Trolling 



Longlining 



By means of surface trolling 2, 397 fish 

 were captured from January 1955 to February 

 1956. Of this number 980 (40.9 percent) were 

 yellowfin tuna and 43 (1.8 percent) were skip- 

 jack. Most of the remainder were wahoo (1,160 

 or 48.4 percent), and there were 214 (8.9 per- 

 cent) miscellaneous fish including rainbow runner, 

 jack, dolphin, barracuda, red snapper, little 

 tunny, needlefish, leather jacket, and sharks. 



The yellowfin caught by trolling ranged 

 from 50 cm. (5 lb.) to 151 cm. (148 lb.). The 

 size-frequency distribution of these catches 

 shows a single mode at the 70-79 cm. class 

 interval (fig. 7). Bates (1950) reported the 

 presence of a pronounced mode between 70 and 

 75 cm. (15 to 18 lb.) and another near 110 to 

 115 cm. (57 to 65 lb.) in the size distributions 

 of troll-caught yellowfin from the Line Islands 

 (April to June 1950). 



30 



20 



LU 

 O 



q: 



10 



20 



o 

 cr 



Q. 



10 



20 



LlI 



cr 



I I I 



I I I I 



■yypy^ 



INSULAR LONGLINE 



N = 524 



1 — r 



40 



I 

 49 



LENGTH CLASS(CM) 



Figure 7, --Length frequency distributions of 

 oceanic and insular yellowfin caught by long- 

 lining and trolling (data in Appendix, table 5). 



The longline catches yielded 2,215 fish; 

 of these, yellowfin totaled 1,002 (45.2 percent), 

 bigeye 31 (1.4 percent), skipjack 32 (1.4 per- 

 cent), and sharksl/ 1,051 (47,4 percent). The 

 remainder of the catch, 99 fish (4.5 percent), 

 was composed of small numbers of marlin, 

 broadbill, sailfish, dolphin, wahoo, barracuda, 

 lancet fish, sunfish, and puffer. No albacore 

 were caught during these cruises. The absence 

 of albacore is interesting because some albacore 

 were taken on nearly all previous cruises to this 

 area. 



The size of the oceanic yellowfin ranged 

 from 47 cm. (4 lb.) to 163 cm. (186 lb.). The 

 size distribution shows a single modal group 

 with a mode located at the 140-149 cm. class 

 interval (fig. 7). The frequencies in the class 

 intervals below the mode drop sharply with each 

 smaller class interval. 



The size of the insular yellowfin ranged 

 from 56 cm. (8 lb.) to 163 cm, (186 lb,). The 

 size distribution s ho w s a single mode, also 

 located at the 140-149 cm. class interval (fig. 7). 

 This distribution Indicates that there were more 

 small fish present in relation to the large than 

 in the case of the oceanic catches. This sub- 

 stantiates previous findings that there are more 

 small yellowfin close to islands than in the open 

 sea. 



The ratio of male to female yellowfin was 

 2.26:1,00, which is consistent with past observa- 

 tions, 



YELLOWFIN TUNA ABUNDANCE 



Trolling 



Beginning with cruise 20 of the Charles 

 H. Gilbert surface trolling was made a regular 

 part of the equatorial program to (1) supplement 

 our biological knowledge of the yellowfin, (2) 

 provide snnall yellowfin for tagging, and (3) pro- 

 vide another measure of abundance of yellowfin. 

 Prior to 1955 only occasional trolling surveys 

 had been made In the central equatorial Pacific 

 and then usually as a secondary operation to 

 longline fishing surveys. Since the early surveys 

 were not continuous throughout the year there 



— The various species of sharks were 

 lumped under this general heading both here and 

 in the Appendix, tables 17 to 25. These include 

 brown sharks, white-tipped sharks, great blue 

 sharks, thresher sharks and bonito sharks. 



