220 



Fishery Bulletin 100(2) 



parameters of the gi-owth curves differed between the 

 sexes. For this cui^ve, the parameters L., k, and t„ and 

 their 959; confidence hmits were estimated to be 929 

 (908 to 949) mm, 0.111 (0.107 to 0.116)/year, and -0.141 

 (-0.183 to -0.100) years, respectively, for females, and to be 

 1025 (1003 to 1048) mm, 0.111 (0.107 to 0.116)/year. and 

 -0.052 (-0.088 to -0.0161 years, respectively, for males. 

 The growth curves for females and males were significant- 

 ly different (P<0.001), with the asymptotic lengths hav- 

 ing the most influence on the difference between the sex- 

 es. The estimated constant of proportionality between the 

 variance of the residuals and age were 363 for females and 

 320 for males. 



The von Bertalanffy growth cui-ves demonstrated that 

 females gi'ow slightly slower than males. Thus, at ages 2 

 to 5. females had reached lengths of 196, 273, 342, and 

 404 mm, compared with 209, 294, 371, and 440 mm for 

 males. By the time G. hebraicum had attained 10, 15, and 

 20 years, the females had reached ca. 628, 756, and 830 

 mm, respectively, and the males had reached ca. 689, 832, 

 and 914 mm, respectively (Fig. 4). The maximum ages re- 

 corded for females and males were 39 and 41 years, re- 

 spectively, and the maximum total lengths of females and 

 males were 981 mm (=ca. 15.3 kg) and 1120 mm (=ca. 23.2 

 kg), respectively. The ages at which female and male G. he- 

 braicum reach the minimum legal length for capture (500 

 mm TLi were 7.0 and 6.0 years, respectively. 



Trends exhibited by reproductive variables 



The macroscopic characteristics of the different stages in 

 gonadal development, and of the cytological characteris- 

 tics of the ovaries at different stages based on an examina- 

 tion of histological sections, are given in Table 1. 



Because stages I (virgin) and II (immature) in the de- 

 velopment of both the ovaries and testes of G. hebraicum 

 were difficult to separate macroscopically, data for these 

 two stages were pooled in the case of both sexes. Further- 

 more, it is also important to recognize that spawning stage 

 (VI) ovaries are distinguished from prespawning stage 

 (V) ovaries almost exclusively on the basis of their posses- 

 sion of hydrated oocytes or postovulatory follicles (or both) 

 when histological sections were employed to examine the 

 ovary at a finer scale. However, because G. hebraicum is 

 a multiple spawner, i.e. produces eggs in batches at in- 

 tervals, any "prespawning" stage ovary may already have 

 produced some hydrated oocytes, but been at an interme- 

 diate phase in which the next batch of yolk granule oocytes 

 had not yet become hydrated. The prevalence of females 

 with prespawning ovaries that had already spawned on 

 one or more occasions would be expected to increase dur- 

 ing the spawning period. Likewise, the main difference be- 

 tween prespawning and spawning testes, i.e. the ability 

 of the testes to produce milt when subjected to physical 

 pressure, may often represent different phases in the cy- 

 clical changes undergone in the testis during the spawn- 

 ing period. For the above reasons, the data on stage-V and 

 stage-Vl ovaries and testes were pooled for describing the 

 change in compositions of the gonadal maturity stages of 

 each sex during the year. 



Between May 1996 and April 1998, the mean monthly 

 GSIs for females of G. hebraicum that were greater than 

 the L-ii of 301 mm at first maturity were always low in 

 winter (June to August) and early spring (September), i.e. 

 <1.0 but then rose sharply to reach a peak of ca. 2.8 in 

 mid-summer (January), before declining markedly during 

 early to mid-autumn ( March and April i ( Fig. 5 ). The trends 

 displayed by the mean monthly GSIs for males of G. he- 

 braicum, that were greater than the L-^of 320 mm at first 

 maturity, paralleled those just described for females. 



Because the trends exhibited by the mean monthly GSIs 

 for females and males were the same during both 12 month 

 periods, the percentage contributions of the different go- 

 nadal stages of the females and males of G. hebraicum, that 

 were longer than the L^,,, were pooled for each of the cor- 

 responding calendar months. The gonads of female G. he- 

 braicum in July were at stages I-II, i.e. virgin or immature 

 (Fig. 6). Fish with ovaries at stage III (developing) were first 

 found in August, albeit only a few fish, and those at stage IV 



