140° 160° 180° 160° 140° 
— ——— — ———— 
i AW, 
i} 41g 
| }.° MATURE as 
}20° * LATE MATURING 20° 
1] %, a | 
oe 5 
CAROLINE Be os . a8 = s) ° 
Os. we *. ts z& s } 
52 eo ye GILBERT RTs - oP 
| : PHOENIX ° 
} S 3 
SOLOMON MARQUESAS 
1S. e IS. 
| 
}20° Ge ——a ——— —— ———— +10) 
|._140° 160° 180° 160° 140° 
Figure 6, --Locations of capture of bigeye in late 
maturing and mature stages. 
40 T T Ba al 
— 
ZZ EARLY MATURING 
30+ A ae a5 | 
| ZA WZ LATE MATURING 
GZ WB ature 
o of CA 
= Wy, 
ira 
< 
> 
fo) 
w 
ro) 
« 
WwW 
o 
= 
> 
Zz 
lOF =| 
ZZ. aaa Kes Y Y) AA, 
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 
T IME (MONTHS) 
Figure 7, --Plot of numbers of bigeye at various 
stages of maturity against time. 
A - bigeye from the western Pacific; 
B - bigeye from the central Pacific. 
The numbers of fish in the different 
stages of maturity are shown for each month 
for each equatorial area (fig. 7). The 
separation into stages was done according 
to the relative ovary weights, All fish under 
20 kg. or with relative ovary weights of 
less than 4 were judged to be sexually 
immature and were omitted, 
Mature fish were found throughout 
the period of collection, April through 
October, in the western equatorial Pacific 
(fig. 7A). This lengthens the known period 
of occurrence of mature fish in this area, 
Shimada (1951) and Kikawa (1953) had 
previously found mature bigeye from June 
to September and June to August, the periods 
to which their collections were limited, 
The data from the central equatorial 
Pacific suggest two separate spawning 
periods, one in January and February and 
the other from July to October (fig. 7B). 
This cannot be accepted as a firm conclu- 
sion, however, because of the small number 
of samples per month and the lack of data 
in April, the month of apparently greatest 
spawning activity in the western equatorial 
area, 
Data from the Hawaiian area show a 
more definite but somewhat different 
picture, Relative ovary weight frequencies 
for each month (fig. 8) reveal an increase of 
relative ovary weights from winter to 
summer, The monthly mean modal dia- 
meters (table 11) calculated from the 
equation Y = 0.6935 X - 0.1367 (see page 13) 
show a definite seasonal increase when 
plotted against time (fig. 9). The mean 
diameter at the peak month of June, however, 
is far below that expected of a spawning 
population, It is interesting to note here 
that the commercial catch of bigeye in Hawaii is at its annual minimum during the summer 
(Otsu 1954). The cessation of mean modal diameter increase in June coupled with the low summer 
catches suggests that maturing bigeye in Hawaiian waters leave before they are mature, The 
possibility of their being present but not biting can be ruled out by the fact that they do bite on 
the same type of gear in equatorial waters, 
TYPE OF SPAWNING 
If one looks at the frequency distributions of egg diameters of the entire ovary (figs. 1 
and 2), several modes of maturing eggs are seen, 
These modes could represent either groups of 
eggs that will be spawned in one season or groups of eggs that will be spawned in succeeding 
seasons, depending upon the rate of growth of the egg. It was intended at first to find the growth 
tate of the maturing egg and thus find out whether the modes of the smaller maturing eggs could 
advance to the position of the mature eggs within the length of the spawning season, This plan had 
to be abandoned when it proved impossible to define the spawning season with the available data, 
17 
