14 September 2008

How to avoid being eaten by a shark

What could bring "a shark to an abrupt halt just as it was about to close its mouth" over it? Here's a humble creature that does just that.

Natural Shark Repellent is Alluring to Scientists
Walter Sullivan, New York Times 20 Jan 81;
TORONTO: A MILKY substance exuded by a Red Sea fish known as the Moses sole has proven to be frustrating to scientists, as well as repulsive to sharks.

The substance's shark repellent properties are so powerful that a scientist describing it at a recent meeting of the American Association for the Advancement of Science said it could bring a shark to an abrupt halt just as it was about to close its mouth over the sole.

But in recent research, the fish's toxin, whose promise first became known in 1973, has eluded practical application for human swimmers because it is perishable and difficult to handle. Nevertheless, it remains the focus of research and an important hope for the Navy, which has sponsored much of the work in a 20-year search for an effective repellent.

Despite the difficulties with the Moses sole, scientists at the meeting here were optimistic about eventually finding a repellent from one source or another, because of the discovery that organisms living on the sea floor or within coral reefs produce hundreds of substances fatal to fish, presumably as a form of defense. However, few have yet been tested for their effects on sharks.

Eight researchers in shark behavior and the chemistry of marine organisms met here to discuss the development of an effective shark repellent from naturally occurring, biologically active substances.

The most powerful repellent found so far is that of the Moses sole (Pardachirus marmoratus). It is stored in glands along the dorsal and anal fins. Its dramatic effect was described by Dr. Eugenie Clark of the University of Maryland, widely known for her work on shark behavior.

The shark bears down on such a fish with its jaws wide, she said, until the fish is inside its maw, whereupon the shark suddenly stops, without closing its jaws, and pulls back.

The shark can then be observed, she continued, "jerking its head from side to side; dashing around the tank, bumping sides; holding its mouth open for several seconds to over three minutes; curling on the bottom of the tank, belly up."

The makers of Coppertone suntan lotion hoped the toxin, called pardaxin, could be incorporated in their product to provide simultaneous protection against two hazards of ocean swimming, Dr. Clark told a press conference. Unfortunately, she added, at room temperature the toxin remains effective for only about a day. If frozen it becomes only one-seventh as effective.

Dr. Gerald Bakus of the University of Southern California reported the finding that many bottom-dwelling creatures such as sea cucumbers, sponges, soft corals and gorgonians produce substances that kill fish. Admittedly, he said, to stop a fish as large as a shark would take an extremely potent toxin. Nevertheless, he added, "the probability of discovering effective shark repellents in the near future would appear to be very high."
A relative of the Moses sole is found on our shores.
Peacock sole (Pardachirus pavoninus)
The pretty Peacock sole (Pardachirus pavoninus), is said to produce a "
mucus appears to have shark-repellent qualities", from FishBase.

The astringent, frothy, soap-like toxin of the Moses sole, however, proved difficult to package and store and thus could not be developed into a product to protect humans from shark attacks.

More about shark repellents on Discovery Shark Guide, which concludes that for humans, “The best repellent is humans using their head.”

It also adds "The fact is that only four to five people each year lose their lives due to shark attacks. More people, 150, die each year from being knocked in the head by a falling coconut."

Sharks, coconuts, death. The common denominator seem being in the wrong place at the wrong time and not using your head.


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