Rocky Mountain College student studies relationship between trout presence and frogs in Absaroka-Beartooth Wilderness – via Herp Digest

October 29, 2012 12:01 pm  •  By Brett French BILLINGS GAZETTE

For two months this summer, Bo Walker had something of a Huck Finn existence.

The 22-year-old Rocky Mountain College environmental science student spent five or six days a week hiking in the Absaroka-Beartooth Wilderness, looking for frogs and fishing.

“This is why a bunch of my friends called me a lazy bum,” he told a small gathering at the Audubon Conservation Education Center on Tuesday.

Walker’s hiking and fishing was actually in pursuit of scientific knowledge. He was gathering information for his independent research project, an undergraduate thesis examining what effect the introduction of trout to lakes in the Beartooth and Absaroka mountains may have had on amphibian populations.

Wet mountains

It would seem that the A-B Wilderness is the perfect place to search for frogs. Hundreds of lakes dot the landscape at elevations ranging from 5,000 to 11,000 feet. Fish were planted in the lakes in the early 1900s – everything from rainbow to brook and Yellowstone cutthroat trout. The idea at the time was to provide fisheries for horsepackers and hunters who ventured into the rugged region. There were few backpackers back then.

Of 1,000-some lakes in the wilderness, more than 340 have been stocked with fish. Out of all those lakes, only two held native fish, Walker said.

He came up with the idea for his study while working for Fish, Wildlife and Parks on its mountain lakes crew in the A-B Wilderness two years ago. The crew annually assesses a portion of the lakes that have been stocked with fish and plants fish in some of the waters.

As Walker worked with FWP he began to wonder: “What are we doing to the landscape if we’re stocking nonnatives?”

“That’s one of the questions that fueled me in this study,” he said.

Frog land

The Absaroka and Beartooth mountains are home to two main species of frogs: the Columbia spotted frog, which tends to live at 3,500 feet elevation and higher, and the boreal forest frog. Both species can be found in waters as high as 9,500 feet in the A-B.

The frogs provide food for a variety of species. Besides fish, they are also on the menu for ducks, herons, otters, snakes and even other frogs. The frogs tend to also eat what fish do – mainly aquatic insects. So fish and frogs compete for the same foods where they are found together.

So what makes a place frog-friendly? Water is a must, but frogs also generally like to breed in shallow, warm waters where there is emergent vegetation. Sometimes, to find just the right place to live or breed, the frogs will migrate. They can travel up to 2 kilometers, or about a mile-and-a-quarter, sometimes covering up to 500 meters in a day.

“Which, when you consider they’re about the size of your fist or smaller, that’s pretty impressive,” Walker said.

The findings

Without researching the subject, it would seem logical that since frogs are fish food, amphibian numbers would be much lower in lakes where trout have been stocked. But that’s not what Walker found in the 50 lakes he examined — 22 of which had fish and 28 didn't.

Thirty-two percent of the lakes that did not have fish had amphibians. Yet 72 percent of the lakes with fish also had amphibians. If the lake had no fish, he had a 67 percent chance of finding amphibians and an 88 percent chance of finding evidence of amphibian breeding.

The problem, Walker said, is that to make the data statistically valid he needed to investigate 50 lakes with fish and 50 without, instead of 50 lakes total. To do that, he would have needed another him and more funding.

Despite his research, Walker said, scientific literature is full of studies that say “Fish do affect amphibians.”

But his study can’t say that fish are affecting frogs significantly. And there are a lot of other factors that could have skewed his one-time sample, everything from the dry, warm summer, to a milder winter that may have increased frogs’ overwinter survival. Ideally, Walker would like to persuade FWP to remove fish from a series of lakes to see if frog numbers rise in those waters.

Taking fish from waters would likely anger anglers, but Walker sees the issue more holistically.

“It’s important to keep frogs because they are part of the natural community,” Walker said. “What the ripple effects are of a species’ disappearance is not known.

“We should be good ecological stewards.”