822 



Abstract— Age and growth of the 

 swordfish {Xiphias gladius) in Taiwan 

 waters was studied from counts of 

 growth bands on cross sections of the 

 second ray of the first anal fin. Data 

 on lower jaw fork length and weight, 

 and samples of the anal fin of male 

 and female swordfish were collected 

 from three offshore and coastal tuna 

 longline fishing ports on a monthly 

 basis between September 1997 and 

 March 1999. In total, 685 anal fins 

 were collected and 627 of them (293 

 males and 334 females) were aged suc- 

 cessfully. The lower jaw fork lengths of 

 the aged individuals ranged from 83.4 

 to 246.6 cm for the females and from 

 83.3 to 206 cm for the males. 



The radii of the fin rays and growth 

 bands on the cross sections were mea- 

 sured under a dissecting microscope 

 equipped with an image analysis 

 system. Trends in the monthly mar- 

 ginal increment ratio indicated that 

 growth bands formed once a year 

 Thus, the age of each fish was deter- 

 mined from the number of visible 

 growth bands. Two methods were used 

 to estimate and compare the standard 

 and the generalized von Bertalanffy 

 growth parameters for both males and 

 females. The nonlinear least square 

 estimates of the generalized von Berta- 

 lanffy growth parameters in method II, 

 in which a power function was used to 

 describe the relationship between ray 

 radius and LJFL, were recommended 

 as most acceptable. There were sig- 

 nificant differences in growth param- 

 eters between males and females. 

 The growth parameters estimated for 

 females were the following: asymptotic 

 length (Lj = 300.66 cm, growth coef- 

 ficient (K) = 0.040/yr, age at zero length 

 «o) = -0.75 yr. and the fitted fourth 

 parameter Imi = -0.785. The growth 

 parameters estimated for males were 

 the following: asymptotic length iL..,) = 

 213.05 cm. growth coefficient lA') = 

 0.086/yr, age at zero length (/„) = -0.626 

 yr, and the fitted fourth parameter ( m ) = 

 -0.768. 



Age and growth of the swordfish 

 (Xiphias gladius L.) in the waters 

 around Taiwan determined from anal-fin rays 



Chi-Lu Sun 

 Sheng-Ping Wang 

 Su-Zan Yeh 



Institute ol Oceanography 



National Taiwan University 



No 1, Sec, 4, Roosevelt Road 



Taipei, Taiwan 106 



Email address (for C L Sun) chilu'Sccmsntuedu tw 



Manuscript accepted 21 February 2002. 

 Fish. Bull. 100:822-835 (2002). 



The swordfish iXiphias gladtus L.) is a 

 cosmopohtan species found in the trop- 

 ical, subtropical, and temperate waters 

 of the world's oceans and adjacent seas 

 (Sakagawa, 1989). In the Pacific Ocean, 

 swordfish is generally distributed from 

 Asia to the Americas between .50°N 

 and 50°S (Bartoo and Coan, 1989). In 

 the waters of Taiwan, the swordfish is 

 an incidental bycatch of the offshore 

 tuna longline and harpoon fisheries. 

 Both fisheries contributed an esti- 

 mated 1528 metric tons (99%) to the 

 total swordfish landings from Taiwan 

 waters in 1999. 



Information on age and growth of 

 fishes is a central element in fishery 

 management (Brothers, 1983). Mea- 

 surement of the age of the fish provides 

 the key variable of time needed to es- 

 timate life history and biology factors, 

 such as mortality and growth. Mortal- 

 ity and growth-rate models provide 

 quantitative information on the status 

 offish stocks and at the same time may 

 be used in more sophisticated models, 

 such as yield-per-recruit analyses and 

 cohort analyses (Powers, 1983), which 

 will directly contribute to the rational 

 exploitation offish resources, as well as 

 to the development of proper manage- 

 ment plans. 



Most age determination studies of 

 swordfish have dealt with Atlantic pop- 

 ulations and have used different hard 

 parts, such as anal-fin rays (Berkeley 

 and Houde, 1983; Wilson and Dean 

 1983; Prince et al., 1988; Ehrhardt, 

 1992; Esteves et al., 1995; Ehrhardt et 

 al., 1996), otolith (Radtke and Hurley, 

 1983; Wilson and Dean, 1983; Esteves 



et al., 1995), and vertebrae (Esteves et 

 al., 1995). In contrast, only a few at- 

 tempts have been made to determine 

 the age of swordfish in the Pacific 

 Ocean. Yabe et al. (1959) estimated the 

 growth of swordfish caught in the 

 western North Pacific (140°-160°E) by 

 longline during the period from 1948 

 to 1956 using the modal analysis of 

 length frequencies. Castro-Longoria 

 and Sosa-Nishizaki (1998) compared 

 the age estimates of swordfish caught 

 by drift gillnet vessels off Baja Califor- 

 nia from 1992 to 1993 based on otolith 

 microstructure and cross sections of 

 the second ray from the first anal fin, 

 and highly recommended the use of 

 cross sections of the second ray to de- 

 termine the ages of swordfish in the 

 Pacific Ocean. Uchiyama et al. (1998) 

 evaluated various hard parts (includ- 

 ing rays of the first dorsal and first 

 anal fins, vertebrae, and sagittae) for 

 aging swordfish in the central North 

 Pacific by Hawaii longline fishery from 

 1991 to 1993, and provided preliminary 

 estimates of length-at-age. 



The objectives of our study were to 

 estimate the age and growth of sword- 

 fish by counting the growth rings on 

 the cross sections of the second ray of 

 the first anal fin and to compare the 

 generalized growth function proposed 

 by Richards (1959) with the standard 

 von Bertalanffy model for represent- 

 ing the best growth model of swordfish 

 around Taiwan waters. The informa- 

 tion is crucial because it will allow 

 the age composition of the catch to be 

 determined, which in turn will allow 

 the status of the swordfish stock in the 



