Researchers hunt for clues in stingray health

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A group of veterinarians and marine researchers from the United States visited Cayman four times this year to study the rays at Stingray City. Their preliminary diagnosis: The population is healthy, despite the drastic changes to the rays’ diet and behavior when they live on the sandbar. 

Most days during the tourist season, dozens of boats visit Stingray City, clustering around the sandbar and showing off the famously tame stingrays to tourists. Cruise passengers and stay-over visitors shriek and delight in holding the large rays in a spot that is a go-to for Cayman’s tourist industry. 

The stingrays know the drill as well as the tour operators. Some of the rays have been working the sandbar longer than the tour guides, earning an easy squid meal instead of tips from cruise passengers. 

Bradley Wetherbee, with the Guy Harvey Research Center, said since the center started tracking the rays in 2002, more than two dozen big female rays have stayed at the sandbar that entire time. It’s a good life for the stingrays, he said. “You just have to perform a few tricks for some tourists and you get fed.” 

Mr. Wetherbee has been coming to Cayman since the Guy Harvey Research Center began sponsoring the regular stingray population counts. He said it’s no surprise that the stingrays stick around on the sandbar. “Once you’re in the sorority, you don’t leave – it’s a good club to get into if you can.” 

Not all stingrays that make their way to the sandbar stay there. The research shows that many of them will come and go, but there is a core group that calls Stingray City home full-time. 

The biggest question from the researchers has been about the impact on the animals, which are normally nocturnal and lead solitary lives. The rays at Stingray City have completely changed their behavior, Mr. Wetherbee said.  

“I guess it shows you the power of food,” he said. 

That food is another cause for concern among researchers. Tour operators predominately use squid to feed the animals – an “unnatural diet,” Mr. Wetherbee said. Stingrays have an “opportunistic” appetite and normally live off a diet of mollusks, crustaceans and other creatures they find on the sea floor. 

Tonya Clauss, director of the Georgia Aquarium who has been leading the veterinary studies at Stingray City, said she and her colleagues took blood samples on recent trips to study how the change in eating habits and behavior impact the rays. 

So far, Ms. Clauss said, the preliminary results show the change in diet and behavior has not had a negative impact on the health of the stingrays. Her team, including another veterinarian and a nutritionist, is still going through all the results from blood tests but has not found anything of concern. 

Another big question the veterinarians wanted to tackle was on the mating cycle to see if the rays mated during a specific season. They used ultrasound, much like the system used on pregnant humans, to see if the rays were pregnant and to assess their overall reproductive health. Ms. Clauss said they found a number of pregnant rays throughout the year and they did not seem to have a specific season for mating. 

Ecotourism 

Guy Harvey spoke recently with the Cayman Compass about why he has funded research on Stingray City for more than a decade. The value of the stingrays, he said, “gets down to dollars and cents.” 

Stingray City is a major draw for tourists from cruise ships and visitors staying in hotels. Mr. Wetherbee put the value this way: “If a million people a year visit Stingray City, each of those people can pay up to $40 or $50 for a tour guide to bring them out there.” That’s a lot of money for the Cayman economy. 

Mr. Harvey said keeping the stingray population healthy is critical to the tourism industry. Data from the census shows a dramatic decline in the number of rays in Stingray City from 2008 to 2012. The population six years ago was about 100, but four years later it was down to 60.  

Since then, the population has recovered and this year has hovered around 90. That’s still far from the population in the first census done in 2002, when researchers counted 146 stingrays. 

“There have been so many rumors as to why the population crashed, that’s why it’s important to do this research,” Mr. Harvey said. 

The veterinarians and marine researchers don’t know why the population took a hit at the end of the last decade or how it’s recovered.  

Gina Ebanks-Petrie, director of the Department of Environment, said the Southern Stingray is not at risk of extinction. The research, rather, is because of the animal’s “tremendous economic value” to Cayman. 

Ms. Clauss said that aside from the direct economic benefit, the stingrays are “ambassadors for our oceans.” Without resources like Stingray City, she said, “people would never be able to interact with sea life like that.” 

The Guy Harvey Research Institute and the Guy Harvey Ocean Foundation paid for most of the research. The Cayman Department of Environment provided staff and research support. 

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Researchers lift a stingray onto a boat at Stingray City.