Costs of group-living for a normally solitary forager: effects of provisioning tourism on southern stingrays Dasyatis americana

Animals can perceive tourists as predators and will incur fitness costs should their predator-avoidance behaviours result in forgone resource acquisition. Not all wildlife, however, treat tourists as predators; animals can respond positively to tourists, especially when food is used as an attractant. We investigate the costs posed by novel grouping over a tourism-provisioned food resource in a normally solitary forager, the southern stingray Dasyatis americana, in Grand Cayman. Specifically, we test the hypotheses that group-living stingrays in a new environment-which includes both the presence of tourists and quickly renewing food patches-will be exposed to increased injuries, ecto-dermal parasites and aggressive interference competition that result from the unusual grouping behaviour. We found that, in comparison to stingrays from non-tourist sites, tourist-fed stingrays are more likely to have lower body condition, be injured by boats and predators, be susceptible to ecto-dermal parasites, and be engaged in intense interference competition (in the form of conspecific bite marks). Stingrays from tourist sites also have significantly higher mean numbers of injuries, parasites, and median bite marks. By exploring alternative hypotheses to explain the pattern of our findings (e.g. natural causes/behaviour), we unequivocally show that the impacts incurred by the stingrays stem from the effects of tourism. These findings suggest that novel grouping poses costs to the stingrays; the tourist site represents a riskier habitat with regards to injury and predation; and there may be long-term fitness consequences. From a management perspective, measures should be taken to alleviate the crowded conditions at tourist sites, in terms of both boat and stingray density.