LITTLE ROCK – Anyone who has ever had their breath taken away after sitting in a car that’s been parked in the summer sun will tell you that even a momentary drop in oxygen can turn things upside down. The same holds true for fish if the dissolved oxygen in a pond or lake crashes.
According to Eric Brinkman, Assistant Chief of Fisheries for the Arkansas Game and Fish Commission, fish kills associated with low oxygen levels can be common in many small bodies of water during summer.
“It can happen on any body of water or a section of a body of water, but the most common places we get fish kills like this are smaller ponds on people’s property,” Brinkman said.
Brinkman says the factors leading up to a fish kill because of low oxygen are more complex than the simple fact that hot water holds less oxygen.
Life Overload
“There’s a lot going on in summer,” Brinkman said. “Fish are cold-blooded creatures, so their metabolism rises with the temperature. A higher metabolism means more activity and more oxygen demand.”
The amount of life in the system also is at its peak. Fish and insects that hatched all spring add more demand for the dissolved oxygen available.
“Summer also brings an abundance of vegetation, phytoplankton and zooplankton,” Brinkman said. “Which all use oxygen as well.”
It’s common knowledge that plants provide oxygen when they create sugars through photosynthesis, but few people realize those same plants use part of that oxygen when they use those stored sugars to survive.
“An abundance of fish, insects and plankton can consume a lot of dissolved oxygen, especially at night or during prolonged periods of cloudy weather, when photosynthesis slows due to lack of sunlight,” Brinkman said.
Many fish kills associated with this sort of oxygen depletion occur in the very early morning, when oxygen levels are at their lowest, but they may happen at any time of day if cloud cover has prevented photosynthesis for multiple days.
In the case of a recent fish kill on Lake Conway, the primary culprit likely was low oxygen as a result of this overabundance of fish and vegetation.
“The fish that once occupied nearly 6,000 acres of water are now sharing 2,000 acres, so oxygen is at a premium,” Nick Feltz, fisheries supervisor at the AGFC’s Mayflower Office, said. “This was inevitable and is one of the reasons we lifted the limits on fishing since the announcement of the drawdown last year. Most of the fish we’ve seen affected by this fish kill were drum, yellow bass and other rough fish, but a few largemouth bass, crappie and catfish have been seen as well.”
Feltz says he expects to have additional natural fish kills on portions of Lake Conway throughout the drawdown.