Simplest and cheapest of devices in use is a short club, the "shark 

 billy," which is rated moderately effective. At the other extreme are 

 electrical or electronic shield devices which are expensive and complex. 

 So far these have not proven to be effective and in some instances have 

 constituted a hazard for the user (Gilbert, 1968). 



Conventional power heads or "bang sticks" are relatively inexpensive 

 and have some effectiveness, but are not readily reloaded. The recently 

 developed "Sea-Way" power head is highly effective and easily reloaded, 

 but, like bang sticks, would be of limited utility to military divers who 

 are often burdened with other gear and sometimes required to operate 

 clandestinely. 



The electronic dart, which is designed to electronarcotize a shark, 

 and the C0„ dart, which injects carbon dioxide into the shark under high 

 pressure (Langguth, 1972), are moderately effective but relatively 

 expensive, and unless equipped with extension poles (which reduce their 

 portability) require that the user be in very close contact with a shark. 



One novel device, the drogue dart, is a barb with a small parachute 

 attached. When the barb, mounted at the end of a pole, is implanted in a 

 shark it breaks away and the parachute provides an off-balance impediment 

 to the shark's swimming. This device, while cheap and effective with 

 small sharks, has not been tested with large sharks. 



Recent accounts of acoustic devices that repel sharks warrant investi- 

 gation (see Banner, 1972; Myrberg, 1974), although they raise questions of 

 cost and practicality. The great advantage of an acoustic device, assuming 

 that there is a sonic stimulus which will repel sharks, is that it would 

 operate at a distance. A disadvantage is that it could not be used in 

 clandestine swimmer/diver operations. 



In summary, no existing device satisfactorily meets the specifications 

 for military swimmer/diver use, although some have utility in special 

 circumstances. 



4) Area Protection 



Area protection may at times be desirable at an underwater construction 

 site or a recreational bathing area. Again, no wholly satisfactory device 

 or system is known, each being deficient in one respect or another. A net 

 enclosure is effective but expensive and usually impractical. Gill-netting 

 and fishing for sharks have proved effective in Australian beaches but 

 are expensive, long-term measures. An electrical device called "Shark 

 Shield" has seen some use by shrimp fishermen to keep sharks out of their 

 nets, but it is expensive and of limited practicality for area protection 

 (Gilbert and Gilbert, 1973). The possibility of attracting sharks away from 

 the area of concern by means of acoustic techniques developed in the course 

 of ONR-sponsored research might prove moderately effective but has obvious 

 drawbacks. 



The fact that porpoises have on occasion been known to attack and kill 

 sharks has led to the suggestion that they be specially trained to provide 

 protection for swimmers and divers. In an ONR-sponsored project conducted 

 at the Mote Marine Laboratory a bottlenose dolphin was indeed trained to 

 harass a large sandbar shark and drive it out of the pool, but when a bull 



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