For the week of October 8 - 14, 2003

Shocking fish accounting

Fish and Game study numbers

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By MATT FURBER
Express Staff Writer

Donning kitchen gloves, wading boots and sun hats, volunteers and employees of Idaho Fish and Game participated in a fish population study Thursday, Oct. 2, on a section of the Big Wood River called the Hailey reach.

Volunteer ninth-grader Bob Lewis on his sixth day of fishing puts another fsih in the bucket.  Express photo by David N. Seelig

Armed with large nets and electrically charged poles, the crew creates an environment that is not very sporting for fish, but the task is highly scientific despite the thrashing about of fish and humans.

The resource management agency studies fish populations on the Big Wood every year in specific sections to compare densities of fish over time. The studies can also help determine the health of fish.

With a generator and a $6,000 variable voltage production unit loaded in a canoe with a collection bucket, the crew did their second sweep of the river in a week. The fishing trips supply scientists with data they will use to crunch a population estimate once the fieldwork is completed.

Crew leader and fishery research biologist Doug Megargle gives the full measure of the science behind the study.  Express photo by David N. Seelig

"We keep checking and compare the weight and length of the fish," said fishery research biologist Doug Megargle. "We are doing this study in a cooperative arrangement with the Wood River Land Trust to help them document the work they have done in this highly channelized section of the river."

The fish population study focused on the section of river downstream of the Croy Street bridge. The Wood River Land Trust work was part of the remediation project of the old Hailey sewage treatment plant near Heagle Park. In early summer, Fish and Game and the Land Trust joined forces to hold a successful free fishing day at the new pond. As part of the effort to improve fish habitat in the section, rocks were dropped in the river to create eddies. There are also more root structures on the river bank to create hiding places.

The Fish and Game research and management crew annually reviews specific transects in several sections of the Big Wood River system from Boulder Creek, north of Ketchum, down through the Hailey reach.

The fish above Greenhorn Gulch tend to be fatter and healthier looking because fishing is catch-and-release from Greenhorn to the North Fork, said Megargle.

An Idaho Fish and Game crew tenders gear for shocking and collecting fish. The canoe holds a gas generator, an adjustable voltmeter and measuring and accounting equipment. Express photo by David N. Seelig

Thursday’s effort was the second part of the full data collection for the section. The crew took a first run of the river to collect and mark fish that were caught. To complete the data collection on the second pass of the section, the crew found both marked and unmarked rainbow trout, mountain whitefish and Wood River sculpin. They only count fish over 100 millimeters in length and are primarily focused on the game fish.

Fish caught on the first day of the study are marked with a hole punch in their tail fins. The missing bits of fin heal within two weeks, Megargle said over the din of the generator. The team fishes to the roar of the motor and counts to the peaceful rush of the rapids.

"Recapture 230 ... 480 kinda skinny, 210 ... 390, 100 whitefish, 200 left over hook in his lip," recites regional fisheries biologist Chuck Warren as he measures the length of the fish anesthetized in a mixture of clove and ethyl alcohol. Recaptured fish are the marked fish from the week before.

Megargle compares the process to fishing in a jar of jellybeans. You mark the ones you take out, put them back in and then fish again. The second turn will draw a mix of marked and unmarked beans. The numbers are factored into an equation to supply an estimate of the contents of the full jar.

The ratio of recaptured fish to unmarked fish is used in an equation to compute the population estimate.

Fisheries biologist Chuck Warren measures a sedated fish as conservation officer Lee Garwood and seventh-grade science teacher and volunteer Janene Alleman look on. Fisheries technician Karen Frank keeps a tally on a hand held computer.  Express photo by David N. Seelig

Once measured and recorded in a handheld computer complete with GPS coordinates, the fish are released back in the river near where they were captured.

"We try to get the fish in and out of the drugs as soon as possible," Megargle said. "Not everyone understands what we are doing. People think we’re killing the fish." Watching the crew chase after the shadowy fish with electrically charged poles it is hard to think otherwise.

The power coming from the generator is about 250 volts and 2 to 3 Amps. The crew can barely feel a tingle in the water.

Managing the catch, several crew members take more than a little water over the tops of their waders. Just as a safety precaution the boat steward manages a release button on the power, which automatically stops the flow of current if the tender lets go.

As fish come in contact with the circle of electricity, the impact—called galvanotaxis—causes an involuntary muscle contraction that forces the fish to swim upstream, making them easier to catch.

There is natural mortality in any stream, Megargle said. But even compared to angling mortality and first year mortality, only one half of a percent don’t make it because of fish shocking.

"More fish die over the winter," he said. "Most fisherman who stop by and see what we are doing are gracious and understanding."

 

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