What caused mass fish deaths on Texas Gulf Coast?

Officials said the species most affected by this fish kill was the Menhaden in the Gulf, and the dead fish began washing up on Friday.

Thousands of fish washed up along the Texas Gulf Coast due to “a low dissolved oxygen event” in warm water, US officials said.

Quintana Beach County Park officials said Sunday that the species most affected by this fish kill was the Gulf Menhaden, adding that the pedestrian beach has been largely cleared with the “exception of one splashy fish that the machines couldn’t catch.” .

“This kind of fish kill is common in the summer when the temperature rises. If there isn’t enough oxygen in the water, fish can’t breathe,” the park officials said in a statement Facebook statement, adding that the “perfect storm” led to a lack of oxygen on the coast.

Warm water contains much less oxygen than cold water, and fish that are in warm water can get into big trouble.

“When the water temperature rises above 21 degrees Celsius (70 degrees Fahrenheit), it becomes difficult for menhaden to get enough oxygen to survive,” the statement said.

“Shallow water warms faster than deeper water, so if a school of menhaden gets trapped in the shallows as the water starts to warm, the fish will suffer from hypoxia.”

Authorities have investigated whether the cause of fish deaths was due to marine pollution or low oxygen levels in coastal waters due to warming ocean waters [File: Quintana Beach County Park/Getty Images]

Calm seas and cloudy skies

Calm seas and overcast skies also contributed to the lack of oxygen, authorities said.

Waves add oxygen to the water as air encounters the water through wind and waves “and subsequent vertical mixing with the ocean’s interior”. During this time there was minimal wave action.

A second way to create oxygen is through photosynthesis by microscopic phytoplankton or macroalgae; this is powered by sunlight and cloudy skies reduce the ability of organisms to produce oxygen through photosynthesis.

“Sunlight-driven photosynthesis creates more dissolved oxygen during the day,” Lerrin Johnson, spokesperson for Texas Parks and Wildlife’s Kills and Spills Team Region 3, told the CNN network.

“Photosynthesis stops at night and can slow down on cloudy days, but plants and animals in the water continue to breathe and consume free oxygen, decreasing the dissolved oxygen concentration,” she said.

The dead fish began washing up early Friday morning into Sunday.

On Friday, the National Weather Service recorded a high of 33C (92F) in Brazoria County.

“Looks like the last of the fish has washed up,” Quintana Beach County Park said Sunday. “The most recent have deteriorated to the point that they are fragmented skeletons,” it added.

Dead fish on the coast of the Texas Gulf
Officials in Texas’s Brazoria and Quintana counties said thousands of dead fish had washed up on beaches since Friday [File: Quintana Beach County Park/Getty Images]