270 
Fishery Bulletin 107(3) 
Table 3 
Sample sizes and estimates of age at full recruitment for female and male sailfish ( Istiophorus platypterus ) by year in the waters 
off eastern Taiwan during the period from July 1998 to July 2005. 
Sample 
size 
Age at 
full recruitment 
Sample 
size 
Age at 
full recruitment 
Female 
Male 
1998 
131 
6 
1998 
525 
6 
1999 
702 
5 
1999 
1943 
5 
2000 
387 
7 
2000 
578 
7 
2001 
358 
6 
2001 
730 
5 
2002 
349 
7 
2002 
576 
5 
2004 
484 
5 
2004 
1123 
5 
2005 
1121 
6 
2005 
3316 
5 
Overall 
3532 
5 
Overall 
8791 
5 
Table 4 
Estimates of current fishing mortality (E CUR ), current 
yield per recruit ( Y/R cur ), and the reference points of F 0 x 
and Y/R 0 x at different levels of natural mortality (M) for 
female and male sailfish (Istiophorus platypterus ) in the 
waters off eastern Taiwan during the period from July 
1998 to July 2005. F 0 : = the fishing mortality rate corre- 
sponding to Y/R q 1 ;Y/R 01 = the point of a yield-per-recruit 
curve where the slope equals 10% of the slope at the origin. 
M 
(1/yr) 
F CUR 
(1/yr) 
K. i 
(1/yr) 
Y!F C ur 
(kg) 
57*0.1 
(kg) 
Female 
0.20 
0.26 
0.54 
5.36 
7.08 
0.26 
0.24 
0.62 
3.37 
5.11 
0.30 
0.22 
0.69 
2.45 
4.13 
0.35 
0.20 
0.80 
1.63 
3.19 
Male 
0.20 
0.46 
0.70 
5.79 
6.66 
0.27 
0.43 
0.79 
3.72 
4.68 
0.30 
0.41 
0.83 
3.06 
4.04 
0.35 
0.38 
0.91 
2.21 
3.17 
Figure 4 
The estimated selectivity curves for female (dashed line) 
and male (solid line) sailfish (Istiophorus platypterus ) 
in the waters off eastern Taiwan. Selectivity is the 
relative vulnerability of different age or size classes to 
the fishing gear. In this study, selectivity is assumed 
to be dome shaped because length-frequency data were 
mostly collected from gillnets. 
The rapid growth and relatively late t c (5 years) of 
sailfish in the waters off eastern Taiwan produced low 
Y/R and high SPR at current fishing mortalities com- 
pared with reference points (Figs. 4 and 7). The esti- 
mates of F SSB25 , F SSB40 , SPR and Y/R under the various 
values of M are summarized in Table 5 and Figure 
8. The base-case estimate of F CUR for females (0.24/ 
yr) was lower than the corresponding reference points 
F SS B 4 o (0.46/yr) and F gSB25 ( 0.94/yr); the current SPR 
was estimated to be about 57.20% of its unfished level. 
Under the low value of M (0.2/yr), the estimate of F CUR 
for females (0.26/yr) was lower than F ggB40 (0.36/yr) 
and substantially lower than F ggB25 (0.67/yr). Increas- 
ing t c to older than six years of age would ensure that 
the SPR was maintained at a value higher than the 
threshold level (i.e., 25% of its unfished level) at almost 
any level of fishing mortality (Fig. 9) with relatively 
little effect on Y/R. 
Simulation scenarios 
The box plots of the estimates of F 0 1 and F CUR /F 0 1 are 
shown in Figure 10 for scenarios A-J with the assump- 
tion of uncertainty in F, M, and t c defined in Table 2. 
Although the medians of these two quantities were 
close to those of the base case for most scenarios, the 
variations of these quantities were diverse depending 
on the assumptions of uncertainty of the parameters. 
For scenarios A-D with only one parameter subject to 
uncertainty, the estimates of F 0 4 were independent of 
