Pernn et al.: Geographic variation in morphology of Stenella longirostns 



419 



Figure 9 



Percentage of spinner dolphins exhibiting (A) Code 1 (most 

 "eastern-like"), (B) Codes 2, 3, and 4 (intermediate), and (C) 

 Code 5 (most "whitebelly-like") ventral fields, by area. 



Contouring We used the ZSMTH, ZGRID, and ZCSEG 

 subroutines of the PLOT88 graphics software package 

 (Young and Van Woert 1987) to generate contours of 

 ventral coloration scores for unweighted 5-degree 

 blocks. The center of a block was used as the position 

 for the mean ventral coloration score of specimens col- 

 lected within the block. We used ZGRID with the "cay" 

 parameter set at 5 and "nrng" set at 4 to generate a 

 data grid for contouring. ZSMTH with "nsm" set at 

 1 was used to smooth the grid. Contour lines were 

 generated using ZCSEG with "ndiv" set at 4. 



150° 140" 130° 120" 110° 100° 90° 80° 70° 



Figure 10 



Contours of ventral-field codes for spinner dolphins > 120 cm. 

 Based on 5-degree block averages (see text). 



130" 120° 110° 100' 90* 80* 70' 



150" 140* 130* 120* 110* 100* 90° 80* 70* 



Figure 1 1 



Percentage of spinner dolphins with observed cape, by area. 



Results 



Ventral field 



The pattern of disjunct axillary and genital white areas 

 (Code 1) occurred at high frequencies (3*75%) in a 

 relatively small part of the study area, in 12 5-degree 

 blocks north of 10°N and east of 120°W (Fig. 9A). It 

 was totally absent south of 5°S and absent from most 

 of the peripheral blocks between 15° N and 5°S. It 

 occurred at intermediate frequencies near Central 

 America and northern South America, between 10°N 

 and 5°S. The steepest gradient would appear to have 

 been at about 10° N, extending from the coast out to 

 possibly beyond 125 C W. This pattern was mirrored in 

 the relative distribution of the Code-5 ventral field 

 (most "whitebelly-like"), which was absent or nearly 

 absent from most of the northeastern blocks where the 

 Code 1 pattern predominated and occurred at frequen- 



