Perryman and Lynn: Stock and school structure of Stenella coeruleoalba 



127 



The sample from the northern region 

 was too small to test for a seasonal pat- 

 tern in reproduction, but the distribution 

 of back-projected births from the south- 

 ern region differed significantly from the 

 uniform distribution (P<0.01; Figs. 5 and 

 6). Reproduction for striped dolphins 

 from the southern region appears to be 

 broadly pulsed in the fall through spring 

 period. 



Photogrammetric and specimen 

 data 



Since significant differences between 

 length samples from the northern and 

 southern regions could not be detected, 

 we pooled length data from the two re- 

 gions in the tests that follow. We found 

 that "adult females" were significantly 

 longer (4.8 cm) on average than adult 

 females from the specimen data base. 

 When the test was repeated by using 

 length data for lactating females from 

 the specimen data base, the two samples 

 no longer differed significantly (Table 3). 

 Striped dolphins > 180 cm in length from 

 the photogrammetric sample were sig- 

 nificantly longer on average than the 

 sample based on the same length crite- 

 ria from specimen data. We also per- 

 formed a Kolmogorov-Smironov test to 

 compare the two distributions (Fig. 7) 

 and found that they differed signifi- 

 cantly (P<0.01). 



Northern Region 



6 - 



5 



R . R 



fl . H , . R fl 





Southern Region 



1 



m 



i 



i! 





lis. 



o 

 =1 

 < 



Northern and Southern Region 





,fl, .B RTOlfc 



i 



Figure 5 



Distribution of back-projected birth dates for striped dolphins, 

 Stenella coeruleoalba, from the northern and southern regions 

 and for the two regions combined. 



School size and structure 



We performed a chi-square test to determine whe- 

 ther the number of dolphins in our two size catego- 

 ries were distributed randomly between schools (Fig. 

 8) and the hypothesis was significantly rejected 

 when the maximum length for the juvenile category 

 was 195 or 190 cm (P<0.001). With a maximum 

 value of 190 cm, four expected values generated by 

 the test were lower than five. When these schools 

 were deleted from the test or lumped with adjacent 

 schools to eliminate these low expected values, the 

 test results remained highly significant. 



When school size was regressed against propor- 

 tion in the juvenile category, the slope of the regres- 

 sion was not significantly different from zero. Thus, 

 in our sample, the proportion of small dolphins in a 

 school was not related to school size. 



