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Volume 38 Issue 1 • April 10 - 23, 2008
now in our 38th season

Mystery Creature of Summer 2007:
Torpedo Rays Strand in Madaket Harbor

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

It all started with a phone call to the UMass Boston Nantucket Field Station office from the Madaket Harbormaster, Chris Van der Wolk, on a warm June morning in 2007.  Chris had discovered an unusual creature trying to beach itself at the Walter Barrett Pier in Madaket.  Local fishermen had pushed it back into the water near the pier using a wooden handled gaffing pole, but the creature had once again beached itself in shallow water.  So Chris called the Field Station to see if we would be able to come collect the creature, which was quickly stuffed into a large trash bag to protect the deceased animal from the summer sun.

Little was known about the creature initially, as its nearly four foot length, three foot width, and impressive 98 lb weight suggested it was too large to be a little skate (Raja erinacea), common to the island waters.  Features that confounded the identification included a shark-like tail in place of a stinger type elongate tail and a flattened body and anterior (front) section, instead of the typical diamond shaped “wings” most people associate with rays. This creature had soft brown skin with no spines, thorns, or large scales, was disc-shaped with a flattened front section, and sported a paddle-shaped caudal fin as long as it was high.  The eyes were very small and set far forward.  None of the local fishermen or boaters who saw the creature could identify it, with guesses ranging from barn door skate to unusually large flounder.

Approximately twenty-four hours later, after employing increasingly creative terms in internet search engines such as Google and Wikipedia and rummaging around images on sites like the Reef Quest Centre for Shark Research’s http://www.elasmo-research.org/index.html, a verdict was reached: this was an Atlantic Torpedo Ray (Torpedo nobiliana Bonaparte 1835) also known as an electric ray, numbfish, or crampfish.  These creatures have an ancient and storied past.  Plutarch, in the first century A.D., wrote of the torpedo:

“... swimming circularly about its prey, he shoots forth the effluviums of his nature like so many darts, and first infects the water, then the fish through the water which is neither able to defend itself nor escape, being (as it were) held in chains and frozen up.” (Plutarch, Morals, 978B)

Both Plato and Aristotle included descriptions of the electric shock and numbing sensations encountered upon touching a torpedo ray.  The Roman and Greeks used the electrical shock of the Atlantic torpedo to treat gout, headache, mental illness, and other maladies from 50 to 400 A.D.  Desperate times apparently led to desperate measures!  According to zipecodezoo.com, torpedo nobiliana have been sluggishly swimming around the world’s oceans since the Lower Eocene (40 million years ago) Epoch.

The term “torpedo” was coined by the Greeks to describe these animals by naming them after their numbing effect. The word torpedo comes from the Latin "torpere" (to stun or paralyze).  Naval buffs may find it interesting that the first military usage of the term “torpedo” was by Robert Fulton, who used it to refer to a towed gunpowder charge (shaped somewhat like a torpedo rays and with equally stunning effect) used by his submarine Nautilus to sink warships.

The torpedo ray is a cartilaginous fish that stuns its prey with an electric shock while hovering above it.  Many people do not know that all living creatures produce electricity—even humans—but electric rays have two special kidney-shaped organs that generate and store electricity like a battery using a process known as electrogenesis.  Large Atlantic torpedo rays can generate enough power to produce a shock of about 220 volts!

With the proper identification of this mystery animal as a torpedo ray, more questions emerged: Are they common to this area? Are these unusually large ones? What do they eat? Why do they beach themselves? How old are these animals? The next step in answering these questions is to do an animal autopsy, called a necropsy. 

The necropsy done revealed that it was female, with two unusual looking large grayish organs that looked somewhat like large gray livers. These were identified to be the electrical organs, which can comprise 20% of the total body weight.  Electric rays belong to the superorder Batoidea, which includes stingrays, skates, guitarfishes, and sawfishes.  Like their relatives the sharks, batoids have skeletons made of tough connective tissue called cartilage.  One of the first confirmations that this was indeed a batoids was the discovery of the cartilaginous spine during the necropsy.  These creatures are benthopelagic, living near the bottom but capable of swimming higher in the water column than most benthic creatures and can also go further offshore than many common inshore rays.  Typically, the torpedo ray swims slightly above their prey and sends out an electric field that stuns their victims which they then scoop up in their highly “protrusible” mouth.  If you picture the bizarre folding pincer-like mouth of the alien from the 1987 movie, Predator, you are in the right ball park.

Torpedo nobiliana is the only torpedo ray found in the Northwest Atlantic Ocean of the 14 species (43 subspecies) world-wide. The Atlantic torpedo is a benthic species that is generally restricted to the continental shelf. They range from Nova Scotia to Venezuela in the western Atlantic, and from northern Scotland to the west coast of Africa in the eastern Atlantic. Adult Atlantic torpedo are believed to range in size from 30 to 180 centimeters total length (approximately one to six feet), with the largest known individuals reaching weights of up to 90 kg (200 pounds!). So although these were large specimens, they were not the largest on record. Fishermen will occasionally bring up torpedo rays as “by-catch” (non-targeted species) while trawling and some dive websites warn scuba divers to be aware that they may encounter them. Although the voltage level is high, the pulse has a very short duration of 5 ms; therefore it has not been shown to cause cardiac arrest, although divers and swimmers have been knocked unconscious for several seconds and can become disorientated. As to their occurrence in our waters, they have been reported sporadically, with one report of a 5-foot-wide torpedo ray seen on the bottom 1.5 nautical miles southwest of Martha’s Vineyard who temporarily paralyzed a research diver from Woods Hole Oceanographic Institute. As to the reason why these creatures both beached themselves, area ray experts thought they may have been caught as by-catch and then disposed of overboard, but no marks, or gashes, or evidence of a struggle with man or beast was apparent, nor were the creatures obviously emaciated, although further tissue and stomach analysis may reveal more clues.

Amazingly, Mr. Van der Wolk found a second ray in Madaket just one week later, and again called the Field Station. A staff member and a volunteer with the Marine Mammal Stranding Team went out and performed an on-site necropsy, taking additional photos and critical measurements. This ray was considerably larger; five feet long and 122 lbs, also a female with eggs. In general, the female rays are larger than males. Torpedo rays give birth to live young that hatch in utero after a one year gestation period and have been known to give birth to up to 60 pups.

The photographs and measurements were sent to the New England Aquarium, as well as to two area ray experts, W. David McElroy and Sandra Downing with the University of Rhode Island. The extracted organs, currently in cold storage at the Field Station, will be shipped to area researchers who are investigating the diet and fecundity of these elusive and bizarre creatures. Stomach content research, although sparse, shows that the prey of the Atlantic torpedo ray is predominately fish such as the silver hake with the occasional small shark, eel, or flounder on their dinner plates. Fortunately, torpedo rays prefer to be in relatively deep water (30-6- meters), so a close encounter is not forecast anytime soon off Nantucket, although you should keep a WOOD handled gaffing hook handy just in case.

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