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-o CHARLES H GILBERT CRUISE 20 (COTTON GEAR) 



-X JOHN R MANNING 

 ■ 1 JOHN R MANNING 



CRUISE 24 ( COTTON GEAR ) 

 CRUISE 24 (STEEL GEAR) 



30 

 MARCH 



31 



4 5 6 



APRIL 1955 



Figure 1, --Comparison of yellowfin catch rateB on »teel and cotton gear and compariaon of catch 

 rates between two vessels fishing simultaneously in the same area (data in Appendix tables 17 

 and 18). 



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SMALL MEDIUM LARGE 



(74-I03CM) (I04-I33CM) (134-I63CM) 



fished simultaneously within 20 miles of one 

 another from April 3 through April 8. Figure 1 

 shows that the catch rates of both vessels agree 

 very closely. This same conclusion was drawn 

 from the catches of commercial vessels fishing 

 together in this area during 1954 (Iversen and 

 Yoshida 1956). Therefore, we do not believe 

 that variation among vessels was a distorting 

 factor in our examination of differences among 

 seasons, areas, etc. 



It has been previously shown that close 

 to isleinds (within 80 miles of land) yellowfin 

 catch rates on longline gear were higher than 

 at distances greater than 80 miles (Shomura 

 and Murphy 1955). Since there appears to be 

 a population of snnall yellowfin intinnately asso- 

 ciated with islands, in this study the line of 

 demarcation between "oceanic stations" and 

 "insular stations" has been placed at 10 miles 

 from land. 



DEPTH REACHED BY LONGLINE GEAR 



Figure 2. --Catch rates for three size classes 

 of yellowfin captured on cotton and steel long- 

 line gear on John R. Manning cruise 24, 



It is of considerable importajice to have an 

 evaluation of the variation in catch rates between 

 vessels. The Charles H. Gilbert during cruise 

 20 and the John R. Manning during cruise 24 



Knowledge of the depth at which longline 

 gear is fishing is important since there appears 

 to be a differential catch rate by hook depth, 

 with the better catches usually made on the 

 deeper hooks. This variation was observed by 

 Nakannura (1949) and was reported previously 

 in the various POFI longline reports. Prior to 

 1955 depth measurements of the nnainline were 



