Schaefer. Geographic variation in morphology and menstics of Thunnus albacares 



295 



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CANONICAL VARIABLE 



Figure 5 



Frequency distribution of individual canonical scores based on 12 adjusted morphometric characters 

 for yellowfin tuna from Mexico (open squares) and Ecuador (black squares). Centroid values for 

 Ecuador and Mexico are -1.31 and 1.12, respectively. 



of mixing of the groups of fish within this region. My 

 results agree with other studies on the morphometries 

 of yellowfin tuna from the Pacific Ocean: morpholog- 

 ical differences exist among fish in the eastern, cen- 

 tral, and western Pacific (Godsil 1948, Godsil and 

 Greenhood 1951, Schaefer 1955, Kurogane and Hiyama 

 1957, Royce 1964). 



One of the objectives of this study was to further 

 evaluate the previously reported morphometric differ- 

 ences between northern and southern groups in the 

 eastern Pacific (Schaefer 1989). The morphometric 

 analysis of yellowfin tuna from the eastern Pacific by 

 Schaefer (1989) was based upon samples from 55 loca- 

 tions and comprised a total of 2701 fish collected dur- 

 ing 1974-76. Only the first eight morphometric char- 

 acters shown in Figure 2 of this study were recorded 

 and included in the analyses of that investigation. The 

 correct classification rates from the discriminant anal- 

 ysis of the morphometric data from yellowfin tuna 



sampled from north of 15°N-20°N was 68.0%, and for 

 those sampled from the south was 73.7%; the overall 

 correct classification rate was 72.1%. In this study two 

 additional morphometric characters (second dorsal and 

 pectoral fin lengths) were selected first and second in 

 the stepwise discriminant analysis of morphometric 

 characters of fish from Mexico and Ecuador, indicating 

 their discriminatory power (Table 5). The correct 

 classification rate from the discriminant analysis for 

 these two groups was 84.6% (Table 5). The correct 

 classification rate from the discriminant analysis for 

 these two groups, using the eight morphometric 

 characters (Fig. 2) investigated by Schaefer (1989), was 

 only 68.6%. 



Total gill-raker counts of yellowfin tuna appear to be 

 important characters which permit separation of fish 

 from the eastern, central, and western Pacific. This 

 meristic character also has the potential for separation 

 of fish on a latitudinal scale as clearly indicated by the 



