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Dive Dry with Dr. Bill

#465: It's Shocking, It's Electrifying

While socializing down at the dive park back in September, I encountered three divers who had an electrifying experience underwater. Each one had encountered a strange fish that looked something like the Starship Enterprise on Star Trek. Each one violated a primary rule of interacting with marine life... Do Not Touch. Each one felt a tingle when they did. Yes, all three encountered a Pacific torpedo or electric ray, Torpedo californica.

I've encountered many of these myself, including one in the dive park with my buddy Kelly Tyler back in October. Of course as a highly trained marine biologist/divebum, I knew exactly what it was and adhered to the rule. I remembered back to 1985 when I was working with Jean-Michel Cousteau and Dr. Dick Murphy aboard the windship Alcyone on one of The Cousteau Society's TV documentaries. Diver Clay Wilcox spotted one of these and, knowing exactly what it was, conducted a "touching" experiment. The jolt he received kept him out of the water for 24 hours, although that was mostly precautionary.

At least Clay knew what he was interacting with. I think back a few years to a group of divers that exited the dive park stairs talking about the thresher shark they had just seen in the park. I listened to their description and comments with more than a little skepticism. Then I called them over to the Dr. Bill Mobile golf cart and showed them the sharks and rays segment of my Fish ID video. Just as I suspected, when the torpedo ray came into view they said "that's it!" It is truly amazing how little some divers know about the marine life they encounter... but then, that's job security for yours truly. If I actually had a job that is.

There are a reported dozen to two dozen species of "electric rays" around the world. They are actually divided into the true electric rays, and the torpedo rays to which this species belongs. The genus name Torpedo comes from the Latin word for "numbness," which is what you feel if you get shocked by them. And if you do, I refer to you as a "numbskull." This group "dates" back to the early Eocene, about 50 million years ago... which coincidentally is about the time I had my last date!

The Pacific "electric" ray was believed to be endemic to the northeastern Pacific Ocean from British Columbia to Magdalena Bay in Baja. However, scientists now think ones found off Japan and off Peru and Chile may be the same species. In our waters they are generally found down to 100 feet, although I've seen them much deeper (180 ft) at Farnsworth Bank off the windward side of Catalina. Apparently they are seen in depths down to 600 feet off Baja, perhaps to achieve their optimal water temperature of 50 to 55 F. They are generally seen on sandy bottoms, often near rocky reefs and kelp.

This torpedo ray is oval in shape and usually uniform gray to bluish or brown on the dorsal surface with a white belly. They generally have small black spots and other markings on top, often with patches of loose skin. The eyes are small and larger openings known as spiracles, used in breathing, are located above them. The spiracles open and close, taking in oxygenated water which then passes over the gills and out. The mouth and gills are on the underside. The tail is much thicker than other rays seen in our waters such as the bat ray or round stingray, and they have no stinger. The dorsal fins are located on the tail and the caudal or tail fin is flattened.

The electric charge is produced in two kidney shaped organs known as electroplaques located on either side of the head. These are modified muscles that no longer contract and expand. Instead they produce an electrical charge using calcium ions, rated at about 50 volts and one kilowatt. Other species use voltages of 8 to 220. There may be 500 to 1,000 layers of muscles in the organ with nerve endings all on the same side. They detect their prey using small pores in the skin known as the ampullae of Lorenzini. These organs detect weak electrical fields generated by the muscle activity of their food.

Apparently this species can direct the discharge either up or down. They may wrap their pectoral fins around fish prey and stun it with a sharp jolt, or warn a predator (or human) by sending a milder jolt upward as they approach. Even sharks are said to avoid them. With this effective defense, torpedo rays do not feel threatened often. When I approach too close to one, I've had them turn around and come at me instead of fleeing.

This torpedo ray feeds mainly on fish including flatfish like halibut, kelp bass, anchovies and mackerel. Perhaps it is from their prey's bones that they get the calcium to charge their "batteries" since they don't drink milk. They will also take invertebrates including squid. During the day they usually lie on the bottom and ambush prey that comes too close. At night they actively swim about to feed. On one night dive, I had a torpedo ray swim up my body and over my head. Fortunately it thought I was just part of the reef for it did not give me a jolt.

Males can be distinguished from females by the presence of "claspers," reproductive structures at each side of the vent. These are also present in their relatives the sharks. Males mature at about seven years and reach a maximum length of about three feet. Females mature two years later and may reach 54 inches. Some scientists believe both genders can reach lengths like that. Males are believed to mate every year while females may do so every other year. The eggs develop within the mother's body, with the embryos initially nourished by the yolk. Later, food comes from fluids secreted by specialized structures in the wall of the uterus. Litter size may average 17-20 and the pups are about 7-9 inches at birth.

In my research I discovered that the ancient Greeks and Romans used the electric currents from a related species as an anaesthetic to relieve the pain of operations and childbirth. It was also used to treat gout and headaches. Personally, I'll take aspirin instead for the headaches!

© 2011 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. 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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Torpedo ray from behind, and from side (at Farnsworth Banks);
lying on bottom in dive park and close-up showing spiracles and eyes.

This document maintained by Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia