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Winter fish kills no cause for alarm

Winter fish kills no cause for alarm

Phenomenon widespread because of severe winter

March 9th, 2014 by Missouri Department of Conservation (press release) in News

The sun comes out and the temperature climbs bravely into the 40s. You shake off cabin fever with a stroll around a lake or pond and through the neighborhood. Birds are singing and the fish in the pond are ... dead!

People are calling Missouri Department of Conservation (MDC) offices with stories like this one. They are sad to see dead fish and concerned about what might be killing them. The Department appreciates callers' vigilance, but officials said the fish die-offs documented so far are not related to serious pollution or disease issues.

MDC resource scientist Rebecca O'Hearn said winter fish kills are normal occurrences. What is not normal, she said, is the number and size of this year's kills.

"We are getting dozens of reports of significant winter fish kills from all over the state," O'Hearn said, "from places with shallow water, such as Eagle Bluffs Conservation Area, and from huge water bodies such as Truman and Table Rock lakes, Lake of the Ozarks, and Pomme de Terre and Stockton reservoirs."

The abnormal size and number of fish kills is related to abnormally cold weather. Missouri State climatologist Pat Guinan said the period from Dec. 1-Feb. 28 was the coldest since the winter of 1978-79 and the ninth-coldest on record.

How cold was it? Guinan said it was cold enough to cause a rare phenomenon known as "frost quakes" in eastern Missouri. These occur when the temperature drops so fast freezing soil expands rapidly and builds up pressure similar to the pressure in much bigger seismic zones deep in the earth's crust. Release of this pressure produces popping, cracking noises like the ones people reported hearing Jan. 26 and Feb. 2.

That same cold dropped the temperature of water and created unusually thick, widespread ice. Conservation Department fisheries management biologist Greg Stoner observed Lake of the Ozarks was a solid sheet of ice from Bagnell Dam to Truman Dam in January, a rare occurrence.

Then came the snow. Winter storms dumped more than a foot of snow overnight in parts of Missouri. O'Hearn and Stoner said that can be a lethal combination.

"Deep snow can prevent light from reaching aquatic plants," O'Hearn said. "Without light, plants begin to die, and when they die, they not only are not releasing oxygen into the water, their decomposition actually consumes oxygen. If that goes on for long enough, like it has this year, fish can suffocate."