Farley and Davis: Reproductive dynamics of Thunnus maccoyii 
231 
Table 2 
Spawning fraction and spawning interval of southern bluefin tuna, Thunnus maccoyii, by month for all females and females in 
prime spawning condition collected from the spawning ground between October 1992 and March 1995. POF = postovulatory 
follicles, n = no. of fish in sample. 
Females in prime spawning 
All females condition (<10% atresia) 
n with 
Spawning 
Spawning 
n with 
Spawning 
Spawning 
n 
POF’s 
fraction 
interval (days) 
n 
POF’s 
fraction 
interval (days) 
1992 
Oct 
3 
1 
0.3 
3.0 
1 
1 
1.0 
1.0 
Nov 
1 
1 
1.0 
1.0 
1 
1 
1.0 
1.0 
Dec 
1 
1 
1.0 
1.0 
1 
1 
1.0 
1.0 
1993 
Jan 
9 
8 
0.9 
1.1 
7 
7 
1.0 
1.0 
Feb 
3 
1 
0.3 
3.0 
2 
1 
0.5 
2.0 
Mar 
4 
4 
1.0 
1.0 
4 
4 
1.0 
1.0 
Apr 
2 
0 
0.0 
Aug 
3 
3 
1.0 
1.0 
1 
1 
1.0 
1.0 
Sep 
9 
4 
0.4 
2.3 
3 
3 
1.0 
1.0 
Oct 
11 
8 
0.7 
1.4 
9 
8 
0.9 
1.1 
Nov 
7 
4 
0.6 
1.8 
4 
4 
1.0 
1.0 
Dec 
26 
20 
0.9 
1.1 
19 
19 
1.0 
1.0 
1994 
Jan 
11 
6 
0.5 
1.8 
6 
6 
1.0 
1.0 
Feb 
53 
36 
0.7 
1.5 
34 
31 
0.9 
1.1 
Mar 
48 
31 
0.6 
1.5 
31 
28 
0.9 
1.1 
Apr 
16 
13 
0.8 
1.2 
11 
11 
1.0 
1.0 
May 
1 
0 
1 
0 
Aug 
1 
1 
1.0 
1.0 
Sep 
32 
12 
0.4 
2.7 
16 
11 
0.7 
1.5 
Oct 
43 
26 
0.6 
1.7 
26 
22 
0.8 
1.2 
Nov 
40 
22 
0.6 
1.8 
21 
19 
0.9 
1.1 
Dec 
40 
23 
0.6 
1.7 
26 
22 
0.8 
1.2 
1995 
Jan 
47 
30 
0.6 
1.6 
31 
28 
0.9 
1.1 
Feb 
32 
20 
0.6 
1.6 
19 
19 
1.0 
1.0 
Mar 
8 
3 
0.4 
2.7 
4 
3 
0.8 
1.3 
Unknown 
16 
11 
0.7 
1.5 
8 
8 
1.0 
1.0 
Total 
467 
289 
0.62 
1.62 
287 
259 
0.90 
1.11 
all months except July, although the main 
spawning season appeared to be from Sep- 
tember to April when CPUE was highest. Pre- 
viously, the spawning period was reported to 
be limited to the months of September to 
March (Mimura, 1958; Kikawa, 1964a). Our 
study included fish from areas north of that 
traditionally fished by Japanese vessels, 
which may explain the extended spawning 
season. An increase in the length of the 
spawning season towards equatorial waters 
has been suggested for many species includ- 
ing black skipjack, Euthynnus lineatus 
(Schaefer, 1987), yellowfin tuna, Thunnus 
albacares (McPherson, 1991), blue marlin, 
Makaira nigricans (Hopper, 1990), and other 
multiple spawning fish (Qasim, 1955). 
The actual duration of spawning in indi- 
vidual southern bluefin tuna could not be de- 
100 
80- 
cc 60- 
o. 
o 
t: 
o 
o. 
40 - 
20 - 
7 26 
32 
43 47 
_ 40 
i i i i i i — i i m i i i — i — i — i — i — i — i — i 
A S O N D J FMAMJ JASOND'j FM 
1993 
1994 
1995 
Figure 7 
The proportion of southern bluefin tuna, Thunnus maccoyii , spawn- 
ing by month. The vertical bars indicate 95% confidence limits of 
the mean for samples sizes >5. The numbers indicate sample sizes. 
