Heat a factor in Dexter fish kill

Thursday, July 5, 2012

DEXTER, Mo. -- Thousands of fish, most of them gizzard shad and small crappie, washed up on the banks of Dexter City Lake over the weekend, the result of what the Missouri Department of Conservation and Dexter Parks director Lawson Metcalf say was a "natural event," primarily due to the recent extreme heat.

Metcalf said the kill is the first one of its kind since the pond was renovated 15 years ago and perhaps in the pond's history. The five-acre pond is about 11 feet deep at its deepest point near the fishing dock, but only about five feet deep in the center.

A local resident fishing there Sunday morning witnessed several fish surfacing.

A natural fish kill occurs when a number of factors are in its favor, and for the local pond, all circumstances were in the kill's favor Saturday.

"We were set up to fail with conditions being what they've been," Metcalf said Monday. "We had the extreme temperatures and the pond is shallow, plus we have an algae bloom which also contributes to this happening."

The algae, Metcalf explains, puts off a toxin when it blooms.

"Even though the water is a couple of feet deeper this year than last year due to the placement of rip-rap to solve the muskrat problem, the heat, the pond levels, and the algae bloom combined to make this happen. All of those factors caused the dissolved oxygen in the water to become depleted."

And when fish lack oxygen, fish die. When they die, they lie at the bottom of the lake for 10 to 12 hours before surfacing. So the kill is believed to have occurred sometime Saturday night.

Another factor working against the local pond was the population of shad and crappie there. Neither species was introduced to the city pond when it was originally stocked because neither is beneficial to a pond the size of the city's.

"We believe some anglers probably threw some in thinking it would be beneficial," Metcalf said, "but you can see by the numbers on the bank how they've multiplied and they're using much of the pond's oxygen. Those fish are massively overpopulated. The lake is too small for those numbers. That, I believe, also contributed to the fish kill."

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