Dive Dry with Dr. Bill

#127: Round Stingray

While diving off Hamilton Cove with Scott Patterson over the holidays, my Chinese friend Xiaoyan proved again she had better eyes than I do! In addition to locating the well-hidden swell shark I wrote about previously, she also spotted a distant relative which is far more dangerous to beach goers. Remember when you were told to shuffle your feet as you enter or exit the waters off southern California's sandy beaches? Shame on your parents if you don't! One of the main reasons for this warning is the round stingray, known as the raya de espina or raya redonda de Haller by my Spanish-speaking friends.

This fish is probably responsible for most of the stings inflicted by rays on bathers in our waters. While painful, the sting and venom is not life threatening. The rays are small bottom-dwellers, reaching a maximum length of 22 inches and just under three pounds. Being small, they undoubtedly perceive the much larger bather as a potential predator. If they aren't fast enough to scoot away, and get stepped on, the bather often gets the business end of the venomous spine at the base of the ray's tail. Although these rays are caught occasionally by fishermen, there is no real market for their flesh... but the poor stingray doesn't know this! They are not aggressive, but are just trying to defend themselves.

As you might expect from their common name, these sting rays have circular bodies like all members of the round stingray family. Other stingrays are more diamond shaped. They lack dorsal fins but have a true tail fin. The tail itself is fairly short and thick. Their bodies are usually some shade of brown or gray (or occasionally black) with pale spots on the surface. When not disturbed by divers or swimmers, they usually rest on the bottom and may be partially or fully buried with only their eyes exposed. When they do move (see pictures), they do so using a wave-like movement of the body. The one we observed took off as I approached and swam first with one side along the bottom and then with the other when it switched direction.

Round stingrays are known from Eureka south to Panama, and into the Sea of Cortez. They frequent habitats of soft sand or mud bottom down to depths of about 70 feet. Dr. Milton Love states that in southern California, mature females tend to be in deeper water (40-60 ft.) offshore, while the boys play in the shallower water nearshore. Adults of either sex are rarely seen in shallow water during the winter, so Xiaoyan's discovery was a bit unusual for December. When it is time to mate in early summer, the females enter the shallow water "where the boys are" (with apologies to Neil Sedaka and Connie Francis)... and what happens next is beyond the scope of this G-rated column!

Well, not really. After all, it is one of the two primary activities of any species... but I'll leave out the details out of respect for my younger readers. Oh, heck... round stingray mating is pretty exciting so I'll reveal their rather interesting bedroom secrets. Round stingrays are sexually mature at about 10" in length (about three years old). Many of you know that sharks and rays are able to sense electrical signals in their environment. Sexually ready female stingrays emit electrical signals from the head region just behind the eyes. The male is attracted to the female by these signals and by sight. Like other sharks and rays, the male often bites the female when initiating mating. If the male grasps the rear of the female's disc, she often escapes and copulation is unsuccessful. However, if the male bites the forward part of the disc, the female does not attempt to escape and the result is... whoopee!

Once mated, the embryos develop inside the female's body. After a gestation period of about three months, they may give birth to as many as eight small (3-4" long) young, although triplets is the norm. This usually happens in quieter, more protected waters. The young remain in shallow water until they nearly double in size and then head out to deeper and more exposed habitats.

The small rays feed on a variety of seafood (what did you expect... steak tartar or eggplant parmesan?). Delicacies include worms and amphipods (not my personal favorites), but also shrimp, crab and small fish (I'll accept that dinner invitation). As they grow, their diet changes, and clams become a large part of their intake. Like bat rays, they dig in the bottom sediments to find their food, often using their waving pectoral fins to excavate. In turn they are eaten by northern elephant seals and black sea bass. If they don't get munched by these giants, they may live about eight years.

© 2005 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Round stingray on bottom and moving on either side of its body; close-up (see below)

Close-up of round stingray taken by dive buddy Xiaoyan Li

This document maintained by Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia