and in both 1964 and 1965 they were not as extensive 

 as in 1967. Here as in other regions interyear differ- 

 ences probably relate to changes in gross oceanogjaphic 

 conditions. 



In region B, south of latitude approximately 10°N, 

 the high-CPUE cells were most extensive and persistent 

 throughout the year. In most quarters, these cells strad- 

 dled the equator, but in some they were displaced 

 slightly to the south. The cells also expanded and 

 contracted, or were displaced to the east or west sea- 

 sonally, but without any obvious regularity. The number 

 and locations of these cells varied from quarter to 

 quarter and from year to year. Of particular interest 

 about the area is that it is also where skipjack tuna 

 larvae have been found in abundance (see later discus- 

 sion), and it may well be the main spawning grounds of 

 skipjack tuna of the central and eastern Pacific. 



North of lat. 10°N, the high-CPUE cells occurred in 

 the Hawaiian to Leeward Islands area and in the Wake 

 to Marcus Island area west of long. 180°. These high- 

 CPUE cells generally occurred farther to the north in 

 the fourth and first quarters than they did in the second 

 and third quarters. The cells in the Wake-Marcus area 

 were not consistent from year to year; the CPUEs were 

 high in the fourth quarter in 1964 and first quarter in 

 1965, nil in 1966, and high in the first and second 

 quarters of 1967. In the Hawaiian area, the high-CPUE 

 cells were often contiguous with the large high-CPUE 

 area straddling the equator. This occurred in the first 

 quarter 1964, second, third, and fourth quarters 1965, 

 and second and fourth quarters 1966. The contiguity of 

 high-CPUE cells in Hawaiian waters with the large 

 equatorial high-CPUE cell in the east-central Pacific 

 seems to be associated with the annual surface catches 

 of the Hawaiian pole-and-line fishery. In 1964, 1966, and 

 1967, when the high-CPUE cells in the two areas were 

 contiguous in fewer than two quarters, the Hawaiian pole- 

 and-line catches were below the 1952-70 long-term average 

 catch of 4,311 metric tons, in 1965, however, when the 

 high-CPUE cells were contiguous in three successive quar- 

 ters, the Hawaiian pole-and-line catch was 7,329 metric 

 tons, the highest in the history of the fishery and 70% above 

 the long-term average catch. 



In region C, south of the equator, the high-CPUE 

 cells were not extensive, but were persistent throughout 

 most of the year. During some quarters these cells were 

 contiguous with those of region B; in others they were 

 discrete and were found either further south or east. 

 North of the equator high-CPUE cells generally occurred 

 near the equator adjacent to and often as part of the 

 central Pacific (region B) high-CPUE area. They ap- 

 peared more consistently in the first and fourth quar- 

 ters. In waters closer to Mexico and California, the cells 

 of high CPUE occurred in aU 4 yr but they were not all 

 large or equally close to shore. Prominent high-CPUE 

 cells nearshore occurred only in the fourth quarter of 

 1965 and in the third and fourth quarters of 1967. In 

 both years, the skipjack tuna landings in the eastern 

 Pacific surface fishery were high; in fact the 1967 catch 

 was the highest ever recorded there. 



In region C north of the equator, particularly around 

 the southern half of Baja California in waters bounded 

 by lat. 20° and 30°N and long. 110° and 120°W, the 

 Japanese longliners also fish for swordfish, Xiphias 

 gladius. This fishing is done at night, and both the gear 



change and the time of fishing adversely affect the 

 capture of skipjack tuna. According to Kume and Joseph 

 (1969, Fig. 4), night fishing in the area accounted for 

 21% of the longline effort (in sets) in 1964-66, mostly 

 (about 75%) in the fourth quarter. If the night fishing 

 effort is deducted from the total longline effort, the 

 CPUE of skipjack tuna in this area will be higher. The 

 resulting changes in CPUE, however, will not materially 

 change the contours as shown in Figures 4-7. 



Salient Features in the Distribution of 

 Catches and Catches Per Unit Effort 



Several features stand out in the distributions of 

 catches and cells of high CPUE in the Pacific. The first 

 is the irregular north-south displacement of boundaries 

 of skipjack tuna catches (Fig. 8). The northern and 

 southern boundaries do not move in unison with respect 

 to seasons, nor uniformly across the ocean. In the 

 western Pacific (west of long. 180°), the maximum 

 northward displacement of the northern boundary occurs 

 in the third quarter and maximum southward displace- 

 ment in the second quarter. To the east of long. 180°, 

 however, the maximum northward displacement of the 

 northern boundary occurs in the fourth quarter and the 

 maximum southward displacement occurs in the third 

 and fourth quarters. Such differences also are evident in 

 the shifting of the southern boundary in the eastern, 

 central, and western Pacific. 



Irregular north to south movement is indicated also 

 in the high-CPUE cells. In the Hawaiian to Leeward 

 Islands area, the high-CPUE cells occur throughout the 

 year, with the maximum southward displacement oc- 

 curring in the second quarter. In Philippine and Japan- 

 ese waters, the northward displacement of high-CPUE 

 cells occurs in the second and third quarters and the 

 southward displacement in the fourth and first quarters. 



The second feature is the apparent disparity between 

 the high catch areas of the longline fishery and those of 

 the surface fisheries. The bulk of the skipjack tuna 

 production in the Pacific comes from the northwestern 

 (Japanese pole and Une) and the eastern (United States 

 purse seine) surface fisheries, yet the high-CPUE areas 

 in both places are not as extensive as one would expect. 

 This is likely due 1) to gear selectivity, longlines fishing 

 deeper and being more effective on large fish and 2) to 

 the relative absence of large fish near the surface in 

 these areas. The predominance of younger fish in the 

 two surface fisheries has been shown by Kawasaki 

 (1965) and Broadhead and Barrett (1964). In the Hawai- 

 ian Islands area, where large skipjack tuna are better 

 represented in the surface fishery (Rothschild 1965), the 

 disparity between the longline and surface fishery catch- 

 es is less evident. In fact, as previously mentioned, 

 there may be some association there between the long- 

 line and surface pole-and-line catches. 



The third feature is the extent and persistence of 

 high CPUE in the central equatorial area (region B, 

 south of lat. 10°N), where presently there is only a 

 small surface fishery in Tahiti (Brun and Klawe 1968). 

 The high-CPUE areas there not only persist throughout 

 the year, but are more extensive than aU other high- 

 CPUE areas combined during most quarters. The gen- 

 eral location of this high-CPUE area is of particular 



