Normally during summer, most of my diving is done at night to avoid the crowds in the dive park, especially the snorkelers who all-too-frequently have no clue about park etiquette. However, this summer I've done very few night dives. One reason has been the lousy visibility in our waters this season. The other is the recovery from my recent appendectomy that kept me out of the water. As you read this, I'm recovering from a second surgery, a right hemicolectomy (look that up in your Funk & Wagnalls) and will be sidelined for another 4-6 weeks.
The focus of my column today is the round stingray (Urolophus halleri). I rarely see them during the day since they are fairly well camouflaged against sandy bottoms and often buried beneath the substrate. I did see one weekend before last on a day dive with buddy Catherine. However, they are observed fairly often on my night dives as they come out of hiding to feed. I've frequently had them bump into my camera as I filmed... or into the subject I was videotaping. Not once have I been stung by one.
These are relatively small relatives of the sharks, reaching up to 22 inches in length with a disc diameter of about a foot. Although their northern range may extend to Humboldt Bay, they are only common from Santa Barbara south as far as Ecuador. Usually they are seen in reasonably shallow water well within SCUBA diving limits.
Feeding can be similar to that of a bat ray with the round stingray flapping their fins and ramming their heads into the soft substrate to dislodge prey. Apparently they are not very finicky eaters and will take many species I wouldn't touch with a ten foot pole. These include worms, burrowing anemones and sea cucumbers (perhaps for extra endurance when mating). I might be willing to share clams, crustaceans or fish with them. In turn they are chowed down on by giant sea bass and certain marine mammals.
Now we get to the exciting part, mating. Yeeha! My columns are almost as good as Playboy since I always try to focus on both munching and mating. Actually I don't think I've seen a copy in decades. Like humans, the male stingray engages in a range of behaviors such as chasing and circling. Like many sharks and other relatives (not to mention me during a full moon), the male chomps down on the forward region of the female's disc. I prefer the neck myself. Dr. Milton Love states that the females don't try to get away... unlike the human females I bite.
Females may carry up to a dozen young inside their two uteruses. There is no placenta and they are not nourished from the mother. Instead they develop using nutrition stored in the egg's yolk. While inside the womb, the spines of the developing young are positioned before birth so as not to penetrate the mother. Fortunately for my Mom, despite the fact I was almost 10 pounds my fangs hadn't developed before delivery. The 3" young (stingrays that is) appear in summer and fall.
Although somewhat small, these rays are to blame for most of the stings experienced by southern California beach goers. Chris Lowe of Cal State Long Beach reported that 350 stings are about average each year in Seal Beach but the numbers may reach 560. These stingrays grow a new spine each summer, with the old one usually discarded.. However, more than one spine may be present at a time.
Although stings here on Catalina beaches are not very frequent, it is suggested that bathers shuffle their feet as they enter the water to scare them off if present. This probably is even more important for those who decide to skinny dip here at night! If you are of the female persuasion and do so on nights of the full moon, you should also watch out for a man in a long cape with sharp canine teeth.
© 2016 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!
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Round stingrays on the prowl in the dive park at night.
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Dr. Bill Bushing.
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