Chasing rainbows: Fish and Game follows Kenai River trout movements

Posted: Tuesday, November 16, 2010

The bow of Tony Eskelin's boat sinks down into the glacial blue waters of the Kenai River as he cuts the throttle and reaches for the large antennae mounted to the side of the boat's center console.

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Photo By M. Scott Moon
Photo By M. Scott Moon
Tony Eskelin uses a radio antenna-equipped boat to track tagged trout in the Kenai River near Sterling last week.

Somewhere in the riffles ahead, a radio transmitter is sending out a signal for all the world to hear -- all the world tuned into the right frequency anyway.

Eskelin, a sport fish biologist with the Department of Fish and Game has a fish on, figuratively, as he sweeps the antennae back and forth, trying to hone in on the chirping transmitter's location.

Eskelin has caught this fish before; he had to in order to surgically implant the transmitter in the fish's abdomen.

This fish, a Kenai River rainbow trout, along with 60 others, is part of a study being conducted by Fish and Game to follow the movement of the rainbows through this stretch of river.

Eskelin tagged the fish he caught between Slikok Creek and the Naptowne Rapids -- an expanse of 20 river miles -- in mid-July.

Since than he's been following them around the river as they move from their summer feeding zones to their winter residences.

The idea is to get a glimpse into the watery world of these fish and learn more about where they spend their time.

Eskelin said the main thrust of the study is to examine where the fish are spawning. He said they plan to compare that data to a study conducted in the mid-1990s by the U.S. Fish and Wildlife Service that tagged rainbows upstream of the rapids.

Eskelin said that while rainbows have been studied above the rapids before, this will be the first time anyone has looked at the fish in the stretch of river below them.

Each of Eskelin's specimens is swimming around with a transmitter about the diameter of a roll of nickels, but half as long, with an antennae protruding out the back, implanted behind its anal fin.

As Eskelin makes his way up the river, running clear and low with its shores weighed heavy in fresh snow, he picks up on the transmitter's unique pulse codes, allowing him to identify each fish individually.

His receiver is accurate enough that he could practically park his boat on the fish's head, or just mark that it's in a particular hole or section of river.

He'll plug the fish's location into a GPS, sometimes finding a few different fish in the same location, before he hits the throttle and moves on.

Since he can't be out on the river every day either, Eskelin has made use of fixed stations located at the Skilak Dunes near the outlet of the lake, as well as at the Lower Killey River's confluence with the Kenai.

These data loggers run non-stop and can record when tagged fish swim by. They'll also record if the fish are hanging around the area or buzzing on through.

If a transmitter in a fish stops moving for a length of time, it will change its pulse code to tell Eskelin the fish may be dead, too.

Eskelin said he's had pretty good survival with his specimens, and as of late September, he had counted as many as 47 in a single outing.

A few died from the invasive surgery required to tag them, and while technically none of the fish tagged, which were all over 21 inches, could legally be kept by an angler, Eskelin said a few may have died by hook and line.

A couple other specimens meanwhile, have found themselves in nature's talons, literally.

A few weeks ago Eskelin said he had a transmitter beeping at him from up the bank, an unlikely place to find a trout.

He said he hiked into the woods with his antennae and honed in on a tree sporting an eagle's nest in its crown.

Mystery solved.

So far he said he's recovered about a dozen of the transmitters that have been washed to the banks of the river, their host likely to have been turned into a protein meal for one of the rainbow's many predators.

At this point, most of Eseklin's remaining specimens have moved upstream, and are now above the rapids, with a majority hanging out in the depths of Skilak Lake.

Biologists already have a sense of what rainbows do and where they go through the year.

Unlike some of the other denizens of this river who will travel far and wide during their lives, rainbows tend to be sort of the homebodies of the Kenai.

While exceptions to the rule are in fact a rule in nature, most Kenai rainbows are known to overwinter in Skilak or Kenai Lake, head to spawning grounds in spring and then move on to summer feeding grounds where they stay put for most of the warmer months until they eventually return to the lakes.

So far, Eskelin has been seeing a similar pattern with his fish.

"From what I've looked at, they stabilize in their summer feeding area," he said. "I started seeing migration upstream as early as say mid-August and it really picked up after that." The migration peaked, he said, in mid-September, and by mid-October half of his specimens were in Skilak.

On Nov. 11, Eskelin motored around the section of river referred to as the upper-middle, between the rapids and the outlet of Skilak, still picking up several stragglers.

Some fish probably won't go to the lake either, he said, while others that are in the lake now might shoot out and spend time in the river during the winter.

After Nov. 15, however, the transmitters will shut themselves off until mid-April.

This will help save the battery life on the devices so Eskelin can continue to the study them through next fall.

Dante Petri can be reached at dante.petri@peninsulaclarion.com.



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