Sharks, Snakes and Experts

Walter Starck

For some reason Gray Reef Sharks in the central Pacific are especially aggressive and a number of divers have been attacked. After several unpleasant experiences there in the early 70's I was inspired to come up with something which might deter them. This was the banded wetsuit.

The banded wetsuit as an anti-shark device achieved some notoriety and became a subject of controversy as to its effectiveness. The story affords some interesting insights into the behavior of both sharks and humans. It begins in Panama where Dr. Ira Rubinoff of the Smithsonian Tropical Research Institute told me how predatory Caribbean reef fishes held in large tanks with sea snakes from the Pacific would try to eat the venomous snakes and frequently die as a result. Pacific reef fishes, however, wouldn't bother the snakes. There are no sea snakes in the Caribbean so it appeared that fishes normally living together with the snakes have learned to leave them alone.

Later in the western Pacific I noticed that the majority of sea snake species had banded color patterns. I knew that banded patterns were employed as warning coloration in various venomous creatures thus the idea of a banded pattern to warn off sharks was born. I first tried it in the Coral Sea on Gray Reef Sharks (Carcharhinus amblyrhynchos). They exhibited notable reticence to approach me nearly as close when wearing the banded suit. Subsequently I used the banded suit for extensive diving at Lord Howe Island, New Zealand, New Caledonia, the New Hebrides, the Solomons, New Guinea and the Great Barrier Reef.

      
(Click for large view)

Left: Inspiration at hand. 
Right: At Ontong Java. 

Response to the suit varied with species. Reef Whitetips (Triaenodon obesus) displayed little reaction showing their usual indifference or mild curiosity towards a diver. Silvertips (C. albimarginatus) and especially Grays were less prone to approach, the closeness of approach was noticeably more distant and the frequency and intensity of aggressive displays much less with the suit. In a few instances the response to the suit was dramatic. At Lord Howe on several occasions dozens of Galapagos Sharks (Carcharhinus galapagensis) surrounding divers in plain suits at close range immediately moved away when the banded suit appeared. On various occasions elsewhere, particularly aggressive Grey Reef Sharks quickly dispersed when approached with the banded suit.

After the banded suit appeared in articles, books and films several other divers and researchers reportedly tried experiments with the idea and reported negative results. My experience based on thousands of hours underwater over a wide geographic area both with and without the suit clearly indicates a decided effect on the curiosity and aggressiveness of Gray Reef Sharks in particular and to a less noticeable degree other reef sharks. So, how to explain the difference in opinion, all expert of course.

First let's consider the matter of sharks and sea snakes. Sharks are not afraid of sea snakes they just tend not to bother them. This is not absolute. Tiger sharks in some areas are reported to regularly eat them but then tiger sharks also have been known to eat highly venomous stonefish, poisonous puffers, bottles, tins, a ships logbook and a wooden tom-tom. On the other hand the common reef sharks are much smaller species, perhaps thus more susceptible to a snake bite, and seem normally not to eat them. This immunity is in turn reflected in the behavior of sea snakes toward sharks, whom they tend to ignore. I have seen a sea snake swim slowly and steadily with apparent nonchalance through a feeding frenzy of Gray Reef Sharks. Though sharks may not readily attack sea snakes, insofar as a banded pattern resembles a snake there is no reason to expect sharks to exhibit fear of it.

The problem though is more complex than that. Sharks have sophisticated sensory systems which must also be considered. They have a contrast enhancing mechanism in their visual system which enables them to see farther underwater than we can. The tradeoff however, is that a high contrast black and white pattern may appear to them as disconnected objects against a contrasting background without the finer degrees of shading which join the pattern into a whole.

Sharks also have excellent receptors for sound and smell. In addition to the sounds of bubbles and compressed air coming through a regulator they can hear swimming sounds and even heartbeats. Their sense of smell is especially acute though what they detect of humans in that regard is unknown. Their most unusual sense, however, is their ability to detect the weak electrical fields generated by living creatures. This sense is so acute they can even use it to respond to the minute current generated by their movement through the Earth's magnetic field. In effect this gives them an in-built fluxgate compass, something we have only recently found a way to do with sophisticated electronics.

A scuba diver must present a confusing sensory picture to a shark. Swimming sounds, heartbeat, electrical fields and perhaps smell may be more or less familiar but shape, bubbles and regulator noises are not like anything normal. Add to this a high contrast pattern which presents the appearance of a disjointed jumble of bits moving in strange ways and you greatly add to the confusion. That this pattern resembles that of highly venomous creatures the sharks usually leave alone can not but help. The natural response to all this is curiosity moderated by caution. Depending on whether the diver is relatively inactive or conversely moves towards the shark the response may range from curiosity to flight.

Of the negative results reported regarding banded suit experiments all involved misperceptions of either what to do or what to expect. One used yellow and black bands which of course reduces the contrast of the pattern. Then, not noticing any dramatic effect on the behavior of sharks attracted by spearing fish he decided the banded pattern had no effect. Another stuffed a banded suit with fish and not surprisingly sharks soon took it. The absence of any of the bubbles, motions, sounds, smells, or electrical fields associated with a diver were apparently not considered as relevant. The most recent such pseudo-experiment of which I am aware consisted of using bait to attract Whitetip Reef Sharks to a diver wearing a banded suit. The effect was apparently about like that one would expect from wearing a gorilla suit while passing out candy at a children's birthday party.

In each case a brief poorly conceived trial was sufficient to convince these individuals that I was wrong and they were right. This phenomena is common enough to have a name. It's called the NIH factor. To persons familiar with the world of scientific research NIH brings to mind the National Institutes of Health, the U.S. government agency which is probably the single largest disburser in the world of funds for scientific research. The NIH to which I refer, however, is not that well known one but rather the lesser known Not Invented Here factor.

The greatest resistance to new ideas or inventions seems to come from those who are themselves already established in that field, unless of course, they were the ones to come up with them. The simpler and more obvious the idea is, the greater the resistance. The principle is simple. If something that simple had any merit I as an expert would have thought of of it. Since I didn't, it obviously has no validity. Now that I have dismissed the experts, including myself, who are you to believe?

The island peoples of the Pacific have lived in intimate relationship with the sea for thousands of years and know much about that realm we have yet to learn. At Mota Lava in the Banks Islands are a people who have a legend about how the sea snake once saved all the fish in the sea by driving away the shark who was threatening to eat them. This legend is commemorated in a sea snake dance in which the dancers paint themselves with black and white bands.

       
(Click for large view)

 Sea snake dance, Mota Lava. 

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