SHARKS: THE DANGER IN THE SEA

A roster of shark attacks, a list of all known shark incidents since man began to write, is kept for the Navy by Dr. H. David Baldridge, a [music] former Navy captain, now a scientist at Molt Marine Institute in Sarasota, Florida. Examination of the information which we have in the shark attack pile certainly has it answered all of our questions about shark attacks on humans. Neither has it provided with us with sufficient information to allow people to avoid shark attack to any significant degree. But at least it's allowed us to examine some of the old popularly held beliefs and perhaps dispel some of the old myths. This picture shows a slash wound in a boy's arm received during a shark attack. This sort of wound is clearly not the result of a bite. It was probably produced not by biting, but by having the shark slash the boy with its flat serrated upper teeth. The upper jaw being able to be protruded a considerable distance. This raises a basic question for us since we have in the past primarily tested sharp repellents to overcome a feeding drive. Perhaps this isn't the case at all. Perhaps there is territorial behavior involved. Perhaps perhaps the victim inadvertently interferes in courtship behavior. Whatever it is, it remains for basic research to uncover for us. Another of the popularly believed myths about shark attack has to do with depth of the water. We actually have attacks on records where overly eager sharks have actually beat themselves in attempts to reach victims at the water's edge. Also, it's been popularly believed that sharks always circle before they attack their victims. This is not the case at all. In fact, one should realize that in the majority of shark attacks, the shark is not seen either by the victim or by anyone else around before it attacks its victim. Another question very basic to the protection of human beings against shark attack has to do with the use of chemical shark repellents, particularly those in which there is a very dark black dye, such as the case with the Navy Standard Shark Repellent [music] packet. This reduces itself to a matter of quantity. That is, can we put enough material actually into the water to protect the man? When we submerge the man totally in water, we find that there is an awful lot of water around the man. And if we consider only that amount of water which the shark would pass through during its last 5 seconds of approach to the man, we find that that amount of dye does not at all adequately shield the man from vision of the shark. Actually, it would take something of the order of 100 of these packets [music] dissolved in the water around the man to shield him from sight of the shark. One of the developers of the World War II shark repellent was Stuart Springer, [music] now also a senior scientist at Moat. Uh we included in a kind of repellent copper acetate and uh from later work done at Naval Research Laboratory, niggressine dye. This combined material worked fairly well and uh attested by some uh results that we heard about. Uh, it actually saved lives. It did wonders for the morale, which was the important thing at the time. Most repellents have two purposes. [music] To repel the shark, and to mask the man. There are black repellents, yellow repellents, green repellents. The research [music] goes on. But the emphasis today is on studying the many species of sharks, on learning enough about these animals and their habits to outwit them. Much of the research is sponsored by the Office of Naval Research, which has many questions to ask. How far away can [music] a shark smell blood? What colors does a shark see best? And which most dimly? Some questions [music] can be asked in laboratories, but others must be carried to the shark in his own environment. The University of Miami maintains a marine institute on the very edge of the Gulf Stream, a natural center for shark research in the open ocean. Like Dr. Arthur A. Merberg studies of shark response to underwater sounds. We have to move where these sharks rain and where they, so to speak, oftentimes call the shots. My fine graduate students, [music] research assistants, and I move out on this vessel, the RV Observer, into the blue waters of the [music] Florida Straits, or as far away as the deep waters of the Bahamas, such as the tongue of the ocean. Before getting into the water, however, [music] we often times put over our underwater cages. [music] Underwater sound transducers are dropped off the vessel also and come to rest approximately [music] 10 to 15 m below the vessel. Hydrophones, [music] underwater microphones are also dropped off the aft section of the vessel in order that we may monitor the sounds that [music] we transmit. A television camera is also carried down with us. And these divers also carry with them underwater communication systems. Right, we're rolling. [music] Okay, picture's coming through pretty good. Recording. [music] The tremendous acoustic and vibratory sensitivity that many species of sharks possess indicate that underwater sounds possess important function for these animals. One such function is no doubt the perception of an orientation to possible prey. In fact, the most attractive sounds found to in our work indicate that they are rapid irregularly pulse sounds of very low frequency bands. These sounds are extremely similar when one hears them to those produced by an object such as a large fish when under stress when such an animal shutters or shakes or rapidly moves in the water. [music] We wish not only to seek out these functions, but also determine just how precise are the hearing and vibration senses of these animals who are obviously so well adapted to their environment. [music] Dr. Merberg's former students now carry on shark research at many other institutions. Dr. Donald Nelson of California State University at Long Beach has worked with reef sharks at any weak atal in the Pacific under a [music] Navy contract. He has learned that these sharks, like those studied by Dr. Murburgg off Florida, seem to prefer an intermittent pulsing sound. 