ECOLOGY: INDIAN OCEAN SHARKS 



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Figure 4 Seasonal distribution of Carcharhinus 

 obscurus juveniles tagged and released in Durban 

 and of those recovered from the Cape coast to the 

 southwest of East London, together with the mean 

 surf temperatures in Durban and Port Elizabeth. 

 (After Figure 23 of Bass et al. 1973.) 



the mating habits of sharks but it is unlikely that they form extended 

 pair-bonds and a relatively small proportion of adult males may be able 

 to serve a high proportion of females. This is particularly likely in 

 galeoid sharks where in many cases the females mate at most every two 

 years, a situation which holds true for C. obscurus. It would thus be 

 advantageous for the bulk of the female young to grow up in that part 

 of the range where they stand the best chance of survival. The move- 

 ment of males into less suitable parts of the range may be a result of 

 selection for an even spread of the population over the secondary 

 nursery area despite a tendency for the females to move into a limited 

 part of the region. The genetic dimorphism resulting in a spreading out 

 of the sharks from the primary nursery area, which may have evolved to 

 avoid competition between the newborn and the slightly older animals, 

 would thus be partially linked with sex. 



