Lee Holt, a fisheries biologist for the Arkansas Game and Fish Commission, works mostly in the state’s eastern counties in the Mississippi River Delta. In several years of working the area, he says he’s never seen as many waterways as low as they are right now.
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“In addition to the drought, as hot as it is, there’s a lot of surface evaporation,” Holt said. “It’s reducing the amount of available water and pushing the fish populations into a smaller area.”
Such conditions can lead to fish die-offs, and Holt says it’s almost inevitable that his telephone starts ringing with reports of dead fish when scorching temperatures and drought are in play.
“Summertime conditions like this exacerbate things,” he said. “And every time that happens this time of year, we’re going to get a call.”
You don’t need an advanced fisheries biology degree to know that droughts are bad for fish populations. But with drought conditions expanding across much of the U.S., the dry weather’s harmful effects on fisheries are becoming much plainer to see.
As this year’s drought tightens its grip on the U.S. – more than half of the continental U.S. is now under some level of drought, according to National Climatic Data Center – numerous fish kills are being reported.
Thousands of fish died earlier this month in Arizona’s Salt River, where tests showed toxins caused by Golden alga were the culprit. Although biologists don’t know exactly what causes the fish-killing toxin to develop, experts have noted a connection between extended drought, elevated salinity in waterways and fish kills.
In Missouri, where many parts of the state are more than a foot below normal rainfall, biologists from the Missouri Department of Conservation have received several recent reports of fish kills.
“The hot, dry weather isn’t just hard on humans, it’s hard on fish, too,” Jake Allman, a Missouri Department of Conservation fisheries biologist, said in a news release. “Most problems occur in ponds that are not deep enough for fish to retreat to cooler and more oxygen-rich water.
“Hot water holds less oxygen than cool water. Shallow ponds get warmer than deeper ponds, and with little rain, area ponds are becoming shallower by the day. Evaporation rates are up to 11 inches per month in these conditions.”
Fish kills also have been reported in Indiana and Kentucky, part of the same large drought area that extends from Arkansas through Missouri and up the lower Ohio River Valley.
Indiana Department of Natural Resources spokesman Phil Bloom blamed low water and high water temperatures for hundreds of dead fish at Atterbury Fish and Wildlife Area in Johnson County, 30 miles southeast of Indianapolis.
According to a news release from the Kentucky Department of Fish and Wildlife Resources, a “significant fish kill” took place on the Pond River north of Madisonville, Ken., after a brief rain shower pushed a slug of heated water containing little or no dissolved oxygen downstream. The fish kill mainly affected catfish, but carp and buffalo were also victims. Kentucky Fish and Wildlife biologists recorded water temperatures of 95 degrees in the river.
Plants and algae in waterways can lead to additional problems for fish during times of extreme heat and drought, when less water can lead to increased aquatic plant growth.
“Too many plants or too much algae causes wild daily fluctuations in oxygen levels,” said Missouri’s Allman. “Sunlight during the day fuels aquatic plants and algae to produce oxygen through photosynthesis. At night the same plants use this oxygen at a high rate for respiration.”
Even clouds aren’t necessarily good news.
“An overcast day with little sunlight can prevent plants from producing oxygen during the day,” Allman said. “That can cause oxygen levels at night, when plants are using the oxygen, to dip below levels needed to sustain fish.”
In the Mountain West, thin snowpack and a dearth of spring and summer rain have reduced flows in many streams. In the Northwest, reservoirs on the Columbia, Snake and Salmon rivers have forced managers to scale back power generation at hydroelectric dams, and even though water is being released for agriculture and salmon, the fish likely will find fewer places to spawn.
According to the National Drought Summary released July 19, stream flows were in the lower 10th percentile of record, or at record-low values, across much of the Midwest and parts of the Central Plains, West, Southeast and even parts of New England.
“I’m kind of concerned that by the end of August or early September, if we don’t see some relief from the drought, we could have some major problems,” said Steve Filipek, the Arkansas Game and Fish Commission’s assistant chief of fisheries and the state’s Stream Team program coordinator. “Streams are certainly being affected, and also ponds and lakes. The real problem will be if the conditions persist for consecutive years, then we could see major impacts.”
In addition to problems with low dissolved oxygen, biologists also note that lower water levels brought on by drought and the evaporation associated with high temperatures can cause unhealthy concentrations of fish in a body of water.
“It can concentrate the prey fish with the predators,” Filipek said. “And if those conditions persist over a long period of time, you can start to see some problems.”
Filipek suggested that anglers can help by putting less pressure on fish populations during times of drought.
“I went out the other day on the Caddo River with my son and we had a great day of fishing,” he said. “The fish were concentrated in a few areas. But I’d just encourage anglers not to wear out the fish just because you can. Think about it from a conservation standpoint. If you want to keep some fish, that’s OK, but take out fewer fish than you usually would.”