Information on habitat use and movements by Sarasota Bay resident bottlenose dolphins is very well known; yet, the reasons for observed movement patterns and habitat choices are not fully understood, especially as they may be influenced by their potential predators, sharks. My dissertation research focuses on understanding the impacts of predatory sharks on the habitat use, survival, and behavior of Sarasota dolphins. Information regarding habitat use of large sharks is extremely limited in coastal nearshore habitats, including Sarasota Bay. By tagging and tracking sharks, I hope to provide a better understanding of habitat-associated predation risk within the estuary and its impact to the dolphin community.
During the May 2016 Sarasota Bay Dolphin Health Assessment Project, we observed F165 with her newly born calf, 1652. The calf had extensive shark bite wounds behind its right eye and on its dorsal fin. After observing the mom-calf pair several times in May, we grew concerned when we did not see them during regular population monitoring surveys in June and July. We were relieved when we finally saw the duo again during August-November; thankfully the wounds appear to be healing well on 1652.
In addition to keeping track of shark-bitten dolphins, this summer we set out for two nights of shark fishing in hopes of tagging a bull shark to gather preliminary movement information. The first night of shark fishing was conducted in the northern half of Sarasota Bay, with no success except for a fantastically large catfish. The second night of fishing was conducted from the Ringling Bridge to the south, with the most effort occurring in Big Pass. During the second night of fishing, we successfully caught two blacktip sharks and one 7-ft bull shark. All three sharks were caught on drumlines in Big Pass. The bull shark was caught at 2:20 AM on June 16, 2016 and was tagged with a continuous acoustic tag, as well as a satellite-linked tag. The female bull shark was named “Merry,” and was successfully tagged and released. A few hours post-release, we received four satellite signals roughly 1.8 nautical miles off north Siesta Key. Unfortunately, we have not received any additional satellite-linked tag signals since June 16. Thanks to a scholarship received from the Guy Harvey Ocean Foundation, I plan to continue shark fishing efforts next year to gather more data on shark movements in Sarasota Bay.
This project is made possible from funds graciously provided by an anonymous donation to the Chicago Zoological Society, the University of Florida, Mote Scientific Foundation, and through partnerships with the Sarasota Dolphin Research Program, Mote Marine Operations Department, and Mote’s Shark Biology and Conservation Research Program. Many thanks to to University of Florida students Steven Longmire, Ashley Meade, Remy Phillips, and Zach Steinhauser for volunteering countless hours to aide in the success of this research!
This article appeared on page 25 of the 2017 SDRP Annual Report, Nicks n Notches.