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Fishery Bulletin 107(4) 
and preserved samples should be compared in order 
to more fully evaluate the gravimetric and other (e.g., 
volumetric) methods. 
Individual estimates of batch fecundity ranged from 
2.11 to 13.50 million eggs (6.94 ±0.54; size range 
174-242 cm EFL). Batch fecundity of blue marlin is 
estimated to be larger than that of the black marlin 
( Makaira indica) in the waters off Taiwan (0.32-3.2 
million eggs; Liu, 2007), than that of sailfish in eastern 
Taiwan waters (0.2-2.48 million eggs; Chiang et al., 
2006a), and that of swordfish (Xiphias gladius) in the 
waters off eastern Australia (1.16-2.50 million eggs; 
Young et al., 2003). 
Spawning frequency 
We assumed that the hydrated oocytes of blue marlin 
were spawned in less than 24 hours (the hydrated oocyte 
method) and that the POFs were detectable for no more 
than 24 hours (the postovulatory follicle method), given 
observations for other pelagic fish (yellowfin tuna, Thun- 
nus albacares ; Schaefer, 1996). However, these assump- 
tions need to be verified in the future. The mean time 
between consecutive spawning events was 2.4 days based 
on the postovulatory follicle (POF) method (2.9 days 
based on the hydrated oocyte method). There was no sig- 
nificant difference in spawning fraction among months, 
which indicates that females were spawning asynchro- 
nously throughout the spawning season. Furthermore, 
there is no relationship between the monthly spawn- 
ing fraction and the two methods, which may indicate 
that the estimates of the spawning frequency 
are accurate. However, there are two caveats 
which need to be examined when applying the 
POF method. First, the degeneration of POFs 
varies among species and may be influenced 
by the preferred spawning temperature of a 
species (Chiang et al., 2006a). Second, the 
fish we collected from the fish market may 
have been caught a few days earlier. Because 
of that, it is possible that the POFs degener- 
ated before we obtained the fish and therefore 
the fraction of ovaries with POFs may have 
been underestimated. 
Conclusion and recommendations 
EFL (cm) Round weight (kg) 
Figure 9 
Batch fecundity as a function of (A) eye-to-fork length (EFL), and 
(B) round weight for blue marlin (Makaira nigricans) collected 
from the Tungkang fish market between September 2000 and 
December 2001. The solid lines denote the predicted fecundity, 
and the dashed lines the 95% confidence intervals for the mean 
relationship. 
This study provides reproductive parameters 
and their associated uncertainty as inputs 
for use in stock assessments of blue marlin 
in the western Pacific Ocean. The analyses 
were based on large samples from Taiwanese 
offshore longliners that cover broad areas in 
the western Pacific Ocean. Consequently, the 
estimates should be reliable. However, collect- 
ing by ships a greater number of specimens 
over the entire stock’s spatial distribution 
(especially for hydrated ovaries, and testes 
during the spawning season) is recommended 
so that estimates of male size-at-maturity 
and egg production will be more robust. The 
spatial variation in some of the reproductive 
