Winter affects fish in different ways

Sandusky, Ohio — While there’s plenty that fisheries biologists don’t know yet about how a warm winter affects fish in Ohio, there’s much they do.

This year’s warm winter has offered Ohio fishermen more opportunities to fish open water, but it’s not necessarily a joy ride for the fish.

When it comes to two of the state’s most sought-after fish species – walleye and yellow perch – warm winters have been generally associated with poor reproduction, said Roger Knight, Lake Erie fisheries program administrator for the DNR Division of Wildlife.

“There’s research that go back to the 1970s that suggest that walleye and yellow perch, that family of fish, need a period of cold weather for their gametes to mature. … The bottom line is there’s scientific evidence that suggests that cold winters are necessary for them to throw good hatches,” he said.

Troy Farmer, a graduate student at Ohio State University, is testing that hypothesis on yellow perch in the university’s aquatic ecology laboratory.

He’s got 300 perch all experiencing simulated winters. They’ve been divided to experience either a mild, average, or extremely cold winter.

“Then we’ll open them up and score their egg development,” Farmer said.

He’s also using historical data to test another theory that poor reproductive years are a result of warm winters, making it easier on invasive white perch, which in turn gobble up the young yellow perch at higher rates.

As Knight put it, there are so many possible factors that play into reproductive success.

For example, regarding the closely related walleye, the cold winter theory doesn’t guarantee reproductive success. If a cold winter is preceded by a very wet spring, that could also spell trouble.

A theory is that the small walleye are either flushed past the plankton-abundant bays that provide the forage, turbidity and cover they need and back into the main part of Lake Erie to soon or that the river, with its increased velocity, is just too harsh on a developing walleye.

“When it’s really wet, they might be pushed out too quick,” Knight said.

But what of Ohio’s inland fish?

Ethan Simmons, a fisheries biologist, said it means some fish, such as saugeye, appear to be a little more active, which is good for fishermen.

“More fishermen can get to them easier,” Simmons said.

The increased temperatures means the fish may have to eat more, since they need more energy.

“When it’s really cold, their metabolism slows down,” he said. “They don’t have to move that much and they don’t have to eat that much. When it’s warmer, their metabolism increases so they need to move around more.”

Simmons hesitated to say that there would be a drastic effect.

“It’s hard to say,” he said. “It’s not like the water out there is 60 degrees. It’s still almost freezing. We don’t have the ice cover, which can be beneficial.”

Lack of ice cover can also be of benefit to fish.

If there’s ice and a sheet of snow sitting on top, it can block out sun, and shut down photosynthesis of plankton and algae, which are needed to provide oxygen.

If oxygen levels get too low, that can lead to winter fish kills, so that’s something entirely avoided by a warmer winter.

And thus far, it hasn’t been so warm that another species associated with regular winter die-offs, gizzard shad, get a free pass.

“That’s the most abundant fish in any of our reservoirs,” Simmons said.

Typically, it’s the young-of-year shad, at about four inches, which die off when the water temperature drops to about 40 degrees. That’s an important mechanism in keeping shad from multiplying out of control.

“The temperatures are still at a level where they’re still going to die off,” Simmons said.

As a general rule, Simmons stressed that most of the state’s inland fish can handle the year-to-year swings.

“These fish are so adapted to variability in their environment,” he said. “I don’t think these minimal changes have a big impact. It’s more so just us saying, ‘This is a really crazy winter.’”

From a fisherman’s perspective, it has been crazy. There’s been open water on Lake Erie, open water on the reservoirs, and the state’s steelhead streams have also been wide open.

“It more impacts the fishermen,” Simmons said. “They can get out and enjoy some of that soft water.”

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