Tens of thousands of fish washed ashore along the gulf coast of Texas starting on Friday after being starved of oxygen in warm water, officials said.
Park officials for Brazoria County said that a cleanup effort was underway but thousands more fish were expected to wash ashore.
Officials for Quintana Beach County Park published photos on Saturday showing scores of dead fish floating in the coastal waters.
The cause was a “perfect storm” of bad conditions, said Bryan Frazier, the director of the Brazoria County Parks Department.
Warm water holds much less oxygen than cold water, he said, and calm seas and cloudy skies in the area had stymied the ways oxygen is usually infused into ocean water. Waves add oxygen to water, and cloudy skies reduce the ability of microscopic organisms to produce oxygen through photosynthesis.
When schools of fish are trapped in shallow, warm water, they can start to act erratically as they are starved of oxygen, which further depletes oxygen in the water.
Katie St. Clair, the sea life facility manager at Texas A&M University at Galveston, said that the warming of gulf coast waters through climate change could have contributed to the fish kill.
“As we see increased water temperatures, certainly this could lead to more of these events occurring,” Ms. St. Clair said, “especially in our shallow, near-shore or inshore environments.”
The National Weather Service recorded a high of 92 degrees in Brazoria County on Friday, the day the dead fish were first reported washing ashore.
Mr. Frazier added that such fish kills are “not that uncommon” in the area and start to occur when the water warms during the summer.
“It is a little alarming to see a wave of dead fish wash ashore,” Mr. Frazier said. But he added that local water conditions would improve as ocean waves add oxygen back into the water and as fish swim away from areas with low oxygen.
“Mother Nature has a way of balancing that out,” Mr. Frazier said. “It should correct itself here in the pretty near future.”
A United Nations report concluded in 2019 that warming ocean water had increased incidences of hypoxia — or low oxygen levels — in coastal waters, threatening fish populations. One of the authors of the report said at the time that oxygen loss and other effects of global warming would “create enormous pressure” on the Gulf Coast region in the future.
In addition to localized cases of hypoxia, a large “dead zone” of water spanning thousands of square miles is known to form in the Gulf of Mexico during the summer months.
The National Oceanic and Atmospheric Administration forecast on Monday that this dead zone would be smaller than usual this year, covering about 4,155 square miles of coastal waters.
Ms. St. Clair said that the fish kill could have a significant environmental impact because the dead fish — mostly Gulf menhaden — play a “critical role” in the local ecosystem.
“You could see cascading impacts if we continue to have these large fish kills,” she said.
The dead fish started washing ashore in Brazoria County, roughly 65 miles south of Houston, early on Friday morning, Mr. Frazier said, and park crews were quickly dispatched to clear and bury them before they started to rot in the midday heat.
“We need to get those moved off fairly quickly,” Mr. Frazier said. “It doesn’t take long for them to sit there in 90-degree heat to really rack up an unpleasant smell.”
