208 



Fishery Bulletin 94(2), 1996 



round, and the proportion of larger fish increased 

 during the breeding season (Fig. 10). The proportion 

 of these large fish (both sexes) increased in catches 

 from 31.1% during the "nonspawning period" (May 

 to December) to 61.3% during the "spawning period" 

 (January to April). 



Examination of size composition and sexual ma- 

 turity data for females >55 cm FL allowed broad dis- 

 tinction of three groups offish in commercial catches 

 during the breeding season (Fig. 10): 1) preadult fe- 

 males at size below the average size at maturity (i.e. 

 <69 cm FL), most in the developing stage of matu- 

 rity, but only a few of which would spawn during the 

 current spawning period; 2) females just reaching 

 size at maturity (i.e. between 69 and 75 cm FL), rang- 

 ing from developing to ripe stages of maturity, about 

 half of which would spawn for the first time during 

 the current spawning period; and 3) large females 

 (i.e. >75 cm FL), most in the fully developed stage of 

 maturity and likely to spawn. Preadult females were 

 caught all around Tasmania from November to May; 

 first-time spawners were caught mainly off the north- 

 east coast of Tasmania and were more abundant be- 

 tween January and April; largest females were also 

 caught primarily off the northeast coast of Tasmania 

 but only during a brief period, from early March to early 

 May, and quickly disappeared from catches afterward 

 (very few were caught in postspawning condition). 



For males, several groups could also be distin- 

 guished (Fig. 10), although not as clearly as those 

 for females, because of their generally more compact 

 length-frequency distributions. 



Preadult females (<69 cm FL) represented as much 

 as 45.69r of all three groups defined above. Similarly, 

 31.5% of males >55 cm FL had not reached the aver- 

 age size of sexual maturity. In addition, first-time 

 spawners (i.e. mature females at <75 cm FL and ma- 

 ture males at <65 cm FL) represented as much 

 as 56.7 and 75.9% of all mature females and males, 

 respectively. 



2.5' 



5 1-5 

 c I 



3 



2 0.5 



- 



o-f- 

 70 



7^ 



— I — 

 85 



'«i 



fork length (cm) 



Figure 9 



Linear relationship between batch fecundity and size of 

 females for blue-eye trevalla, Hypcroglyphc antarctica . Line 

 drawn from the equation Batch Fec.= 0.097 x FL - 6.28 

 (F=20.2, df=5, P<0.001, fl 2 =0.80. K 2 increased from 0.65 to 

 0.80 when the outlier was excluded from the regression). 



Discussion 



Ovary maturation, spawning frequency, and 

 fecundity 



Maturation of ovaries appears to be group-synchro- 

 nous for blue-eye trevalla, spanning from spring to 

 summer (October-February ) and followed by a brief 

 spawning period in late summer-autumn (early 

 March-early May). As observed for other fish spe- 

 cies (Hunter and Macewicz, 1985b), the occurrence 

 of atretic ovaries marks the end of spawning. The 

 timing of spawning coincides well with the discov- 

 ery, in June 1991 and May 1993, of a few juvenile 

 blue-eye trevalla among floating seaweed off the 

 Tasmanian east coast (Last et al., 1993). These juve- 

 niles ranged in size from about 30 to 60 mm stan- 

 dard length and were estimated to be about 2.5 to 3 

 months old on the basis of daily ring counts of otoliths 

 (Proctor 3 ). 



Blue-eye trevalla reach sexual maturity at a large 

 size, and according to yet unvalidated age data, 4 fe- 

 males are about 11-12 years old and males about 

 8-9 years old at sexual maturity. The bulk of imma- 

 ture fish in commercial catches are about 3 to 4 years 

 old. Analysis of data collected in the 1950s showed 



! Proctor., C. 1994. CSIRO, Division of Fisheries, Hobart, 

 Tasmania. Personal commun. 



4 Morison, S. 1995. Victorian Fisheries Research Institute, 

 Department of Conservation and Natural Resources, P.O. Box 

 114, Queenscliff 3225, Australia. Unpubl. data. 



