The more nets they throw into Yellowstone Lake, the more pesky lake trout they seem to catch.

At Yellowstone National Park, the uphill struggle continues to catch and kill as many non-native lake trout as possible in order to preserve dwindling numbers of native Yellowstone cutthroat trout. Lake trout eat the cutts in great numbers.

Park Service crews pulled in their last nets of the year on Tuesday, ending yet another record catch on the lake.

The six-month gill-netting effort killed 73,279 lake trout, said Patricia Bigelow, a Yellowstone fisheries biologist who oversees the program. That's 13,000 more than caught last year and twice the number netted two years ago.

All told, more than 268,250 lake trout have been removed from the lake since the program started in 1994.

Even so, the work seems only to be curbing the explosive growth of lake trout in the lake, not driving down overall numbers, Bigelow said.

And it isn't just the yearly catch that's increasing. Over the past several years, the rate at which fish are caught - measured by the number of nets used each day - has risen, too.

"That bothers me the most," Bigelow said.

There were signs of hope, though.

Checks at 11 sites around Yellowstone Lake showed more Yellowstone cutthroats than had been seen since 1998, Bigelow said.

And fewer large lake trout were caught this year - the biggest was 22.4 pounds - indicating there might be fewer big appetites hunting for Yellowstone cutthroats.

The cutthroats have been hit hard in recent decades by lake trout, natives of the Great Lakes that were first confirmed in Yellowstone Lake in 1994. The lake trout crave the Yellowstone cutthroat trout in the lake, long seen as one of the species' best strongholds.

Fisheries biologists have watched the decline of cutthroats at key spawning migration points at the lake. The most dramatic drop has been at Clear Creek, on the eastern edge of the lake, where just 471 were counted last year, the lowest number since record keeping began in 1945. Five years ago, more than 6,600 were counted there.

Park officials say the number of cutthroat, part of the diet of more than 40 species including grizzly bears and osprey, are down to a fraction of what they once were.

The gill-net program is meant to reverse that trend.

Between May and October, crews on two boats ply Yellowstone Lake dropping nets small enough to catch lake trout by the gills but big enough to let most cutthroats slip through.

Crews were out earlier than usual this year because they've learned that lake trout are particularly active just as the ice melts on the lake. In the first five days, they caught more than 10,000 lake trout, Bigelow said.

For most of the days they were out on the water, about 16 miles of nets were in the water. The experienced crews now have a better idea about which areas to cover at particular times.

That helps to explain at least some of the catch increase this year, Bigelow said, but part of it is simply that there are more of the rapacious lake trout patrolling the waters.

"It's still an expanding population," she said.

Keeping it further in check, and actually diminishing its numbers, will require more time and effort, Bigelow said.

The Park Service spends about $400,000 a year on the gill-netting program.

Meanwhile, there's been talk in recent years about finding ways to mass-kill lake trout eggs laid on the lake bottom or to lure large numbers of the fish to one area to make gill-netting more effective.

Until those ideas come to fruition, though, crews are left to simply catch and kill as many as they can.