Mark Corcoran, Mahmood Shivji, Demian Chapman & Guy Harvey – Guy Harvey Research Institute, Nova Southeastern University
Brad Wetherbee – Department of Biological Sciences, University of Rhode Island

The Cayman Islands are home to two of the world’s best known dive and snorkel sites, Stingray City and the Sandbar, where large numbers of southern stingrays (Dasyatis americana) aggregate in response to feeding by dive operators. These sites attract nearly half a million visitors per year from around the world who enjoy a unique educational experience interacting with these charismatic animals.  There are concerns, however, that extensive human interaction and supplemental feeding almost daily may be having subtle negative impacts on the behavior and general ecology of the stingrays. Maintaining the biological health of these stingray populations for the long-term will require management and conservation programs based on a thorough knowledge of the biology of these animals.  Intentional supplemental feeding of southern stingrays has occurred at Stingray City Sandbar (SCS) since 1986.

This study investigated how the movement patterns of stingrays receiving supplemental food differed from non-fed stingrays.  PIT tags were implanted in 327 stingrays (164 provisioned and 163 wild), 183 of which were recaptured.  Tagging data indicate that a spatially isolated community of approximately 160 stingrays utilize SCS.  Seven wild and seven provisioned stingrays were tracked manually from five to 72 h, and site fidelity of five mature females at SCS was investigated for one year using automated acoustic bottom monitors.  Provisioned female stingrays at SCS utilized significantly smaller 24 h activity spaces (0.132 ± 0.079 km²) than wild female stingrays (0.876 ± 0.171km²).  Provisionedstingrays were active over a small area during daytime supplemental feeding with limited nocturnal activity, whereas wild stingrays were more active during the night with limited activity during the day.  Core areas of wild stingrays overlapped little (3%), whereas the core areas of provisioned stingrays showed significant overlap (72%), indicating that supplemental feeding has disrupted the spatial distribution of the community at SCS and increased the local density ofstingrays to atypical levels.  Provisioned female stingrays consistently frequented SCS during periods of supplemental feeding and exhibited long term (at least up to one year) site fidelity to this site.

These findings suggest that the availability of food resources is a significant factor regulating the size and location of core areas and activity spaces, population density and the diel activities (i.e. the spatial and temporal distribution) ofsouthern stingrays at Grand Cayman. This study raises concerns that supplemental feeding is likely altering the movements and spatial distribution of elasmobranchs and other marine organisms at many sites worldwide.