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David Grubbs, Billings Gazette via Assoicated Press
FILE - In this Aug. 18, 2006, file photo, the crew of the Freedom pull fish from nets and restocks nets while fishing for lake trout on Yellowstone Lake in Yellowstone National Park, Wyo. In 2015, crews recorded their biggest catch yet in a long-running effort to reduce the number of non-native lake trout from Yellowstone Lake. The National Park Service reports some 315,000 lake trout were captured and killed in 2015.

CHEYENNE, Wyo. — Crews this year recorded their biggest catch yet in a long-running effort to reduce the number of non-native lake trout in Yellowstone Lake, a National Park Service fisheries biologist said.

Some 315,000 lake trout were captured and killed during netting operations that began in May and ended in October, Todd Koel, leader of Yellowstone National Park's native fish conservation program, said.

"That's more than we've ever caught," Koel said. "It's because we put out even more effort than we have ever before to catch them. ... And also there's a lot lake trout out there."

Non-native lake trout were first discovered in the 132-square-mile Yellowstone Lake in 1994. Lake trout is a voracious species that feeds on the native cutthroat trout in the lake.

Cutthroat populations plummeted because of the lake trout, affecting other species like the grizzly bear that feed on cutthroats.

In order to boost the cutthroat population, park managers have been trying since the mid-1990s to reduce the lake trout numbers. The effort was ramped up in 2012 with netting, electroshocking and other methods.

The program costs about $2 million a year — funded by the federal government and private donations.

Koel said about 1.2 million lake trout have been killed in just the last four years.

In 2012 and 2013, about 300,000 lake trout were removed each year and another 277,000 in 2014.

"Each year, we're putting more and more effort out there and each year we've been killing a lot of fish," Koel said. "We're still waiting for that crash in our catch. We haven't seen that yet, but the predictions are there that's going to happen. So we'll keep this up until it does."

Meantime, cutthroat populations have been showing signs of rebounding.

"There are a lot of cutthroat in Yellowstone Lake and they're really big. They're huge. They're beautiful," Koel said.

He said the aggressive fight against lake trout will continue next year.

Fisheries biologists are working to restore cutthroat, arctic grayling and westslope cutthroat trout to various streams elsewhere in the park.