Idaho biologists pitch tagged trout to pelicans

Idaho Department of Fish and Game biologist Kevin Meyer prepares to throw a rainbow trout at C.J. Strike reservoir Thursday, June 12, 2014.

BRUNEAU, Idaho (AP) — Trade the ball for a dead fish, and distance throwing requires an unfamiliar technique.

Put your back into the windup, and the fish leaves the launcher at the top of your arc and flies straight into the air. But save your thrust for the end of the swing instead, and that trout splashes down far away from the boat.

“Nice toss!” Kevin Meyer said.

All the better to lure a wary pelican.

“I got it figured out now,” Pat Kennedy said.

Kennedy and Meyer, fisheries research biologists from the Idaho Department of Fish and Game’s Nampa research office, drove their boat June 12 to two pelican loafing areas on C.J. Strike Reservoir, southwest of Mountain Home. Their cooler of hatchery rainbow trout — overdosed on anesthetic that morning — was the bait in an innovative research project.

Two dead trout at a time, the biologists injected air and tiny passive integrative transponders, or PIT tags, each with a lengthy identification number. They edged the boat near the resting pelicans, tossed out two trout, then drove slowly away, watching with binoculars.

The injected air, of course, ensured the free lunch would float.

The PIT tags are the key to determining how many Idaho hatchery trout, raised and released to be caught by anglers, are instead consumed by pelicans. Later in the year, researchers with antennas scan pelican nesting sites at Lake Walcott and elsewhere, searching for PIT tags left in the birds’ droppings.

In November, the Times-News followed along on a poop-scanning session at Lake Walcott near Rupert. Filthy and fascinating.

But the late-spring feeding, such as the June 12 excursion at C.J. Strike, is the secret to some fancy math. The usefulness of the data rests on whether the team can get pelicans to swallow particular tagged trout — and watch them do it.

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The cooler of water June 12 was stocked with dead fish too large for sea gulls to swallow. But Meyer and Kennedy counted on the gulls’ interest to stir up the pelicans.

“We just need a sea gull to sit on it, because that’ll kind of get it going,” Meyer said, watching from the idling boat as a pair of their offerings floated near an island in the reservoir’s Snake River arm. Perhaps 40 pelicans loafed around the island’s shoreline or circled in the air above. “C’mon, gulls! What are you waiting for?”

Meyer’s narration sounded a little like a parent at a child’s ballgame — a game with unusual rules.

“There we go, there we go,” he said, as a gull settled on one of the floating trout, drawing the pelicans’ attention.

A pelican in the crowd scooped its long beak in the water, tipped back its head and gulped. One down.

Meyer got impatient as the second trout remained uneaten and wondered aloud whether they should go pick it up to save the $2 PIT tag. But another pelican perked up.

“Oh, c’mon, dude! He looked right at it,” Meyer said. “Yeah, he’s on it. There he goes. He just grabbed it.”

Gulp.

That strange exercise — repeated with more pairs of tagged trout that day at the island and at the upper end of C.J. Strike Reservoir’s Bruneau arm — is what distinguishes Idaho’s research on pelican predation.

Fish researchers in other states count PIT tags at pelican nesting and loafing sites to form minimum estimates of predation. But Idaho is pioneering a “correction factor” that can also account for the PIT tags that pelicans excrete elsewhere — on the water or in the air.

What’s the secret to that math? Directly feeding tagged fish to pelicans during spring nesting at C.J. Strike, Lake Walcott, Riley Pond and elsewhere provides a correction factor that measures the efficiency of tag recovery.

Here’s how: The percentage of directly fed PIT tags that are later recovered on the ground can be applied to the number of recovered PIT tags that were once embedded in fish released in the water for anglers. Just use the ratio to get the result: a total estimate of hatchery-released fish eaten by pelicans.

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Arriving at the upper end of C.J. Strike’s Bruneau arm June 12, Meyer estimated the pelican gathering there at about 100 — fewer than he was used to seeing during last year’s visits.

Perhaps the pelicans heard Idaho wasn’t pelican-friendly, an observer joked.

Actually, Meyer said, Idaho is getting an undeserved reputation as biologists elsewhere overreact, thinking the state is trying to eradicate pelicans.

Not so. In November, State Fishery Manager Jeff Dillon said the project’s aim is “finding the right kind of balance.”

Within a couple of years, Dillon said, Fish and Game will take its findings to the U.S. Fish and Wildlife Service to propose options such as hazing birds in certain areas. Fish and Game might simply stop stocking fish in others.

Another mitigation option is already at work on a Blackfoot Reservoir island where pelicans nest, Dillon said. There, fences restrict the birds to a portion of the island, reducing the number of nests from several thousand to about 350. Exclusion fencing works because pelicans typically land in the water — not on the ground — then swim up to the island.

Pelicans are a remarkable conservation success story across the West, he said. So successful, in fact, that scientists are seeing conflicts with other species they’re trying to protect. On the Blackfoot River, pelicans have consumed most of the Yellowstone cutthroat spawning run in some years.

By now, Fish and Game biologists have analyzed data from PIT tags they scooped from the poop last year. Meyer summarized major findings from 2013:

. At the Lake Walcott pelican nesting colony, Fish and Game recovered PIT tags from 10 of the 13 Idaho waters where tagged fish were released or fed to pelicans, including C.J. Strike; Freedom Park, Rupert Gun Club and Riley Creek ponds in south-central Idaho; Lake Walcott; Jensen Grove Pond in Blackfoot; Blackfoot Reservoir; Chesterfield Reservoir in the Portneuf Basin east of Pocatello; and Henrys Lake near Island Park. Henrys was the farthest away — 170 miles from the nesting island at Lake Walcott.

. The only study waters in 2013 where tagged fish were fed or released but none of their tags were recovered at Lake Walcott were Cascade Reservoir, Foster Reservoir by Preston and Glendale Reservoir, also near Preston.

. Estimates of pelican predation on planted hatchery fish averaged 16 percent. At seven waters predation was very low (7 percent). At the five water bodies where predation was higher, it averaged 33 percent. At two waters — Rupert Gun Club Pond and Burley’s Freedom Park Pond — it was estimated at almost 50 percent.

“In 2013, angler harvest was low at nearly all the water bodies we studied, regardless of whether pelican predation was high or not,” Meyer wrote. “In 2012, there was a much stronger correlation between pelican predation and angler harvest, meaning that when pelican predation was high angler harvest was low, and vice versa.”

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For their data’s precious “correction factor,” Meyer and Kennedy must attempt to avoid feeding two tagged fish to a single pelican. One of the assumptions in their statistical analysis is independence in tag recovery.

Easier said than done.

At C.J. Strike, the two tried to watch where the pelicans that scooped up free fish flew next. But the feathered crowds — flying, floating and on land — kept shifting, and the task seemed impossible.

Near the island in the reservoir’s Snake River arm, a group of particularly savvy pelicans seemed to monopolize the action. At the upper end of the Bruneau arm, a labored sound from the motor indicated the boat was hanging up in mud as Meyer tried to edge closer to birds that weren’t feeding. Pelicans need shallow water to catch fish, so their loafing areas aren’t easy to approach in a boat.

Wary of contaminating the data with double-feeding, Meyer called it off early. That day, their fourth of feeding at C.J. Strike, the team fed 22 tagged fish to pelicans, putting their four-day total at 61.

With a goal of feeding 100 at C.J. Strike this season, they knew they’d be back, pitching to pelicans in their peculiar ballgame.

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Information from: The Times-News, http://www.magicvalley.com

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