Griffiths: Life hiistory of Thyivtes atun 



703 



S 



29" 



30" 



31" 



32° 



33"'b- 



34' 



35"! 



36° ^ 



15" 



16° 



17" 



18° 



19" 



20° 



21° 



22° 



23° 



24° 



25° 



26° 



Figure 10 



Catch per unit of effort (kg/h) by 20-niile block ( 1986-97) for Thyrsites atun caught by commercial trawls 

 in the southern Benguela system during the spawning season. 



of the WAB than offshore along the WC, where 

 hake was dominant. Sex ratios and feeding 

 patterns of adult snoek in the present study 

 were confirmed as persistent biological features 

 of the western Agulhas Bank by experimental 

 trawl surveys on the spawning ground of region 

 4 during August 1999 and August 2000. The 

 principal prey taxon for 1875 snoek with a sex 

 ratio of 1M:1.2F (P<0.001) was Clupeidae (67% 

 by weight); mean stomach content masses were 

 58.2 g for females and 27.6 g for males. 



Even though young-of-the-year snoek were 

 sampled (with fishing gear) in each of the 

 seven regions, they formed a larger proportion 

 (by mass and frequency of occurrence) of the 

 diet of gannets at Bird Island (Lamberts Bay) 

 than in gannets at Malgas Island. Either early 

 juveniles are more abundant north of Cape 

 Columbine than between Cape Columbine and 

 Cape Infanta or they are selected at a higher 

 frequency by gannets in the former area. 

 Higher propoi ions of snoek smaller than 70 

 cm in the handline and pelagic-trawl catches 

 of regions 0-2 than in catches from region 3 

 support the first suggestion, confirming that 

 the area north of Cape Columbine has an im- 

 portant nursery function. Length frequencies of pelagical- 

 ly trawled, demersally trawled (<150 m), and line-caught 



Figure 11 



Photomicrograph of transverse section of Thyrsites atun ovary stained 

 with haemu.oxylin and eosin. showing co-occurrence of postovulatory 

 follicles (POF) together with primary growth (PGl and advanced yolk- 

 stage oocytes (YO). 



snoek, nevertheless suggest a second nursery area to the 

 east of Danger Point. But because handline catches in 



