But he and partner Nick Peterson have no rods or reels, no lures and lines, no tacklebox, no bait, no net.
Instead, they have headphones. And laptop computers. And underwater video cameras. And they do not like what they are catching.
“From what we're seeing, it's now or never.”
Kill the lake trout now, or never more catch native bull trout in this, one of their last great strongholds.
Six weeks ago, in the middle of September, Cox and Peterson and biologists from an alphabet soup of state and federal wildlife agencies took to Swan Lake, joined by a couple of commercial fishermen turned research assistants.
For three weeks, they cast their nets - trap nets and gill nets - straining the lake from bottom to top. Cox, a graduate student from Bozeman, remembers it as a slimy, tiring, exciting time.
“You're just fishing, you know? Catching these big fish.”
They caught 2,200 lake trout, and stuck tiny tags on 1,400 of them, computer chips that send a signal when you wave a special wand over their scales.
They also carefully sliced open 30 of the larger lake trout, and slipped a transmitter - about the size of a roll of dimes - into the body cavities. Those 30 fish send out signals that travel some 3,000 meters, straight into Peterson's headphones.
Those are the fish Cox and Peterson now are looking for, night after night, from dusk to midnight, “the fishing hour,” when lake trout are up and eating. The sound of transmitters fills the cabin - ping, ping, ping.
“If you wear the headphones too long,” Peterson said, “you dream the ping. It's mesmerizing.”
The rhythm tells him exactly which fish it is, and the pace how deep it is.
“They like these ledges,” Cox says, “where the water drops off.”
Last month's intensive netting work told Cox a few things. Told him, for instance, that there are a whole lot more young adults in the lake trout population than anyone thought.
And lake trout, unfortunately, like to eat. High on their menu are native fish, like bull trout, treasured by anglers and protected by federal law.
Swan Lake remains one of the few places in the nation where anglers can catch and keep bull trout, but their future here has been in doubt since 1998, when the first lake trout invader was recorded in the Swan.
In other waters, north of here in Glacier National Park, long-running studies suggest that once lake trout invade, they out-compete and fully replace native bull trout in about 30 years.
Much of that Glacier Park work was done by Wade Fredenberg, a biologist with the U.S. Fish and Wildlife Service, and tonight he's onboard with Cox and Peterson.
Fredenberg had hoped the netting frenzy would help him establish a lake trout population estimate for the Swan, but that didn't happen.
He hoped to catch a mess of fish, tag them and then keep on catching fish, including some he had already caught. By comparing the total number caught to the number recaptured, he could peg populations.
“But we didn't recapture very many,” Fredenberg said. Perhaps that's because fish once handled are too traumatized to move around and get snagged again. More likely, it's because there are so very many lake trout - way more than anyone thought.
“From what we can tell, there are one hell of a lot of lake trout out there,” Fredenberg said. “Multiple thousands, if not tens of thousands.”
Fredenberg didn't get his population estimate, but he did learn where the lake trout tend to live. Back in his office, he unrolled a colorful map, a detailed view of Swan Lake's bottom.
“It all looks the same on top,” Fredenberg said of the lake. “All blue and flat.”
But beneath are deep holes, rocky shallows, broad desert flats of sand and silt, broken only by the occasional pop can. Rugged cobble litters parts of the lakebed, and it's there they find the lake trout.
By comparing net-catch records to bottom geography, “we can figure out where they live,” Fredenberg said.
All the better to track them down and kill them.
Biologists have tried to kill off lake trout populations in other waters, mostly without success. But Fredenberg is optimistic, in part because Swan Lake is so small, and in part because he's going at it in a whole new way.
Right now, in these fall weeks between Halloween and Thanksgiving, lake trout are gathering to spawn. Each female unloads 10,000 eggs or more, and the males cruise over like crop dusters, spraying the eggs with gametes and fertilizing the clutch.
“Some of the fish we caught were big females full of eggs,” Fredenberg said. “It was tough to just cut them loose, but we felt the research made it worth it.”
Cox and Peterson follow their signals - most nights the fish cluster in shallows, over big cobbles strewn from a recent road-cut above - and with the video camera they watch as lake trout gather to spawn.
Now Fredenberg knows where to find them in big, concentrated numbers. Now he knows where the eggs are.
Maybe, he said, this is the spot to attack. To kill fish. To smother eggs. To electrocute eggs. Maybe even to vacuum eggs up. To hit the lake trout hard, without catching too many endangered bull trout at the same time.
(In last month's netting operation, they inadvertently hauled in 378 bull trout, 141 of which died. It was a good record, really, but any major lake trout eradication program would need to be highly focused, to minimize bull trout bycatch.)
“Who knows,” Fredenberg said. “Maybe if we can figure out what they need in a spawning site, we can build perfect spawning places of our own.”
Places that would attract lake trout. Places where they could be concentrated and killed.
He imagines baiting the sites with pheromones, perhaps, to lure them in.
“We have to consider everything,” Fredenberg said, “because there are no easy answers.”
For now, the answer is to net. That's what they've been doing down at Yellowstone Lake, and on Lake Pend Oreille, and in other regional waterways.
And it's a good time to be fishing for lake trout, here in the fall, because the bull trout are off spawning on their own, upstream in the little creeks where cold water runs fast.
But netting is still tough on bycatch, Fredenberg said, and it's expensive and time-consuming, too, and it doesn't always work that well.
“We need a new way,” he said.
The new way, he knows, will have to go well beyond pheromone baiting and artificial spawning grounds, because the youngsters - lake trout up to age 8 - won't show up to spawn.
For them, Cox said, you still need a gill net.
And that takes Fredenberg back to his fancy new map of Swan Lake's underbelly, to the chart that helps him pinpoint bull trout habitat, so he can place his nets more carefully.
The trick, he said, is to read the bottom, to leave the bull trout and nab the adolescent lake trout.
Cox is worried about those sub-adult lake trout, because they simply filled the nets last month. What will happen, he wonders, when that population bulge hits maturity?
Quite likely, they'll eat all the kokanee in Swan Lake, then all the bull trout.
“They'll eat it all,” he said. “They'll eat everything. Swan Lake will be full of nothing but stunted lake trout.”
The nets told these biologists where to find lake trout, and how best to catch them. They identified hotspots, which could be checked against that topographic map.
The subsequent “fishing,” this tracking that Cox and Peterson do each evening, running their transects down the middle of the lake, is telling them where lake trout spawn, how they travel throughout the day and even through the season.
“Until now, it's been like trying to manage timber without being able to see the trees,” Fredenberg said. “Now we have GPS on these fish. We can see every tree. Everything's on the table.”
The light, quite literally, has been shined on these invader fish Fredenberg calls “cockroaches, because they eat everything, expand, infest.”
And there they are, caught in the glare of an underwater strobe, that illuminates a rocky bottom captured on video, transferred up to Cox's laptop computer.
This is how he fishes these days, notebook in hand, tracking these 30 lake trout that are, he hopes, unwittingly leading their kind into oblivion.
“What we're trying to do here is to not do the same thing everyone else has done,” Cox said. “We want to use some smart science to focus our efforts.
“We'll gather the data. Then it's up to someone else to make some decisions.”
Like whether bull trout should be helped to survive here. And whether native fisheries are worth the effort.
“Like how to kill lake trout effectively,” Cox said. “Because if we don't get a handle on this, Swan Lake will never be the same.”
Reach reporter Michael Jamison at 1-800-366-7186 or by e-mail at mjamison@missoulian.com.
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