoed to Big Salmon Lake, a remote lake known for indigenous westslope cutthroat trout that biologists believed would make an excellent basis for the department’s first cutthroat brook stock. Over several days, they caught 32 cutthroat trout through the ice with hook and line. These fish, flown out and held in the Jocko River Hatchery in Arlee, formed FWP’s initial brood stock.

Throughout much of the next three decades, young trout reared from these and later generations of brood stock were stocked in lakes and streams. Then, in 1977, geneticists detected a serious loss of genetic diversity in the brood stock. By 1983, outward signs of problems were emerging, such as low egg hatching success and fin deformities in many of the fish.

Building a more diverse stock
Hatchery managers took this opportunity to start over and form a new, genetically diverse westslope cutthroat brood stock that would survive and reproduce in a variety of habitats. The present stock used by FWP (referred to as the westslope stock) was founded in 1983 when FWP biologist Joe Huston and his crews collected 6,445 westslope cutthroat from 12 Hungry Horse Reservoir tributaries and two Clark Fork tributaries. Pathologists tested the fish from each of these 14 creeks and found them to be disease-free and genetically pure. The fish were then cross-bred to combine the various gene pools and create brood stock containing genes from all 14 unique strains.

Huston says that a diversity of creeks was chosen to ensure that the various life forms of cutthroat trout—those that lived their entire lives in streams, called residents, and those that migrated from rivers and lakes to spawn in tributaries—would be included in the new brood stock. The Clark Fork tributaries were included to ensure that resident fish would be part of the mix.

Managers moved the wild fish to holding facilities at Murray Springs State Fish Hatchery near Eureka. Later the stock was transferred to FWP’s Washoe Park Hatchery at Anaconda, where water temperature can be varied to increase spawning success for this subspecies.

The westslope stock grows well and maintains excellent condition in lakes ranging from potholes at 3,000 feet elevation to the highest lake (8,000feet) that supports fish in northwest Montana. In that region alone, 125 mountain lakes maintain popular sport fisheries due to periodic planting of the westslope stock. Many valley floor lakes benefit as well.

“ The westslope stock has been a phenomenal producer for us,” says Gary Bertellotti, FWP fishery chief. “But, like anything else, these fish are not ideal for all situations. They work well in small to medium lake systems, and they are especially good in high mountain lakes to maintain a sport fishery.”

“ Anyone who thinks of modern hatchery stock as inferior,” Bertellotti adds, “is thinking ancient history.”

Appropriate for at-risk populations?
Though few question the success of the westslope stock to improve recreational fishing in lakes, these fish usually aren’t considered for stocking in streams (or in lakes that have outlet streams) where small, unique populations of westslope cutthroat are in danger of disappearing. The hatchery fish could interbreed with wild fish in nearby waters and thus compromise the genetic uniqueness of cutthroat populations downstream of areas where the hatchery fish are planted.

Biologists generally believe it is better, when possible, to restore dwindling cutthroat populations using unique cutthroat stocks that have a genetic makeup similar to that of the population being restored. This “nearest neighbor” concept holds that cutthroats from a nearby stream are a better source for genetically specific cutthroat than are FWP’s westslope hatchery stock.

Rob Leary, a University of Montana fish genetics expert who has studied cutthroat genetics for nearly two decades, works closely with FWP staff. He agrees that the westslope stock has a role in westslope conservation and restoration. But because that mixed-origin stock is more genetically diverse than the average westslope cutthroat population, it may have limitations for any restoration program where the paramount goal is to maintain the original genetics of a specific cutthroat population.

“ Essentially, these fish are mutts,” Leary says. “For management situations, that may be good. But I’d avoid using them where they have a chance to interbreed with existing native cutthroat.”

In a situation where westslope cutthroat stocks are needed for recovery, Leary and FWP biologists say it’s best to use fish from the closest possible source geographically. If that’s not possible, they maintain, using the westslope stock is still better than stocking fish other than cutthroat, such as rainbow trout.

Leary says that there are large genetic differences among populations of westslope cutthroat, which probably indicate a lack of interbreeding among these many small populations. And that, he says, may give each population important local adaptations. Each may be better adapted to its particular stream than the more genetically diverse westslope stock would be, although this has not been documented.

Leary and many other fisheries scientists contend that keeping particular strains of cutthroat as unique and distinct as possible may, in some cases, allow the subspecies to survive better in the long run.

Bertellotti agrees, but he adds that the westslope hatchery stock should not be discounted entirely for its potential for future restoration on some streams where other techniques aren’t feasible. He notes that the hatchery stock could actually provide more of the genetic fitness that swindling strains may need to survive. What’s more, Bertellotti says, hatchery managers continue to improve the westslope stocks by mixing in wild fish from genetically pure populations.
“ With new research and careful hatchery practices, we can produce an excellent native fish in terms of genetics and performance,” he says.

Though FWP isn’t currently using the hatchery stock for westslope restoration, it remains a tool that fisheries managers can use if other options aren’t possible. Bertellotti points out that because of the westslope stock’s genetic diversity—finding its origin in more than a dozen pure populations that were then mixed together in the hatchery—it could actually introduce genetic resilience into diminished populations.

