FISHERY BULLETIN; VOL. 69, NO. 4 



adults. Several investigators have made obser- 

 vations on the spawning of albacore in the South 

 Pacific. On the basis of an examination of ova- 

 ries, Otsu and Hansen (1962) concluded that 

 peak albacore spawning occurs in the southern 

 hemisphere summer between the equator and lat 

 20° S. Their results also suggest a spawning 

 season of at least 5 months. Ueyanagi (1969), 

 who based his study on the distribution of larvae 

 and on the stage of maturity of ovaries of adults, 

 also suggested a southern summer spawning 

 season. The seasonal apparent abundance of 

 juvenile albacore does not disagree with the 

 above conclusions. The fact that juveniles were 

 found in all but 2 months of the year suggests 

 a long spawning season. The presence of juve- 

 nile albacore during and beyond the southern 

 hemisphere summer indicates some spawning 

 during the summer. My data also suggest an- 

 nual variations in adult spawning. The virtual 

 absence of juvenile albacore north of lat 10° S 

 in 1965 indicates little or no spawning in this 

 area during that year. 



COMPARISON WITH 

 SKIPJACK TUNA 



A comparison of the distribution and abund- 

 ance of juvenile albacore and skipjack tuna of- 

 fers some interesting contrasts. Although bill- 

 fish stomachs were sampled from long 135° W 

 to 177° E, juvenile albacore were found only 

 between long 153° and 179° W (Figure 5). The 

 juveniles were found throughout the latitudinal 

 range of sampling between lat 5° and 31° S. Ju- 

 venile skipjack tuna are distributed over a wider 

 area: between long 137° W and the 180th mer- 

 idian from lat 5° to 32° S ( Yoshida, 1971 ) . These 

 distributional patterns indicate that skipjack 

 tuna spawn over a wider area than the albacore 

 in the South Pacific. 



Comparing the abundance of the two species, 

 in 1964 juvenile skipjack tuna were more nu- 

 merous north of lat 10° S than from 10° to 20° S, 

 but in 1965 they were more numerous between 

 10° and 20° S than in the area to the north (Yo- 

 shida, 1971 ) . Juvenile albacore were consistently 

 more abundant between lat 10° and 20° S than to 



the north. Also, juvenile skipjack tuna appar- 

 ently were from 4.5 to 15 times more numerous 

 than juvenile albacore between the equator and 

 lat 20° S (Table 2). It is also interesting that 

 the apparent abundance of both species declined 

 from 1964 to 1965. 



Table 2. — Apparent abundance of juvenile albacore and 

 skipjack tuna in the South Pacific. The apparent abun- 

 dance is e.xpressed as number per 100 billfishes. Data for 

 juvenile skipjack tuna are from Yoshida (1971). 



North of lot 10' S 



Skipiack tuna 



Lot 10°-20° S 



Albacore Skipjack tuna 



1964 

 1965 



6.7 

 1.9 



46.3 

 28.8 



9.3 



5,8 



42.6 

 35.6 



FiciiRE 5. — The distribution of billfishes (shading) 

 sampled by the cooperating longline vessels and the dis- 

 tribution of juvenile albacore (dots) found in the billfish 

 stomachs. 



826 



