698 



Fishery Bulletin 100(4) 



40 



30 - 



20 



10 



Region 



^Jhl 



n = 42 

 n = 549 



go 1 Region 1 



50 

 40 

 30 

 20 

 10 



30 

 20 

 10 



30 

 20 

 10 



.^A 



k 



n = 206 

 n=968 



Region 2 



140 



:1 597 



ii 



Region 4 



 n=0 

 ^ n= 1 017 



Region 5 



 n = 411 



E3 n = 1 405 



Region 6 



 n = 82 



m n = 47 



mil «'.ia,^. 



Region 3 



 n = 37 

 E n = 1 785 



_J__Jj 



.? -? <§^ 'P c? 



Fork length class (5 cm) 



Demersal trawl <150m 

 Dennersal trawl >150m 



M 



Fork length! class (5 cm) 



Figure SA 



Fork-length distributions of Thyrsites atun caught by (A) demersal trawl and 

 (B) handline and midwater trawl in each region. Handline and midwater 

 catches were made shorewards of the 150-m isobath and demersal catches 

 were divided into those made deeper and shallower than this depth. The 

 dotted line indicates length at maturity ^L^,-,). 



in the diets of gannets and in pelagic trawls during spring 

 (Oct-Nov) at lengths 7-12 cm and grew rapidly to 33-44 

 cm by the spawning season (winter) of the following year 

 (±3.25 cm/month). Early juveniles (<1 year old) were 

 sampled (with fishing gear) in each of the seven regions 

 (Fig. 5) but formed a larger proportion (by mass and 

 frequency of occurrence) of the diet of gannets at Bird 

 Island (Lamberts Bay) than in gannets of Malgas Island 

 (Fig. 13). Snoek smaller than 70 cm comprised a far higher 

 proportion of the handline and pelagic trawl catches of 

 regions 0-2 than those from region 3 (Fig. 5B). Length 

 frequencies of pelagic trawl, demersal trawl (<150 m), 

 and line-caught snoek suggested that juveniles were also 

 found in reasonable numbers to the east of Danger Point 

 in regions 4 and 5. Thyrsites atun collected in demersal 



trawls deeper than 150 m were mostly >65 cm, whereas 

 those from shallower bottom trawls included substantial 

 proportions smaller than this length (Fig. 5A). Juveniles 

 <30 cm, although present in pelagic trawls (Fig. 5B), were 

 notably absent from demersal trawls, including those 

 shallower than 150 m (Fig. 5A). 



Diet 



Snoek prey on a wide variety of demersal and pelagic 

 organisms, including teleosts, crustaceans, and cephalo- 

 pods (Tables 3 and 4) and show ontogenetic shifts. The 

 diet of T atun sampled inshore of the 150-m isobath along 

 the west coast (regions 0-3) consisted predominantly of 

 pelagic fishes, and crustaceans comprised a smaller but 



