“records of the last 18 years contain no authenticated accounts of shark attacks on personnel.”—“I tackled the stomach of a captured 12-foot Brown shark with my knife . . . the round end of a bone came out, and in withdrawing the entire object, I was horrified to find it to be a recently swallowed human arm with the hand intact!”
In the face of such widely opposing statements typical of the prevalent schools of thought on the subject of man-eating sharks, one of the strangest programs of research of World War II was launched by scientists of this country.
Relinquishing to the statistician the task of determining the “optimum percentage possibility” of shark attack to which a man is subjected should he find himself adrift by choice or pressure of circumstances, it was obvious to several of the life protecting agencies of the Services that a definite need existed for some measure of physical and mental protection against such a widely occurring natural foe.
No available data or literature on the life habits of the shark revealed whether the protection of a man from this carnivorous fish would require physical methods such as light and sound waves, or whether chemical substances dissolved in the water through which the shark must pass would deter his attack. Practically all existing information on the subject could aptly be called “shark lore”—denoting its probable extent of coloration and expansion by overzealous writers and raconteurs.
Thus, with practically no limitations as to method or agent to be used, investigation on the problem was commenced by zoologists and marine biologists under a contract with the Committee on Medical Research of the Office of Scientific Research and Development.
The work was initiated at the Woods Hole Oceanographic Institute and consisted in the most exacting observations of the feeding reactions of the dog shark (Mustelus), the closest relative of the shark available under confined conditions. These fish were placed in large tanks in the laboratory and were conditioned to attempt to obtain food from a small wire cage in which fresh bait was placed along with a test material deemed capable of deterrent action on the fish’s feeding habits. By the use of control periods during which some arbitrary value could be assigned to the “degree of hunger” of the test fish, a percentage numerical value could be determined for the repelling ability of each test substance. A total of 78 different substances were experimented with in this manner, including ordinary ink, concentrated rotenone (which is a very potent fish poison), and several of the poison gases. In addition to these materials yielding both sight and taste changes in the water surrounding the bait, a test was made using only supersonic sound waves to protect the food. Practically all these methods and materials failed. It was found that only three substances were capable of preventing the dog shark from feeding on a bait with any degree of certainty. These were, in the order of their apparent superiority:
1. Extract of decomposing shark meat
2. Maleic Acid
3. Copper Sulphate
Strangely enough, both the decomposing shark meat and the copper sulphate were already known to be useful in preventing types of marine activity. It is related by shark fishermen along the coast of Florida that when captured shark are not taken up from the hooks, or for some reason are allowed to die on an anchored fishing line, no other sharks or fish will be caught in the same vicinity, and the fishermen are forced to seek fish at a distance of several miles from the contaminated area. The use of copper salts in the destruction of the lower forms of marine life, such as barnacles, is familiar to shipowners.
Obviously, the commercial production of an extract of decomposing shark meat to government specifications would be an enormous task, consequently the material was chemically analyzed for its most active constituents. These were found to be ammonium acetate and acetic acid, both being common and easily obtainable chemicals.
Since it had been decided that mere laboratory tests were no substitute for actual field tests on sharks, an expedition was organized by these scientists to proceed to the Ecuador coast, the only area in which sharks were known to be abundant at that season (December, 1942).
These field tests conducted in the Gulf of Guayaquil were practically the same as fishing with hook, line, and sinker, except that two lines were used about 20 feet apart, so that some measure of the number of sharks which were repelled during a time period could be easily determined. One of these duplicate lines was baited with fresh mullet fish alone, while the other line was baited with mullet fish having a porous bag of chemical hung over the bait to protect it from attack. A single test was considered completed when either of the lines was pulled out of the water with a captured shark, thus assuming that the subject shark had equal opportunity to attack both lines. Since the analysis of the extract of decomposed shark meat had shown that the acetate radical was in great abundance, and also that copper had shown very good results in the laboratory, the ichthyologists decided to combine copper and acetic acid in the form of copper acetate, and try it as a protecting chemical in addition to the three materials discovered to possess repellent proclivity in the laboratory.
These fishing tests revealed that copper acetate was by far the most efficient repellent, showing no attacks by the sharks on a bait protected by the chemical suspended over it in a porous bag which allowed only one-tenth to one-half a pound per hour of the copper acetate crystals to diffuse into the water near the bait. As a proof that the sharks were feeding during the tests using this chemical, the nearby unprotected control bait and hook captured a total of 26 sharks during the twelve different test periods. None of the other substances showed as phenomenal results using such small amounts of chemicals. It was now felt that an extremely promising shark repellent chemical was in hand.
However, one important question remained to be answered. This concerned the reaction of the shark under other conditions of food hunting. Evidently the shark has a dual personality. He is inclined to be very careful in selecting his food when he travels alone and comes upon some scent or taste in the water which leads him to a likely meal. He approaches a bait and carefully makes sure that it is safe to eat—even nudging it with his body to see if it is dead or alive before he attempts to devour it. However, when he travels with other sharks seeking food, all this changes and he very speedily selects what he wishes to eat without any attempt at classification of its character or edibility. He merely wants to insure that he gets his share, and the effect is evidently contagious to the other sharks in the pack, for food is very ferociously attacked by the entire group when it is once located.
Consequently, it was necessary that tests be made where packs of sharks were known to feed, so their reactions could be observed. One locality where such a test would be possible was found near St. Augustine, off the coast of Florida. Here shrimp boats cruised back and forth in a shark-inhabited area, periodically taking up their nets, separating the shrimp from the unwanted fish and miscellaneous sea denizeris, and throwing the trash fish overboard to the packs of sharks which are accustomed to following the boats in search of just such a meal. Visual observations were relied on in these tests to determine the efficiency of the material. The results were most discouraging. When a shovel full of a mixture of trash fish and copper acetate was thrown overboard among the hungry sharks, they immediately seized upon the trash fish and the copper acetate, showing no discrimination in their choice. To test their reactions further, a pail full of ordinary wooden chips about the size of the trash fish which they were accustomed to receive was thrown out among them, and these were eaten as rapidly as the chemically treated bait.
To check this test another similar test on this condition of shark pack-hunting was conducted near Biloxi, Mississippi. Here various gradations of activity could be assigned to each individual test due to the presence or absence of a large number of sharks at one time. It was quickly verified that as the number and activity of the pack increased, the effectiveness of copper acetate decreased.
It was now evident that only 50% protection could be presumed by the use of this copper acetate; and since it was supposed that a great deal of the need for a shark repellent would be in mass abandonment of ship or some other situation where large numbers of sharks might be attracted to human bait, it could be seen that some additional material would have to be added to decrease the possibility of attack under shark “mass psychology” conditions.
About this time chemists from the Naval Research Laboratory were called upon by the Bureau of Ships of the Navy Department to assist in perfecting the shark repellent chemical. Being closely connected with the origination of the now-common “Sea Marker” fluorescent dye used for rescue purposes, and other Naval problems involving new uses of dyestuffs, these scientists reasoned that perhaps an imitation of the natural defense of the squid and octopus against marine enemies would be of use to man. This could be most simply done by the use of black dyestuff, injected into the water by floating personnel threatened by a shark attack. During the Biloxi tests a small amount of dark-colored dyes had been thrown overboard, and an apparent influence was noticed in repelling the sharks.
Immediately a schedule of tests was drawn up to conduct the same type of duplicate-line fishing tests performed by the ichthyologists in the Gulf of Guayaquil, but using different black dyes as repellents.
