FISHERY BULLETIN: VOL. 70, NO. 3 



spent). Only one school of small skipjack was 

 fished by pole-and-line, at lat 4°S, and the fish 

 were from 36 to 51 cm (mean 40 cm). How- 

 ever, enroute to and from Hawaii (lat 10°N-5°S, 

 long 125°-145°W) troll catches of skipjack were 

 mainly of small fish, <45 cm. The data from 

 this cruise add little to the proposed migration 

 models except to indicate the wide geographic 

 range of recruit size skipjack west of long 125 °W 

 in October-November 1969. In addition, east of 

 long 125°W fish were in the medium to large cat- 

 egory and in schools large enough to be fished 

 successfully by a commercial method — live bait 

 pole-and-line. None of these fish had recently 

 spawned, 



Williams (1971) described plans for a series 

 of eight cruises, initiated by the NMFS, La Jolla, 

 and the Scripps Tuna Oceanography Research 

 (STOR) Program, to investigate the distribution 

 of skipjack in relation to environmental condi- 

 tions in two offshore areas of the eastern Pacific. 

 The two areas, (A) lat 15°N-5°S, long 115°- 

 125°W, and (B) lat 5°N-15°S, long 95°-115°W, 

 were considered the most important for testing 

 migration models for skipjack, including the 

 three now proposed for recruits. 



The first cruise (two vessels) was to Area A 

 in October-December 1970, with trolling as the 

 principal fishing method. Recruit size fish 

 (^40 cm) were found in the NEC some distance 

 to the north of the NECC, as well as immedi- 

 ately to the north and south of the NECC. Large 

 fish were widely distributed, but with fewest 

 found in the NECC and most in the section of 

 the SEC north of the equator. About 27% of 

 the fish ^45 cm, the gonads of which were ex- 

 amined, were found to be in a spent or spent-re- 

 covering condition; most were found in or close 

 to the NECC, and none south of the equator. A 

 first sorting of midwater trawl samples showed 

 no skipjack juveniles; data on occurrence of 

 larvae are not yet available. 



The second cruise to the same area, in March- 

 April 1971, caught few small fish and none 

 <40 cm. More large fish were caught north of 

 the equator than on the previous cruise. The 

 presence of a surface NECC, even though weak 

 and narrow (180-120 miles wide), at this time 

 of year and at this meridian was anomalous. 



About 60% of the fish examined had gonads in 

 a recovering state and were from all current 

 systems north of the equator. 



The results of these two cruises confirm that 

 some skipjack spawn in the equatorial zone not 

 too distant from long 120°W. Those fish taken 

 in March-April 1971 appeared to have gonads 

 in a more advanced state of recovery than most 

 taken in October-December 1970 (subjective 

 analysis). Presence of these spent and spent- 

 recovering fish could indicate support for the 

 gyral migration models, where it is proposed that 

 after spawning west of long 130°W adults move 

 eastwards paralleling the movement of the young 

 stages. However, even with the active and pas- 

 sive migration models there could be small-scale 

 diffusion movements of adults out of the central 

 Pacific (including east of long 130°W) subse- 

 quent to spawning. The appearance of spent and 

 spent-recovering gonads in October-December 

 skipjack suggests they were of northern sum- 

 mer spawning origin, while the recovering go- 

 nads in March-April fish rather indicate south- 

 ern summer spawners; or alternatively that 

 spawning in skipjack is truly a year-round func- 

 tion in the equatorial zone. The apparent ab- 

 sence of juveniles in the trawl hauls may be due 

 to ineffective sampling gear. The presence of 

 very small fish (<40 cm) in areas of high for- 

 age concentrations at the NECC boundaries, as 

 well as in the NEC somewhat further north, 

 would tend to support the active migration mod- 

 els. They could be either some of the last re- 

 cruits destined for the southern fishery or early 

 ones for the northern fishery; their presence in 

 the NEC as far north as lat 13°N, and size (30- 

 40 cm) suggests the latter. The significance of 

 the shift in the center of apparent abundance 

 of large fish from lat 1°-5°N to 9°-ll°N between 

 October-December and March-April is not yet 

 apparent. 



A further six cruises, starting with one to the 

 southern area (B) in August-October 1971, are 

 planned. Data from this series of cruises will 

 undoubtedly increase our ability to describe, par- 

 ticularly for offshore areas, the distribution, ap- 

 parent abundance, life history, and environment 

 of the skipjack. Although input of these data 

 will be valuable in preparing models, such as 



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