Bull Sharks of Bimini
Overview:
Bull sharks, Carcharhinus leucas, are large bodied, broadly distributed, sharks found in tropical and temperate coastal and shelf habitats. As mid to upper trophic level predators, they are naturally low in abundance, but play a significant role in ecosystems. For ecologically “K-selected” species, such as bull sharks, that are late to mature (9-11 years old) with long life spans (32 years), and slow reproductive cycles (2 years) a long-term, multi-year study is needed for revealing life-history traits that will be instrumental for devising effective conservation methods. However, generating such information for large marine vertebrates is challenging as typically they are vagile, live in concealing, aquatic environments and are logistically difficult to handle.
The Bahamas is established as a ‘Shark Sanctuary’ but previous research has shown there is a high level of connectivity between the Bahamas and the Southeastern USA. The warm productive waters of the Bahamas have been suggested to be important for supporting gravid females during the gestation period for other species such as tiger sharks Galeocerdo cuvier (Sulikowski et al. 2016). It is predicted Bimini also plays an important role as a stopover area during gestation for bull sharks. Elucidating the role of reproduction in the movement and connectivity of shark between The Bahamas and USA will allow for more effective conservation and identification of key habitats. A thorough understanding of drivers for movement patterns is critical for designing effective conservation and management initiatives of highly mobile species.
Identification of essential habitat for shark pupping grounds has been determined to be a priority for conservation and management (Heithaus 2006). NOAA Fisheries Service has established the Cooperative Atlantic States Shark Pupping and Nursery (COASTSPAN) to help identify shark nurseries along the east coast of the USA. Bimini is in close proximity to the Southeast USA and along the eastern edge of Gulf Stream, a proposed migratory pathway for many species. The present project will provide critical and unique data investigating the role reproduction plays in these movements and will help to identify important areas of parturition for these mobile species. Fortunately, modern telemetry technologies allow us to monitor individuals over to a decade. Thus, the next few seasons of this project will reveal whether Bimini is a key location of gestation for bull sharks which could have implications for the broader north-west Atlantic stock.
Upon capture, reproductive status of sharks will be determined using an ultrasound. We will use passive acoustic telemetry-tags (Vemco V16H) which are surgically implanted in a shark’s body cavity. For automated tracking in Bimini, Bahamas we have deployed 68 VR2W receivers in various habitats from the deep drop off, to the reef, flats and mangrove shoreline. The Florida Atlantic Coastal Telemetry (FACT) array group which today comprises over 850 receivers ranging from the Dry Tortuga’s to South Carolina and across to the Bahamas, greatly increasing acoustic coverage. The newly established iTag cooperative telemetry network contains 1,100 receivers positioned throughout the Gulf of Mexico, South Florida, and Caribbean. Furthermore, the Atlantic Coastal Telemetry (ACT) array group have deployed up to 3,000 acoustic receivers on the east coast and Gulf of Mexico between the US Virgin Island and the Canadian border. These monitors will provide detailed information about regional movements and identify key areas during time of parturition.
Research Questions
-
How long mature bull sharks remaining around Bimini, where do they go when they leave, and how often do they return?
-
Are females returning over multiple years during their gestation periods and at which stage of gestation?
Principle Investigator:
Matthew Smukall — Bimini Biological Field Station
Matt Smukall
Principle Investigator
At Lab Since: July 2015 - First came to the lab in January 2012 and volunteered over 3 winters during leave from work
From - Orlando, Florida / Kenai, Alaska
Education/Work Experience - PhD student, University of Alaska Fairbanks, School of Fisheries and Ocean Sciences
BSc University of Florida, Wildlife Ecology and Conservation
Masters University of Florida, Fisheries and Aquatic Sciences
2009 - Florida Keys, Caribbean spiny lobster research project, University of Florida
2009 to 2015 - Fisheries Technician/ Biologist, Cook Inlet Aquaculture Association, Kenai Alaska. Studying salmon populations in Southcentral Alaska, movement patterns of invasive northern pike, and the impact of pike on native salmonids.
Research Interests - Movement patterns of sharks. In particular the residency time, dispersal patterns, and philopatry of tiger sharks around Bimini. I am also interested in the use of longlines to assess shark populations and how sharks are interacting with the longlines.