An important factor in obtaining densely black dyed areas of water surrounding a man or other bait was that the dye should have immediate solubility in the water and possess high tinctorial value so that extremely small amounts of the dyestuff would provide large volumes of black water. If it was to be used with copper acetate, it also had to be compatible with this chemical in sea water. At the time of inception of the tests by the Naval Research Laboratory, the black dyes domestically available were not considered satisfactory from these viewpoints, and the industry was called upon to produce a more soluble, “blacker” dye. A new, more soluble dyestuff of the Nigrosine type was submitted by the Calco Chemical Division of the American Cyanamid Company, and used in the duplicate-line fishing tests then being conducted. The results of the tests with this dye alone were amazing. In one series of tests, when a total of 50 sharks of several different types were caught on the unprotected control bait, the food protected by a cake of diffusing black dye was only attacked twice.
Now one might reason that it was a visible color reaction alone which prompted the sharks to avoid any contact with the dyed water or protected bait, so one “black night” fishing test was made when there was no moonlight or visible illumination, thus almost completely eliminating the question of visibility or sight. Here again the dyestuff proved itself to be of undiminished strength in preventing the shark from eating a very favorable bait.
One of the several types of repellent tests which were conducted on this dyestuff is worthy of special note and its graphic- pictorial representation appears in Figure 1.
This test was performed with the fishing vessel proceeding on a steady course at one- quarter throttle, attracting the sharks by means of chumming (small fish macerated with a steadily operated meat grinder placed at the stern of the vessel underway). Assuming a constant rate of attraction of fish to the area, fishing was conducted in three periods: the first, 100 minutes in duration, using only baited lines in order to establish the rate at which fish were being attracted; the second, 100 minutes in duration, using identical lines and bait, but with all bait protected by a slowly dissolving block of solid repellent-dyestuff, Calco WBSR; and the third, a period of 58 minutes, using the same conditions as those existing during period one. This latter period established the important point that the chumming action of the fishing boat was still effective in attracting sharks.
After these successful tests had been completed it was believed that a new type shark repellent material had been evolved, but again it remained to be subjected to the test involving the mass psychology of the shark packs following the shrimp boats.
The cooperation of the shrimp fishermen operating off Mayport, Florida, was again obtained by the Naval Research Laboratory test-fishing unit, and similar tests were made with large proportions of the black dyestuff, as had been conducted with the pure copper acetate salt. The effect of mixing the dye with the trash fish and throwing it over to the sharks as food was immediately apparent. All sharks forthwith left the area and could only be lured back to accept clean bait from the boat after the vessel had proceeded some distance from the black spot formed by the dyestuff in the water. A complete Koda-chrome motion picture record was made of these tests in lieu of other factual data.
Since it was concluded from the large number of previous tests conducted with copper acetate alone that this substance was certain to be distasteful to the olfactory senses of the shark, but it was not certain that any olfactory reaction could be ascribed to the black dyestuff (because of the impossibility of dissociating and testing individually the color component from the taste component in the compound), it was decided to use as a final product, a mixture of 80% dyestuff (Calco WBSR), and 20% copper acetate, thus assuring that both olfactory and visual stimuli were being produced in the fish.
All that remained now was the task of designing a suitable packet to contain this material compacted in the form of a 6-ounce cake of chemicals contained in a cloth bag, so that individual personnel could release the chemical easily and quickly, producing a visible colored spot in the water and around his body when he thought an attack from sharks impended. The present design is very similar to the easily used “Sea Marker” packet, with the added factor that an inner pocket was incorporated into its construction so that floating personnel could return the chemicals to a waterproof cell if no danger from attack existed, thus saving it for further use. With several changes in fabrication, this same packet and material was later adopted by the Army Air Forces.
The U. S. Navy “Shark Chaser” represents the answer to two important questions: (1) Given the fact that shark attack does occur in certain tropical waters, how can the human body be protected expeditiously?; and (2), How can personnel be provided with the necessary moral support in the form of such a chemical weapon, so that psychological fear of sharks can be eliminated in tactical problems over shark-infested waters? Even if not one of the “Shark Chaser” packets now issued to Naval or Army personnel was ever opened in expectation of an actual shark attack, the second problem involving an even more baffling obstacle can be said to be solved, and additional tactical operations can be performed where they would be much more difficult if no such device as the “Shark Chaser” were existent.