BLACKBURN and WILLIAMS: DISTRIBUTION AND ECOLOGY OF SKIPJACK TUNA 



Table 17.-Analysis of covariance: schools/hour (7) on catch /line-hour (X) for the 1969, 

 1970, and 1971 cruises, data of Tables 3, 4, 15, and 16. 



Table 18.-Relative abundance (catch/!ine-hour) of troll-caught skipjack and other tuna, on track to and from the study area. Cruise 



Gilbert 116, October-November 1969. YF and BE mean yellowfin and bigeye. 



Pole-and-Line Fishing 



Hida (1970) recorded 109 schools of fish sighted 

 during cruise Gilbert 116: 27 skipjack, 1 bigeye 

 tuna, 1 yellowfin tuna, 2 mixed tunas (skipjack- 

 bigeye-yellowfin), 13 of nontuna species, and 65 

 unidentified. On the outward track and in the 

 southern part of the study area (from lat. 4°27'S, 

 long. 133°22'W, to lat. 6°25'S, long. 117°47'W: 13 to 

 20 October 1969), at least 13 tuna schools were 

 sighted or discovered by jig strikes. They were 

 chummed, but did not respond to live bait. From 21 

 to 27 October in the study area (between lat. 

 4°09'S, long. 117°47'W and lat. 5°04'N, long. 

 118°50'W), at least 11 schools of tuna were 

 chummed with live bait and of these 6 were suc- 

 cessfully fished by pole-and-line (these schools 

 were sighted and pursued, not discovered by jig 

 strikes). Details are given in Table 19. All schools 

 fished successfully by pole-and-line were located in 

 the South Equatorial Current. These results are of 



special interest because they were obtained by a 

 commercial fishing method. Trolling is not a com- 

 mercial fishing method for skipjack in U.S. 

 fisheries. 



Size of Skipjack and Other Tuna 



Table 20 shows the percent of skipjack in three 

 broad size categories by fishing method and area. 

 Only one skipjack (45 cm) was taken on the inward 

 track to Honolulu. In the study area the percent- 

 ages in size groups are similar for the two fishing 

 methods. The percentage of fish < 45 cm, namely 

 8 to 11%, is much the same as that in the area in 

 November-December 1970. The smallest skipjack 

 measured 34 cm. The largest skipjack (mean 

 lengths > 75 cm) were taken in the extreme south 

 of the area. Elsewhere mean sizes of skipjack 

 ranged from 46 to 67 cm, with two exceptions: 34 

 cm (trolling) and 40 cm (pole-and-line). On the 

 outward track to the area, troll-caught skipjack 



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