142 UNDERWATER GUIDE TO MARINE LIFE 



5. Influence cf Movement. Sharks seem to be attracted by inert objects at 

 the water's surface. During the last war, it was urged that men in the 

 water stay in a group and keep moving slowly. The effect of movement on 

 sharks is poorly understood. 



6. Influence of Various Scents. 



a. Refuse. Continuous dumping in any one area will soon train sharks to 

 visit there frequently. Many food scents are attractive to sharks and 

 dumping grounds are often danger spots to be avoided. 



b. Blood. This is the strongest attractant of sharks. Almost any shark may 

 be dangerous in the presence of blood, which serves to drive them into 

 a frenzy leading up to the dangerous "feeding mood." De Witt (1955) 

 records an instance of a 3-foot leopard shark, Triakis, attacking a diver 

 when blood was in the water. Fast (1955) states that there is "a strong 

 possibility that with the present increase of spearfishing along our 

 [Pacific] coast, the number of attacks by sharks will increase. Those 

 individuals who indulge in this sport should . . . avoid seepage of blood, 

 fish juices, or other attractants." 



c. Man. Sharks seem neither attracted nor repelled by the scent of man. 



d. Shark Repellents. During the last World War it was found that 

 decomposing shark flesh had a repellent effect on sharks. Further 

 investigation by the United States government during World War II 

 led to the development of cupric acetate cakes, which can have up to 

 100 per cent effectiveness (but usually less) in repelling sharks from 

 baited lines for 3 to 4 hours. Springer lists several of these experiments 

 in which baited lines, some repellent-treated and some not, were used 

 to fish for sharks. The repellent lines were vastly less attractive to the 

 sharks, and most bites on repellent lines were made before the repellent 

 had had a chance to dissolve in the surrounding water. 



There are no proven color-cloud repellents as is sometimes supposed, 

 but sound may occasionally serve to repel sharks. The definitive work 

 on the effect of sound on fishes is yet to be done. 



To these factors we add several suggestions for an advisable course of action 

 when the swimmer is in the presence of sharks under water. 



1. Observe all you can about the shark's behavior. Try to identify the shark. 

 Identification is most important. The swimmer's actions should be very 

 different if he meets a white shark than if he meets a nurse shark. 



2. Don't panic. Keep moving in a fishlike way, smoothly and regularly. Try 

 to stick fairly close to protected places, like coral heads or rock outcrops. 



3. If there are several of you, stay close together. 



4. Avoid blood and offal in the water. 



5. If attacked, fight back. This may serve to drive the shark away. The most 

 efficient way to disable a shark is to grasp a pectoral fin tightly as the shark 

 passes by and then to sht open its belly or gills with a knife. This, however, 

 is not a job for amateurs. 



6. Don't attack sharks. They may look docile and timid and present an easy 

 target, but a shark, if attacked, cornered, or wounded is very liable to 



