260 



Fishery Bulletin 102(2) 



0.9 



08 

 0.7 - 

 0.6 

 05 - 

 0.4 - 



0.3 



09 

 08 

 07 

 06 

 05 

 0.4 

 03 

 02 



40 Ages 1-5 



- 1 r~ 



—l 1 1 1 



Ages 6-12 



— i 1 1 1 1- 



JFMAMJJASOND 

 Month 



Figure 6 



Monthly means of marginal increment ratio for the female sailfish (/. 

 platypterus) in the waters off eastern Taiwan for all ages combined and 

 for age classes 1-5 and 6-12, respectively. Vertical bars are ±1 SE; num- 

 bers above the vertical bars are sample sizes. 



(1996), and Sun et al. (2002) favored method 2 because 

 they believed it to be more biologically realistic. When 

 the back-calculated lengths-at-age are generated with 

 this method the Richards function provides a statistically 

 superior fit to the length-at-age data. Therefore, the pa- 

 rameter estimates for the Richards function with method 2 

 listed in Table 4 are recommended as the most appropriate 

 for calculating the age composition of sailfish in the waters 

 to the east of Taiwan. It is perhaps worth noting that the 

 t u values estimated for the Richards function with method 

 2 are much closer to zero than those estimated for the 

 Richards function with method 1. 



Comparison with previous studies 



Figure 9 compares the age-length relationships of this 

 paper with those for Atlantic (de Sylva, 1957; Hedgepeth 



and Jolley, 1983; Farber 1 ) and Pacific sailfish (Koto and 

 Kodama, 1962; Alvarado-Castillo and Felix-Uraga. 1998). 

 De Sylva ( 1957 ) and Koto and Kodama ( 1962 1 used length- 

 frequency analysis and concluded that sailfish are a very 

 fast growing and short-lived species. However, they likely 

 underestimated age and overestimated growth rate when 

 their results are compared with those of other more recent 

 studies. 



The maximum ages found in this study (11 years for 

 males and 12 years for females) are close to the maximum 

 longevity of at least 13 years proposed by Prince et al. 

 (1986) based on tagging data. Farber 1 analyzed Atlantic 

 billfish tagging data and suggested that the asymptotic 

 size was essentially reached by age 3 (Hedgepeth and Jol- 

 ley, 1983). whereas the present study found a more gradual 

 increase in length with age. in common with the results of 

 Hedgepeth and Jolley (1983). 



