How Many Trout Do Pelicans Eat?

2013-11-14T02:10:00Z How Many Trout Do Pelicans Eat?By Virginia Hutchins Twin Falls Times-News

RUPERT, Idaho • With an antenna shaped like an oversized metal detector, Kevin Meyer sweeps the bizarre landscape of a small island in Lake Walcott.

During nesting season, migratory pelicans and cormorants populated this island, feeding on the lake’s fish and regurgitating for their chicks. Now the island is deserted and the waters have receded, leaving rocks coated in monochromatic mud. Above the high-water line, between the departed cormorants’ towering nests of sticks and mud, fish bone fragments and bird poop cover the dirt.

Meyer, a Nampa-based fisheries biologist for the Idaho Department of Fish and Game, moves his antenna across ground that used to be just under the waterline. Beeping indicates he’s found what he’s looking for: a tiny passive integrative transponder — or PIT tag — once embedded in a rainbow trout.

That trout, like many others, became a pelican’s meal instead of an angler’s triumph.

But how many? Meyer’s innovative research project aims to find out.

At the spot the antenna indicates, State Fishery Manager Jeff Dillon scrapes the white crust with a garden trowel. Meyer divides Dillon’s little pile of dirt, scans with a handheld detector, divides and scans again. When the detector’s beeping narrows the search to a handful of dirt, Meyer scoops that handful into a tray of graduated screens.

After a moment of puzzlement, Meyer breaks apart a clod to reveal the PIT tag.

A lengthy identification number assigned to that tag — which is filed in a vial and recorded in Dillon’s notebook along with GPS coordinates — will help Meyer build a picture of how many hatchery-raised trout are consumed by pelicans at Lake Walcott.

This island is the largest of three near the lake’s south shore, east of Minidoka Dam. Google’s satellite image of the island shows a dense pelican population. Even now, on Nov. 1, a faint but nasty smell on the breeze recalls those summer residents.

Costly Competition

Why count the trout that migratory pelicans consume during their months in southern Idaho?

Some of those trout are raised in Idaho’s hatcheries, funded in part by anglers’ license fees. Those trout are meant to become the tug at the end of a fishing line, and Fish and Game managers want to be efficient with their hatchery spending.

“Anglers traditionally have not liked to see pelicans swimming around,” Dillon said, and the bird’s population has increased in the past two decades.

Still, this research isn’t about punishing pelicans. It’s about balance.

Meyer’s goal is learning where in southern Idaho pelicans are eating game fish — rather than other species — and how large the effect is.

A Fish and Game employee in Pocatello began related research about a decade ago. But following a 2012 pilot, 2013 is the first year for a full statewide study expected to end in 2014.

Researchers released tagged, hatchery-raised rainbow trout in Cascade Reservoir, C.J. Strike Reservoir, Lake Walcott and several smaller ponds, mostly in the Magic Valley, Meyer said. And they tagged 2,000 or 3,000 wild, native cutthroat trout at Henrys Lake and in the Blackfoot River and Blackfoot Reservoir.

PIT tag detectors deployed at pelicans’ nesting and loafing sites help show what happened next. At ponds where pelican predation was high, anglers’ harvest of hatchery-released trout was low.

At Connor Pond near Burley, for example, pelicans ate 68 percent of Fish and Game’s stocked fish in 2012, and anglers caught fewer than 10 percent, Meyer said. But at Filer Pond near Filer and at Riley Pond near Hagerman, pelicans ate about 10 percent and anglers caught more than 50 percent.

The Correction Factor

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

“No one else is doing this kind of work,” Dillon said.

So what’s the secret to that math?

Fish and Game crews directly fed tagged fish to pelicans during spring nesting at C.J. Strike Reservoir, Lake Walcott, Riley Pond and elsewhere. Yes, that job is crazier than it sounds. The birds are wary, Dillon said, but they eventually get used to free handouts from people in boats. In some waters, the crews had to launch the tagged fish away from the boat with a throwing stick, then watch while pelicans scooped them up.

The correction factor 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.

And what about those cormorants that built their elaborate nests on the Lake Walcott islands? Don’t they eat fish, too?

Meyer’s team set up remote cameras on the islands this summer to determine a ratio of pelicans to cormorants. And the PIT tags found beside cormorant nests aren’t blamed on the pelicans.

Finding a 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 introduced 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.

“It’s about finding the right kind of balance,” Dillon said.

Virginia Hutchins is managing editor-online of the Times-News and

Copyright 2015 Twin Falls Times-News. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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