FISHING -- How many of the lake trout die after being caught from the depths of Priest Lake and released?
Idaho Fish and Game Department fisheries biologists have launched a study to find out.
The study survival rates will help biologists understand whether mortality of caught and released fish is high enough to be an issue of concern, said Jim Fredericks, department regional fisheries biologist in Coeur d'Alene.
"Lake trout are typically found near the bottom of relatively deep lakes, often in 100-200 feet of water," he noted. "When brought to the surface from such depths by anglers, they sometimes get a fishy version of the bends. The pressure change causes a condition in the fish known as barotrauma in the scientific world.
"As many species of fish, lake trout have an internal air bladder that helps them regulate buoyancy. When a fish swims from deep to shallow water, it naturally expels air from the bladder, just as a scuba diver releases air from a dive vest. Deepwater dwelling fish can have difficulty expelling air when pulled from depth by anglers, causing over-inflated gas bladders."
Extensive research has been conducted on the effects of barotrauma on survival of caught-and-released marine species, but little has been done on lake trout, he said.
Research based on angler creel surveys conducted on Priest Lake in 2014-2015 indicate that fishermen release about a third of the lake trout they land. "What is less certain is the number of fish that die after being released," Fredericks said.
"If the number released that die turns out to be a small percentage, then it really is not a concern," he said, noting that management considerations would be made if the number is high.
"With the help of volunteer anglers, IDFG will be capturing up to 200 lake trout in early May. The fish will be released into a large pen anchored in Indian Creek Bay. Each fish will be individually tagged to enable the biologists to record the depth of capture. Once released, the size of the pen will allow the fish to return back to a depth of 100 feet. After about a week, the pen will be pulled and the fate of the fish will be evaluated."
The study is part of a much larger lake trout-related research effort that began in 2013 as the agency develops a long-term management plan for the Priest Lake fishery.
Researchers did a large-scale population assessment in 2013 using commercial-scale netting equipment. An angler creel survey conducted over the past year has provided an estimate of how many lake trout, kokanee and other species are caught and harvested or released in a given year.
- Updates on several Priest Lake fishers studies will be presented by Idaho Fish and Game Department fisheries staff at 7 p.m. on May 27 at the Senior Center in Priest River.