In a wide delta hemmed in by 8,000-foot mountains, the Yellowstone River pours its nourishing waters into the Southeast Arm of Yellowstone Lake.
This is a remote area, seen by few of the 3 million visitors to Yellowstone National Park each year, but these cool, deep waters may be the next battleground for the preservation of native Yellowstone cutthroat trout.
Last week, the commercial netting boat Northwester spent two days in the remote area, setting and pulling up mesh nets to capture lake trout. The park’s fisheries biologists were hoping to get an idea of the number of lake trout in the arm, as well as an indication of how many cutthroat trout they were eating.
“The lake trout are staging at the mouth of the Yellowstone and Beaverdam Creek and eating the young cutthroats as they come back into the lake,” said Pat Bigelow, a Yellowstone fisheries biologist who oversaw the netting.
The boat had to get special permission to work in the Southeast Arm, which contains a large nonmotorized zone to protect the wilderness characteristics of the area.
“The thought is that we get these big pulses of cutthroat trout down in here and the lake trout stage in an area where we don’t have a net,” said Todd Koel, Yellowstone’s supervisory fisheries biologist. “It’s kind of a refuge for the lake trout, which I think is going to change.”
Since efforts began in 1998 to remove nonnative lake trout from Yellowstone Lake to protect native Yellowstone cutthroat trout, most of the efforts had been concentrated in the lake’s West Thumb. Those deeper waters were shown to hold the most fish, so targeting that area made sense. And netting in deeper waters avoided a by-catch of cutthroat trout, which tend to live in shallower regions of the lake.
Although that effort has been successful, over time the netting has expanded to include trap nets in shallow areas and concentration at lake trout spawning areas in the fall. This year’s netting operation is being undertaken by three contract boats and one Park Service boat, the most ever.
“The effort is greater than we’ve ever put out here before, by far,” Koel said. “There are 50 miles of net out on any given day.”
To track how lake trout use the 212 square miles of lake, 200 fish have been tagged with monitors that send signals to 50 receivers stationed around the lake to gather data on movement.
This year the venture into the Southeast Arm, as well as plans this fall to use a dredge to suck up lake trout eggs at one of their popular spawning grounds, are being added to the control efforts.
Koel will test the effectiveness of the dredge at Carrington Island, a popular lake trout spawning ground where the fish often move into relatively shallow water to deposit their eggs. An electrically charged blanket that can be anchored to the bottom to kill eggs will also be tested.
“Overall it’s a $2.3 million program per year with the monitoring,” Koel said.
“There’s a lot of effort out here.”