265 
Abstract — Analyses of sex-specific 
yield per recruit and spawning stock 
biomass per recruit were conducted to 
evaluate the current status of the sail- 
fish ( Istiophorus platypterus) fishery 
in the waters off eastern Taiwan. 
Natural mortality rates estimated 
from Pauly’s empirical equation were 
0.26/yr for females and 0.27/yr for 
males. The current fishing mortal- 
ity rates were estimated as 0.24/yr 
and 0.43/yr for females and males, 
respectively, which are much lower 
than the estimated F 0 x (0.62/yr 
and 0.79/yr for females and males, 
respectively) and F SSB40 ( 0.46/yr for 
females) which are commonly used as 
target reference points in fisheries 
management. The effects of the fish- 
ing mortality, natural mortality, and 
age at first capture on the estimates 
of biological reference points were 
evaluated by using the Monte Carlo 
simulation. The results indicate that 
failure to consider the uncertainty in 
parameters such as natural mortality 
or age at first capture may lead to 
the improper estimation of biological 
reference points. This study indicates 
the possibility of current fishing mor- 
tality exceeding the target biological 
reference points may be negligible 
for sailfish in the waters off east- 
ern Taiwan. However, in view of the 
recent rapid increase in fishing effort, 
it is evident that the stock status and 
development of the fishery need to be 
closely monitored. 
Manuscript submitted 17 July 2008. 
Manuscript accepted 28 January 2009. 
Fish. Bull. 107:265-277. 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Analysis of sex-specific spawning biomass 
per recruit of the sailfish ( Istiophorus platypterus) 
in the waters off eastern Taiwan 
Wei-Chuan Chiang ' 
Chi-Lu Sun (contact author) 2 
Sheng-Ping Wang 3 
Su-Zan Yeh 2 
Yong Chen 4 
Wei-Cheng Su 5 
Don-Chung Liu 5 
Wen-Yie Chen 1 
Email address for contact author: chilu@ntu.edu. tw 
1 Eastern Marine Biology Research 
Center of Fisheries Research Institute 
No. 22 Wuchuan Rd. 
Chenkung, Taitung, Taiwan 961 
2 Institute of Oceanography 
National Taiwan University 
No.1, Sec. 4, Roosevelt Rd 
Taipei, Taiwan 106 
3 Department of Environmental 
Biology and Fisheries Science 
National Taiwan Ocean University 
No. 2, Beining Rd. 
Keelung, Taiwan 202 
School of Marine Science 
University of Maine 
218 Libby Hall 
Orono, Maine 04469 
Fisheries Research Institute 
No. 199, Ho-lh Rd. 
Keelung, Taiwan 202 
Sailfish ( Istiophorus platypterus) is 
a circumtropically distributed spe- 
cies (Hoolihan, 2005). Sailfish is a 
member of the billfish family, Istio- 
phoridae, which also includes marlins 
and spearfishes, and is considered a 
bycatch species in commercial fisher- 
ies. Off the eastern coast of Taiwan, 
sailfish are economically important 
and seasonally abundant from April to 
October (abundance peaks from May 
to July). Sailfish are mainly caught 
by drift gill nets, although some are 
also caught by set nets, harpoons, and 
as incidental bycatch in inshore long- 
line fisheries (Chiang, 2004). There 
are virtually no discards of sailfish 
in Taiwan. For the past decade, the 
annual landings of sailfish off Taiwan 
waters have fluctuated between 500 
and 1000 metric tons, of which over 
50% have come from waters off Tai- 
tung (eastern Taiwan). 
Globally, large predatory fish spe- 
cies, including billfish, are declining 
at alarming rates because of exces- 
sive exploitation (Myers and Worm, 
2003). Recent increases in the ex- 
ploitation of billfish stocks by both 
commercial and recreational fisheries 
clearly point to the need for accurate 
assessments, if the goal is to develop 
sustainable billfish fisheries (Uozumi, 
2003). However, because few fisheries 
target sailfish, assessments have not 
been conducted, resulting in few or 
no effective management measures. 
For sailfish in the Pacific Ocean and 
Indian Ocean, no assessments have 
been conducted, and stock status re- 
mains unknown. Historical sailfish 
catch data from the Pacific Ocean 
are scant, as are data on the length 
and age composition of the catch. 
This lack of data precludes the use 
of most stock assessment tools such 
as production models and age-struc- 
tured models (Punt, 1997; Prager and 
Goodyear, 2001; Liu et al., 2006). 
However, recent biological studies 
on sailfish in the waters off eastern 
Taiwan (Chiang et al., 2004, 2006) 
have provided an opportunity to apply 
yield per recruit ( Y/R ) and spawning 
biomass per recruit ( SSB/R ) models 
(Govender, 1995; Griffiths, 1997) to 
estimate biological reference points 
including the fishing mortality rate 
corresponding to the point where the 
slope of the yield-per-recruit curve 
