Jefferson: Sexual dimorpfiism and development in Phocoenoides dalli 



121 



Figure 2 



Measurements taken of Ball's porpoise specimens (see also Table 1). 



a females 



n=66 



t:ii 



Total Length (cm) 



c 



01 10 



b males 



n=33 





Total Length (cm) 



Figure 3 



Frequency histograms of total lengths of Dall's porpoise specimens. 



zero and one. The higher the Canting Index, the larger 

 the degree of foreward canting. 



Sexual differences in morphology between immature 

 males and females and between mature males and 

 females were tested with a f-test, and age variation 

 was tested separately for males and females with a one- 

 way analysis of variance (ANOVA). Variation in dorsal 

 fin coloration was tested with a chi-square test. Be- 

 cause proportions are known not to be normally dis- 

 tributed, an arc sine transformation was performed on 

 all proportions for statistical analyses (the resulting 

 data approached normality). 



Results 



External morphology 



Dorsal fin shape The dorsal fins of Dall's porpoises 

 cant foreward to varying degrees (Fig. 4). The Cant- 

 ing Index of the dorsal fm shows a tendency to increase 



