614 



Fishery Bulletin 91(4). 1993 



the northern offshore spotted dolphin and 9.8 years 

 (SE=0.264; n=403) for the southern offshore spotted 

 dolphin (Fig. 2). This difference in the ASM was sta- 

 tistically significant (t= 14.32, df=13, P< 0.001). The 



™ 15 



b ,3 



DC 



I- 12- 

 < 



11 

 —I 

 < 



3 10 

 X 



LLI 

 <S> 9 



Li. 



O 8 -| 



LU 

 (J 

 < 



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M l ' + 





YEAR 



Figure 2 



Estimates of the average age at attainment of sexual matu- 

 rity i ASM i by stock for the offshore spotted dolphin with 1 

 SE. If no SE bar was plotted, then there were no overlapping 

 indeterminate age classes. Circles represent estimates of ASM 

 for the northern offshore stock and triangles are the esti- 

 mates for the southern offshore stock. The pooled estimate of 

 ASM for the northern offshore stock IN) is 11.1 years (solid 

 line) and 9.8 years (dashed line I for the southern offshore 

 stock IS). 



range in age of animals attaining sexual maturity was 

 largest for the northern offshore stock. The youngest 

 mature animal was 7 years, and the oldest immature 

 was 16 years. The same range for the southern off- 

 shore stock was 6 to 11 years (Fig. 3). 



Reproductive rates 



The statistically significant trends in the reproductive 

 parameters examined were an increase in the propor- 

 tion of mature females simultaneously pregnant and 

 lactating in the northern offshore stock, the predicted 

 compensatory response, and a decrease in the propor- 

 tion of mature specimens in the sample from the south- 

 ern offshore stock. When the data for all years were 

 pooled, no statistically significant differences between 

 the mean parameter estimates for the northern offshore 

 and southern offshore stocks were detected (Table 2). 



AGE (years) 



Figure 3 



Age-frequency distribution of the northern offshore and south- 

 ern offshore spotted dolphin specimens aged. The open bars 

 represent the sexually immature females in the sample, and 

 the solid bars represent the sexually mature females in the 

 sample. 



