A crowd-feeding session with stingrays. The animals have come to expect food handouts and adjusted their daily activities accordingly. (Matthew Potenski)

Being fed by tourists has transformed the behavior of a group of Southern stingrays in the Caribbean over the past three decades, according to a study in the journal PLOS One.

Female rays fed packaged squid by vacationers at Grand Cayman Island’s Stingray City sandbar have switched from being nocturnal to being active during the day, and they now confine their activities to the feeding site.

“Ecotourism-provided food is drastically changing the behavior of these stingrays, including shifting their activity rhythms from night to day and causing overcrowding,” said one of the paper’s authors, Mahmood Shivji, who is director of the Guy Harvey Research Institute at Nova Southeastern University in Dania Beach, Fla.

A team of American researchers used radio tags and data from rays they tagged and recaptured to track the roughly 164 stingrays, 80 percent of them female, that were swimming freely at the tourism site. In contrast to wild stingrays, whose activity sites overlapped with other rays’ territory 3 percent of the time, the stingrays that were fed moved in areas that overlapped 72 percent of the time.

The animals adjusted their behavior to take advantage of tourists’ daytime visits, the authors wrote, “being constantly active during the day with little movement at night compared to the nocturnally active wild stingrays.”

Feeding operations for marine species, including whale sharks, have become increasingly popular across the globe.

Shivji noted that the rays’ radical shift in behavior in Grand Cayman, which is part of a British territory south of Cuba, “raises questions about how the long-term health of these animals is being affected — an issue that should be carefully considered before establishing new feeding operations elsewhere.”

Juliet Eilperin