By Jim DeLa
This year’s red tide blooms along the Gulf Coast killed millions of fish and other creatures, including manatees, sea turtles and dolphins. But for the creatures that survived, where did they go to escape the toxic soup that fouled their habitat?
New College researchers recently received a $17,000 grant from the Mote Scientific Foundation to try to find some answers.
Assistant Professor of Biology and director of the New College’s Pritzker Marine Biology Research Center, Jayne Gardiner, has been conducting fish surveys in local waters for three years. Gardiner and her students are part of a research experiment called the Sarasota Bay Coast Acoustic Network, or SCAN. Researchers tag sharks and fish, including the endangered small-tooth sawfish, with devices that send signals recorded by strategically placed listening stations anchored in the water as the fish swim near them.
Gardiner’s team has been specifically tracking 50 sharks of various species, including black tips, hammerheads and bull sharks.
Mauryn Brownback, a thesis student, is participating in the project. Her focus is on doing fish surveys by fishing one day a month, using gillnets and longlines, to study the diversity of species. “Before we started conducting surveys, there had not been any recorded research of what species were in the river, so we initially did not know what we would find, since any data provided new information about the area,” she said. Any bull sharks caught are measured, tagged and released.
In April, Brownback said, numbers started to fall. “We didn’t catch anything.” In June, they managed to catch and release one juvenile bull shark.
In July, as the red tide bloom increased in size and intensity, the trend continued. “We stopped seeing black tips,” Gardiner recalled. As the summer wore on, they saw even more devastation — thousands of sting ray carcasses, and dead bull sharks. The live populations fled the area. “They got out of Dodge before the [toxic] levels got bad.”
Exactly where the sharks and rays went was a mystery. But Gardiner had a theory. Just north of Sarasota Bay, Terra Ceia Bay and the Manatee River could be natural refuges from the toxic bloom because of their lower salinity. “The Manatee River is salty but not enough for red tide,” Gardiner said.
Gardiner had listening stations in Terra Ceia, but there were none in the Manatee River. Could the fish be migrating far upstream into the Manatee River?
Gardiner and her SCAN colleague, Tonya Wiley, a consultant based in Manatee County, proposed adding an electronic listening “gate” at the mouth of the river and putting additional devices upstream in various locations. The Mote Scientific Foundation responded with a grant.
The nine new Manatee River listening stations were installed by early November, and four additional sharks have been tagged with transmitters, Brownback said.
On a regular basis, the team pulls the listening stations from the sea bed, to download any data collected and change batteries. No data has yet been collected from the new stations, Brownback said.
Her thesis work, which also measures salinity and oxygen levels in various locations, could identify criteria necessary for an area to be considered a shark nursery habitat. “This research provides a baseline for that and could definitely be expanded upon with future fish surveys and theses of New College students.”
Meanwhile the SCAN research continues. “No one has even done this in the Manatee River before,” Gardiner said. “We’d like to be doing more between April and October … We’re hoping to secure more funds for year-round work.”
— Jim DeLa is digital communications coordinator for the Office of Communications and Marketing.