When Hurricane Debby churned over North Florida this month, flooding the Suwannee River, ancient fish that can grow up to 8-feet long and 300 pounds hid in holes in the dark riverbed, seeking protection from the storm and its aftermath.
The Gulf sturgeon, whose 200-million-year history is older than the river itself, is used to storms. But today, Gulf sturgeon face increasing human-made challenges. Pollution has expanded in the Suwannee River, according to new draft maps from the Department of Environmental Protection. Hurricanes and flooding can worsen chemical runoff making its way to sturgeon habitat. At the same time, climate change is contributing to swings between high and low water levels; last week’s more than 20-foot rise on the Suwannee followed a period of abnormal drought.
Florida’s prehistoric fish are surviving as they have for eons, scientists say. But they’re not invincible.
Brought back from the brink
When the fish’s ancestors first evolved, the Florida peninsula was underwater. Dinosaurs roamed North America. Sturgeon, with their spiky armor and snouts full of whiskers, fit right in among the Jurassic ocean’s toothy beasts – and then outlasted them.
Even to the scientists who study them, Gulf sturgeon are enigmatic. At first glance, they don’t seem like fish at all, but strange, primitive creatures with unusually large (but still marble-sized) brains, no clear X and Y chromosomes and a pop-out vacuum for a mouth.
Gulf sturgeon are hardy travelers. They weather the winter in the salty waters of the Gulf of Mexico before making the 100-mile journey up seven coastal rivers of Louisiana, Mississippi, Alabama and Florida in the spring to spawn.
A sturgeon’s ideal spawning water is cool, fresh and predator-free. The Suwannee, which flows unimpeded from the Okefenokee Swamp in Georgia to its mouth at the Gulf, is likely their main summer home. The river’s dark, tannic waters offer camouflage, its 70-95 ℉ temperatures a break from the Gulf’s record heat.
Exhausted after their journey from the Gulf, sturgeon spend the summers resting in dark, secluded alcoves, barely moving or eating.
In the 1900s, Suwannee fishers took advantage of the Gulf sturgeon’s lethargic summer state to catch and kill them, harvesting their eggs to be sold as caviar on upscale dining menus.
Sturgeon numbers dropped “down to zilch,” said retired fish biologist Ken Sulak. By 1980, only one fisherman was known to fish for Gulf sturgeon on the Suwannee. Four years later, Florida banned the practice.
In 1991, the federal government listed Gulf sturgeon as threatened under the Endangered Species Act, protection the fish maintain today. The U.S. Fish and Wildlife Service also listed the sturgeon’s riverine and coastal homes as critical habitat areas, boosting their priority for conservation.
Just as they have for bald eagles, alligators and other once-imperiled species, the federal protections worked. Gulf sturgeon made quite the comeback in the Suwannee. An estimated 10,000-15,000 adults now fill the river, often surprising boaters with their sudden, haphazard jumps.
But other stressors in the Suwannee have grown since the turn of the century.
Water is becoming more polluted, and flooding rains and fluctuating river levels more common. Sturgeon have persisted for thousands of years across a wide range of environmental conditions, said retired University of Florida fisheries professor Bill Pine, but their threats may be increasing.
Choked out by hurricanes
Gulf sturgeon’s sharp, chiseled armor and unbothered demeanor keep them safe from most predators in the river. Their weak spot is much more subtle: low oxygen.
Like humans, sturgeon breathe oxygen. Unlike humans, they pull it from water. So, when oxygen levels in water drop, Gulf sturgeon are hit particularly hard. The blood vessels in their gills struggle to capture oxygen, causing the fish to lose energy and, in extreme cases, die.
Florida’s rivers have some of the longest low-oxygen events in the country. A big culprit is hurricanes, which flood rivers with pollution-contaminated waters that algae slurp up, blooming sickly green. When algae die, they zap oxygen from the water, causing ‘dead zones’ that Gulf sturgeon can’t survive.
If they’re lucky, Gulf sturgeon will sense oxygen levels falling and flee downriver to the Gulf. Other times, they can’t outswim it. In 2018, Hurricane Michael quadrupled estimated mortality rates of adult Gulf sturgeon in the Apalachicola River. Ten days after the hurricane made landfall, the Florida Fish and Wildlife Conservation Commission reported 50-100 dead Gulf sturgeon in the river system.
According to Sulak, scientists saw "tremendous" mortality in other Florida rivers with Hurricanes Irma in 2017 and Ivan in 2004, but exact numbers were hard to estimate. U.S. Fish and Wildlife Service officers used their boats for human rescue, said Sulak, and “the last thing they had time for was to cruise the rivers and look for sturgeon bodies.”
In 2019, the National Oceanic and Atmospheric Association launched a sturgeon hotline at 844-788-7491 that the public can call to report dead or injured sturgeon. About 20 people have called the hotline since its launch, seven already in 2024.
