Winter die-offs of fish likely, DNR says

I was slogging along the edge of my pond the other afternoon and was surprised to find a painted turtle along the edge, its neck stretched out of the water, taking some fresh air.

The painter was understandably sluggish as it floated in the two-foot-wide band of icy meltwater that had elbowed its way along the edge of the mostly iced-in pond. He barely moved as I approached; in summer, painters and other turtles disappear at first sight in a plunge to the safety of the depths.
Most of my pond remains a very thick ice cube, likely frozen deeper from this past record-cold winter than any time in its 40 years. The ice only slowly is relaxing its death grip.

But the turtle was a sign that at least some aquatic creatures survived the winter’s ravages. I suspect the frogs, buried in bottom much for the duration, will reappear as well in due course as the thaw proceeds. The fish may not have been so lucky, according to state fisheries biologists, who have issued the annual don’t-be-surprised-if warning about overwinter fish kills.

Small shallow ponds like mine are especially vulnerable to these “winterkills.” They are caused when thick ice shuts off circulation of oxygen between water and air and by the blockage of sunlight into water beneath the ice. If these conditions persist, the oxygen levels draw down so low that some or all of a pond’s fish suffocate to death. Also, with a lack of penetrating sunlight, plants stop making oxygen and eventually start to burn it as they die and decompose.

The Ohio Department of Natural Resources says that some fish die-offs are expected statewide this spring, including in larger lakes as well this year, though in the latter case for different reasons. Species such as gizzard shad are less tolerant of long, cold winters, and dieoffs of shad commonly seen along the shorelines of reservoirs and even Lake Erie during moderate winters. But in larger bodies of water, these species that commonly die off following winter are resilient and return in great numbers following a single spawning season.

The Ohio Division of Wildlife notes, however, that unusual water coloration, strong odors or other unusual conditions in association with fishkills may indicate something other than a natural winterkill. In which case, call 800-WILDLIFE to report the case.

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