A rise in water temperatures contributed to a mass fish casualty near Freeport in June, with the Texas Parks & Wildlife Department (TPWD) saying it was the result of low dissolved oxygen levels. The state agency said those events typically happen during the late spring and early summer as the weather warms.
But three months later, as Houston-area air temperatures gradually cool off after an especially scorching summer, masses of dead fish continue to wash ashore on beaches south of the city. There were smaller-scale fish kills in the Galveston area during each of the last two weekends, according to the TPWD and Katie St. Clair, the manager of the Sea Life Facility at Texas A&M University at Galveston.
"Some years are hotter and drier than others, and this summer, conditions have added stress to aquatic resources along the Texas coast," said Stephanie Garcia, a spokesperson for the state wildlife department. "In the case of the large-scale fish kill in Galveston last week, impacts to fish the public are seeing are largely attributed to localized low dissolved oxygen events."
Fish kills are "normal" occurrences in a coastal ecosystem, according to St. Clair, who also said they are intermittent as oxygen levels in the water rise and fall because of a range of factors. Temperatures, algae blooms, fish populations and waves and wind action can cause fluctuations in the presence of dissolved oxygen, which fish need to resperate.
St. Clair said the Gulf menhaden species is among the most vulnerable to low oxygen levels, because they tend to live in shallow waters and swim in large schools. They appeared to be most impacted during the fish kill near Freeport in June and also during the events this month, she said, which further supports the idea that low dissolved oxygen levels were the culprit.
"Those are very dynamic, complex events sometimes with a multitude of factors leading into it," St. Clair said.
The multiple fish kills in the region this summer are not necessarily cause for alarm, according to St. Clair, but she said they need to be studied and monitored. She also said she's thankful to Galveston-area residents and beachgoers who report what they see to organizations such as hers and the Texas Parks & Wildlife Department, so marine life casualties can be investigated.
Because there is less dissolved oxygen in warmer waters than in cooler waters, St. Clair said, there could be more fish kills both in the immediate future and long term. She said water temperatures figure to remain relatively warm into the fall, because air temperatures in the region remain warm.
The climate also is warming in general. Average summertime temperatures in Houston were 4.2 degrees hotter in 2022 than they were in 1970, according to data released this year by nonprofit organization Climate Central, and two studies published this spring found that sea levels along the U.S. Gulf Coast are rising at an unprecedented rate.
"If we have elevated temperatures, and warmer water typically holds less oxygen, it's not a reach to think these types of events might be more common or more frequent," St. Clair said. "This summer's been a great example."