200 



Fishery Bulletin 94(2), 1996 



month from most fishing grounds 

 around Tasmania ( Fig. 1 ). A sample rep- 

 resented the total catch made during 

 one fishing trip (of 1-3 day duration) 

 on the same ground. Fish were exam- 

 ined individually as they were hauled 

 on deck, and the entire catch (or the 

 majority of it) was processed during 

 each fishing trip (representing between 

 50 and 500 fish). Fish were measured 

 (fork length [FL]) to the nearest cm be- 

 low the true length, sexed, and staged 

 macroscopically by using the maturity 

 stages described in Table 1 (adapted 

 from Hunter and Macewicz, 1985, a and 

 b; Schaefer, 1987; West, 1990). To cal- 

 culate the gonadosomatic index (GSI), 

 ovaries and testes were collected to be 

 weighed in the laboratory to the nearest 

 0.1 g. The GSI was calculated as the pro- 

 portion of gonad weight divided by body 

 weight with the following length-weight 

 relationship: Log (gutted weight) = 3.081 

 x Log {fork length ) -4.385, where weight 

 is in g and length in cm ( Baelde, unpubl. 

 data ). For later histological examination 

 and measurement of whole oocytes, ova- 

 ries at various stages of maturity were 

 preserved in Davidson's solution imme- 

 diately after the catch. Nearly all ma- 

 ture ovaries (stages 4 to 6, Table 1) were 

 preserved. 



Histological staging of ovaries 



A total of 447 ovaries were examined histologically 

 to check macroscopic staging and to note the pres- 

 ence of atretic oocytes and postovulatory follicles (see 

 description in Table 1; Fig. 2; Fig. 3, A and B). Ovary 

 sections were stained in haematoxylin and eosin and 

 ovaries were staged on the basis of the most advanced 

 type of oocytes present, regardless of their abundance 

 (West, 1990). 



Size at maturity 



The average size at maturity (FL ()5 ) was the size at 

 which 50^ of the fish caught during the breeding 

 season were mature (i.e. stages 4 to 6 for females, 

 and stages 3 and 4 for males). For each sex, the pro- 

 portion (p ) of mature individuals, by 1-cm fork length 

 intervals, was fitted to the logistic function 



grounds 



K) 



\2 



43 



I) 



Figure 1 



Proportions (as a percentage) by sex of immature f 1 1, mature (Ml, and rest- 

 ing (Rl blue-eye trevalla, Hyperoglyphe antarctica, in samples collected 

 from major fishing grounds around Tasmania. I = stages 1 to 3 for females, 

 1 to 2 for males; M = stages 4 to 6 for females, 3 and 4 for males; and R = 

 stages 7 and 8 for females, stage 5 for males. Depth contours in meters. 

 WA = Western Australia, SA = South Australia, Vic = Victoria, and NSW = 

 New South Wales. Numbers in graphs are the number offish sampled. 



by using generalized linear models (Genstat 5 Ref- 

 erence Manual). The average size at maturity was 

 also estimated for length and maturity data collected 

 off the east coast of Tasmania during the 1950s 

 (Cowper and Downie 2 ). 



Spawning freguency and fecundity 



Hunter et al. ( 1992) have identified three main fac- 

 tors that can affect fecundity estimates: 1) the rate 

 of atresia in reducing the number of oocytes spawned; 

 2) the occurrence of previous spawnings (as shown 

 by the presence of postovulatory follicles); and 3) the 

 accurate identification of which oocytes to include in 

 estimating fecundity. These three factors were ex- 

 amined as shown below. 



Rate of atresia The proportion of atretic oocytes was 

 determined in ovaries at various stages of maturity 



ia+bFL> 



'(i 



+ e 



ia+bFLi 



' Cowper, T. R., and R. J. Downie. 1995. CSIRO, Division of 

 Fisheries and Oceanography. Cronulla, New South Wales, 

 Australia. Unpubl data. 