10 seconds after the sound starts, the sharks are gathering. In [music] 20 seconds, the number has substantially increased. [music] This is the scene after 2 minutes. Sounds that call to sharks. [music] Perhaps one day to lure them away from divers or crash survivors. Perhaps to tell us what sounds not to make underwater. [music] Now, Dr. Nelson and his companion enter the water to study shark behavior firsthand. Their only defenses are a bang stick with a shotgun shell in the end, a knife, and a club. [music] The gray reef shark of the Pacific is mildmannered enough to allow this intrusion. He is [music] only curious, not yet annoyed by the strange swimmer. Other species might attack immediately. [music] But Dr. Dr. Nelson wants the shark to be annoyed so that he can photograph and study its pre-attract behavior. Now, in a daring and deadly research experiment, the scientific team deliberately provokes [music] the shark. These are the first films ever made of a shark's agonistic behavior, his pre-attack demonstration [music] of anger, like a dog snarling and stalking of an enemy. [music] A deadly dance beneath the sea. The shark's [music] body arches and undulates. The petrol fins beneath, normally almost straight out, begin to point downward. This species of shark at least gives warning of his attack [music] to others. It's too early to tell, but the boldness of Donald Nelson [music] and his team may help many a diver to recognize the signs of danger and to escape [music] [music] [music] at the University of Miami. A Navy sponsored study of shark eyesight is being made by Dr. Sam Gruber. I became interested in the vision of sharks when the Navy came to us with the following story. In an air sea disaster, pilots were wearing orange suits while the crew was wearing green khaki suits. The pilots to a man were attacked by sharks apparently because they were wearing the orange suits while the men in the green suits were left entirely alone. The Navy came to us and asked us therefore whether sharks had the possibility of seeing colors. Our first study concerned retinal hisystologology of sharks. [music] We examined eye sections of many species under the normal or light microscope. We found both rod and cone-shaped light receiving cells in their retinas which was in direct contradiction to the classical literature. This indicated at least the shark had the kind of eyes ordinarily associated with color perception in other animals. However, we needed even more detailed evidence for the final proof. And for this, we turned to the electron microscope. Here, under the electron microscope, we're obtaining the kinds of detailed information necessary to reveal the ultra structure of the rods and cones in the great white shark retina. We are now looking at the retina of the great white shark under the electron microscope at 2,000 magnification. The dark masses in the lower screen are the light receiving cells, the rods and cones. One obvious difference is that the cone outer segment is more dense and therefore more dark. Now we'll switch to 20,000 magnification. Here the differences become more apparent. This is still the cone. We'll now move over to the rod outer segment. These analyses have led us to believe that the shark has a duplex retina and we have carried out complimentary laboratory experiments to separate out the relative functions of the rods and cones which we saw under the electron microscope. Dr. Hamasaki will now anesthetize the lemon shar. We are now inserting a tube of fresh running sea water into the shark's mouth. This water will run over the shark's gill and maintain the animal for the 8 to 10 hours of the experimentation. Dr. Hamasaki will insert a corneal electrode attached to a contact lens. With this electrode, we pick up the electroretinog generated each time a flash of light strikes the eye. In this experiment, we measure the sensitivity of lemon sharks to light of different colors. It shows at least two things. First, the limits of vision, and second, that the lemon shark retina, when tested in darkness, is most sensitive to green light. When we did it in daylight, the sensitivity moved toward the yellow. This movement is known as the perkini shift and is evidence for cone function. [bell] [music] In this experiment, we condition a fully conscious shark to blink each time it sees a flash of light. In the beginning, sharks never blink to flashes of light. [music] Now we add a mild shock to each flash. The shock is so positioned that the animal must blink. When we combine shock and light, after a few flashes, the animal begins to expect a shock with each flash. After about 40 trials, we [music] disconnect the shocker. Now the animal blinks to light alone and is conditioned in the same way as Pavlov's dogs. I can now communicate in a sense with the shark and ask it questions about its visual system. Through experiments such as these, we have come to know a great deal about the shark's vision and are beginning to believe it can detect colors. Okay, ready? Throw it. The shark's color vision is checked in his own environment. Which color will attract more sharks to [music] the bait beneath? The first answer is a surprise. They seem to favor the black ball over the brightly [music] colored one. But more than a thousand tests must be made before there is any sort of a scientific determination. Navy scientists observe sharks from a variety of platforms in the open ocean. At the Naval Undersea Center in San Diego, shallow undersea observations are made through this plastic bubble mounted under the research vessel [music] CC, a catamaran. [music] For deeper observations, Navy researchers use the Nemo acrylic bubble, a unique undersea observation vehicle developed by the Navy. Some kinds of shark [music] research require constant observation of captive animals under controlled conditions. One of the most complete facilities for such work [music] is the Moat Marine Laboratory, Sarasota, Florida, directed by Dr. Perry Gilbert. It is often necessary to supplement field observations on large and dangerous marine animals with studies under partially [music] controlled conditions. Boat scientists can study groups [music] of sharks in the great pool or isolate individuals in a connecting shark run. Young sharks are raised in