ECOLOGY: PORT JACKSON SHARKS 539 



subpopulations among the sharks. (Semi-isolated subpopulations may be de- 

 fined, for the purposes of this discussion, as adjacent groups of animals 

 of one species between which there is limited genetic interchange.) 



From the data in Tables 3 and 4, it appears that the species is divided into 

 at least two major populations. The eastern population extends from the 

 northern limits of the sharks' range to the vicinity of Jervis Bay, and the 

 western population probably extends southward and eastward from the 

 northeastern Victorian water. However, while the Jervis Bay population 

 does not differ significantly from the more western populations it is sig- 

 nificantly different from the Sydney population, and the Newcastle popu- 

 lation differs significantly from all other populations. (For reasons dis- 

 cussed more fully later, the latter deviation may be due to other factors.) 

 Consequently, the eastern population could be comprised of two or three 

 subpopulations based on the Newcastle, Sydney, and Jervis Bay breeding 

 grounds. 



The existence of two major populations is in accord with the patterns of 

 flow of the principal ocean currents around the southern half of the con- 

 tinent (Figure 6). These currents could direct the movements of the sharks 

 at migration time and hence act as a natural barrier between the two popula- 

 tions. However, the current patterns of Figure 6 apply to the major currents 

 off the Continental Shelf, which is beyond the shark's range. While little is 



Table 4. Chi-square values and probabilities for 

 pairwise comparisons of gene frequencies between 

 populations of H. portusjacksoni from various 

 localities. 



Localities x 2 



Newcastle/Sydney 

 Newcastle/Jervis Bay 

 Newcastle/ Victoria 

 Newcastle/S. Australia 

 Newcastle/W. Australia 

 Sydney /Jervis Bay 

 Sydney/Victoria 

 Sydney /S. Australia 

 Sydney /W. Australia 

 Jervis Bay/Victoria 

 Jervis Bay/S. Australia 

 Jervis Bay/W. Australia 

 Victoria/S. Australia 

 Victoria/W. Australia 

 S. Aust/W. Australia 



*Significant difference in gene frequencies. 



