By Abby Weingarten
Shark tracking and tagging in Sarasota Bay have been longtime New College endeavors, but a collaboration with Florida International University (FIU) and Havenworth Coastal Conservation (HCC) is taking the research one step further.
On July 16, Scientific Reports published a paper entitled Environmental DNA detection tracks established seasonal occurrence of blacktip sharks (Carcharhinus limbatus) in a semi-enclosed subtropical bay that highlighted this joint fieldwork. The findings revealed that it is possible to detect sharks moving into an area without actually seeing them (all that is needed is a couple liters of water).
“Humans leave DNA wherever they go, and it’s a great way to track their behavior (like the way it is done with CSI),” said New College Associate Professor of Biology Jayne Gardiner, Ph.D., who is one of the study’s co-authors. “Sharks also leave evidence behind in the water (from skin, mucus, etc.) and the DNA released from it is called environmental DNA or eDNA.”
Starting in 2018, the researchers for this eDNA study set out to see if a spring and summer influx of blacktip sharks into Terra Ceia Bay could be detected by filtering and extracting eDNA from water samples. On the team are Gardiner; researcher Tonya Wiley from HCC; FIU marine scientists Demian Chapman, Ph.D., Bautisse Postaire, Ph.D. and Judith Bakker, Ph.D.; and New College thesis students. The study was funded by the Paul G. Allen Family Foundation and the Shark Conservation Fund.
“Catching sharks is hard but catching water is easy,” Postaire said. “This study is an important step in the development of new methods to detect and monitor sharks.”
Terra Ceia Bay is a nursery for blacktip sharks in the spring and summer.
“Corresponding to seasonal migration, we detected the presence of blacktips in 27 out of 58 water samples during that time period,” Bakker said.
Gardiner had been working with blacktips since 2012, studying their seasonal presence in Terra Ceia Bay when she was a postdoctoral fellow at Mote Marine Laboratory & Aquarium.
“There’s a blacktip nursery area in the bay with abundant food, and the females give birth there from May to July,” Gardiner said. “The pups leave when temperatures start getting cold and then migrate south.”
Typically, eDNA does not travel too far from where it is shed or linger long in the water (only a few hours to a few days). So, if the eDNA of a species is found, it lets scientists know that the animal is or recently was in that specific area. This information is helpful for conservation and management of different species.
While blacktips are not threatened in the United States, the sharks are one of the top species in the global shark fin trade, which puts them at risk of overexploitation and population declines.
“In addition to being ecologically important, blacktip sharks are economically valuable—the dominant species in the Gulf of Mexico’s large coastal shark fishery,” Gardiner said. “This fishery is currently incredibly well-managed, but continued monitoring is critical to ensuring that these populations remain healthy.”
Chapman has used DNA analysis since 2014 on fins and shark meat found in markets to monitor the global fin trade. He is also the co-lead of Global FinPrint, which released a groundbreaking survey revealing that sharks are disappearing from the world’s coral reefs. And eDNA is another tool to help tell the story of what is happening to sharks globally.
“We look at the blacktip in the Gulf as a success story. The updated stock assessment in 2018 is saying that the species is not overfished, so we’re really managing this species well. But we need to continue to stay on top of it,” Gardiner said. “Some of the things we learned from blacktips in this study we can hopefully apply to other species. The more we learn, the more we can improve our management efforts for all shark species.”
Earlier in the spring, Gardiner also received new funding to expand another shark-related local research project. Mote Scientific Foundation, Inc. provided a grant for Gardiner to be the principal investigator on a project entitled Red Tide Recovery: Effects of Karenia brevis on Upper Trophic Level Fish Communities of Sarasota Bay. Gardiner will work on this extended research until October 31 alongside HCC and multiple New College students in Sarasota Bay, Terra Ceia Bay and the Manatee River.
Abby Weingarten is the editor/writer in the Office of Communications & Marketing.