Florida Sturgeon "Attacks" Over For Now
for National Geographic News
|November 12, 2002|
Florida boaters can heave a collective sigh of relief as the last of
the Gulf sturgeon head to their winter feeding grounds in the Gulf
The fish's leaping ability and its sizethe Gulf species can grow to between six and nine feet (1.8 to 2.7 meters) long and weigh 200 pounds (90 kilograms)have led to close encounters of a dangerous kind for boaters.
Last summer, at least four people were injured when the fish with prehistoric roots leapt out of the water and crashed into them.
The injuries were not minor; they included concussions, broken ribs and sternum, a collapsed lung, cracked teeth, and gashes requiring stitches.
Still, biologists laugh at the media's characterization of the incidents as "attacks."
"This fish is a living dinosaur," said Frank Parauka, a fish biologist with the U.S. Fish and Wildlife Service. "It's a really docile fish, easily exploited."
He likens the encounters to deer crossing in front of vehicles. "These things just happen," he said.
If the incidents are happening more often, it's almost certainly because there are more boaters on the rivers today.
Sturgeon first appear in the fossil record about 225 million years ago, and they've been leaping ever since. But why do they jump?
"The big ones are the most noticeable, especially when they're jumping in the boat and taking out the driver. But all sturgeon jump," said Daniel Roberts, a research scientist with the Florida Marine Research Institute.
"There are several theories about why they jump, but no real proof to back up any of them."
The theories are wide ranging. They start with the possible but non-provable: "Because they can," suggested Parauka. "For joy," said Roberts.
Both men, being scientists, quickly offered a plethora of other possible explanations.
One theory says the sturgeon leap to avoid predators. "Of course, the ones in the Suwannee River are so big you wouldn't think they had predators," said Roberts, "but it's possible they could be avoiding alligators."
Some fish species jump in an effort to dislodge clinging parasitic crustaceans. "The fish we see don't look like they have enough parasites to make them irritable, though," said Parauka.
There could be an anatomical reason. "Some fishes can actually gulp air," said Roberts. "Sturgeon like high oxygen levels, and in some parts of the river the dissolved oxygen levels go down below two parts per million. So they may just be compensating."
Because the fish are bottom dwellers, they might be leaping to flush out their gills. Or it could be a way of communicating with their buddies.
Somewhat ominously for boaters, it's also possible that the sound of approaching boats spurs them on.
Hunted to the brink of extinction for their meat and eggscaviar to humansGulf sturgeon were listed as threatened under the Endangered Species Act in 1991.
"This fish is a living dinosaur," said Parauka. "They've been here for over 200 million years and once they're gone you'll never see it again. We wouldn't want to be responsible for seeing the end of these animals."
Their recovery is hampered both by environmental reasonsdestruction and degradation of habitat, deteriorating water quality, dams blocking their passage upstreamand biological reasons. They can live to be 40 years old, and are slow to mature and reproduce. Females are thought to spawn only a few times during their lifetime.
There are also gaps in what is known about the Gulf sturgeon.
Researchers know that the fish winter in the Gulf of Mexico, but it's not clear exactly where they go, and whether they prefer deep waters or coastal waters.
Bottom-dwelling and toothless, they feed by vacuuming up their prey. Yet for some reason, they eat only in late fall and winter. In the spring they return to the streams where they were born.
Parauka estimates that the overall sturgeon population today is 10,000 to 12,000. Florida's Suwannee River, which is where the bulk of the jumping incidents occurred, has the largest population, with estimates of between 5,000 and 7,500, he said. Other river systems in Florida, Louisiana, Mississippi, and Alabama have estimated populations of several hundred sturgeon.
Scientists have been struggling to determine what minimum number of the fish would be required for their populations to be self-sustaining, thereby allowing Gulf sturgeon to be de-listed as a threatened species.
"We really have no accurate historic information telling us what the river systems originally held," said Parauka. "Landing records from commercial fisheries in the early 1900s tell us that there were once tremendous populations in these systems."
The U.S. Fish and Wildlife Service is expected to designate critical habitat for the sturgeon in February 2003 as the result of a lawsuit filed by the Sierra Club.
More fish and more boaters will almost inevitably lead to more people-sturgeon encounters.
But until February, when the sturgeon reverse their migration to return to the streams where they were born, Florida boaters can ply the waters without worrying whether some prehistoric fish is lurking below, poised to leap.
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