How tourists have changed the behaviour of stingrays

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Stingrays at a popular tourist site have altered their lifestyle, showing clear changes in behaviour.

Stingray City in the Cayman Islands sees around a million tourists every year, who come to swim alongside, pet and feed the stingrays.

But this has resulted in the rays altering their natural behaviour as they take advantage of all the food on offer.

"We saw some very clear and very prominent behavioural changes, and were surprised by how these large animals had essentially become homebodies in a tiny area," says study co-author Mahmood Shivji, director of the Guy Harvey Research Institute and NSU Oceanographic Centre professor, who led the study.

Researchers tagged and monitored a group of Southern stingrays (Dasyatis americana) at the tourist site.

They found 164 of them crowded together in less than a quarter of a mile of space at Stingray City. These stingrays formed schools and fed together during the daytime when the tourists were around, rather than living a more solitary existence and hunting for food at night as is usual with these fish. In fact the Stingray City group was found to be resting at night.

In wild stingrays, activity sites overlap with other rays’ territory 3% of the time, but in Stingray City this rises to 72% of the time.

80% of the rays at Stingray City were female, possibly as smaller males were outcompeted for food. There was also found to be no particular breeding season for the rays at Stingray City as there would normally be in wild populations. Instead the females were becoming pregnant all year round.

Bite marks on both sexes also suggested a level of aggression which is unusual in stingrays, probably as a result of fighting over food.

At Stingray City each ray is thought to be worth $500,000 a year in income from tourists. Researchers intend to continue monitoring the impact of human interaction on the stingrays there.

"Right now, these animals have no protection at all," said co-author Guy Harvey, who initiated the project. "Without more studies like these, we won’t know what that means for the wildlife or if we need to take action. It’s unclear how much of the stingray’s daily diet comes from tourism provided food, but the good news is we have seen the animals forage when tourists are absent suggesting that these animal are not completely dependent on these handouts."

The research is published in PLOS ONE.

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