Griffiths: Life history of Thymtes atun 



697 



LU 

 Q. 



o 



Region 4 



Region 5 



Region 3 



1— «. ■-- -■—»—«- «. >^ « i 

 100 200 300 400 500 600 

 Depth class (50 m) 



June - October 

 November - May 



100 200 300 400 500 600 

 Depth class (50 m) 



Figure 4 



Catch per unit of effort (CPUE; kg/h) per 50-m depth category for Thyrsites 

 atun commercially bottom trawled in each of the seven regions during 

 winter-spring and summer-autumn, 1986-97. 



passed the western edge of the Agulhas Bank and most of 

 the South African west coast, to a point just north of Hon- 

 dekhp Bay. 



The predominance of ripe (stage-3) females (both inshore 

 and offshore) throughout the protracted spawning season 

 (Fig. 9) is indicative of multiple spawning (Griffiths, 1997). 

 Moreover, the simultaneous occurrence of postovulatory 

 follicles (POFs) with both primary growth and advanced 

 yolked-stage oocytes (Fig. 11) confirmed that snoek are 

 indeterminate, serial spawners. 



Sex ratio 



Sex ratios in regions 0-3 were skewed towards females 

 inshore and males offshore (Table 2), a pattern most pro- 

 nounced during the spawning season (winter-spring). 



Inshore, this pattern was most evident in the adult size 

 class (>75 cm). Adult sex ratios in regions 0-3 during 

 the spawning season were 2.9F:1M inshore and 1F:2M 

 offshore. Inshore and offshore sex ratios of adult snoek 

 in regions 4 and 5 (Table 2) revealed no clear pattern; 

 although moderately more females were sampled on 

 the trawl grounds of these regions during the spawning 

 season ( 1.6F:1M), the inshore ratio ( 1M:1.2F) did not devi- 

 ated significantly from unity. 



Nursery areas 



Monthly length-frequency distributions comprised fairly 

 discrete modes in spite of variation in collection method 

 and sampling period and clearly depicted early juvenile 

 growth (Fig. 12). Young-of-the-year snoek first appeared 



