Table 6. --Regression coefficients for regressions of various dimensions 

 on total length for samples of yellowfin taken off Costa Rica 



Islands, Phoenix Island, Society Islands, Caro- 

 line Islands, Philippine Islands and Japan. 



The difficulties in analysis of morphomet- 

 ric data are emphasized by Royce. He also 

 stresses the fact that when yellowfin samples 

 from different areas are compared in all possible 

 ways by means of covariance analysis, highly 

 significant differences result from most compari 

 sons. This even applies to some comparisons 

 between samples from adjacent areas . He is 

 skeptical of conclusions based upon such analyses, 

 especially in view of the fact that racial studies 

 on other species which have shown highly signif- 

 icant statistical differences between stocks have 

 been contradicted by tagging studies. The ex- 

 istence of a statistically significant difference, 

 consequently, is evidence merely that populations 

 of fish are not homogeneous. They are not com- 

 pletely mixed although there may be considerable 

 mixing. 



Royce obtained some interesting results by 

 comparing tuna of the same length in different 

 areas. He used 100 cm. fork length. He found 

 a tendency for the samples collected along the 

 Equator to form clines or gradients. For cer- 

 tain characters- -head length, distance from 

 snout to insertion of the unpaired fins (first dor- 

 sal, second dorsal, anal), and body depth- -the 

 measurements were greatest in the Eastern 

 Pacific and least in the Caroline Islands area . 

 A cline in the other direction is indicated for the 

 size of fins --fish in the western Pacific having 

 the longest pectoral, second dorsal and anal fins . 

 The regularity of the clines is shown by plotting 

 individual characters, such as head length, 

 against longitude. 



An index of racial likeness was computed 

 by Royce for simultaneous comparison of a num- 

 ber of characters in the larger samples. He 

 obtained values ranging from 2.3 to 456.4. Al- 

 though there is no exact scale for interpreting 

 the results, small values show closer association, 

 larger values a greater divergence. The largest 

 value of 456.4 was obtained from the comparison 

 of samples from Costa Rica and Eastern Caroline 

 Islands, the smallest of 2.3 from a comparison of 

 samples from Eastern Caroline Islands with 

 central Caroline Islands . Samples from adjoining 

 localities along the Pacific Equator have small 

 coefficients. An exception is the comparison be- 

 tween the Marshalls and eastern Carolines, with 

 a coefficient of 74.2 . Most of the samples ob- 

 tained some distance from the Equator are not 

 related to other samples as closely as are adjacent 

 samples from the Equatorial area. The Philippine 

 samples, for example, are greatly divergent from 

 the adjoining Caroline Islands area and more 

 closely related to samples from the eastern Pacific . 



Royce concludes "our samples have been 

 taken from stocks, which, with the exception of 

 certain adjoining areas in the equatorial Pacific, 

 are at least semi -independent" (ibid. -161). 



The latest paper in the series comparing 

 morphometric measurements of yellowfin tuna of 

 different areas is by Schaefer (1955) . He com- 

 pares yellowfin from southeast Polynesia (Mar- 

 quesa, Society, and Tuamotu Islands) with those 

 he had previously reported on from Costa Rica 

 and Hawaii. The Polynesian specimens are similar 

 to yellowfin from Hawaii in having very long 

 second dorsal and anal fins; in fact, these fins are 

 even longer on Polynesian specimens than on those 



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