Tens of thousands of dead fish washed up on the beaches of Texas’ Gulf Coast over the weekend—and wildlife officials say low levels of oxygen in the water are likely to blame.
The carcasses began covering sand in Brazoria County south of Houston on Friday, prompting beach closures and creating a stinky mess for clean-up crews. County officials initially urged people to steer clear of the beaches because of high bacteria levels and sharp fins. On Tuesday, after employees cleared away or buried the dead fish, they gave the all-clear for beachgoers to return.
When members of the “Kills and Spills” team for Texas Parks & Wildlife sampled the area, they found almost no dissolved oxygen in the water.
“Fish kills like this are common in the summer when temperatures increase,” according to a statement shared on the Quintana Beach County Park Facebook page. “If there isn’t enough oxygen in the water, fish can’t ‘breathe.’ Low dissolved oxygen in many cases is a natural occurrence.”
Officials say the disaster started with a “perfect storm” that depleted the water’s dissolved oxygen levels near the shore, per a Facebook post. As summer weather heats up, the shallow water near the beach also gets hotter. When temperatures increase, the water cannot hold as much oxygen. If a school of fish was swimming in shallow water as temperatures rose above 70 degrees Fahrenheit, they may have found themselves “in big trouble,” per the post.
In addition, the nearshore waters of the Gulf of Mexico in Brazoria County have been calm for the last three weeks, with limited wave action. This means very little oxygen had been entering the water by mixing in at the surface.
Lastly, the region has experienced many overcast days lately. With clouds blocking the sun, microscopic phytoplankton and macroalgae cannot photosynthesize as much, and as a result, they produce less oxygen. Meanwhile, plants and animals in the water continue to consume the same amount of oxygen as they normally do, leading to decreased overall levels.
“Often, before a kill event occurs, fish can be seen trying to get oxygen by gulping at the surface of the water early in the morning,” per the statement. “Some fish may also be lying on the bottom or at the edge of the water.”
However, oxygen levels should return to normal in the near future, because “Mother Nature has a way of balancing that out,” says Bryan Frazier, Brazoria County Parks Department director, to the New York Times’ Chris Cameron.
Most of the dead fish are Gulf menhaden, also known as pogie. These small, oval-shaped fish travel in large schools in nearshore waters in the northern Gulf of Mexico. They serve as a food source for dozens of animals, including turtles, sharks, birds and other fish, per the National Oceanic and Atmospheric Administration—which is also why fishermen like to use them as bait.
Though the massive die-off has caused some temporary unpleasantness for beachgoers, it also likely contributed a “huge nutrient pulse into our environment,” as Katie St. Clair, sea life facility manager at Texas A&M University at Galveston, tells NPR’s Juliana Kim. Many of the fish washed up on shore as “shredded skeletons,” per a Facebook post from Quintana Beach County Park, meaning their flesh got eaten or was left to decompose in the water.
“It’s kind of a circle of life,” St. Clair says to NPR.