Fisheries biologists at ready after long winter

Springfield — There’s a good chance that fish living in smaller ponds across Illinois didn’t make it through the winter, Dan Stephenson, Illinois DNR assistant fisheries chief, said.

“As soon as the ice goes out, private pond owners are going to see dead fish along the shoreline,” Stephenson said.

And it isn’t necessarily the extremely cold temperatures, which were once much more common, that directly causes winter kill. Instead, it’s the lack of oxygen, which was made worse this winter in Illinois since snow sat atop many ponds across the state for the better part of winter. The snow blocks sunlight from penetrating the ice, which prevents any oxygen-creating photosynthesis from occurring.

In that respect, the consistently cold temperatures played a role by not allowing that snow to melt.

Stephenson said any ponds or smaller lakes with maximum depths shallower than 15 feet could see problems, with potentially substantial fish kills. Deeper water and volume allows lakes to maintain higher oxygen levels.

And even if not all fish were wiped out, winter kills can knock a pond’s fish community so out of balance that what is remaining needs to be killed off before the pond can be restocked.

“If you lose all of the bass but the bluegills live, you never get the pond back in balance,” said Ken Clodfelter, an Illinois DNR district fisheries biologist in northwest Illinois. “You need predators, and you need prey for the predators.”

Gizzard shad and freshwater drum are often associated with sensitivity to extreme cold, but it’s larger fish such as catfish, bass, carp and some of the larger sunfish that tend to die first when there is a lack of oxygen, since they require more oxygen to survive than smaller fish.

The good news is that those conditions don’t exist in most larger bodies of water, rivers and Lake Michigan.

“Major lakes and river shouldn’t have any problems at all,” Stephenson said.

Clodfelter, whose district borders the Mississippi River, said while the big river should be largely immune to winter kill, there is some potential for the problem in backwaters of the river, especially if fish get trapped in shallow water.

Unfortunately for private pond owners, DNR discontinued a program that helped them restock their ponds at a cost of $25 plus a dollar per acre.

Stephenson said DNR’s district fisheries biologists, which can be looked up by county on the DNR website, can still be of help.

“They can discuss the next steps,” Stephenson said.

One of those steps will likely be contacting the local soil and water conservation district office, which often hold fish sales. Another option would be to contact a private fish hatchery.

Clodfelter said exacerbating the problem this year is the fact that many ponds that might have narrowly avoided a winter kill had lower than normal water, making them more susceptible to a die-off.

“It’s a big concern this year,” Clodfelter said early in March. “Usually we get a time where it melts down and we clear the snow off the ice, but not this year. We’ve had snow cover since December.”

While winter kill is more likely in the northern part of the state, the generally warmer southern end of the state won’t likely be completely immune, said Chris Bickers, a district fisheries biologist in southern Illinois.

“I think it’ll be less of an issue than it is north of us, but I’m expecting some,” said Bickers. “We’ve had more ice cover for a longer period of time and with snow on it for longer than we’ve had in a long time. … We’ve seen winter kills here with conditions less severe than this winter.”

For that matter, landowners of small, shallow ponds are urged to shovel snow off the surface of their ice if they can safely do so.

“Open up some windows for that sunlight to shine through,” Bickers said. “It will definitely help. It’s like cracking a curtain.”

And it’s possible some winter kill will go unnoticed, especially if it occurred early in the winter, Bickers said.

“A lot of times they don’t notice until later in the year, when they start fishing,” Bickers said. “Sometimes they don’t see dead fish, but when they don’t catch anything they start to wonder. Then they start describing the conditions on their pond and it’s pretty obvious [to a fisheries biologist].”

But it’s best to keep an eye out as the ice begins to recede.

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