Tag, you’re it! Game and Fish tagging walleye in Buffalo Bill reservoir to estimate population

Posted 5/3/16

Five Game and Fish employees worked west of Buffalo Bill Dam on Wednesday.

Only a light breeze ruffles the surface of the lake, but falling snow accentuates a soggy night for the men in two boats doing very wet work. A portable generator provides …

This item is available in full to subscribers.

Please log in to continue

E-mail
Password
Log in

Tag, you’re it! Game and Fish tagging walleye in Buffalo Bill reservoir to estimate population

Posted

The Wyoming Game and Fish Department is catching, tagging and returning hundreds of walleye in Buffalo Bill Reservoir to determine if suppressing the unwanted fish is feasible.

Five Game and Fish employees worked west of Buffalo Bill Dam on Wednesday.

Only a light breeze ruffles the surface of the lake, but falling snow accentuates a soggy night for the men in two boats doing very wet work. A portable generator provides electricity for the booms’ electrical arrays they lower into the shallow water where the walleye spawn. The arrays send a jolt of electricity to stun the fish. Then the guys net the dazed walleye near the surface to deposit them in a live well.

If they haven’t been tagged before, each fish receives two tags that resemble short, wire antennas jutting from their sides. Five hundred of the tags will offer either a $10 or $100 reward.

“Here’s one of the bigger females,” said Jason Burckhardt, Game and Fish Department fisheries biologist with a walleye that would tickle any angler. It weighed 2.58 pounds.

Next, Burckhardt notes a tagged male of smaller proportions, but worth its weight in gold with a $100 tag.

Sean Cooley, Game and Fish fisheries technician, determines each walleye’s sex and size and then inserts the tags before returning them to the lake. “Looks like seven recaps,” Cooley said.

They call them “recaps” or recaptures; walleye previously caught and tagged.

The higher the recapture rate, the less variance in the abundance estimate, said Daniel Kaus, Montana State University-Bozeman graduate student working on the project so he can build a walleye population model.

The guys wear protective gear to avoid being shocked. They tag at night because the walleye are easier to catch where they are spawning, Burckhardt said. They launch at dark, sometimes remaining on the lake until 3 a.m.

The walleye bounty is to encourage fishermen to report the tagged walleye they catch whether it is a reward fish or not. The more anglers report their marked walleye, the more accurate the mortality estimate will be, Burckhardt said. The purpose of the tagging program is to determine a means to suppress the walleye population.

By catching, tagging and then releasing the walleye, they can estimate walleye mortality when anglers report the tagged fish they caught, Burckhardt said.

It’s called mark and recapture to estimate a population’s size. A portion of the population is captured, marked and released. Later, another portion is captured and the number of tagged walleye within the sample is counted.

Since the number of marked walleye within the second sample should be proportional to the number of marked individuals in the whole population, an estimate of the total population can be calculated by dividing the number of marked walleye by the proportion of marked walleye in the second sample.

For example, if Game and Fish tag and release 100 walleye and 50 tagged fish are caught by anglers, they can assume that is half the population and further deduct that the population totals 200 walleye, Burckhardt said.

“We’re going between 500 and 700 (walleye),” Burckhardt said. As of April 26, about 350 had been tagged. They have caught females drained of eggs, so they know the fish are spawning. They will keep catching walleye until 700 are tagged or the spawn ends.

There are two components of the study, angler-caused mortality and Game and Fish-caused mortality, Burckhardt said.

The walleye prey on trout inhabiting the wild fishery in Buffalo Bill. A wild fishery means fish are not stocked.

Previous studies showed walleye eat a lot of juvenile trout, Burckhardt said. Game and Fish wants to maintain the wild fishery in Buffalo Bill that in turn supports trout on the North Fork of the Shoshone River.

A lake trout female produces several thousand eggs, compared to a walleye female that bears 20,000 to 200,000 eggs, Kaus said. Although the walleye hatchling survival rate is much lower than lake trout, the sheer number of offspring one female can produce makes a big difference.

If Kaus can obtain the vital rates (survival and death), then he can run a simulation model to determine population growth each year. From there he can calculate the rate of mortality needed to suppress the population, Kaus said.

At Lake Pend Oreille in northern Idaho, years of effort to stamp out lake trout has seen progress in the last few years, Kaus said.

If enough effort is exerted, walleye can be suppressed in Buffalo Bill, but the question remains, how much would that effort cost, Kaus said. Game and Fish wants to know the degree of suppression needed and the price tag.

The illegal walleye introduction likely occurred from 2002 through 2004.

If a tagged walleye is caught, anglers are asked to call the Cody Game and Fish office at 307-527-7125 or the phone number provided on the tag.

Comments