Many more lake trout released by Lake Superior anglers die when water temperatures are over 50 degrees than originally thought, according to a new fisheries study on Lake Superior and Lake Huron.
Results of the study, led by a researcher at the Michigan Department of Natural Resources in Marquette, will soon be published in the North American Journal of Fisheries Management.
Research from the 1980s indicated that only about 15 percent of lake trout died after being released, said Cory Goldsworthy, Lake Superior Area fisheries supervisor for the Minnesota Department of Natural Resources. The new research indicates that more than 40 percent of lake trout caught and released by anglers die when surface water temperatures exceed 50 degrees.
The study's findings will be important for trollers on Lake Superior, Goldsworthy said.
"It means that when you let lake trout go in water over 50 degrees, you're killing a lot of fish," Goldsworthy said. "You should do your best to keep the fish you hook rather than sorting through 10 or 12 fish to get the size you want."
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Typical surface temperatures on Minnesota waters of Lake Superior are over 50 degrees in July, August, September and early parts of October, Goldsworthy said. This year surface water temperatures already exceed 50 degrees, according to data from a weather buoy near the McQuade Small Craft Harbor, he said.
The lead researcher for the study was Shawn P. Sitar with the Michigan DNR.
Lake trout regulations in Minnesota waters include no minimum size limit and no slot limit, so anglers are free to keep any size of lake trout in a limit of three fish.
According to recent creel survey data - based on interviews with anglers at boat landings - anglers in Minnesota waters released about 2,500 lake trout in 2015, or about 10 percent of the estimated harvest of 26,627 lake trout, Goldsworthy said.
Wisconsin's lake trout regulations vary by zone under a recent rule change. In the area west of Bark Point (near Herbster), the area known as WI-1, the daily bag limit is three, with a 15-inch minimum size limit, and only one lake trout may be over 25 inches.
In the area known as WI-2 extending east of Bark Point, only two lake trout may be harvested per day. They must be greater than 15 inches, but only one may be greater than 25 inches.
"(The study) changes our perception of catch-and-release," said Bradley Ray, senior fisheries biologist with the Wisconsin Department of Natural Resources at Bayfield. "We incorporated this in the latest emergency (lake trout) rule. Instead of having a 'skinny' slot (a 20- to 25-inch harvest slot limit) as we did in the previous two years, we went to the 15-inch minimum size and one over 25 inches. We knew this was coming, and we didn't want to encourage the release of those fish under 20 inches that could experience this high mortality."