As of Aug. 16, the hotline hadn’t received any calls about dead Gulf sturgeon in the wake of Hurricane Debby, which made landfall along the Big Bend Aug. 5. But the storm raised water levels more than 20 feet along the Suwannee, threatening to bring fertilizers, salts and other nutrients into fish’s habitat – and dropping oxygen levels.
Unfortunately for sturgeon, this sudden influx of chemicals adds to chronic pollution that plagues the Suwannee every day.
Contaminated by chemicals
Every two years, the state updates its list of waterways that violate the Clean Water Act because of contamination from heavy metals, fertilizers or other pollutants.
In the draft for 2024 —scheduled for approval late this summer— the Florida Department of Environmental Protection added 25 more sites along the Suwannee River Basin to the list, for a total of 71. Under the list, nearly a third of the Suwannee is considered “impaired” by contaminants, among them lead, iron, E. coli, phosphate and nitrate.
One such hotspot is where the Withlacoochee and Suwannee rivers meet, just north of I-10. The site is listed as impaired due to high E. coli and iron levels, likely from human sources upriver. A mile downriver, a poultry processing plant and power plant discharge wastewater into the Suwannee.
In a 2017 lawsuit settlement, the poultry plant, Pilgrim’s Pride, agreed to pay a $1.43 million penalty and reduce future pollution.
“They’re obeying the law. They’re not discharging chicken waste; they’re discharging chlorinated water,” said Sulak, who regularly observes the area, “that chlorinated water has a pH that’s rather different than the river per se and it’s right there where one of the [Gulf sturgeon] spawning grounds is.”
He was referring to Anderson Spring, an area two miles further downriver where Gulf sturgeon are known to spend summer and spawn.
Lead, E. coli and chlorinated water in sturgeon spawning grounds could be fatal, both to adult fish and their eggs. Lead can damage a fish’s cardiovascular and nervous systems, atrophy muscles and make them behave abnormally. E. coli can reduce oxygen levels in water. The high pH of chlorinated water can increase fish stress and damage their eyes and gills.
“On their own, individual stressors may or may not be lethal to Gulf sturgeon. But when you add additional stressors,” said Mississippi State researcher Peter Allen, who studies environmental effects on fish, “you may create a problematic situation for the fish.”
Perhaps an even bigger problem is the threat the contaminants pose to sturgeon eggs. When they spawn, each female Gulf sturgeon releases up to 500,000 eggs each that cling to the river’s gravely bottom.
Sturgeon eggs are peppercorn-sized, sticky and perforated with tiny holes to let in sperm. During fertilization, a male’s sperm swims through the water and into one of these tiny holes, causing it to close.
A high pH derails the delicate process. The eggs lose their stickiness and can be washed away. Sperm struggle to find and push through the egg’s holes. A generation is lost.
Dried up by pumping
Just as important as keeping sturgeon’s spawning grounds clean is keeping them flowing.
Prior to Hurricane Debby, more than a third of Florida was abnormally dry. High temperatures and low rainfall puts strain on agriculture, so farmers must use more water to keep their crops alive. This water is pumped from the Floridan Aquifer that in turn helps feed springs and rivers, which causes lower water levels.
When water levels drop, sturgeon can’t reach their spawning grounds. Sulak recalled a particular incident at Twin Rivers State Forest in 2002, after an extended drought narrowed the Suwannee to just eight feet across.
“I got a call from the manager, and he said, ‘hey, there's a whole group of sturgeon here trying to get through this gap, and they can’t get through because the gap is narrow and shallow,’ Sulak said.
By the time Sulak arrived, the sturgeon had gone, likely back downriver. He didn’t know whether they had managed to successfully spawn.
Water management in the Suwannee River is routinely under scrutiny by developers, farmers, utility companies and conservation groups. A rulemaking workshop in July about water use on the Santa Fe River, a Suwannee tributary, drew more than 50 participants.
According to Sulak, sturgeon are a stakeholder, too.
Scientists recently discovered that a quarter of Gulf sturgeon now spawn months later than expected, in the fall. Their spring spawning season is considered in water permitting and use, but “we also need to think about minimum flows in the fall, because those fish are trying to get up [the Suwannee] to spawn and if the river is very low, they probably can't do it,” said Sulak.
Still, resilient and recovering
What Gulf sturgeon can do is adapt. In fact, they’re pros at it.
Gulf sturgeon have up to 20 times more genetic information than other fish. Environmental conditions, such as changes in temperature or nutrients, can switch different versions of traits on or off. With such a huge genetic reservoir, sturgeon may be able to deal with changing conditions better than other animals can.
“That's sort of like a hedge against environmental change, or climate change, or anything,” said Sulak. But it takes time.
A Gulf sturgeon’s lifespan is usually 20-25 years, with some documented to have lived past age 50. If pollution, climate change and other threats continue to harm their home waters faster than sturgeon can adapt, it could mean trouble for the ancient fish.
“These sturgeon have persisted for a long time. It just doesn't mean that they're going to persist forever,” said Pine. “We can’t just pretend that they're resilient to everything.”
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