Supplemental feeding of southern stingrays, Dasyatis americana, has occurred at Stingray City Sandbar (SCS) at Grand Cayman as a tourist attraction since 1986. We investigated the influence of supplemental feeding on the movement patterns of stingrays by actively tracking both fed and non-fed stingrays using acoustic telemetry. Seven wild and seven provisioned stingrays were tracked manually for between 5-72 h, and site fidelity of five mature females at SCS was investigated over the course of one year using automated acoustic receivers anchored to the seafloor. Female stingrays at SCS utilized significantly smaller 24 h activity spaces (0.13 ± 0.08 km2) than wild female stingrays (0.88 ± 0.17 km2). Fed stingrays were highly active over a small area during daytime at the feeding site, but had limited nocturnal activity, whereas wild stingrays were more active during the night with limited activity during the day. Core areas of activity overlapped little among wild stingrays (3%), whereas core activity areas of provisioned stingrays at SCS overlapped much more (72%). Provisioned female stingrays consistently frequented SCS during periods of supplemental feeding and exhibited long term (up to six years) site fidelity to this site. Supplemental feeding has altered diel activity patterns and spatial distribution of stingrays at SCS and has enabled the local density of D. americana to increase to atypical levels. Our study suggests that food availability directly influences size and location of core areas of activity as well as population density of southern stingrays. The dramatic shifts in behavior and the altered population structure of stingrays also suggest that the aggregation of stingrays at SCS may alter predator-prey relationships and nutrient cycling, and possibly mating systems within the entire community at this location over long time periods. Supplemental feeding of wild marine animals may potentially alter movement patterns of individuals being fed, modify population structure and may ultimately affect the entire marine ecosystem. Managers charged with regulating existing sites where marine animals are fed by humans and policy makers responsible for management of similar sites established in the future should recognize potential far-reaching impacts of such activities on the local marine environment and take appropriate measures to monitor and if necessary enact mitigation measures.
Available at: http://works.bepress.com/mahmood-shivji/109/