Ask Zimo: Some fish die as a result of studies at Idaho’s alpine lakes

July 25, 2013 

Q: A group of us walked to a high mountain lake in the Frank Church - River of No Return Wilderness this past weekend, and on the way in we passed two Fish and Game guys who said they had gillnetted all four lakes to see how the fish are doing.

Walking around the first lake, I found 23 dead California golden trout. This lake is not very big and this put a huge dent in the population.

How are the fish doing? They are dead now. What purpose did this serve?

Needless to say, we only caught three fish out of that lake over three days. I have been going in every year for the past 25 years (except when fires have closed the road) and we usually catch and release 15 to 20 fish out of that lake.

I sure hope the hell they don’t “study” that lake again anytime soon! What a waste.


A: The Idaho Department of Fish and Game does have crews that sample fish populations in mountain lakes, and part of the sampling process does result in the killing a small number of fish in each lake.

That’s according to David Parrish, sport fishing coordinator with Fish and Game.

Fish and Game crews conduct a detailed analysis of an alpine lake on the average of once every 10 to 12 years. Sampling mountain lakes is a time- and labor-intensive management activity, he said.

“We stock most mountain lakes once every three years with roughly 500 to 1,500 fish that are about an inch in length, so we probably have two or three different year classes of fish in a lake when we sample,” Parrish said.

“If our crews just sampled fish using hook and line, we may or may not get a clear picture of how the overall fish population is doing in a lake,” Parrish said. “To maximize efficiency, we place one gill net of about 30 feet in length (a monofilament net to entangle fish) overnight at each lake we visit,” he said.

The gear is lethal for the fish, but it gives Fish and Game a better idea of the sizes (ages) and body condition of all fish in a lake, he said.

The information is used to adjust the number of fish stocked in the lake during the next planting cycle.

To make information comparable between lakes, Fish and Game standardizes net length, mesh size and soak time — which is typically overnight.

“You never know how many fish will be killed when you set a net,” he said. “It is unfortunate that 23 fish died because of our population sampling effort, but it did indicate the population of golden trout in the lake was healthy, and we were meeting management objectives.”

Parrish went on to say that the dead fish from sampling efforts were left in the lake because most mountain lakes lack nutrients that other fish and insects need to grow and reproduce.

“Allowing these fish to decay in the lake will hopefully, lead to better fishing and a healthier overall fish population,” he said.

Fish and Game decides which lakes need sampling each year based on how recent of information the agency has on the fish population in a lake.

“If we have numerous reports from anglers about outstanding catch rates and size of fish in a mountain lake, we’ll assume our fish management is working well and move the lake to a lower sampling priority,” he said.

If the agency doesn’t have recent information about the lake, it will be a higher priority for sampling.

Parrish says that if anglers want to help Fish and Game be more efficient at monitoring alpine-lake fish populations, they should provide feedback to the state agency on what kind of fishing they found at a lake.

The best way is to provide the name of the lake, location and a brief description of the size and condition of the fish that were caught. Pictures are good, too.

This can be done by going to Fish and Games’s website at and click on “contact us.”

Pete Zimowsky: 377-6445, Twitter: @Zimosoutdoors

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