Perrin et al.: Geographic variation in morphology of Stenella longirostris 



413 



Character 

 dolphins. 



The data on color pattern and dorsal fin 

 were collected by biologists during the 

 period 1974-88 aboard commercial tuna 

 seiners (see Acknowledgments). The 

 length data were collected in 1968-89. The 

 biologists completed a field "life-history" 

 form for each dead dolphin examined, 

 recording basic information such as sex 

 and length and (starting in 1974) sketch- 

 ing in the ventral field, cape (if prominent- 

 ly visible; see below), and dorsal fin on a 

 preprinted generalized dolphin outline. 

 When feasible, the observer also traced the 

 dorsal fin on the back of the data form. 

 Body length was measured to the nearest 

 cm with calipers mounted on a 2-m wooden 

 ruler. For male specimens, a testis with 

 epididymis attached was preserved and 

 weighed ashore. For females, the number 

 of corpora in the ovaries was determined 

 in the laboratory (methods described in 

 Perrin et al. 1976). 



The quality of the sketches varied great- 

 ly. Although a few color pattern sketches 

 were discarded as totally unusable, the 

 basic features of the color pattern could be 

 discerned in relatively inexpert sketches. However, the 

 fin sketches proved to be unreliable. We found that for 

 the cases where the observer both sketched and traced 

 the dorsal fin, the correspondence between fin shape 

 in the sketch and tracing was often poor. Therefore we 

 used only the fin tracings, which reduced the sample 

 size for dorsal fin shape. We also examined photo- 

 graphs of the specimens if they were available. 



The analyzed data consisted of body length in cm and 

 coded values for ventral field, cape, and dorsal fin 

 shape. These were accompanied by date and location 

 of capture and reproductive data (weight of testis + 

 epididymis for males; number of ovarian corpora for 

 females). 



The ventral field received a code from 1 to 5 (Fig. 

 2). Code 1 is the state typical of the eastern subspecies; 

 Code 5 is that typical of the pantropical subspecies (Fig. 

 1). Codes 2-4 are intermediate. In Code 1, the animal 

 is gray laterally and ventrally, with white patches in 

 genital and axillary regions. In Code 2, the separate 

 genital and axillary white areas of Code 1 are joined 

 by a speckled zone. In Code 3, the two areas are con- 

 fluent, forming a white ventrum. In Code 4, the ven- 

 tral field extends dorsally above the umbilical-genital 

 region, yielding a stepped pattern in lateral view. In 

 Code 5, the anterior portion of the ventral field extends 

 dorsally to behind the eye, eliminating the step of Code 

 4. This variation is continuous, of course; a code was 

 assigned for the state closest to that evident in the 



VENTRAL 

 FIELD 



CAPE 



Code 1 



Code 2 



Code 3 



Code 4 



Code 5 



Code 1 



Code 2 



FIN 



Code 



Code 2 



Code 3 



Figure 2 



states for coding of ventral field, cape, and dorsal fin in spinner 



sketch. The sketches themselves already incorporated 

 some artificial stratification. For example, in some 

 animals the darker region yielding the step of Code 4 

 is only faintly evident. Some observers indicated the 

 presence of this faint feature, leading us to code the 

 animal as Code 4; others undoubtedly overlooked such 

 faint markings or failed to record them, leading us to 

 code the animals as Code 5. While such errors could 

 be expected to blunt the resolving power of the anal- 

 yses, there is no reason to suspect that they inject a 

 systematic spatial bias that would affect the accuracy 

 of the conclusions; the data were collected by a large 

 number of observers working over large areas. 



The cape (Fig. 2) was coded as "not noted in the 

 sketch" (Code 1) or "noted in the sketch" (Code 2). In 

 a living or freshly dead spinner dolphin, the cape can 

 be discerned on close and careful inspection, if only 

 very faintly, in all cases. In the eastern spinner, the 

 dorsal overlay (terminology of Perrin 1972) is very 

 dense, almost obliterating the underlying cape in even 

 very fresh specimens. When a carcass of an eastern 

 spinner has lain on the deck of a tuna boat for more 

 than a few minutes, the dorsal overlay darkens to the 

 point of completely obscuring the cape. In the live pan- 

 tropical spinner, the dorsal overlay is less dense and 

 the cape is sharply defined and obvious. It is detectable 

 even in specimens dead for several hours, albeit more 

 faintly. Thus the absence of the cape in a sketch means 

 that the observer did not note it upon fairly cursory 



