Determination of age and growth of 

 swordfish, Xiphias gladius L., 1 758, 

 in the eastern Mediterranean 

 using ana\-f\n spines 



George Tserpes 



Institute of Marine Biology of Crete 

 RO. Box 22 1 4. 7 1 03 Iraklion. Greece 



Nikolaos Tsimenides 



University of Crete, Department of Biology 

 RO. Box 1470, 711 10 Iraklion, Greece 



in anal-fin spines used for age de- 

 termination of swordfish are depos- 

 ited annually. Because Ehrhardt 

 (1992) reported that the von Bert- 

 alanffy growth function did not ad- 

 equately represent swordfish 

 growth, we propose a second objec- 

 tive, namely to compare the growth 

 function proposed by Ehrhardt 

 (1992) with the standard von 

 Bertalanffy model for representing 

 growth of Mediterranean sword- 

 fish. 



Materials and methods 



Estimates of growth rates of bill- 

 fish are important because they are 

 necessary elements of population 

 dynamics models used in the as- 

 sessment of stocks for this family 

 offish. Otoliths have been used for 

 ageing most billfish species (Radtke, 

 1983; Radtke and Hurley, 1983; 

 Wilson and Dean, 1983; Prince et 

 al., 1984; Hill et al., 1989) but sev- 

 eral authors have pointed out that 

 the use of dorsal- and anal-fin 

 spines are more practical in terms 

 of ease of collection and processing 

 (Berkeley and Houde, 1983; Hedge- 

 peth and Jolley, 1983; Hill et al., 

 1989; Tsimenides and Tserpes, 

 1989). Other skeletal structures 

 such as vertebrae have rarely been 

 used and results have been poor 

 (Prince et al., 1984; Hill et al., 

 1989). 



The swordfish, Xiphias gladius, 

 is a cosmopolitan billfish species 

 that is highly exploited in the At- 

 lantic Ocean and the Mediterra- 

 nean Sea. In the Mediterranean the 

 average size of harvested swordfish 

 has declined over the last decade 

 such that juveniles compose as 

 much as 50-80% of the catch (Di 

 Natale, 1990; Tserpes et al., 1993). 

 However, the existence of contra- 

 dictory estimates of growth param- 

 eters makes assessment of sword- 



fish stocks difficult (Anonymous, 

 1990; 1993). 



Age of swordfish has been esti- 

 mated from otoliths (Radtke and 

 Hurley, 1983; Wilson and Dean, 

 1983), and sections of anal-fin 

 spines (Berkeley and Houde, 1983 ). 

 Of these ageing methods only 

 Ehrhardt (1992) achieved partial 

 validation of the anal-fin method 

 through marginal increment analy- 

 sis. This analysis assumes that 

 time of annulus formation corre- 

 sponds to the time when marginal 

 increments are minimal, and it has 

 been widely used to determine the 

 timing of annual increment forma- 

 tion in otoliths and scales of vari- 

 ous fish species (Wenner et al., 

 1986; Maceina et al., 1987). Al- 

 though the assumption of the 

 analysis is valid for any ageing 

 structure, the method has rarely 

 been applied to structures other 

 than otoliths and scales. 



Tsimenides and Tserpes (1989) 

 conducted growth studies on sword- 

 fish from the Aegean sea using 

 anal-fin spines but did not attempt 

 validation. They concluded that 

 there was "a degree of uncertainty" 

 in age estimates due to the loss of 

 the first annulus in older animals. 



The primary goal of this paper is 

 to determine whether growth bands 



Fish sampling and spine 

 preparation 



A total of 1,325 swordfish samples 

 were obtained from commercial 

 longline catches landed at the ports 

 of Kalimnos (n = 782), Kithnos 

 (rc = 185), and Chania (n-358) in the 

 Aegean sea. These ports, located on 

 the islands of Kalimnos, Kithnos, 

 and Crete are part of a national 

 project addressing the fishery and 

 biology of swordfish in the Greek 

 seas (De Metrio et al., 1989). 

 Samples were collected from 1987 

 to 1992 during alternate months 

 from February to October. How- 

 ever, most were collected from May 

 to September when the majority of 

 catches occur. 



Measurements of lower-jaw fork 

 length (LJFL to nearest cm) were 

 taken for all fish, sex was deter- 

 mined, and the anal fin removed 

 and frozen for storage. In the labo- 

 ratory, fins were thawed and sec- 

 tions of the second spine of the anal 

 fin were prepared for reading ac- 

 cording to the method described by 

 Tsimenides and Tserpes (1989). 

 Specifically, each anal fin was im- 

 mersed in boiling water for a few 

 minutes before the second spine 

 was removed, freed from skin and 

 tissue, cleaned with water, and left- 



Manuscript accepted 13 March 1995. 

 Fishery Bulletin 93:594-602 (1995). 



594 



