Cat Island- Science in a Sharks’ Safe Haven

Written by Lucy Howey

Gill Club members Lucy Howey, Brenda Anderson and Debbie Abercrombie just wrapped-up another successful oceanic whitetip field season in Cat Island, The Bahamas. The oceanic whitetip was once one of the most numerous large vertebrates on the planet, but unfortunately, overfishing and demand for their fins have severely declined their numbers. Beautiful Cat Island is one of the last known places in the world that oceanic whitetips can be found with such reliability. Our team is incredibly fortunate to have the opportunity to work in Cat Island and to be so welcomed by its kind people. The sharks are lucky too; The Bahamas has been a shark sanctuary since 2011, meaning there is no trade or landing of sharks within its EEZ. Longlining is also illegal and the effects of this legislation are evident – sharks are abundant – making it a shark scientist’s dream study site. We’ve dedicated such a large amount of energy and time to this project and it is amazing to watch its evolution over the last four years. In 2011 a group of us decided to do this project with one small center console boat, no bait freezer (not pleasant), small rations of peanut butter and jelly for lunch and absolutely no funding, and now in 2014 we’ve captured almost 100 oceanic whitetips and satellite tagged 83. In addition to the tracking project, this year we were also working on a reproductive study, an accelerometry study, a genetics study, and a stable isotope project, concurrently. Definitely an exhausting trip, but it was scientific collaboration at its finest. Every shark, caught on circle hook and baited polyball, is carefully tied to the side of the smaller work-up boat, measured and sexed. DNA and stable isotope samples are collected from a fin and muscle, respectively. A number ID tag is attached to the dorsal fin in the event that a SCUBA diver sees the shark again, and the satellite tag is placed with a small plastic dart into the dorsal musculature. Lastly, blood is taken from the caudal vein for a reproductive hormone study and, if the shark is a female, an ultrasound is completed to determine pregnancy status. This year collaborators from the University of North Florida were able to positively identify pregnancy in 13 mature females. When coupled with tracking data, the ability to identify the movements of pregnant females is an extremely exciting prospect. Since we use pop-up archival transmitters (PSATs) we will have to wait until the tag detaches from the animal (in this study between 8-10 months) and transmits its data through the satellite system before we have any insight into the sharks’ behavior. In addition to migration data, the X-Tags that we use also collect ambient pressure (depth) and temperature data every two minutes during their deployment. When studying migratory species it’s important to examine not only where they move but how they move. The depth data are where the “real” conservation implications lie. At what depths are these endangered sharks spending their time, and how does that information correlate to fisheries data? How can the biological and environmental data that we’ve collected be used for oceanic whitetip preservation and management? Now that the gear is stored and the samples are labeled and catalogued, these are the types of questions we will spend the next year working hard to answer, truly a small price to repay the amazing creatures that allow us share to their world for two weeks every May.

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Photos by: Stan SHEA/BLOOM

This project is generously supported by The Moore Charitable Foundation, Stony Brook University, Microwave Telemetry, Inc., The Cape Eleuthera Institute, The University of North Florida, The Save Our Seas Foundation and The National Institute of Polar Research.

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