SIZE FREQUENCIES AND GROWTH OF CENTRAL AND 

 WESTERN PACIFIC BIGEYE TUNA 

 By 



Edwin 5. Iversen 



Fishery Research Biologist 



Pacific Oceanic Fishery Investigations 



U. S. Fish and Wildlife Service 



The purpose of this analysis of bigeye tuna, Parathunnus sibi 

 (Temminck and Schlegel) = P. mebachi (Kishinouye)i- , measurements 

 is to learn about growth and migration of this species from the size 

 composition of commercial longline catches. Consideration of size 

 frequencies fronn the Hawaiian and the Japanese North Pacific fisheries 

 yields evidence of a relationship which suggests that there is but a 

 single stock of bigeye being exploited by both fisheries. These data 

 also furnish evidence of rapid growth of bigeye tuna. Other facets of 

 the biology of the species, such as size differences associated with 

 sex, are revealed by Japanese catches in the equatorial Pacific and 

 Hawaiian catches. Measurements obtained on Japanese mothership 

 expeditions in the western equatorial Pacific, which will be discussed, 

 supply information on size differences associated with sex and evidence 

 pointing to a migration of this species. (The size frequencies on which 

 this study is based are presented in tabular form in the appendix.) 



The bigeye tuna is of considerable importance in the Hawaiian 

 longline (flagline) fishery, where catches are sold on the Honolulu 

 fresh fish market. The operation of the Hawaiian fishery has been 

 described and catch statistics analyzed by June (1950) and Otsu (1954). 

 In 1952, a year of high abundance, the value of the landings to the fisher- 

 men is given by Otsu as $684, 726. The same author also describes the 

 seasonal trend in apparent abundance, pointing out that the lighter catches 

 occur fronn June to September and the heavier catches from October to 

 May. The catch of this species increased sharply from 126,000 pounds 



— Parathunnus sibi (Temminck and Schlegel) is regarded as a 

 synonym of P. mebachi (Kishinouye) by numerous authors, annong them 

 Brock (1949) and Nakamura (1949). For the purpose of this paper they 

 will be considered a single species. 



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