Griffiths: Life history of Thyrsites atun 



695 



33° 

 S 



34' 



35' 



36° 



SOUTH AFRICA 



c? 



^ 



Cape 

 St Francis 



Port 

 Alfred c 



\ PORT 

 ^S" , . \ ELIZABETl 



MOSSEL BAY Knysna ^%Jsitsikamma 



/.. '/■ 



\^' 



-*---— i" ' 



^T 



W' ^ 



: \ 



20° 



21 



22° 



23° 



t 



AUTUMN (Apnl - May) 



KEY 

 . =0 



• < 10 



• 10-50 



• >50 



_ Untrawlable ground 



I I 1 1 I ' I ' ' ^ ' i I ' I I ' 



24° 



25° 



26° 



33< 

 S 



36' 



SOUTH AFRICA 



Cape 

 St Francis 



Port 

 Alfred i 



Cape Seal 



MOSSEL BAY 



Knysna 



Tsitsikamma 



PORT 



ELIZABETH 



I« ™ •• •  ' 

 ^ , s " - yv 



;*. 



t 



WINTER/SPRING 

 (June and September) 



KEY 

 = 



. < 10 



• 10-50 



• >50 

 Untrawlable ground 



hj_L 



lJ_ 



1 I I t I i 1 ' 



I I 1 1 1 I I I I I i 



20° 



21° 



22° 



23° 24° 



Figure 2B 



25° 



26° 



(Fig. 6A), suggesting (as in other teleosts; Griffiths and 

 Hecht, 1995) that substantial proportions of snoek in the 

 smaller size classes undergo partial gonad development 

 during the season prior to maturity. Because these fish are 

 unlikely to spawn, only specimens with gonads developed 

 to at least stage 3 (ripe) were regarded as mature. Given 

 that snoek spawn offshore (see below) and that almost all 

 fish on the trawl grounds (regardless of size) were mature 

 (Fig. 6B). L,,, maturity calculations were limited to fish 

 sampled inshore (<150 m)^: 72.0 cm for males and 73.4 

 cm for females (Fig. 7). Upper and lower 95% confidence 

 limits were 69.3 and 74.3 cm for males, and 71.3 and 75.4 

 cm for females. Lr^^ for combined male and female data was 



73.0 cm with 95% confidence intervals of 70.0 and 75.2 cm. 

 In all cases the L^g values corresponded with an age of 3 

 years (author, unpubl. data). 



In situations where fish migrate to spawn, all fish on the spawn- 

 ing ground are mature. As a result, even if W/i of a particular 

 size class (at-.v cm) in the population are mature, the sampling 

 of that IWc once it had migrated onto the spawning grounds 

 would suggest that IOC'S of that size class are mature. Because 

 mature snoek move back and forth between the spawning and 

 feeding grounds lofTshore and inshore! in regions 0-3 during 

 the spawning season, and could readily be distinguished from 

 immature fish, inshore samples were used to determine size at 

 maturity. 



