Why thousands of fish washed up on these Texas beaches

Over the past weekend, troves of dead fish appeared on the shores of multiple beaches in southeast Texas, after struggling to find enough oxygen underwater.

Quintana Beach County Park announced on Friday that dead fish were washing up by the thousands. The department warned the public to stay clear of the local beaches until all the fish had been cleared, due to risk of being exposed to bacteria and sharp fins.

Crews are continuing to clear the carcasses of dead fish, which park officials described as "shredded skeletons." The Texas Parks and Wildlife Department's Kills and Spills Team responded to the situation and determined the cause of the massive die-off was a "low dissolved oxygen event," meaning fish essentially suffocated.

Here is what to know about what happened:

What caused the Texas fish kill

When asked what contributed to the fish deaths, Quintana Beach County Park officials said it was a "perfect storm" of factors.

First, warm water is not ideal for fish. It tends to hold less oxygen. That is especially true in shallow water, which heats up quicker. So, a school of fish likely found themselves deprived of oxygen as they swam though shallow waters in the summertime.

Another problem was that seas near county beaches were quite calm over the past few weeks, meaning there were few waves and winds to help redistribute oxygen in the water.

Over the past few days, the skies above the the beaches were cloudy. That is an issue for phytoplankton, which help produce oxygen in the water by using photosynthesis. That process is driven by sunlight. So, the less they are exposed to the sun by way of overcast, the less oxygen phytoplankton produce.

Why these dead fish aren't necessarily a bad thing

Most of the fish found dead were Gulf menhaden. They travel in large schools, which can explain how thousands washed ashore at the same time.

Over 32 different predators feast on the tiny fish, including sea birds, sharks and even some fish like mackerel and sea trout, according to the National Ocean and Atmospheric Administration. They provide predators with nutrients. Gulf menhaden also serve as filter feeders, meaning they consume impurities in the water.

Because this species is a popular snack for sea animals, there are potential benefits to the massive die-off, according to Katie St. Clair, the manager of the sea life facility at Texas A&M University at Galveston.

"The flipside is that with this die-off of fish, there is a huge nutrient pulse into our environment," she said. "It's kind of a circle of life."

How climate change plays a role in fish kill

Fish kills are common in the warmer months, like summer time. But oceans at large are heating up because of human-caused climate change.

"Water can only hold so much oxygen at certain temperatures, and certainly we know that seawater temperatures are rising," Clair said. "It is concerning and something that needs to be monitored."

Warmer oceans trigger a cascade of other changes to the ecosystem and the economy. One study from the SeaDoc Society at the University of California, Davis found that starfish were more susceptible to disease because of warm water anomalies. The Environmental Protection Agency also found that fish species are leaving their natural habitat in search for cooler waters, disrupting the fishing industry.

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