534 ECOLOGY AND BEHAVIOR 



returning to reefs after short absences, and many of these absences could 

 be related to oviposition. The return of sharks to the same small sites on 

 reefs, after natural and artificial displacements of up to 6 years, and their 

 movements between specific localities on the same reef, indicate clearly 

 that H. portusjacksoni has a precise and well-developed homing ability. 

 When the female H. portjacksoni visit inshore reefs during September 

 and October to lay eggs, the oviposition sites are invariably in sheltered 

 harbours, bays, and inlets (e.g., Sydney Harbour, Botany Bay, and Jervis 

 Bay), and eggs are deposited on the sheltered areas of a very few inshore 

 reefs (e.g., Long Reef). Eggs are found either in crevices or lying on the 

 open sand and at depths ranging from 1 to 20 m, the vast majority being 

 in the depth range of 1 to 5 m. These eggs can be classified according to 

 age and to contents. The presence of mucous indicates an age of a few 

 weeks, a flexible shell case means that the eggs are a few months old; old 

 eggs are identified by a rigid shell case with spirorbid worms or a brittle 

 shell case containing a fully developed embryo. The contents of the egg 

 case are stated simply as empty or full. In Jervis Bay, 149 eggs were col- 

 lected in rock crevices and on the sand, with the result shown in Table 2. 

 If these data are analysed in 2 X 2 contingency tables for habitat X con- 

 tents, the chi-square values and probabilities are as follows: 



ldf 

 ldf 



Obviously the association between egg deposition site and egg case contents 

 is not random. The data show that (a) eggs are preferentially deposited in 

 rocky crevices, (b) rock crevices are at a premium, and (c) eggs deposited in 

 crevices have a significantly higher probability of survival than eggs deposited 

 on the sand. (As most empty egg cases seen were ruptured rather than drilled, 

 as female sharks have been seen carrying eggs in their mouths presumably 



