274 
Fishery Bulletin 107(3) 
Fishing mortality (1/year) 
Figure 9 
Spawning-potential ratio (SPR) isopleths against fishing mortality per year 
and age at first capture ( t c ) at different levels of natural mortality (M) for 
female sailfish ( Istiophorus platypterus) in waters off eastern Taiwan. 
the estimate of current fishing mortality rate, the status 
of a fishery can be readily determined by comparing 
current fishing mortality with the biological reference 
points. Nevertheless, few results of previous studies have 
been discussed as to how the biological reference points 
based on per-recruit analyses were influenced by the 
uncertainties of biological parameters. 
In this study, the effects of F, M, and t c on the es- 
timates of F 0 v F S sB 4 o> an d -^ssb 25 were evaluated by 
using the Monte Carlo simulation method. Although 
other parameters (e.g., growth) are essential inputs 
for per-recruit analyses, we focused on the effects of 
F, M, and t c which are generally more difficult to esti- 
mate owing to a lack of enough auxiliary information 
(Chen et al., 2007). In addition, the assumption of 
selectivity of fishing gear could influence the results 
of per-recruit analyses. Generally, longline selectivity 
is assumed to be asymptotic and gillnet selectivity is 
assumed to be dome shaped. In this study, a dome- 
shaped selectivity was assumed for incorporating into 
the per-recruit analyses. Sailfish in the waters off 
eastern Taiwan were exploited by various fishing gears 
although large proportion of the catch was made by 
gillnet. However, insufficient length-frequency data 
recorded by fishing gear lead to difficulty in estimat- 
ing the selectivity for different fishing gear. Therefore, 
collecting the information from fishing gear for length- 
frequency data is necessary to evaluate the influence 
of different selectivity assumptions on the results of 
assessment. 
Implications of sex-specific assessment 
and management of the species 
Uozumi (2003) indicated that the problems in the stock 
assessment of sailfish are the inability to obtain reliable 
biological parameters, standardization of catch per unit 
of effort, and a mechanism to develop reliable abundance 
indices. Sailfish are known to be sexually dimorphic 
(females grow faster and to a larger size than males 
(Chiang et al., 2004; Hoolihan, 2007), females become 
mature later than males, and sex ratio varies with 
length (Chiang, 2004). These attributes indicate that 
sex-specific assessments should be done to evaluate the 
status of sailfish. The sex-specific per-recruit analyses 
with the consideration of parameter uncertainty used 
in this study provide a method for evaluating manage- 
ment strategies. 
