It’s that time of year again: lake trout removal numbers for Yellowstone Lake are in—and echoing last year, they’re up significantly.
According to the Bozeman Daily Chronicle, National Park Service crews removed approximately 366,000 lake trout from Yellowstone Lake.
Per Todd Koel, Yellowstone’s fisheries supervisor, NPS crews also tested out a new method for curbing lake trout spawning: dumping the carcasses on the egg beds. Based on research conducted in test plots throughout Yellowstone Lake, as well as in a Bozeman laboratory, smothering the eggs leads to death in about two weeks. From the Chronicle:
“The mechanism we don’t know exactly,” Koel said. “But all of that stuff that causes decay — bacteria and fungus along with no oxygen” resulted in 100 percent mortality.
“It didn’t matter how deep the eggs were.”
The lake trout spawn in the last two weeks of September, so the window to apply the dead fish to the spawning sites — which can be as large as about 1.5 acres — is fairly small. Although netting typically continues into October, the shorter days, colder weather and difficult conditions can mean a lessened take.
“It’s a narrow window,” Koel said.
Dumping fish on carcasses is the latest attempt to find a way to kill lake trout eggs. Experiments with electrified mats to zap the eggs proved ineffective in Yellowstone’s clear waters, which didn’t conduct electricity well, Koel said.
Rotenone, a toxin, was considered but the eggs had to be bathed in a solution of the chemical for 12 hours — an impossible length of time under natural conditions.
Other methods tried and disproved were salting the eggs and suction dredging.
“That’s why this carcass work is so exciting,” Koel said. “We have that material out there already. It’s not introducing anything foreign. So it has all kinds of attractive attributes.
“Part of the issue is how many carcasses does it take to cover a spawning area.”
So far, the Park Service has identified about 12 spawning sites around the 132 square-mile lake using tagged “Judas” fish. Scuba divers and a remotely operated vehicle have helped to narrow down the parameters of the spawning sites, Koel said.
“This isn’t over yet,” he said. “There are a lot of challenges to implementing this on a larger scale.”
Last year, Koel and his crews caught around 315,000 lake trout. Earlier this year, we reported Park officials were cautiously optimistic about the process—about how lake trout removal is clearing the way for continued resurgence in Yellowstone’s cutthroat trout population, which is seen as a keystone species in the Park, providing sustenance to Yellowstone’s bear population.
Lake trout were first detected in Yellowstone Lake in the mid-1990s, which caused alarm in fishery officials, as they ravenously outcompete cutthroats.