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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



the basis of the average length of the fin and 

 disregard the size of the fish. 



We find good agreement between the samples 

 of the same species, but marlina has markedly 

 shorter fins on the average than either audax or 

 ampla (fig. 15). Of the 19 measurements available . 

 for marlina, the average is approximately 26 cm. 

 and only 1 measurement is more than 30 cm. 

 This is in contrast with the other two species in 

 which the pelvic fins average about 33 cm. and 

 in which we find only 19 out of the 95 measure- 

 ments less than 30 cm. In most of the samples, 

 the range extends farther from the mean on the 

 lower side than on the upper and we suspect that 

 some of the smaller measurements may be due to 

 broken fins. If a careful watch is kept for broken 

 fins, this character may then be useful to separate 

 marlina from the other two species when other 

 characters are not available. Any marlins with 

 pelvic fins longer than 30 cm. are probably not 

 marlina. 



Length of pectoral fin 



Length of pectoral fin also was discussed in 

 the section on allometric growth and it was 

 pointed out that while small specimens appeared 

 to have slightly smaller pectoral fins in relation 

 to fork length, specimens of more than 200 cm. 

 fork length had pectoral fins which grew almost 

 isometrically. 



When pectoral fins are compared (fig. 16), it is 

 apparent that they show almost as much variation 

 within species as between species and that the 

 character is useless for distinguishing one species 

 from the other. The means vary from only 18.2 

 percent in ampla from Hawaii to 19.4 in audax 

 from New Zealand and Australia. 

 Height of first dorsal fin 



Heiglit of the first dorsal fin appears to be one of 

 the best means of distinguishing the three species 

 of marlins. Nichols and LaMonte (1941) com- 

 pared tlie anterior lobe witli head length, Jordan 

 and Evermann (1926) usually compared it with the 

 length of the pectoral fin, and Nakamura (1949) 

 with the greatest depth of the body. When we 

 plotted height of the first dorsal in relation to fork 

 length, we found a negligible amount of allo- 

 metric growth and, hence, we can use it as a ratio. 

 The comparison of all samples (fig. 17) shows that 

 marlina has the lowest fin, ampla intermediate, and 

 audax the highest. The averages are approxi- 

 mately 12, 13.5, and 17 percent, respectively; 

 however, the separation between species is not 

 complete, as there is considerable overlap between 

 audax and ampla and between ampla and marlina. 

 The samples show close agreement within species 

 except for marlina, in which there is a suggestion 

 of a clinal difference. The specimens from New 

 Zealand and Australia have the highest first 



20 



25 30 35 



PELVIC LENGTH (CM.) 



40 



45 



FiouRB 15. — Mean, standard deviation, and range of the length of the pelvic fin. 



