Playing “Ring Toss” with a Pelagic Ray

Aquarist Ann Greening gets ready to place a plastic “target” in the water to summon the pelagic rays over for their daily feeding, but it’s not really necessary. They heard her come in, and they’re already flopping about in front of her in anticipation of today’s mixture of squid, fish and shrimp. “They come right over,” says Ann. “I think they hear the door open, and they know it’s their time.”

Ann has been caring for the Monterey Bay Aquarium’s pelagic rays for six years, and the daily feeding is one of the highlights of her day. “They’re very charismatic,” she says. “They flip over on their backs and scoop the food in with their fins.”

Just then she tosses another shrimp toward one of the rays, which quickly scoops it into its central mouth. Feeding them, she says, “is like playing ring toss at the carnival.”

Pups Born at the Aquarium
The Aquarium has a history of success with pelagic rays (Dasyatis violacea). In 2003, one of the Aquarium’s rays gave birth to two pups, one of which is still on exhibit in the Outer Bay, alongside its mother. “We’re one of the only places to have successfully raised a ray to adulthood on exhibit,” says Ann. Another ray qualifies as one of the Aquarium’s elder statesmen, at 15 years of age.

Aquarium husbandry staff and volunteers have also been involved in important studies of pelagic rays. Volunteer Henry Mollett authored papers on the worldwide distribution of rays, and their growth in captivity. Manny Ezcurra, associate curator of elasmobranchs, also wrote a paper on the metabolism and growth of adult pelagic rays. Ann followed this up with an undergraduate thesis on neonatal growth, using the pups born at the Aquarium. “All the information on young rays had been estimated,” she says, “but we could get exact data.”

These Rays Range Widely
While other rays sift through the sand close to shore, pelagic rays have adapted to open waters. They’re dark purplish above and purplish gray underneath—coloration that makes them almost disappear from view against the sky or the dark water below. Pelagic rays occur throughout the world, including Monterey Bay. Adult females can be up to 39 inches across and weigh more than 100 pounds. (Males are generally smaller.) 

Conservation Concerns
Pelagic stingrays are captured as unwanted “bycatch” on pelagic longlines or driftnets. Although they’re not considered threatened, there are concerns. To pelagic rays, sea turtles and other animals that eat jellies, drifting plastic bags look like their natural prey. This can be a deadly mistake. Animals can choke as they try to swallow the bags, or slowly starve as the plastic clogs their stomachs. You can help save a ray just by picking up plastic bags at the beach and making sure trash is disposed of far from the ocean.

Interestingly, recent data indicates that pelagic ray populations may be increasing, but for the wrong reason: populations of their largest predators—large sharks and whales—are declining.

“Beautiful to See”
Back at the Outer Bay exhibit, Ann is lying on her stomach, practically placing the food in their eager mouths. She has to be careful, though. “They have sharp teeth,” she says. “You can get a little paper cut.” There is one other thing that she needs to be careful of: a venomous spine that protrudes above the tail. A sting can be extremely painful.

When they flip over on their backs to be fed, they are actually practicing a skill that serves them well in the wild.  “The way they catch prey is to swim through a school of fish upside-down,” says Ann. “They use their fins as a funnel, to cup food in. They’re well adapted.

“It’s a beautiful animal for visitors to see, and a fun animal to feed. They’re happy to see you, and show a lot of enthusiasm.”

(Website visitors can occasionally view a pelagic ray feeding on our live webcam in the late afternoon, Pacific time.)

 

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