Park biologists say they're winning the lake trout war
Since 2009, biologists from the U.S. Geological Survey and Glacier National Park have been netting non-native lake trout from Quartz Lake to help preserve one of the Park’s last remaining strongholds for endangered bull trout. The effort, biologist Carter Fredenberg was pleased to report last week, appears to be working.
Last fall, biologists counted an historic high 66 bull trout redds in the upper stretches of drainage. Redds are spawning beds fish make in the stream bottoms. The more redds, the better the population is doing.
“That is extremely positive,” Fredenberg said during a public talk last week.
Lake trout out compete bull trout for food and space in the ecosystem. Lake trout are native to Glacier Park east of the Continental Divide, but they were introduced in Flathead Lake about 1905. Since then, lake trout have slowly invaded every lake they can swim to in the Flathead River drainage.
Lake trout reached Lake McDonald by 1959, Bowman Lake by 1962, Harrison Lake by 2000 and Lower Quartz Lake by 2003. Biologists put up a barrier in the creek between Lower and Middle Quartz lakes in an attempt to stop the migrating fish, but lake trout were found in Quartz Lake in 2005.
Biologists knew they had to take action if they were to save the Quartz Lake bull trout population. But in order to do that, they needed to find where the lake trout spawned. Lake trout, unlike bulls, spawn in the lake, a key reproductive advantage.
The biologists invited skilled fishermen up to Quartz Lake, and radio transmitter tags were inserted in the captured fish, allowing them to pinpoint lake trout spawning grounds.
In October 2009, the first netting session, a total of 140 adult lake trout were captured in a few weeks. By 2014, with the same amount of netting effort, that number was down to 26 adults.
But biologists aren’t just after adults — they also pursue juvenile lake trout. A total of 5,119 juvenile fish were caught in 2013, which were likely the progeny of adult fish from 2008, before the netting started. Since then, the number of captured juveniles has dropped sharply.
The plan is to keep the lake trout population down to less than 500 fish in the 200-foot deep, 869-acre lake. The suppression effort will have to continue for the foreseeable future, the biologists say.
Park officials last year released a plan to expand the effort to nearby Logging Lake, which also has been invaded by lake trout.
That project has already started, as biologists moved some fingerling bull trout from Logging Lake upstream to Grace Lake last fall. Grace Lake, which is isolated from Logging Lake by a waterfall, could be a sanctuary for endangered bull trout.
This spring, biologists will begin a full-fledged netting operation on Logging Lake. The Park expects the netting effort will cost about $75,000 to $100,000 per year for the next seven to eight years.
The biggest expense is personnel, Park fisheries biologist Chris Downs said — it takes trained biologists with knowledge of endangered species to work on the project.
The netting will need to continue until a permanent solution is found, Downs said. Electrocuting lake trout spawning beds to kill all the eggs is one possible method.
The Park’s North Fork area lakes have some biological advantages. For one, they don’t have mysis shrimp, a major food source for young lake trout. Swan Lake has mysis shrimp, and lake trout are being netted there, but biologists are not seeing the success they have in Quartz Lake.
Another tactic is to use fish poison. Rotenone has proven effective on smaller lakes — biologists have used it in the Bob Marshall Wilderness. But Quartz and Logging lakes are much larger and have viable populations of bull trout. Biologists don’t want to compromise the bull trout populations, which are genetically distinct to their drainages. Netting is a targeted “scalpel” approach, Downs said.