Press "Enter" to skip to content

Fish and the heat wave

From this week’s Idaho Weekly Briefing: An Idaho Fish & Game report on how this summer’s heat may be affecting fish and fishing rules.

Warm water temperatures came earlier than usual to many of Idaho’s fishing waters, but it’s unlikely to lead to fishing closures or restrictions similar to those that neighboring states have implemented.

“In many streams, what we’re seeing this year with water temperatures happens every year, we’re just seeing it sooner than normal,” said Jim Fredericks, chief of the Department of Fish and Game’s fisheries bureau.

A heat wave in late June and early July spiked water temperatures, but many waters have since cooled to normal summer temperatures. That doesn’t mean fish haven’t been stressed, particularly trout and other coldwater species, but conditions are not likely to affect fish populations now or in the near future based on current water conditions.

Warm water is a common occurrence during summer, and several factors come into play when it happens. Summer migrations into headwaters, cold tributaries or around underwater springs are a normal part of life for trout in many Idaho rivers. In lakes and reservoirs fish move to deeper, cooler water. Many rivers, or portions of them, have dams that allow water temperatures and flows to be adjusted.

The feeding activity of the fish also helps minimize the problem. Fish that can’t find cooler water typically become lethargic and decrease or stop eating, which means slow fishing and a corresponding drop in fishing pressure.
While closures in neighboring states won’t affect Idaho, Oregon and Washington have implemented restrictions on the Snake River where it shares a border with Idaho.

Joe DuPont, Fish and Game’s Clearwater Region fisheries manager, said fishing pressure for sturgeon, and catch rates in the Snake River from Idaho anglers, are likely to be low.

“I’m confident the sturgeon in the Hells Canyon reach of the Snake River are not going to be impacted by anglers due to temperatures,” DuPont said. “Catch rates drop so much that very few get caught. You can’t stress them out if you can’t catch them.”

The department is monitoring the Snake River, and he noted that during spring, two dead sturgeon were reported by multiple callers to the department.

“When a sturgeon dies, we get repeated calls,” Dupont said. “If large numbers were dying, we would know about it.”

Fish and Game officials have the authority to implement emergency fishing closures in extreme cases, although they aren’t expected.

That’s not to say anglers won’t see some noticeable effects from warmer. Anglers and others may see localized fish die offs, a few of which have already occurred. Anglers may also notice the effects of stress on individual fish, such as parasites, lesions and other physical signs.

Anglers can also reduce stress on fish by not fishing during the warmest parts of the day, and if they plan to release the fish, land them quickly and carefully release them. If anglers see fish go belly up after being released, they may voluntarily stop fishing until the water cools. Early mornings are typically when the water temperatures are coolest during the day.

The window when temperatures are above a comfortable level for fish are typically short-lived, and most fish can withstand the temporary stress. As water cools, typically in late summer when days get shorter and night temperatures drop, fish resume their normal routines and anglers will likely see catch rates improve. (photo/Nan Palmero)

Share on Facebook