Margaret Kates | AL.com

21 August 2024

Patric Garmeson, a charter fishing captain, remembers “hundreds if not thousands” of dead bull redfish washed up in Bon Secour Bay in the spring of 2022.

“When you set up a fishing trip, and then you realize that you’re in a dead zone, it can affect morale,” said Garmeson of Ugly Fishing.

But the 2022 redfish kill was not a one-time occurrence. In fact, a so-called “dead zone” returns to the Alabama coast each year, forcing fishermen to sail further out to sea and at times killing off fish that stayed put as the ocean water runs low on dissolved oxygen.

This year’s dead zone off the coasts of Mississippi and Alabama is larger than researchers expected, though its cause remains unclear.

The 2022 fishkill claimed between 1,000 and 1,500 redfish as oxygen levels dropped rapidly in the Gulf of Mexico, researchers from the Dauphin Island Sea Lab and the state’s Marine Resources Division concluded at the time. Fish carcasses were carried by the wind into Mobile Bay and Bon Secour Bay.

Fish and underwater plants need dissolved oxygen to live. Marine life that can swim away, usually does, and the species that can’t, die.

The dead zone of hypoxia—when dissolved oxygen levels in water drop below 2 milligrams per liter—happens almost every year off the coast of Alabama, but the extent, magnitude and duration changes from year to year, Brian Dzwonkowski, a professor of Marine Sciences and researcher at the Dauphin Island Sea Lab, said.

Dzwonkowski has been studying hypoxia off the coast of Alabama for several years. This year’s dead zone surprised him, he said, because of the how large the area is and how long low dissolved oxygen levels have persisted.

Yet little is known about what causes hypoxia on the east side of the Mississippi River.

“We suffer from a lack of observation,” Dzwonkowski said. “We don’t have a clear smoking gun as to what the cause [of hypoxia] is.”

In July, researchers from the Louisiana Universities Marine Consortium (LUMCON) cruised a dead zone that spanned from the Chandeleur Islands off the coast of Louisiana to Mobile Bay. This dead zone is approximately 1,634 square miles, larger than the size of Rhode Island. Logistical concerns forced the LUMCON researchers to turn around, so the eastern border of this year’s dead zone was not defined, according to their report.A much larger dead zone forms every year off the coasts of Louisiana and Texas, caused by discharge from the Mississippi River loaded with nutrients like nitrogen and phosphorous, which cause massive algal blooms. As the algae dies, bacteria eat the dying algae, consuming the dissolved oxygen in the water. This year’s dead zone off the coast of Louisiana is larger than average, roughly the size of New Jersey.

While the discharge from the Mississippi River certainly plays a role in the dead zone off the coasts of Mississippi and Alabama, it’s not the only factor, Nancy Rabalais, a researcher at Louisiana State University, said. Other river systems also drain into the Gulf east of the Mississippi, like the Pascagoula River and the Mobile-Tensaw River Delta. What role those river systems play is unclear.

“We don’t know enough about the rivers to the east,” Rabalais said. “The majority of the Mississippi River’s discharge goes to the west.”

While coastal Alabama residents may welcome jubilees—instances where low dissolved oxygen levels drive fish to shore, which can lead to a bigger yield for fisherman—these hypoxia events are different from jubilees and disruptive to the ecosystem, Dzwonkowski said. Marine life that can’t swim away, like mollusks and worms, dies.

When fish return, they often find that their food source has died off.

Hypoxia events can also harm artificial reefs meant to increase the population of fish, Rabalais previously told AL.com, since they are affected by low oxygen . Alabama has the largest artificial reef program in the United States, and approximately 1,060 square miles of offshore waters are included in the state’s artificial reef areas.

People harvesting mobile species, like fish and shrimp, may have to venture further out into the Gulf of Mexico to harvest, which can lead to higher fuel costs and more time spent on the water, according to Conservancy.

People harvesting mobile species, like fish and shrimp, may have to venture further out into the Gulf of Mexico to harvest, which can lead to higher fuel costs and more time spent on the water, according to Conservancy.

But low dissolved oxygen events are frustrating as a fishing captain, he said. Garmeson has planned fishing trips, only to find his boat is in a dead zone where there are no fish to catch.

“It really makes it difficult to remain positive,” he said. “You could throw bait in and it would die rapidly, because the dissolved oxygen is that low…catfish wouldn’t even bite.”

Sometimes, when a low dissolved oxygen event occurs, Garmeson will have to seek out choppier waters, since the waves infuse oxygen into the water. That’s the only place where the fish will bite, he said.

There’s still a lot to learn about hypoxia on the east side of the Mississippi River. While Rabalais’ team has cruised the dead zone off their coast for more than 30 years, this year is only the second time the dead zone east of the Mississippi River has been surveyed, the last time being in 2011.

The cruise east of the Mississippi River was funded through a grant from the Gulf of Mexico Alliance via President Joe Biden’s Bipartisan Infrastructure Law, in addition to funds from the National Oceanic and Atmospheric Administration that paid for the cruise west of the river. Researchers will cruise the dead zone east of the Mississippi River again next year, Amanda Nalley with the Gulf of Mexico Alliance said.

The Mobile Bay watershed drains most of the state, as well as parts of Mississippi and Georgia, Dzwonkowski said. “Understanding this problem is very important because it may involve communicating with other states,” Dzwonkowski said.

“It’s hard to give guidance on watershed management when you don’t have a clear understanding of what’s going on.”

www.al.com/news/mobile/2024/08/dead-zone-off-the-alabama-coast-larger-than-rhode-island-this-year