small outdoor pools or tested in a controlled indoor environment. In most laboratories, the shark is studied beginning with the embryo and continuing through examination and [music] comparison of the jaws of long dead animals. How strong are these giant jaws? That's the subject of one study underway at Moat. One of the challenges the Navy has posed for us at the Mo Marine Laboratory is to measure the force the jaws of sharks exert when they bite. This problem arose when Navy oceanographers lost expensive instrumentation. The cables the instruments [music] were attached to had been severed by some marine creature. And the question was, could a shark possibly [music] have done this? Jim Snodgrass of the Scripps Institution of Oceanography devised this clever bite meter with which we measure the force the jaws [music] of sharks exert. To make this meter attractive to sharks, we first have to bait it. [music] And here comes a small lemon in. Oh, that that is not a good bite. There it goes. There it goes. [music] It's too early to determine just what the magnitude of [music] the force is, but we have measured forces from an 8 1/2 ft [music] dusky shark. A force exerted by a single tooth over an area of 2 square mm of 60 kg. And if [music] one extrapolates, that's a force of about 18 metric tons per [music] square in. In other words, a shark can exert a very substantial force. Not long ago, um, at the shark lines, [music] a lemon shark about 8 ft in length came up and in a single bite bit through this 1-in manila rope. I have no doubt that with [music] repeated bites, a shark could sever a hawer of this magnet. [music] And since in the MO scale of hardness, we find that a shark's tooth has about the same hardness [music] as steel, it's entirely possible for a shark of some size to sever a/4in steel cable if that cable is under substantial stress. In another [music] series of tests, we have found that sharks respond to an electric field. [music] The instrument we have tested is known as the shark shield. It's a [music] batterypowered instrument. From the instrument, two electrodes [music] extend in this test across the channel. And between those two electrodes, an electric barrier is created when the [music] instrument is on. With the generator off, you [music] will note that a shark passes freely back and forth through the field. When [music] the generator is turned on, the shark is repelled. We have successfully repelled with the shark shield four species [music] of dangerous sharks. A similar electric device has already been installed at a South African beach to [music] protect swimmers. Another has been adapted for divers. Electrodes [music] run along the sleeves of the wets suit and down the legs. Mode scientists have tested dolphins as an anti-shark device and find that contrary to popular belief, the two do not necessarily [music] attack each other. This dolphin, in fact, has to be trained to attack a shark. They first teach him to butt a small dead shark on a signal, rewarding him with fish. [music] By the time the dolphin's training was complete, he was so enthusiastic that [music] he skinned his nose and had to be retrained to accept a sort of boxing glove for his bouts. His first live shark. On signal, the dolphin butts him around the pool until he flees. The experiment seems a success, but later the dolphin refused to pursue a shark of a different and tougher species. Now the researchers must learn whether the dolphin can be trained to pursue any shark which approaches. [music] The research programs we have dealt with thus far are concerned with the shark hazard problem and the shark as a barbarian. It must be remembered, however, that of all the species of sharks, some 250 in [music] number, only about 25 are dangerous to man. and [music] many species are benefactors of man as a source of products useful [music] to man. In recent years, the shark has become a [music] very important experimental animal in biomedical research, including that on cancer. Sharks seldom develop any kind of cancer, but this one has a rare skin carcinoma. Do other sharks have natural antibodies? Why not this one? Sharks are also widely used for studies of the way drugs and other chemicals pass from the blood into the brain. Many a project starts as pure research then leads to practical development. Navy Captain Baldridge assigned to a research project at Moat studied the weights of sharks in water. Today, the retired captain, as Dr. Baldridge, a senior research scientist at Moat, continues the same project. He has shown that even the largest shark weighs only a few pounds when supported by seawater. Most of its weight is supported by the oil in a tremendous liver, often larger than all other body organs combined. Unlike many fish, sharks have no swim bladder, which can be inflated to supply buoyancy. Captain Baldridge found that adding a few pounds of extra weight would almost disable a shark. [music] He and another Navy scientist, Dr. Scott Johnson of the Naval Undersea Center, got the idea of making the shark more buoyant. They developed a CO2 gun to inject gas into a shark to disturb his equilibrium. Another [music] [music] [music] new defense that drove dark to inhibit the shark's swimming ability. [music] A passive defense developed by Dr. Johnson. The scientist [music] himself tests his shark screen. Before inflation, the plastic bag is a small packet attached to the life jacket. It not only screens the man from the shark, but conserves body heat and keeps any blood away from the animal. A highly touted bubble curtain developed by a manufacturer who had tried [music] it on only one species of shark. Unfortunately, it attracted other species. [music] Sharkresistant materials are tested, too. This one might protect a nylon line or a steel hazard, but hardly the fragile [music] bones of a human being. There is more to the shark than lurking danger and a threat of sudden attack. There is much to learn. Perhaps even the secret of longer life. For the shark never seems to age. For man's own protection and perhaps for his future well-being, he is studying this creature of the past. A strange survivor of the days when the earth was young. [music]