'Snitch fish' aid Yellowstone trout removal
YELLOWSTONE NATIONAL PARK, Wyo. (AP) — Increased efforts to capture invasive lake trout in Yellowstone Lake are paying off this summer as the catch rate has increased substantially reports Brett French in the Billings Gazette.
The National Park Service also received help from Wyoming Trout Unlimited to purchase transmitters that were attached to lake trout in hopes of discovering new areas where the predacious fish spawn.
"We're building some momentum," said Todd Koel, Yellowstone National Park's supervisory fisheries biologist. "The predictions are that we can tip this thing over. I don't know how they can sustain this kind of pressure. We're driving them down the other way."
By the end of July, the fleet of netting boats had captured 150,000 lake trout, compared with 100,000 for the same period last year. In 2010, the Park Service finished out the season with a record catch of 150,000 lake trout. Koel said he hopes to hit 200,000 this netting season, which lasts into September.
The lake trout is an introduced species in Yellowstone Lake, which had long been a stronghold for the Yellowstone cutthroat trout. Since its illegal introduction, the lake trout population has grown so large that the cutthroat population has crashed.
The main problem is that lake trout like to eat cutthroat trout. Some captured lake trout have been found to contain several smaller cutthroat trout in their stomachs.
Since 1988, cutthroat numbers in the lake have steadily declined. Several other species in the park used to count on the fish as a part of their diet, including grizzly bears and raptors. That's no longer the case. Last year, even after a record-setting netting season for lake trout, cutthroat trout numbers still declined.
This year, though, Koel is optimistic. The catch of lake trout has been increased through the hiring of an additional commercial netting boat provided by Hickey Brothers Fishery of Bailey Harbor, Wis. That brings the total number of vessels to four, two of which are Park Service boats. In addition to the extra manpower, the commercial boats are capable of setting eight heavy live-trap nets in shallower waters. The nets are capturing larger lake trout of spawning age.
"The nets have a lower catch rate, but when you look at the sizes of the fish, it makes a big difference," Koel said. "We're getting those big spawners."
The live-trap nets also ensure that no cutthroat trout are killed in the process.
The other method of catching lake trout is to use gillnets, which trap lake trout and cutthroat trout as they try to swim through the mesh. If the nets are not pulled quickly, some of the cutthroat trout die. To reduce the chances of catching cutthroat, the nets are set in areas known to be lake trout hangouts.
The live-trap nets also provided researchers an opportunity this summer to tag 140 lake trout with transmitters. With 28 acoustic receivers set up around the lake, researchers will be able to download data in two weeks on the tagged fishes' movements and possibly triangulate the location of new lake trout spawning beds.
"We looked for fish a little over 2 pounds and up to 8 or 9 pounds," said Bob Gresswell, a research biologist with the U.S. Geological Survey in Bozeman who is helping coordinate the work. "We focused on males because they tend to move among spawning areas," whereas the females tend to camp out at one spot.
Once the data are collected, Gresswell said, scuba divers or remote cameras will be used to verify that the sites are spawning beds. Once identified, Gresswell said options for killing the eggs or fry are under study. One method would vacuum the eggs up. Another would use electricity to kill the eggs.
"We want to eventually use these new techniques on spawning beds to have long-term control," Gresswell said. "With a small amount of annual expenditure we could maintain lake trout numbers at a lower level. There's no way we can continue lake trout netting in perpetuity."
Gresswell said lack of funding has stalled any one method of killing eggs or fry from moving forward. But he's hopeful that, like the successful push to raise money for transmitters, other groups will be helpful in raising funds.
"One thing unique about this study is the cooperation of government and nongovernmental entities," Gresswell said.
He said the Greater Yellowstone Coalition, National Park Conservation Association and Wyoming Trout Unlimited contributed substantially to get the project off the ground.
"We had been searching for funding for this for three years," he said.
Since word has gotten out about the project, he said, more money has filtered in. Gresswell said that ideally he'd like to see 350 lake trout implanted with transmitters sending signals to 50 receivers set up around the lake and the hiring of a full-time researcher to analyze the data.
"Hopes are very high," he said.