FISHERY BULLETIN: VOL. 73, NO. 2 



125° W 



i2crw 



lio** 



IS'N 



lont. 



5*N. 



0*. 



S-S 



JORDAN 

 CROUWCLL 



125* V» 



(TN 



KTH 



snt 



.0* 



.S'S 



Figure 7.— Relative abundance of skipjack in schools/hour, 

 cruises Jordan 57-Cromwell 51, November-December 1970. 



fish < 45 cm were largely segregated geograph- 

 ically from the medium and large ones. Figure 9 

 indicates a distinct separation in age as well. Small 

 skipjack were very scarce in March-April 1971. 



Figure 9 shows the percent length-frequency 

 distributions of skipjack by 2-cm classes. In 

 November- December 1970, the principal mode was 

 at 58 cm, with a minor mode at 36 cm and perhaps 

 another at 48 cm. The fish of modal size 36 cm could 

 be about 14 to 15 mo old, if one accepts the growth 

 rates for juveniles indicated by Yoshida (1971) and 

 Joseph and Calkins (1969: from tagging data, 

 averaged). This would suggest a spawning origin 



I5*N 



lO'N 



5'N 



5'S 



SCHOOLS/HR. 



<0.l 

 0I-02 

 O2-0.4 

 >0.4 



^ 



I5*N 



lO'N 



9*N 



5'S 



120'W 



II5*W 



Figure 8.— Relative abundance of skipjack in schools /hour, cruise 

 Jordan 60, March-April 1971. 



in the northern summer. Because no definite in- 

 formation is available on skipjack growth rates 

 beyond this size, the age represented by the 58-cm 

 mode is uncertain, but probably it is 2 to 3 yr. 

 Whether the possible mode at 48 cm represents 

 fish 1 yr or 6 mo between the other two modes is 

 not known. If there were 6-mo difference, it would 

 signify a spawning origin in the southern summer. 



In March- April 1971, there is a single wide mode 

 composed of fish >48 cm (peak 56 to 60 cm). The 

 fish had about the same size distribution in all 

 areas. 



Skipjack in the eastern Pacific coastal fishery 

 ranged from about 3 to 3.5 kg, with mean and 

 modal lengths 50 to 55 cm, in the years 1955-71 

 (Miyake 1968; Inter-American Tropical Tuna 



390 



