598 



Fishery Bulletin 101(3) 



medium-size class of South Wales (35-45 cm TL ). Cluster 

 group III grouped small rays from several geographic re- 

 gions, from South Africa (which also includes some large 

 individuals) to NE Atlantic. Estimates of trophic levels 

 were 3.46 (±0.84 SD) for the rays of the cluster group II 

 (i,e, medium and large), and 3.35 (±0.21 SD) for the rays 

 composing cluster group III (i.e. small ). The estimated tro- 

 phic levels for the three cluster groups were significantly 

 different (P<0.001). 



Tope shark 



The diet of tope shark consisted almost exclusively offish 

 (%IRI=99.95), along with a few crustaceans (%IRI=0.03) 

 and ccphalopods 17r IR1=0.02) (Fig. 3B). Recognizable 

 prey from 14 different taxa were identified (Table 5). 

 The boarfish (C. aper) was the most important prey item 

 (%IRI=93.2), accounting for 65.0% of food by number (%N), 

 25.6% by weight (%W), and occurred in 38.6% of stomachs 



that contained food (%0). The second most important prey 

 item was the snipefish (M. scolopax (%IRI=3.01), which 

 represented 11.2% of food by number and 2.7% by weight. 

 Some commercially important fish species were also found 

 in the stomachs of tope shark; sparids ('7,IRI=4.5, which 

 included Pagellus acarne, P. bogaraveo. and Pagrus pagrus), 

 the chub mackerel iS. japonicus |%IRI=0.9| ), and the blue 

 jack mackerel (T picturatus [%IRI=0.61l. These species 

 were more important by weight than by number or occur- 

 rence. The stomachs of tope sharks also contained 493 pairs 

 of eye lens and fish that were heavily digested, as well as 

 unidentifiable otoliths. 



Discussion 



In general, the percentage of empty stomachs for thornback 

 rays and tope sharks was relatively high compared to the 

 percentage from literature reports. The percentage of empty 



