The Wyoming Game and Fish Department (WGFD) is urging anglers to modify their routine to protect fish. Hot, dry weather can heat up water temperatures and lower the overall dissolved oxygen in the water, which can stress the fish.
Catching and releasing in this weather increases their stress, and some species, like trout, may even die because of it.
“When the water temp gets up above 70 degrees Fahrenheit, there’s less oxygen in the water. Fish being cold-blooded, that creates a much higher metabolic demand on the fish themselves and so they become really stressed and kind of lethargic and then as the water temperature gets up above 75-76 degrees you can actually start to see some mortality in those fish if they don’t get a reprieve,” Casper Region Fisheries Supervisor Matt Hahn said. “If water temps don’t drop at night, it can be lethal to them.”
According to Hahn, the best thing that anglers can do this time of year is to carry a thermometer and monitor water temperatures. Temperatures are usually lowest in the morning and at higher elevations. Don’t catch and release fish if the water temperatures are over 70 degrees.
“In particular, mortality rates for say, a trout that’s caught and released on a barbless fly, under ideal conditions are going to be less than 1%. But as the water gets up above 70 degrees, that mortality rate starts to tick up really quickly. From 70 to 75 degrees, it escalates really rapidly, and so you can get up to 75% plus mortality on fish when you’re in the mid to upper 70-degree range,” Hahn said.
Anglers can also protect fish by reducing fight and handling time.
“Things like artificial flies and lures inherently across all water temperatures result in a lower mortality rate on released fish. So obviously, that’s going to hold true with warmer water as well,” Hahn said. “And then pinching the barbs just makes it that much easier to release the fish. You can usually flip the hook out without even taking the fish out of the water.”
If you choose to fish when water temperatures are over 70 degrees, take into consideration the likelihood of catching fish within legal size limits and keep those that are the correct size.
“If you’re fishing in an area, say there is a 20-inch minimum length limit like is common on some of our popular fly fishing waters, and water temperatures are high, there’s a really high probability that you’re going to kill a large number of the fish that you catch. And it’s not legal to keep them at all, so it really is an ethical thing,” Hahn said. “And people need to be aware of that and think about the future of the resource and try not to cause undue harm.”
Have a question about this story? Contact the reporter, Ivy Engel, at iengel@uwyo.edu.
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