580 ECOLOGY AND BEHAVIOR 



the adults and often in geographically distant localities. It is now apparent 

 that such segregation is not confined to the larger species but is present even 

 in sharks as small as Galeus arae (maturing at 25 to 28 cm (Bullis 1967) and 

 Holohalaelurus punctatus (maturing at 24 to 29 cm (Bass et al. 1975a)). 

 While predation of small sharks by large sharks is one factor influencing the 

 evolution of distinct nursery areas, it is possibly less important than competi- 

 tion between equivalent-sized animals of different species. Food does not 

 seem to be the limiting factor; space or the lack of it must be taken into 

 consideration. The work of Johnson and Nelson (1973) on agonistic display 

 in Carcharhinus menisorrah (=C. amblyrhynchos) was the first systematic 

 investigation of territorial behavior in sharks. These authors quote several 

 other references to territoriality and to interspecific dominance in sharks, of 

 which the observations of Limbaugh (1963) are particularly relevant to this 

 discussion. Writing about the behavior of three species of Carcharhinus 

 found near Clipperton Island in the eastern Pacific, he noted that there was 

 "a definite nip order among these three species of sharks. The larger sharks 

 within a species dominate the smaller ones. Among the sharks of nearly the 

 same length, the whitetip reef shark (C. platyrhynchus, ?=C. albimarginatus) 

 very clearly dominated. The Galapagos shark (C. galapagensis) dominated the 

 blacktip shark (C. limbatus), which seemed almost afraid of its own shadow." 

 Further work will probably emphasize that territorial behavior is wide- 

 spread among sharks. This sort of behavior would probably not have evolved 

 unless populations tended to increase in size until regulation was necessary 

 in terms of space. In the presence of adequate food supplies, territorial con- 

 siderations would seem to be the principal influence on the distribution of 

 the various age and sex groups of any shark species. The study of social be- 

 havior in sharks is thus likely to become increasingly relevant to studies of 

 their ecology and population dynamics. One topic that deserves more atten- 

 tion is recognition among sharks. This includes recognition not only of dif- 

 ferent species but also of sex, size, and physiological condition in the same 

 species. Adult sharks of different species but similar size may inhabit the 

 same area. How do they recognize each other, and what factors ensure that 

 females are fertilized by males of their own species? As sharks are not known 

 to make any sounds it seems unlikely that they communicate in this way, 

 and recognition is probably made by means of visual or chemical signals. 

 Visual signals can be divided into two arbitrary groups for descriptive 

 purposes— locomotory and postural displays and distinctive markings on the 

 body and fins. 



Locomotory and Postural Displays— The best description of this type 

 of display is that by Johnson and Nelson (1973) of agonistic display in 

 Carcharhinus menisorrah (=C. amblyrhynchos). This consisted of a distinc- 

 tive posture as well as laterally exaggerated swimming and rolling or looping. 

 The authors felt this display expressed defensive threat. "It appeared 

 ritualized in nature and is likely to be of value in normal social encounters." 

 Courtship display, in which males make surface bites on the pelvic areas 

 as well as other parts of the body and fins of females, also fits into this 