Importance of genetic diversity
Hatchery managers aren’t the only ones touting the westslope stock’s potential for restoration. “This is a genetically variable stock that performs in a variety of environmental conditions,” says Bob Snyder, FWP native fish coordinator. “We don’t know which genes may impart resistance to drought or impart successful spawning. We don’t have the cutthroat genome mapped, and that’s why these fish are so important. We can introduce a diverse stock and let nature sort it out.”

In fact, genetic inbreeding may have made isolated westslope cutthroat populations more susceptible to environmental threats that the genetically diverse brood stock would be. Geneticists have found that westslope cutthroats from the same stream are nearly genetically identical. Yet those same fish have a far different genetic makeup from that of other westslope cutthroat populations living in different streams, even those within the same drainage.

What accounts for the wide genetic differences among various westslope cutthroat populations? According to Snyder, some scientists theorize that it may be due in part to the species’ harsh environment, which historically has forced many streams’ populations to reestablish themselves with a small number of individual fish, leading to a narrowing of the genetic makeup of the trout in that stream.
For example, if an environmental event such as a drought had killed most cutthroat trout in a stream, then the population would have rebuilt itself by the breeding of just a few surviving individual fish. This phenomenon, known as a population bottleneck, results in inbreeding, a loss of genetic variation, and increased genetic similarity of individual trout.

Long before these changes occurred, says Snyder, all the various cutthroat populations likely came from a more genetically diverse founding population.

Interestingly, FWP’s westslope hatchery stock—which combines genes from fish of many streams—may be more similar to the westslope cutthroat’s original population than the many different unique strains in the streams now.
Genetics issues aside, FWP currently lacks hatchery space to rear dozens of unique cutthroat stocks while maintaining adequate numbers of existing westslope stock. That means citizens and FWP will need to make some hard choices regarding the future of the state’s hatchery brood stock program.
“ Do we want a sport fishery for this native fish and a genetic reserve for a diverse cutthroat stock?” asks Bertellotti. “If so, then the current westslope cutthroat stock is great for both those purposes. Or do we want specific stocks for recovering specific streams? We can’t have a large program for both types of stocks.”

Keep all the parts
In 1994, due to concern over cutthroat recovery, FWP formed an interagency cutthroat technical committee to examine the issue. The committee recommended that managers strive to preserve each existing population of westslope cutthroat trout whenever possible, while acknowledging that this could be difficult in some situations.

“ Managers should be conservative and assume each population should be retained,” says the University of Montana’s Leary, a committee member.

This approach is consistent with a westslope cutthroat conservation agreement among FWP and other agencies.

As part of its commitment to restoring unique cutthroat populations, FWP has created an experimental recovery hatchery program at Sekokoni Springs, east of Kalispell, where biologists soon will be developing nearest neighbor cutthroat stocks for recovery efforts in specific streams of the Upper Flathead River Drainage.

“ This has lots of potential,” Bertellotti says, “but we have to start off small. We can’t do five streams at one time.”
He explains that conserving specific populations is expensive. It also doesn’t produce significant numbers of additional fish for people to catch.

In some at-risk cutthroat populations, not enough fish remain to provide donors that could be reared in hatcheries to help restore those streams. In these cases, Snyder says, one alternative would be to cross a few individuals from an at-risk population with fish from the existing westslope brood stock, and then stock the resulting offspring into a fishless stream. This would preserve the genes of the unique population along with the more diverse genetic makeup of the westslope stock. The approach has not yet been tried, Snyder adds, “but we’re considering it as an alternative for conserving extremely reduced populations.”

Much still yet to learn
Fisheries scientists continue working to improve the genetic quality of westslope brood stock and to understand how inbreeding alters fish health and fitness. One major unknown is the significance of observed genetic differences among fish from different streams. Researchers don’t yet know whether stream-to-stream gene differences reflect evolutionary adaptations or simply random changes due to small population sizes.

Because scientists have much to learn about trout genetics, the various unique westslope cutthroat populations are being conserved and restored whenever possible. In some waters, managers are removing nonnative fish such as brook trout from sections where they might compete with westslope cutthroat trout. And land management agencies are working to lessen environmental damage that threatens westslope cutthroat trout habitat.

Meanwhile, the westslope stock continues to be used mostly in mountain and valley floor lake waters, where it provides an excellent recreational fishery and superb food for a backcountry meal, yet is unlikely to mix with endemic cutthroat populations (which are mainly in streams). Managers maintain that keeping westslope cutthroat available for anglers’ harvest and enjoyment is an important step in maintaining public support for cutthroat conservation.

What about the use of westslope hatchery stock to restore at-risk populations? FWP continues to improve the westslope hatchery stock and hold it available to use in recovery efforts where other options may not work. Fisheries managers, geneticists, and hatchery biologists continue to discuss when and where the westslope brood stock should be used to create new angling opportunities and to restore dwindling populations. But ultimately their common goal is to preserve the species that, on a June evening in 1805, Meriwether Lewis and his men cooked and ate—a species that Lewis afterwards proclaimed “a very fine trout.”Bear bullet

John Fraley is an FWP information officer based in Kalispell