In the summer of 2015, Mote’s Stranding Investigations Program (SIP), received a call regarding a free-swimming dolphin bearing fresh shark bite wounds. The dolphin was identified as 1593, the third calf of Sarasota Bay resident female, F159 (“Aya”). Unfortunately, 1593 did not survive. The animal was recovered by SIP, and while the cause of death has not yet been determined, the extensive shark bite wounds certainly didn’t help the dolphin’s situation. When and where did this interaction between the dolphin and the shark occur? What implications do such interactions have for the resident dolphin community?
There are still many questions to be asked of shark-dolphin interactions in Sarasota Bay, which is the continued focus of my graduate research. My Masters research found that 37% of the members of the Sarasota Bay dolphin community had at least one shark bite scar. Additionally, I found that dolphins bearing a shark bite scar exhibited different habitat use than dolphins without a shark bite scar. In particular, open bay and mangrove habitats stood out as areas where we were more likely to find a dolphin with a shark bite scar. But what is the spatial overlap between sharks and dolphins? My Ph.D. research is focusing on aspects of dolphin survival and behavior, respective to shark encounters, in addition to movement patterns of shark predators. Specifically I am investigating dolphin survival after a shark encounter, and dolphin maternal care, to determine if dolphin mothers change their habitat use with young-of-the-year calves and if mothers with prior shark encounters use habitat differently than those without such prior experience.
Little is known about large shark use of Sarasota Bay and habitat overlap between sharks and dolphins. I am aiming to address this knowledge gap by tagging large sharks with acoustic tags. Working collaboratively with researchers at Mote Marine Laboratory, New College of Florida, and Loggerhead Instruments, we will set up a series of receivers, or underwater “listening stations,” that will detect acoustically tagged marine life and record sounds in the surrounding environment, such as dolphin signature whistles, fish sounds, and boat traffic.
Classifying the interactions between sharks and dolphins and understanding the resources that they share are important because both species are top predators in many coastal areas. The knowledge that we gain from such research provides insight into the complex species interactions and spatial distributions which help structure marine ecosystems. The case of 1593 is a prime example of the types of species interactions we observe in Sarasota Bay and highlights our need to understand the drivers and implications of shark-dolphin interactions.
This project has been made possible by a series of anonymous donations to the Chicago Zoological Society and by the University of Florida, School of Natural Resources and Environment. I would like to thank all past and present SDRP staff and volunteers for collecting decades of capture-release project photos and data and for their participation in SDRP population monitoring surveys. I would also like to extend a special thanks to Mote Scientific Foundation for providing funding support for field materials and shark tagging efforts, and to Bob Hueter, Randy Wells, Michael Scott, Jack Morris, Aaron Barleycorn, Dean Dougherty, Pete Hull, and Greg Byrd for their amazing assistance with shark tagging pilot projects.
This article appeared on page 26 in the December 2015 issue of Nicks n Notches.