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



415 



inspection, not that it was not actually absent. Cape 

 "presence" is a relative measure of the density of the 

 dorsal overlay, with some precision lost due to post- 

 mortem darkening. Again, under the assumption that 

 time before examination of the carcasses and diligence 

 of the observers did not vary with area, there should 

 be no systematic bias. 



The dorsal fin was coded to one of three states (Fig. 

 2): canted— closest to a right triangle with hypotenuse 

 posterior (Code 1; most "eastern-like"), erect— isos- 

 celes triangle (Code 2), or falcate— right triangle with 

 hypotenuse anterior (Code 3; most "pan tropical -like"). 

 Sources of error in this code include partial tracings 

 of fins (part of the base of the fin not included) and 

 injuries distorting the fin. The first was difficult to 

 cope with and could not be resolved completely. Some 

 tracings were discarded because of sharply anomalous 

 shape obviously due to the fin being incomplete, but 

 some small portion of the variation recorded is un- 



doubtedly due to undetected errors of this sort. When 

 a distal portion of the fin was missing due to injury, 

 this was indicated in the observer's sketch, and the 

 tracing was not used. The tracing was also not used 

 if a very large notch or gap was indicated. Small 

 notches and holes do not affect the overall shape of 

 the fin. 



The total of the code scores for the three characters 

 ranged from 3 (typical of the adult male eastern spinner) 

 to 10 (typical of the adult male pantropical spinner). 



The sample 



The sample for color pattern and fin shape included 

 8350 specimens from 971 net sets on "eastern"-type 

 schools, 1200 sets on "whitebelly"-type schools, 27 sets 

 on "mixed eastern and whitebelly" schools, 2 sets on 

 "Costa Rican"-type schools, and 54 sets on spinner 

 dolphins of unidentified stock (Figs. 3 and 4). Not all 



EASTERN 



WHITEBELLY 



EASTERN 



WHITEBELLY 



1977 



W "O" ucr 140* >3o' no" no" too - oo* or ><f 



1979 



ir no- too- «o* io" -o* 



1981 



w irr lso* mo" 130' no" no" 



Figure 4 



Distribution, by year, of purse-seine sets on "eastern" and "whitebelly" schools of spinner dolphins for samples included in analyses. 



