Thousands of dead fish washed up on Texas beaches in June, in part because warmer temperatures heated the waters and lowered the levels of dissolved oxygen fish need to survive.
While the Texas Parks and Wildlife Department hasn’t found any “fish kills” — localized die-offs of fish — in Central Texas, Patrick Ireland, a fisheries biologist with the department, said there is a limit to how much heat any given species of fish can tolerate.
“In Texas, these fish have gotten used to these types of intense heat events throughout history," Ireland said. "But this is particularly hot.”
The National Weather Service issued several Excessive Heat Warnings and Heat Advisories for the Austin area as temperatures hit triple digits several days in a row in June.
Popular sport fish like largemouth bass and sunfish will seek deeper waters or shaded areas to try to keep cool and avoid the solar radiation. Those shaded areas can be near rocky shorelines, under docks or by man-made sunken brush piles. When the fish find a good spot, they can basically hover in a stationary position.
“That’s probably what they typically do in these summer months because the water is so hot that their metabolism’s really burning through energy,” Ireland said. “So, it behooves them to stay stationary in a shaded cooler area.”
But any fish, including the largemouth bass and sunfish, swimming through shallow streams won't have access to the cooler spots typically found in larger lakes or ponds.
“Obviously, shallow water’s going to heat up a lot faster," Ireland said. "I’d imagine in those streams, this is probably pretty extreme for a lot of those fish.”
Ireland said if the weather conditions continue, pockets of fish may die in some bodies of water. A combination of hot water temperatures, cloudy days preventing phytoplankton from producing dissolved oxygen, and no wind to stir the water could result in a rapid drop in dissolved oxygen levels leading some fish to die and others to flee in search of more oxygen-rich waters.
In the meantime, Texas Parks and Wildlife continues to stock local bodies of water with fish from its hatcheries. But the department is measuring water temperatures and dissolved oxygen levels first to ensure the fish can survive — at least until they are hooked by an angler.
