582 ECOLOGY AND BEHAVIOR 



in a great number of cases. The best evidence of this is given in Figure 14 

 which shows lateral views of several of these sharks. In combination with 

 size, habitat, and behavioral differences the distinctive markings of many of 

 these animals probably result in efficient recognition of at least their own 

 species. 



Apart from distinctive markings visible from a lateral view, a ventral 

 view of many sharks reveals distinctive black tips to the pectoral and/or 

 pelvic fins. These can be seen in sharks from diverse groups and habitats such 

 as Carcharhinus longimanus, C. brevipinna, C. limbatus (Figure 15) and 

 Carcharodon carcharias (Figure 8). Noteworthy here is the difference between 

 the pelvic fin markings of Carcharhinus brevipinna and C. limbatus. C. 

 limbatus has distinct black tips to the pelvic fins of adults and all the other 

 fins have rather blurred dark tips. In C. brevipinna, a species growing to a 

 similar size and occupying much the same ecological niche as C. limbatus, all 

 the fins have clearly demarcated black tips except for the pelvic fins, which 

 are completely plain. 



Chemical Signals— I do not know of any references to the release of 

 pheromones by sharks but consider it highly likely to occur, particularly by 

 females ready for mating. Attraction of a mate of the correct species could 

 be by postural or locomotory displays, but it seems far more likely that 

 animals with as highly developed an olfactory system as sharks would at 

 least initiate courtship by means of a chemical signal. 



Knowledge of the ways in which sharks recognize one another is sparse, to 

 say the least. Distinctive markings and postures, locomotory displays, and 

 chemical signaling probably have some part to play, and further work along 

 these lines will not only increase our knowledge of the sensory physiology of 

 sharks but also help us to understand the ecology and population dynamics 

 of these fascinating but poorly known animals. 



ACKNOWLEDGMENTS 



I would like to thank all those people who have been associated with the 

 shark research project of the Oceanographic Research Institute, in particular 

 Miss J. D. D'Aubrey (now Mrs. J. D. Whitehorn), Mr. N. Kistnasamy, Dr. 

 A. E. F. Heydorn (director of the Oceanographic Research Institute), Dr. 

 J. H. Wallace, Dr. J. A. F. Garrick, Mr. S. Springer, Mrs. M. M. Smith, the 

 late Professor J. L. B. Smith (of the J. L. B. Smith Institute of Ichthyology 

 at Rhodes University), and especially the late Dr. D. H. Davies (former 

 director of the Oceanographic Research Institute and the man who began 

 and inspired the entire program). Without the assistance, advice, and support 

 of these people and many others not named here the progress and results of 

 shark research in Durban would have been immeasurably poorer. 



Financial support for the program has come from many sources which are 

 gratefully acknowledged. The early work was chiefly financed by the Marine 

 Research Unit of the Council for Scientific and Industrial Research through 

 its Universities Research Division. The Natal Anti-Shark Measures Board and 

 the Anti-Shark Research Association have given considerable financial aid. 



