Excessive heat, drought taking toll on fish populations

By University of Illinois Extension serving Boone, DeKalb and Ogle Counties

Many people are starting to report massive fish kills around the United States. It is not a surprise to experts who recognize the water habitats, whether they be ponds, lakes or rivers, are suffering with low water levels and rising temperatures.

Peggy Doty, University of Illinois Extension educator, explained: “Often when fish kills are reported, in a more normal weather pattern, experts start looking for point or non-point source pollution as possible causes, if nothing else just to rule them out. In a situation with excessive heat and drought, we don’t have to look for a problem.”

Reduced water amounts, along with high water temperatures don’t carry enough dissolved oxygen for the fish to utilize. As one would expect, the fish that need the most to sustain themselves often die first.

Large catfish may go first, followed by bass, and finally the pan fish.

Private pond owners may notice nothing unusual one day, and find piles of floating fish the next. There is not usually a 100 percent kill in any one body of water; however, the predator/prey balance may get thrown off enough that a fishery management plan for restocking may be in order for the following year.

It is also the time of year when we get algae blooms. An algae bloom simply means a mass amount of small aquatic plants, many of which are microscopic, growing rapidly at the same time in an aquatic environment. We tend to recognize them when they are bright green and floating just below the water surface, but some species may be red, brown or sometimes yellowish in color. Because algae is a plant, it, too, requires the already reduced oxygen from the water.

If that isn’t hard enough for the fish and small aquatic beings, when the the algae dies, bacteria are then needed to consume it, and they, too, require oxygen,” Doty said.

This is one more way of proving how a drought can affect so many levels of our existence.

From the Aug. 1-7, 2012, issue

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