Chiang et al.: Age and growth of Istiophorus platypterus in waters off eastern Taiwan 



253 



SPINE 

 SHAFT 



VASCULARIZED 

 CORE 



SECTION 

 AREA 



0.75 MM 



CONDYLE 

 BASE 



CROSS SECTION 



Figure 2 



Schematic diagram of the fourth dorsal spine of sailfish [I. platypterus) and the 

 location of the cross section (A), and a cross section showing the measurements 

 taken for age determination of sailfish (B). W= maximum width of condyle base, R 

 = radius of spine, r, = radius of ring i, d = diameter of spine, d l = diameter of ring i. 

 The vascularized core and growth rings (1, 2, 3, 4, 5) are also shown. 



section was estimated according to the methods of Cayre 

 and Diouf (1983) (Fig. 2B). The distances (d,l were then 

 converted into radii (r,0 by using the equation (Megalofo- 

 nou, 2000; Sun et al., 2001): 



r ; = d : - W/2), 



where r i 

 d 



radius of the ring i; 



distance from the outside edge of ring i to the 

 opposite edge of the cross section; and 

 d = diameter of the spine. 



False growth rings were defined according to criteria 

 of Berkeley and Houde (1983), Tserpes and Tsimenides 

 ( 1995 ), and Ehrhardt et al. ( 1996 ). 



core of the spine. The number of early but missing growth 

 rings was therefore estimated by the replacement method 

 applied to Pacific blue marlin (Makaira nigricatis)by Hill et 

 al. (1989). This method involved first compiling ring radii 

 statistics from younger specimens that had at least the first 

 or second ring visible. Radii of the first four visible rings 

 from samples that had missing early rings were then com- 

 pared with the radii for these younger specimens. When 

 the radii of at least two successive rings of the first four 

 visible rings each fitted well within one standard deviation 

 from the mean radii of each of two or more rings from the 

 data compiled from the younger specimens, the number of 

 missing rings was computed as the difference between the 

 ring counts for the matched radii compiled from younger 

 specimens and those for the specimen of interest. 



Accounting for missing early rings 



The first several growth rings of the larger specimens may 

 be obscured because of the large size of the vascularized 



Validation 



The marginal increment ratio (MIR), which was used 

 to validate the rings as annuli, was estimated for each 



