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Paddlewheel and fountain aerators help add oxygen to small ponds during extremely hot periods.

Paddlewheel and fountain aerators help add oxygen to small ponds during extremely hot periods.

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, district fisheries supervisor for the Arkansas Game and Fish Commission in Hope, fish kills associated with low oxygen levels can be common in many small bodies of water during late 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.

“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 fish in the system also is at its peak during the summer. 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.”

Everyone who’s had third-grade science learned plants provide oxygen when they create sugars through photosynthesis, but plants also use part of that oxygen when they burn those 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. “Typically fish kills from depleted oxygen will occur in the very early morning, just before sunup oxygen levels are at their lowest.”

Fish kills resulting from low oxygen also can happen during sudden events called “turnover.” During the hottest part of summer, water will separate, or stratify, into two distinct layers. The upper layer will be warmer and contain most of the oxygen. The bottom layer will be cold, and contains little or no oxygen. Most fish will be in the upper layer of the water column, often very close to where the two sections meet – called the thermocline. However, a cool rain or extreme cold front can cool the surface layer rapidly, which causes it to drop to the bottom of the pond, forcing the oxygen-poor layer to the surface zone holding the fish. The rapid drop in oxygen causes large fish kills, including all species present.

No matter the cause of oxygen loss, the best solution is aeration.

“Oxygen diffuses into the water from the surface quicker if there’s a lot of splashing and wave action,” Brinkman said. “On our hatcheries and on many farms with the proper equipment, a paddle-wheel aerator will get oxygen back into the system efficiently. A lower-cost option for ponds and small lakes is an aeration fountain to cause an adequate disturbance.”

Brinkman says once fish begin to go belly up, there’s not much that can be done, but investing in a fountain aerator definitely guards against oxygen loss and helps prevent the water from stratifying.
Another piece of advice for would-be pond owners is to limit the maximum depth of any small pond you build to less than 10 to 12 feet. Shallower systems do not stratify or turnover as easily.

“Many people think you should have some deeper water for fish to use as refuge during the hot summer months, but it’s actually a bad idea when you’re talking about smaller ponds,” Brinkman said.

Anything that adds nutrients to the system during summer also can increase the demand for oxygen. Overabundant fertilization, runoff from agriculture or sewage treatment areas and livestock waste all can increase the fertility of the system too much and eventually lead to a crash.

Telltale indicators that you may have a turnover occurring on a pond are an overnight change in the water color from relatively clear to a “chocolate milk” appearance, a foul, rotting smell and fish opening their mouths, or “piping,” at the surface of the water. These symptoms are much more prevalent in the morning just as the sun rises.

If a person sees a fish kill, they can call their local AGFC office and ask to speak to a fisheries biologist. They can walk you through a series of questions to determine whether the kill is due to oxygen depletion or if other factors are at play. A list of regional offices is available at http://www.agfc.com/aboutagfc/Pages/AboutRegionalOffices.aspx

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John Duncan with yoyoguideservice.com finds crappie deep in summer.

John Duncan with yoyoguideservice.com finds crappie deep in summer.

Each spring, anglers comb the shallows at DeGray Lake in Hot Spring and Clark counties, probing tiny jigs and minnows at any likely looking spot in search of crappie. Rarely do anglers leave empty-handed when the dogwoods are blooming and the fish are spawning. But once summer’s heat sets in and the fish move out of the shallows, most anglers hang up the jigging poles or use the same tactics as spring, leaving the lake with hungry stomachs and a bare live well.

John Duncan, owner of yoyoguideservice.com says catching crappie once the spawn has ended can be just as good as when they’re on the beds. Anglers just have to switch to deep-thinking mode. Once the water’s surface temperature begins to creep into the 80s, crappie seek the comfort of cooler water found a little deeper.

“If you just look across the surface, there doesn’t seem to be hardly anything to hold fish, but it’s a different world under the water,” Duncan said. “The Corps [of Engineers], the Game and Fish and some local anglers have sunk a bunch of brush piles throughout the lake, you just have to look for them.”

The latest electronics can be extremely helpful in finding brush piles made of branches and woody cover, but can be tricky to read when searching for brush made of bamboo or river cane, materials extremely popular with crappie anglers.

Brush piles made of cane or bamboo often appear better on standard 2D sonar instead of side-imaging or down-imaging units.

Brush piles made of cane or bamboo often appear better on standard 2D sonar instead of side-imaging or down-imaging units.

“If you’re using a side-imaging depth finder, wood will show up easily, but bamboo brush piles may only look like a shadow on the bottom,” Duncan said. “Sometimes you have to go right over it before you can really see what it looks like.”

Anglers who can’t afford high-dollar electronics still can find plenty of offshore options for crappie, it just takes a little more effort and elbow grease. A five-gallon bucket, some hand-cut bamboo and some fast-setting concrete is all it takes to create your own brush piles and place them wherever you want.

“Bamboo offers excellent cover, and lasts for a few years in the water, but it’s much easier to work with and not as heavy when it’s time to place your brush pile,” Duncan said. “Just be sure to cut the bamboo where a node or stem is coming off the main stalk so it stays firmly in the concrete for years.”

Duncan says he’s placed about 24 “crappie condos” in DeGray Lake in the last year, and many have turned out very productive.

“You learn as you go along about where to place them,” Duncan said. “If you see a shoreline with a lot of cover, there’s already plenty for the fish to congregate on. Sink your cover in an area with a rocky bottom but no trees or vegetation and it usually is going to produce much better.”

The Arkansas Game and Fish Commission has plenty of fish attractors in DeGray Lake to get anglers started, and all of them are only a click of a mouse away. Just visit www.agfc.com and click on the “Interactive Map” icon underneath the banner on the front page. Zoom in to DeGray Lake, or any lake you’re interested in, to get the locations of any fish attractors found on that body of water.

“As time goes by, some of the attractors deteriorate or are moved by currents or anglers,” said Chris Racey, chief of fisheries for the AGFC. “So you need to get the GPS coordinates for as many as you can to make a ‘milk run’ until you find a good one.”

Racey also says it’s important to contact the owner of a lake before placing any fish attractors.

“Some agencies do not allow sinking brush in their lakes, while others have restrictions on the materials fish attractors may be made of,” Racey said. “

When Duncan hits the water to fish the deep brush he or others have planted, he wastes little time with lure selection. A minnow suspended underneath a slip float gets the nod almost every time when he’s guiding and serious about catching fish.

A standard slip-cork rig using a no. 6 cricket hook baited with a minnow gets the nod when Duncan's serious about catching fish with clients.

A standard slip-cork rig using a no. 6 cricket hook baited with a minnow gets the nod when Duncan’s serious about catching fish with clients.

“My boat is outfitted with enough rod holders to run 32 poles at once, but I rarely will put out more than two poles per person,” Duncan said. “On an older boat, I ran 12 poles with three jigs on each line, but one run-in with a school of white bass left me so tangled up it cured me of that chaos forever.”

One suggestion Duncan offers on the setup is to abandon the gold no. 2 or 4 Aberdeen crappie hooks often used with minnows. Instead, he uses the cricket hook popular with bream anglers in size no. 6. The smaller hook bends enough to free him of snags if needed, but doesn’t flex too much to let fish get away.

“Fishing brush in deep water can mean hitting a lot of brush piles until you find the one the fish want to be around, so I do everything I can to keep things moving quickly,” Duncan said. “A minute or two saved here and there retying can add up to hours of lost fishing time in the course of a month.”

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