251 



Abstract— Age and growth of sailfish 

 (Jstiophorus platypterus) in waters off 

 eastern Taiwan were examined from 

 counts of growth rings on cross sections 

 of the fourth spine of the first dorsal fin. 

 Length and weight data and the dorsal 

 fin spines were collected monthly at the 

 fishing port of Shinkang (southeast 

 of Taiwanl from July 1998 to August 

 1999. In total. 1166 dorsal fins were 

 collected, of which 1135 (97 r £> (699 

 males and 436 females) were aged suc- 

 cessfully. Trends in the monthly mean 

 marginal increment ratio indicated 

 that growth rings are formed once a 

 year. Two methods were used to back- 

 calculate the length of presumed ages, 

 and growth was described by using 

 the standard von Bertalanffy growth 

 function and the Richards function. 

 The most reasonable and conserva- 

 tive description of growth assumes 

 that length-at-age follows the Rich- 

 ards function and that the relationship 

 between spine radius and lower jaw fork 

 length ( LJFL I follows a power function. 

 Growth differed significantly between 

 the sexes; females grew faster and 

 reached larger sizes than did males. 

 The maximum sizes in our sample were 

 232 cm LJFL for female and 221 cm 

 LJFL for male. 



Age and growth of sailfish Ustiophorus platypterus) 

 in waters off eastern Taiwan 



Wei-Chuan Chiang 



Chi-Lu Sun 



Su-Zan Yeh 



Institute of Oceanography 



National Taiwan University 



No 1, Sec. 4, Roosevelt Road 



Taipei, Taiwan 106 



E-mail address (for C L. Sun, contact author): chilufiintu edu.tw 



Wei-Cheng Su 



Taiwan Fisheries Research Institute 

 No. 199, Ho-lh Road 

 Keelung, Taiwan 202 



Manuscript approved for publication 

 22 December 2003 by Scientific Editor. 



Manuscript received 20 January 2004 

 at NMFS Scientific Publications Office. 



Fish. Bull. 102(2): 251-263 (2004). 



The sailfish (Istiophorus platypterus) 

 is distributed widely in the tropical 

 and temperate waters of the world's 

 oceans. According to data from longline 

 catches, sailfish are usually distributed 

 between 30°S and 50°N in the Pacific 

 Ocean, and highest densities are found 

 in the warm Kuroshio Current and 

 its subsidiary currents. This species 

 has a tendency to be found close to the 

 coast and near islands (Nakamura, 

 1985). During the 1990s the annual 

 landings of sailfish off Taiwan ranged 

 between 600 and 2000 metric tons, of 

 which approximately 54% came from 

 waters off Taitung (eastern Taiwan). 

 Sailfish are seasonally abundant from 

 April to October (peak abundance from 

 May to July) and contribute substan- 

 tially to the economic importance of 

 the eastern coast of Taiwan where this 

 species is taken primarily by drift gill 

 nets, although they are also caught by 

 set nets, harpoons, and as incidental 

 bycatch in inshore longline fisheries. 



Age and growth of sailfish caught 

 in recreational fisheries in the Atlan- 

 tic Ocean have been studied by using 

 various methods, including length- 

 frequency analysis (de Sylva, 1957). 

 analysis of release-recapture data (Far- 

 ber 1 ), and inferences from observed 

 marks on hard parts, such as spines 

 (Jolley, 1974, 1977; Hedgepeth and 

 Jolley, 1983) and otoliths (Radtke and 

 Dean, 1981; Radtke, 1983; Prince et al., 

 1986). In contrast, very few attempts 



have been made to age sailfish in the 

 Pacific Ocean. Koto and Kodama ( 1962 ) 

 estimated the growth of sailfish caught 

 with longlines from 1952 to 1955 in the 

 East China Sea using length-frequency 

 analysis, and Alvarado-Castillo and Fe- 

 lix-Uraga (1996, 1998) used the fourth 

 spine of the first dorsal fin to estimate 

 age and growth of sailfish caught from 

 1989 to 1991 in the recreational fishery 

 off Mexico. However, western Pacific 

 sailfish have not been aged with calci- 

 fied structures in any previous study. 



The aging of fishes, and consequently 

 the determination of their growth and 

 mortality rates, is an integral compo- 

 nent of modern fisheries science (Paul. 

 1992). Mortality and growth rates pro- 

 vide quantitative information on fish 

 stocks and are needed for stock assess- 

 ment methods such as yield-per-recruit 

 and cohort analysis (Powers. 1983). 



The objectives of this study were to 

 estimate age and growth of sailfish by 

 counting growth rings on cross sections 

 of the fourth spine of the first dorsal fin 

 and to determine which of the Richards 

 function and the standard von Berta- 

 lanffy growth function best represents 

 growth of sailfish in waters off eastern 



1 Farber, M.I. 1981. Analysis of Atlantic 

 billfish tagging data: 1954-1980 Unpubl. 

 manuscr. ICCAT workshop on billfish, 

 June 1981. Southeast Fisheries Center 

 Miami Laboratory. National Marine Fish- 

 eries Service, NOAA, 75 Virginia Beach 

 Drive, Miami, FL 33149. 



