704 



Fishery Bulletin 100(4) 



50 

 30 

 10 



20 

 10 



20 



-10 



I 



i 



1 



r 

 I 



20 

 10 



20 

 10 



20 



10 



October 



n = 21 



April 



November n = 44 



^ n = 277 



May 



December 



n = 46 June 



January 



r7 = 58 



iBftuHMnttmilaHMmi , I iHa 



February n n = 39 



^ n=72 



^J J ^ J J- U JJJJ ^^/l I 



August 



n= 103 



n= 120 



n = 36 



n = 27 



March 



4 8 12 16 20 24 28 32 36 40 44 48 

 Fork iengtti class (1 cm) 



Gannet 

 —^ Pelagic trawl 

 • Demersal trawl 



4 8 12 16 20 24 28 32 36 40 44 48 

 Fork length class (1 cm) 



Figure 12 



Monthly fork-length distributions of Thyrsites atun <50 cm caught by 

 midwater trawls (1985-971. demersal trawls (1985-97), and Cape gannets 

 ( 1978-97) in the southern Benguela system. ;! = sample size. Dotted line at 

 25 cm is included as a reference point. 



regions 4 and 5 amounted to only 10% of those in regions 

 land 2 (1985-97) and given that juvenile snoek made a 

 substantially lower contribution to the diets of gannets 

 foraging in this area, the area north of Cape Columbine 

 is regarded as considerably more important to juvenile 

 snoek. Thyrsites atun in demersal trawls made deeper 

 than 150 m were mostly >65 cm, whereas those from 

 shallower bottom trawls included substantial proportions 

 smaller than this length. It is therefore concluded that 

 the primary nursery ground is situated on the west coast, 

 north of Cape Columbine and in water shallower than 150 

 m; a secondary nursery exists to the east of Danger Point. 

 The absence of specimens <30 cm from demersal trawls, 

 particularly those made shallower than 150 m, and their 

 presence in pelagic trawls, indicates that 0-year-old snoek 



are largely epipelagic but become pelagic with growth (at 

 ca. 8 months old). 



The northward flowing Benguela Current provides a 

 mechanism for transporting epipelagic snoek eggs and 

 larvae (De Jager, 1955; Olivar and Fortuno, 1991) from 

 the spawning ground to the proposed nursery areas. The 

 Benguela current is found offshore (generally between 

 the 150- and 400-m isobaths) and flows along the western 

 edge of the Agulhas Bank and up the South African west 

 coast; rate of flow is fastest (typically 25-80 cm/s) between 

 Cape Point and Cape Columbine, where it develops into a 

 shelf edge jet (Shannon and Nelson, 1996). Although water 

 movement is primarily parallel to the shelf, inshore advec- 

 tion occurs to some degree due south of Danger Point and 

 to a greater extent between Cape Columbine and Hon- 



