MATURITY AND FECUNDITY OF BIGEYE TUNA IN THE PACIFIC 
By 
Heeny S. H. Yuen 
Fishery Research Biologist 
Pacific Oceanic Fishery Investigations 
U. S. Fish and Wildlife Service 
The bigeye tuna, Parathunnus sibi (Temminck and Schlegel), is one of several commer- 
cially important tunas of the central and western Pacific, In the 7-year period of 1946 through 
1952 the annual catch of the bigeye in the longline fishery of Hawaii increased from 63 tons to 
over 1,000 tons (Otsu 1954), The Pacific Oceanic Fishery Investigations (POFI), investigating 
the tuna resources of the Pacific, is interested in the commercial potentialities of this species, 
the first in importance in the commercial longline catches of the Hawaiian area (Otsu 1954) and 
second to the yellowfin in the western equatorial Pacific (Van Campen 1952), 
In order to understand this increase in the catch and to evaluate the commercial potenti- 
alities of the bigeye, there is need for more information on its biology and the factors contribu- 
ting to the temporal and geographic variations in its distribution, The aspects of spawning 
covered by this study should supply part of the required information. Knowledge of fecundity 
and age at maturity may help in estimates of abundance. Information on the time and place of 
spawning not only may explain some of the distributional variations but will facilitate the collec- 
tion of the embryos and larvae which are necessary for early life history studies. 
The basic method of study was the microscopic examination and measurement of eggs 
taken from the ovaries, as described by Clark (1934). 
Papers on bigeye spawning by Shimada (1951) and Kikawa (1953) deal primarily with the 
time of spawning in the western equatorial Pacific. They found fish in advanced stages of matu- 
rity throughout the periods covered by their studies, June to September 1950 and June to August 
1951. Keats Bank in the Marshall Islands was suspected by Kikawa to be an area of spawning 
concentration. Two reports on the occurrence of bigeye young may have some bearing on the 
time and place of spawning. In one report, Kishinouye (1919) mentioned two postlarval forms 
which he believed to be bigeye in the stomach of a skipjack, Katsuwonus pelamis (Linnaeus), 
caught at Nakasone (28°10'N. ; 129°15'E. ) during May. Inthe other, Marukawa (1941) reported 
finding juveniles in the stomachs of yellowfin tuna, Neothunnus macropterus (Temminck and 
Schlegel), caught in the Tokobei area (Tobi Island, 3°N,, 131931'E.), He did not give the date 
of capture. 
The collection of the ovaries on which this study is based was initiated by Mr. Fred June. 
Material from the western equatorial Pacific was collected by Messrs. K. Ego, T. Otsu, and 
W. Van Campen, who with other members of the POFI scientific staff also participated in col- 
lecting in the Hawaiian and central equatorial Pacific areas. Dr. A. L. Tester of the University 
of Hawaii and Mr. O. E. Sette, Director of POFI, made valuable suggestions concerning analy- 
tical procedures, The assistance and cooperation of these supervisors and colleagues are 
gratefully acknowledged, 
