As Texas continues to suffer from the worst one-year drought on record along with scorchingly high temperatures, area lakes might seem like the best places to find refuge from the heat, but apparently not for fish. According to state wildlife officials, in one lake alone some 124,000 fish perished last week in the extreme weather conditions, not from a lack of water, but from a lack of oxygen -- an oft overlooked consequence of rising temperatures which may become more common as heat-spells grow more intense and prolonged.
Texas Parks and Wildlife Department say that the mass fish die off that occurred recently at Lake Grapevine, near Dallas, involved mostly Threadfin shad, a small species of fish often used as bait, though many others were killed as well. State biologist Tom Hungerford says that among the dead fish "stacking up" at the lake were gizzard shad, bluegill, white bass, freshwater drum, largemouth bass, smallmouth bass and white crappie.
According to the Grapevine Courier, the fish at Lake Grapevine essentially suffocated due to a heat related phenomenon that depletes oxygen levels in water, rendering the lake ecosystem uninhabitable for fish:
Low oxygen Monday and Tuesday killed the fish, [Hungerford] said. On Tuesday, when temperatures reached 103 degrees at nearby Dallas/Fort Worth Airport, the hypoxia, or oxygen depletion, level was 1.2 parts per million.
"Anything under 3 parts per million and you start to see fish die," Hungerford said.
The lake received 0.02 inch of rain Monday, according to the U.S. Army Corps of Engineers, which manages the lake. The lake is down more than 3 feet from its normal level. That decrease and the constant heat are the likely culprits for the fish kill, Hungerford said.
"The hotter the water gets, the less dissolved oxygen it can hold," he said.
As such hot summers and crippling droughts are expected to become more common in many global warming scenarios, more aquatic ecosystems could face similar die-offs -- perhaps one of the least considered impacts of climate change.