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JULY 8, 2010

Weird weather stressful for fish

By Phil Cooper, IDFG

   May and June are stressful months for warmwater fish, such as bullheads, perch, bass, crappie and sunfish.

   These are the months when most warmwater fish spawn, taking a lot of a fish's energy. On top of that, water temperatures typically rise fairly rapidly.

Fish, being cold-blooded animals, are sensitive to temperature changes, so dramatic swings in temperature, particularly around the time when fish are stressed from spawning, can take a toll.

   Jim Fredericks, Idaho Panhandle Regional fishery manager with Idaho Fish and Game, notes that it's common for people to see a few dozen fish dead or dying around the edges of northern Idaho lakes this time of year.

   "It's very common to see a die-off of bullhead catfish and sunfish in some of the regional lakes," Fredericks said.

   In most cases, early summer die-offs are the result of a thermal shock on post-spawn fish. There's generally no risk of swimming in the water or eating healthy fish caught from the lakes.

   The unusually cool May and June this year, with a few warm days mixed in, seems to have been particularly stressful in a couple of area lakes. Fish and Game received a number of reports about dead fish in Spirit Lake as well as Blanchard Lake over the past week.

   Biologists with Fish and Game and the Idaho Department of Environmental Quality have investigated recent fish kills, and they have observed several dozen fish, representing a variety of species and sizes.

   "In terms of the total number of dead fish, it's certainly not what I'd call a major die-off," Fredericks said. He notes that they observed many healthy fish rising and around the shoreline as well. "Based on the condition of the dead fish, the indications are that it was temperature related and not the result of any toxicant or disease," he said.

   Just to be sure, Fish and Game and a U.S. Fish and Wildlife Service pathologist will be collecting some fish to conduct tissue samples next week.

   In addition, Fish and Game and the Department of Environmental Quality will continue to watch Spirit and other lakes around the region where dead fish have been observed.

   “My guess is that we've seen the worst, but we'll definitely keep an eye on it,” Fredericks said.