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Fishery Bulletin 107(4) 
■ Recovering 
□ Spawning-spawned 
□ Mature 
S Maturing 
H Resting 
0 Immature 
El Resting 
□ Spawned 
B Mature 
S Maturing 
0 Immature 
Month 
Figure 6 
Percentage of blue marlin ( Makaira nigricans ) collected from the Tungkang fish 
market between September 2000 and December 2001 in each gonad development 
stage by sex and month: (A) females, and (B) males (monthly data combined 
over years). The numbers indicate how many animals were examined. 
lack of samples in the size range when male blue marlin 
are maturing (i.e., within the transition from immature 
to mature) (Fig. 8). However, male blue marlin larger 
than 131 cm EFL (size-at-onset-of-maturity) were all 
mature. The size-at-maturity of blue marlin appears to 
vary across different regions of the Pacific Ocean. For 
example, the size-at-onset-of-maturity for male blue 
marlin was roughly 130-140 cm EFL in the western 
Pacific Ocean (Nakamura, 1985), and females 171-180 
cm EFL have GSI values larger than three (i.e., have 
reached sexual maturation) in the eastern Pacific Ocean 
(Uosaki and Bayliff, 1999). This variation among areas 
may be due to environmental or genetic effects or simply 
sampling error. In this study, EFL 50 for females was 
based on large sample sizes and a broad size range 
of fish collected throughout the spawning season, and 
maturity was determined by histology. Thus, the results 
of this study should provide an accurate representation 
of the size-at-maturity of blue marlin in the western 
Pacific Ocean. 
Spawning season 
Blue marlin have indeterminate fecundity, exhibit an 
asynchronous oocyte development pattern, and spawn 
multiple times during the spawning season (Hunter 
and Macewicz, 2003; Murua et al., 2003). The major 
spawning season seems to be from May to September 
based on MOD, the GSI values, and staging of ovaries. 
Shung (1975) indicated that blue marlin spawn between 
February and November (with high activity in June and 
September) in the South China Sea, and Hopper (1990) 
argued that blue marlin spawn primarily between May 
and September in Hawaiian waters. Kume and Joseph 
(1969) indicated that blue marlin spawn from December 
to January in the South Pacific Ocean. In the Atlantic 
