“If there is a Ground Zero for spawning that we’re aware of, it’s Carrington Island,” said David Hallac, Yellowstone Center for Resources chief in Yellowstone National Park.
Scientists will use an electrified mat that will cover small areas in the gravel to kill lake trout embryos there.
“We have got a lot of work to do, but we’re hopeful,” Hallac said.
An engineer from Smith-Root, Vancouver, Wash., is designing the electric equipment specific for Carrington, said Dave Sweet of the East Yellowstone chapter of Trout Unlimited.
Big lake trout eat cutthroats. Once, there were an estimated 4 million cutthroats in Yellowstone Lake and its tributaries. By 2009, that number was down to 400,000 cutthroats, according to Trout Unlimited.
The Park Service has escalated its assault of the invasive trout species to give native Yellowstone cutthroat trout a chance to rally.
Lake trout spawn in the lake in September and October, not in shallow streams where cutthroats spawn in the spring. So predators such as bears and osprey can’t thin lake trout ranks from the lake’s narrow tributaries.
More than 300,000 lake trout were removed with nets from Yellowstone Lake this year, bringing the total to more than 1.1 million taken since the fish were discovered in the lake in 1994, said a Yellowstone Park news release.
Net wielding boats were used by both Park Service personnel and a private fishing contractor to snag the lake trout.
There were an estimated 500,000 lake trout this spring prior to the 300,000 death toll. It is a scientific fact that if half the population can be removed, it can be driven to collapse.
“We’re starting to crash that population,” Sweet said.
HOMING IN ON LAKE TROUT
In 2011, 141 lake trout were fitted with radio tags, and another 80 lake trout got tagged this year. Fifty-two receivers stationed on the lake tracking are recording the tagged trouts’ movements.
Half the tagged lakers visited the waters around Carrington in 2011 in the West Thumb area. On Sept. 11, 23 tagged fish visited Carrington, where there are two spawning beds measuring no more than 1.2 acres, Sweet said.
On Sept. 13, a trap net placed adjacent to Carrington Island by a commercial fishing boat removed approximately 540 lake trout.
“Our staff identified most of the fish as mature lake trout that were ready to spawn,” Hallac said.
One of the lake trout weighed 33 pounds; it was the largest lake trout caught thus far, Sweet said.
Fifty fish with tags also congregated around Breeze Channel and Wolf Point around West Thumb, suggesting two spawning beds in those locations as well, Sweet said.
ON THE ROPES
In the 1980s and 1990s, surveyors counted thousands of cutthroat trout in Yellowstone. By the mid 2000s, a couple dozen cutthroats were documented during surveys.
“But in the last couple of years we’ve got a rebound,” Sweet said.
In 2011, 512 cutthroats — mostly measuring 20 inches — were caught in distribution nets. In 2012, 1,070 of various sizes were caught, suggesting more cutthroats are producing young, Sweet said.
In 2011, 8,800 cutthroats were inadvertently caught while netting lake trout. In 2012, 19,600 cuts were netted, indicating the population is growing, Sweet said.
About two cutthroats die for every 100 lake trout caught in gillnets, said Todd Koel, supervisor for the Yellowstone fisheries program, in September of 2012.
There is financial support to rid the lake of lake trout and lake trout are on the ropes.
“It’s really turning around,” Sweet said.