FISHERY BULLETIN: VOL. 73, NO. 2 



Table 19.-Details of successful live-bait pole-and-line fishing of tuna schools in the study area, Cruise Gilbert 116, October 1969. SJ, 



YF, and BE mean skipjack, yellowfin, and bigeye. 



1 After Scott (1969). 



2 Poor biting school. 



3 School abandoned when sample complete. 



* Very large school still around ship at 1500 h. 



Table 20. -Skipjack by size categories as percent of total, and by 

 fishing method and area, Cruise Gilbert 116, October 1969. 



ranged from 29 to 78 cm, mean 41 cm. Although 

 very few were caught, the high percentage of fish 

 < 45 cm is of interest. 



In the study area all small fish ( < 45 cm) were 

 from areas of the South Equatorial Current. In the 

 area west of long. 125°W, small fish were found in 

 all three current systems (NEC, NECC and SEC), 

 approximately from lat. 15°15'N, long. 151°45'W 

 to lat. 0°25'S, long. 137°15'W. 



Skipjack percent length frequency distribution 

 by 2-cm classes is given in Figure 30 for the study 

 area in October 1969. There appear to be three 



>- 



o 



z 



LlI 



Z) 



o 



LU 



a: 



25 p 

 20- 

 15 - 

 10- 

 5 - 



n = 247 



til 



I I I 1 I I I I I I I I I "I "I "I"! Tl  I  |"i'|"I I I 

 26 30 34 38 42 46 50 54 58 62 66 70 74 78 82 



2cm FL CLASSES 



Figure 30.-Skipjack percent length frequency distribution 

 (study area only), cruise Gilbert 116, October 1969. Smoothed 

 curves are from 3-figure moving average. Stated length indicates 

 midpoint of class. 



modes at 46, 56, and 66 cm. Inclusion of data from 

 the outward track would increase the probability 

 of another mode at 36 to 38 cm. The November- 

 December 1970 length data for the study area 

 were similar and showed modes at 36, 48, and 58 

 cm; only the 66-cm mode was absent (Figure 9). 

 The similarity suggests that the modes of 1969 

 (October-November) and 1970 (November- 

 December) represent age-classes. 



On the outward track yellowfin were small, 

 mean lengths 37 and 32 cm, and on the return track 

 bigeye had a mean length of 57 cm (Table 18). In 

 the study area mean lengths of yellowfin ranged 

 from 39 to 47 cm and those of bigeye from 41 to 69 

 cm (Table 19). 



Sex and Maturity of Skipjack 

 and Other Tuna 



The sex ratio of skipjack in the study area was 

 males to females 1:0.89 (w = 249), and on the 

 outward track 1:1 (n = 20). 



Tuna gonads taken on cruise Gilbert 116 were 

 recorded as immature, maturing, mature, or spent 

 and can be roughly compared with those for the 

 other two cruises. The number of skipjack gonads 

 in each maturity stage by size of fish is given in 

 Tables 21 and 22 for the study area and outward 

 track. 



Apart from three females, all immature fish 

 (19% of total in the study area and 80% of total on 

 outward track) were <50 cm. The principal 

 difference between fish caught on this cruise and 

 the other two is the virtual absence of spent fish. 

 Most fish ( > 74%) were classed as maturing, and 



406 



