The bad news about trout and their brethren is about 73 percent of the species worldwide are threatened with extinction.
The good news is Crown of the Continent region and the Flathead in particular is still a bastion of excellent habitat for native trout and char species like westslope cutthroat trout and bull trout, though they still face a myriad of threats, biologists Clint Muhlfeld of the U.S. Geological Survey and Chris Downs of Glacier National Park noted during talks at the Montana Lakes Conference hosted by the Whitefish Lake Institute last week.
Climate change is just one of the threats native fish face. It has actually been warmer in the past. During the Holocene era some 11,700 years ago, temperatures were warmer than they are today, and native fish survived — largely because they sought refuge from warm water in deep glacier-carved lakes that abound in our mountainous terrain.
But today, the Earth is warming at an alarmingly fast rate and air temperatures in this region are rising two times the global rate. Today spring runoff is two to three weeks earlier and in the fall, some recent floods have been bigger than spring runoff; water that should have fallen as snow, fell as rain. In the summer, stream temperatures are reaching highs in July that used to happen in August, Muhlfeld noted.
That doesn’t bode well for a species like a bull trout, that prefers water that’s around 50 degrees or less. So how to trout hack it? They travel — sometimes hundreds of miles to find streams with cold water upwellings that come from underground seeps and springs, where they can spawn in the pristine gravel beds of unscathed streams.
Yes it has been warmer, but back in the Holocene, native fish didn’t have to contend with another threat: The invasion of on non-native species like lake trout and rainbow trout west of the divide.
Rainbow trout can cross breed with westslope cutthroat, destroying the gene pool. The resulting fish is dramatically less fit and the native fishery suffers as a result. There’s also a strong correlation between hybridization in streams and warming stream temperatures.
Bull trout, an apex predator, are less threatened by hybridization and more threatened by non-native lake trout, which outcompete the bulls for a niche at the top of the food chain.
Once lake trout establish themselves in a lake, they all but annihilate the bull population. Glacier Park’s Logging Lake, for example, was once a great bull trout fishery in the 1960s, noted Downs.
Today it has but a handful of fish.
But there are ways to combat hybrization and invasive lakers. In Glacier, biologists have taken an aggressive approach in Quartz and Logging lakes, netting out lake trout from the lakes, killing thousands of fish.
In Quartz, where the effort has been ongoing for years, they’ve been able to knock the lake trout population down from several thousand fish to an estimated few hundred through selective netting. As a result, the bull trout population in the remote lake is holding its own. The native cutthroat population is also doing much better, Downs noted.
Similar efforts are underway in Logging Lake as well, with an aggressive netting program underway.
But Glacier has also started to move native fish to new habitat, places where they’re protected from non-native fishes by natural waterfalls, that block upstream migration of rainbow and lake trout.
In the Logging drainage, they’ve taken native bull trout fry from Logging Creek and placed them upstream into Grace Lake. Grace is protected by a waterfall. They’ve also supplanted that stocking by raising bull trout taken from the Quartz Lake drainage, raised them in a hatchery and planted them in Grace.
Bulls that were 3 inches long when they were stocked in Grace are now 14 inches today, Downs noted, as they eat the Yellowstone cutthroats in the lake. The true test of success will be if the bull trout start to spawn and create a self-sustaining population — evidence of that could come as soon as this year.
The Park has plans to do a similar project in the Camas drainage, where it will rid Camas Lake of non-native Yellowstone cutthroat and try to re-establish native westslope cutthroat and bulls in Camas and Evangeline lake.
Like Grace, that fishery is also protected from invasive species through a series of waterfalls in the drainage.
Meanwhile, biologists continue to track the overall health of the region’s native trout fishery and Muhlfeld and his team have developed a new interactive risk assessment map for the Crown fishery.
It can be viewed online at http://ice.ecosheds.org/cce/