COMPARISON OP YELLOWFIN TtfNA OF HAWAIIAN WATERS AND THE AMERICAN WEST COAST 371 



It seems, then, that where the groups within a 

 region differ in their regression coefficients, as is 

 true in the present instance, we have no method of 

 measuring with any precision the differences 

 among these gi-oups as a basis of judging whether 

 a further sample from another region could 

 reasonably be expected to belong to the same 

 population as that from which the groups in ques- 

 tion were di-awn. Of course, in the event the 

 regression coefficient itself is not size-connected, 

 it may be used to characterize the group, and one 

 might compare the variation among group regres- 

 sion coefficients with the observed value of the 

 regression coefficient from the further sample 

 fi'om another region (e. g. table 7). 



Pending development of a method of precise 

 analysis, comparison of differences among regres- 

 sion lines within regions with differences between 

 regions does not appear to be very fruitful, except 

 in those cases where the difference between regions 

 is so very much greater than differences among 

 samples within a region that it is quite apparent 

 from a simple graph of the data and no precise 

 method of analysis is required. 



As a practical procedure it appears best, perhaps, 

 to select fish from each region from many different 

 schools, and of sizes that wiU cover the entire range 

 available, and then, in comparing data between 

 regions by covariance analyses, to compare sam- 

 ples of similar size range. In this manner any 

 variation between groups within the region will 

 tend to be assimilated into the variance of the 

 total sample for the whole region, and the total 

 sample will be nearly representative of the popula- 

 tion of the region. 



Other dimensions 



Comparison of the regression of diameter of iris 

 on head length of Hawaiian specimens with that of 

 Costa Rican specimens indicates that the relation 

 is different in the two regions. The relations and 

 the means of the two variates for each 10 centi- 

 meters of total length are plotted in figure 11. 



Comparison of Hawaiian and Costa Rican data 

 respecting regressions of length of maxillary on 

 head length, body depth on total length, and 

 weight on total length indicated that in each case 

 the two samples might have been drawn at ran- 

 dom from a single population so far as these 

 characters are concerned. 



Counts of gill rakers 



Counts of total gill rakers of 188 Hawaiian tund 

 (table 1) have a mean value of 29.66 with a stand- 

 ard error of .0870. Schaefer's (1948) Costa Rican 

 data on 45 specimens have a mean value of 30.60 

 with a standard error of .186, while Godsil and 

 Bj'er's (1944) counts of 60 American-west-coast 

 specimens have a mean of 30.35 with a standard 

 error of .146. Comparison of the Costa Rican 

 and Godsil and Byer's data yields a t value of 1.06, 

 so that the null hypothesis is reasonable and we 

 may pool these data to estimate the mean gill- 

 rakcr count of yello^\^fin from the American west 

 coast as 30.46 with a standard error of .116. The 

 difference of .80 between this value and the Hawai- 

 ian mean is associated with a t value of 5.52. 



We have verified from our Hawaiian data that 

 there is no correlation between size of fish and gill- 

 raker count. This character seems to offer good 

 possibihties for racial analysis of tunas for that rea- 

 son, since it wiU avoid the difficulties in comparisons 

 which plagued us in regression analyses. 



DISCUSSION 



Hawaiian yellowfin tuna differ from those of the 

 American west coast in having, on the average, 

 longer pectoral fins at the same fish size, and this 

 difference is greater for the larger fish. The same 

 is true of the second dorsal and anal fins, but in 

 these cases the fins of the Hawaiian fish also grow 

 at an accelerated rate compared to west-coast fish, 

 so that the difference in fin lengths among the 

 largest fish sizes is very striking. The first dorsal 

 spine appears to be consistently shorter among 

 Hawaiian fish, while the longest dorsal finlet is 

 longer. 



Among Hawaiian fish, the distance from tip of 

 snout to the posterior edge of the opercle and to 

 the various fin insertions increases, relative to 

 total length, more slowly than among west-coast 

 fish so that all these dimensions are shorter, on the 

 average, for the large fish from Hawaii than for 

 west-coast fish of comparable size. From this it 

 is evident that the posterior pai-t of the trunk 

 grows faster among Hawaiian fish so that at large 

 sizes, say above 700 or 800 mux., the posterior part 

 of the body is more elongate than among west- 

 coast fish of similar sizes. 



On the basis of the magnitude and consistency 

 of these differences between the biometric charac- 



