SIZES OF YELLOWFIN AND BIGEYE 



Ihe sizes of the yellowfin tuna taken on the five section 

 lines increase from west to east (table 6) with fish averaging abc 

 110 pounds at 180° and 1U0 pounds at 120° W, longitude, l/lfeat of 180° 

 the trend to smaller tuna continues in an irregular manner to 135° E„ 

 longitude, where Japanese commercial longline catches averaged 

 62 pounds (Murphy and OtsuT)- A parallel trend is evident in the 

 bigeye tuna east of 180° (table 7)* and similarly west of 180° long- 

 line catches of this species were roughly J4O pounds lighter in weigl I 

 (Murphy and Otsu**' ) than between 180° and 120 .. _ongitude 



SEX RAH OS 



oh the exception of albacore the various species of tuna 

 in the catches (table 8) have a preponderance of males, although the 

 yellowfin tuna disproportion is the only one that is statistically 

 significant. The excess of males in longline catches of bigeye and 

 yellowfin has been previously noted in catches from H4O E longitude 

 to 150° Wo longitude (Murphy and Otsu= , Murphy and Shomura 1953), 

 In albacore the excess of females is not statistically signiiicanto 



JAPANESE FISHING 



Japanese longline fishermen began operating in the central 

 Pacific in May of 1952 A summary of the most pertinent data from 

 these operations in May and June of 1952 is given in table 9« This 

 fishing along 170° Iff. to 180° shows very clearly that there was a 

 concentration of yellowfin from the Equator north to about 5° N„ 

 latitude, and that yellowfin were relatively scarce north of this 

 zone during both May and June of 1952, It also furnishes a good 

 indication that bigeye tuna were considerably more abundant north 

 of 5° N„ latitude than south of that parallel* Because of the 

 relative scarcity of bigeye and because of the necessarily limited 

 extent of our fishing, it has not been possible to make any such 

 definitive statement from our data s although there have been similar 

 indications in nearly every fishing section, Ihe catches of the other 

 species included in table 9 do not show such pronounced differences 

 in abundance with latitude „ 



The general h of abundance (catch per hundred hooks) 



of both yellowfin and bigeye tuna are in close agreement with results 

 obtained by the Manning ' 3 fishing (compare tables h and 9), even though 

 the Japanese fishing took place 3 months later in the year This is 

 an indication that our catch rates made with 2l|0-hook sets are com- 



i th catch rates from the 1,500- to 2,000-hook sets used 

 by commercial fishermen. In addition the sizes of the tunas were very 

 similar (compare tables 6 and 7 with table 10), for the exploratory 

 fishing and the full-scale commercial operations. 



V Murphy, Garth I., and T„ 0tsu„ MS Analysis of the catches of 



nine Japanese tuna longline expeditions to the western Pacific Ocean, 



111 



