Ferrero and Walker: Growth and reproduction of Delphinus delphis 



493 



and those presented in Hui ( 1979) and Gurevitch and 

 Stewart 3 may be due to ageing methods. Both these 

 studies employed an early technique of reading 

 undecalcified, thin sections of formic-acid-etched 

 teeth. This method is now considered imprecise for 

 ageing small cetacean teeth (Perrin and Myrick, 1981 ). 



Perryman and Lynn ( 1993) documented reproduc- 

 tive seasonality differences between three morpho- 

 logically distinct common dolphin populations from 

 adjacent but differing habitats in the eastern North 

 Pacific Ocean. Calving season in the tropical region 

 was year-round. In the temperate regions, which are 

 characterized by a wider range of oceanographic con- 

 ditions, strong evidence of reproductive seasonality 

 was evident. 



Our sample suggests evidence for a May-June calv- 

 ing peak as well as for schooling segregation of par- 

 turient females in the southern regions of the tran- 

 sition zone, closer to the subtropical domain. Evi- 

 dence for pronounced reproductive seasonality should 

 be anticipated in this region because the North Pa- 

 cific transition zone is characterized by extreme 

 oceanographic conditions, particularly in the north- 

 ern regions adjacent to the subarctic frontal zone 

 (Roden, 1991). 



Acknowledgments 



The authors thank Rod Hobbs, Anne York, and Jim 

 Lerczak for statistical advice and assistance with the 

 growth models. Our special thanks go to Jack 

 Cesarone for his preparation of tooth and reproduc- 

 tive tissue samples. Editorial reviews by Howard 

 Braham, Dale Rice, Doug DeMaster, Kim E. W. 

 Shelden, Gary Duker, James Lee, and two anony- 

 mous reviewers helped improve the manuscript. Our 

 sincere appreciation is also extended to the 1990 and 

 1991 observer teams for their work collecting bio- 

 logical samples on Japanese, Korean, and Taiwan- 

 ese fishing vessels. 



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