Today, the Alabama sturgeon is one of the rarest, most imperiled fish in North America. In fact, if any do remain, they have successfully evaded droves of anglers and government fisheries biologists who for years have been trying to capture the endangered fish in order to develop a breeding program. Conservation officials’ ultimate goal: to breed and release into the Mobile basin juvenile sturgeon that will mature, reproduce and restore the species to the river system.
Auburn University assistant professor Elise Irwin is helping lay the groundwork for the success of that eventual effort. In a study funded by state and federal agencies, Irwin is working to identify the habitat conditions that juvenile Alabama sturgeon need to survive and thrive.
"Releasing juvenile sturgeon at random, in areas that are not suitable habitat, would be irresponsible," said Irwin, who is also a U.S. Geological Survey fisheries biologist and an Alabama Agricultural Experiment Station (AAES) researcher. "It would be like dropping off a six-year-old child in New York City and leaving him on his own. He’s not going to survive, and neither will the fish."
Because no Alabama sturgeon are available for the study, Irwin has found a surrogate in the Mississippi shovelnose sturgeon, the Alabama sturgeon’s sister species from the neighboring Mississippi drainage system.
At a fisheries research station in north Auburn, Irwin has 100 of these juvenile shovelnose sturgeon in holding tanks. Beside the holding tanks is a 24-foot-long serpentine Plexiglas "stream," which an AAES team constructed specifically for Irwin’s project.
A 500-gallon-per-minute pump attached to the three-foot-wide, two-foot-deep tank allows Irwin and her research team to manipulate the water flow in the tank. With this system, Irwin can vary the conditions in the stream to determine how three key factors — river bottom characteristics, water velocity and water depth — influence the sturgeon’s habitat selection.
Irwin places groups of the shovelnose sturgeon in the tank, gives them one hour to acclimate, and then records their movements on video. She will analyze the results to determine whether the young fish show a preference for specific particular habitat conditions.
"We can see, for instance, whether they prefer sand or gravel or woody debris, and whether they prefer a flat or sloping riverbed," says Irwin.
Before building the stream and starting the live fish trials last summer, Irwin and her research team spent time on the Alabama River, measuring depths and currents and analyzing the substratum in areas of the river where mussel beds occur.
"Mussel beds may provide prime foraging for the sturgeon," Irwin said. "So if we find these beds in areas where the other conditions that the sturgeon prefer are present, that should give us a strong indication of where to release the fish when we have them."
While over-harvesting may have played a role in the demise of the Alabama sturgeon, Irwin and many of her colleagues believe that human disturbances of it habitat — such as river dredging for barge transport, pollution and dam construction — are more pertinent reasons for the sturgeon’s disappearance. Marked declines in the sturgeon population became evident after the U.S. Army Corps of Engineers in the 1970s built three dams on the Alabama River, the major part of the basin.
"Our theory is that the Alabama sturgeon traveled upstream in tributaries, such as the Cahaba River, to spawn," Irwin said. "When the dams were built, they likely blocked spawning migrations, and fairly quickly, sturgeon numbers began to decline."
Irwin’s research on the juvenile sturgeon’s habitat will continue through the summer. Her hope is that, by the time her results are tabulated, some lucky anglers will have captured a pair of Alabama sturgeon and set in motion the recovery of the highly endangered species.