MARINE ANIMALS THAT BITE \\ 



dissected before they are seen. When functional teeth are lost, 

 those of the next younger series move up to take their place. This 

 process of tooth replacement continues throughout the life of the 

 shark. Teeth may be replaced singly in some shark species, or as an 

 entire series in others. A series of teeth which form a continuous 

 cutting edge are generally replaced as an entire series. The re- 

 placement process usually requires several days to a week or more. 



The means employed by sharks to detect food and injured animals 

 in the water is a subject that has been of considerable interest to 

 physiologists for many years. Although the intelligence of a shark 

 is probably of a low order and their visual acuity is notoriously 

 poor, their ability to detect food is phenomenal. Food detection is 

 believed to be accomplished by their highly developed olfactory or- 

 gans, and a lateral line system that is extremely sensitive to low 

 frequency vibrations in the water. The auditory nerves undoubt- 

 edly serve as a further aid in locating sources of unusual under- 

 water noises. The ability of sharks to detect a disabled or wounded 

 animal, at great distances, is almost uncanny. Some workers are of 

 the opinion that food detection may be further aided by special 

 gustatory organs. Figure 1, center, shows the external anatomy of 

 a typical shark. 



The feeding habits of sharks appear to fall into two general cate- 

 gories: (1) The individual feeding pattern, which occurs when a 

 single, or several, sharks are normally in quest of food. In most 

 instances, the movements of the shark are relatively slow and de- 

 termined, when making its approach, but at times may be somewhat 

 sudden and swift. The swimming pattern, approach and the final 

 attack seem to vary with the species and the circumstances. (2) 

 In the event of a catastrophic situation, such as might be caused 

 by the sinking of a vessel, the crash of a plane into the water, or an 

 explosion, in which large quantities of food and blood suddenly 

 appear in the water, the entire feeding characteristics of sharks 

 may suddenly revert to a frenzied state which is frequently re- 

 ferred to as the mob feeding pattern. This form of feeding has 

 been commonly observed in some of the carcharhinid sharks. Under 

 these conditions, sharks have been observed swimming vertically 

 from the bottom, straight to the surface, breaking the water, and 

 snapping savagely at anything in sight. It is during periods such 

 as this that the greatest danger is encountered, and almost all re- 

 pellent devices appear to be useless. Cannabalism was observed, 

 in one instance, when a large school of sharks was feeding, in an 

 excited state, on a school of snappers which had been killed in an 

 underwater blast. While one large shark was feeding on a snapper 



