Persistent thick ice and deep snow on Eastern Iowa ponds and lakes has caused an exceptional winter fish kill, according to state fisheries personnel.
“Yes, it’s as bad as we thought it would be,” said Vance Polton, a Department of Natural Resources fisheries technician at Lake Darling in Washington County.
In a normal year, his office, which serves 10 southeast Iowa counties, receives about 12 requests for restocking farm ponds that suffered winter fish kills.
“This year we are at 27 requests and counting,” Polton said.
Biologist Paul Sleeper, who manages fisheries in 10 east-central Iowa counties, said this has been the worst year for farm pond winter fish kills in the 26 years he’s worked for the DNR.
“Early ice, deep snow, no relief. You knew it was going to happen,” Sleeper said.
Polton said southern Iowa ponds were especially vulnerable because the lingering drought had lowered water levels by three to four feet, reducing the dissolved oxygen available to fish.
The ice formed earlier, got thicker and lasted longer than usual, but the kill would not have been as severe if the ice had not also been covered with more than a foot of snow all winter, Polton said.
“That turns off the light. Without sunlight, algae and other aquatic plants die. Not only do they stop producing oxygen, they consume oxygen as they decompose,” he said.
The negative effect of deep snow snaps into sharp focus when southeast Iowa fisheries are compared with those in southwest Iowa, which had similar ice coverage but much less snow.
“We had a lot of thick ice for a long time, but the wind swept off the snow, and our fish came through in good shape,” said Dray Walter, a DNR fisheries technician in the Mount Ayr district.
Walter said his office has had but one call about a farm pond fish kill.
Once oxygen levels fall below 2 parts per million, fish begin to suffer, Polton said.
Four of Johnson County’s most popular lakes — Macbride, Coralville, Sand Lake in Iowa City and the lake at Kent Park — experienced winter fish kills, according to Sleeper. Pleasant Creek in Linn County came through unscathed, he said.
At Macbride, which began to register low oxygen levels in January, many big flathead catfish succumbed, along with lesser amounts of wipers (a white bass-striped bass hybrid), crappie, Kentucky spotted bass and channel catfish.
Sleeper said he thought the 940-acre Lake Macbride was too big and deep to be vulnerable to a winter fish kill.
“But we had a bad algae bloom last year, and I think all that decaying algae on the bottom used up a lot of oxygen,” he said.
Large flathead and channel catfish also were the most prominent victims at Coralville Lake, according to Sleeper, with white bass, buffalo, carp and gizzard shad also sustaining substantial losses.
“Catfish live near the bottom, where oxygen levels are the lowest, and they get very lethargic in cold water — almost in a state of hibernation. They seem unable to move to areas with higher oxygen concentrations,” he said.
Coralville’s crappie, bass and bluegill have for the most part survived the winter, based on the observations of a commercial fisherman seining rough fish in the lake after ice out this spring, according to Sleeper.
Coralville’s fish kill would have been much worse had the Army Corps of Engineers not delayed its annual spring lowering of the lake, Sleeper said.
The Corps typically starts a four-foot drawdown on Feb. 15 to increase the lake’s storage capacity in the event of a spring flood.
“That extra water volume helped a lot,” Sleeper said.
It’s hard to quantify losses because many dead fish simply sink to the bottom rather than washing up on shore where they can be counted, he said.
At Coralville, many dead fish did wash to shore, creating a foul-smelling mess for visitors and a windfall for bald eagles, turkey vultures and gulls, according to Dee Goldman, the Corps’ Coralville Lake manager.
Goldman said as many as 100 eagles and 75 vultures concentrated at times along the shore and below the spillway to feed on dead fish.
While the birds have done much of the cleanup, staff and volunteers may be called upon to remove fish carcasses from some of the beaches, he said.
“The beaches will be ready to go by mid-May,” he said.
On the Mississippi River, low oxygen levels killed crappies and bluegills overwintering in shallow backwaters, said DNR fisheries biologist Scott Gritters.
Many of the marginal backwaters “froze to the bottom,” either killing fish or forcing them to relocate, he said.
“You get 100 days of snow-covered ice and you’ve got problems,” he said.
Despite the losses, Gritters predicts a good year for Mississippi River panfish anglers.
“We went into the winter with incredibly high panfish populations, and many of them survived,” he said.
For pond owners still uncertain of the status of their fisheries, the biologists recommend conducting an assessment with a fishing pole.
“Bass and bluegills will move shallow to spawn in the second and third weeks of May. If you can’t see them or catch them then, they probably are not there,” Sleeper said.
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