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Fishery Bulletin 91(4), 1993 



vergence or parallellism is a more likely cause of 

 the cited resemblances. The near absence of sexual 

 dimorphism in the skull and external features of the 

 dusky dolphin, coupled to the exceptionally large 

 relative testis size, led me to suggest that sperm 

 competition should occur in this species (Van 

 Waerebeek, 1992b). 



Both bivariate and multivariate analysis provide evi- 

 dence of extensive geographic variation in skull mor- 

 phology among the dusky dolphin stocks studied. Most 

 strikingly, adult skulls from the Southeast Pacific stock 

 are considerably larger than either New Zealand or 

 SW African specimens (difference in weighted CBL 

 means is 31mm or 8.5% of CBL); skulls from New 

 Zealand do not differ significantly in size from those of 

 SW Africa. This is corroborated by the greater mean 

 body length (roughly 10cm) at sexual maturity and 

 asymptotic length in Peruvian dolphins than in SW 

 African and New Zealand specimens (Van Waerebeek, 

 1992b). Two non-metrical cranial characters also sup- 

 port the existence of the Peru/Chile and New Zealand/ 



