Megalofonou et al Incidental catch and estimated discards of pelagic sharks in the Mediterranean Sea 



627 



Common thresher shark, the third most abundant 

 shark reported in eight out of nine areas studied, ac- 

 counted for 0.74% of the total shark catches. Catch rates 

 per fishing gear were higher in the SWO-LL A fishery 

 with a mean CPUE of 0.02 fish/1000 hooks and per area 

 sampled in the Aegean Sea, reaching 0.05 fish/1000 

 hooks (Table 8). 



A total of 48 juvenile and adult common thresher 

 sharks were measured. Length-frequency distribution 

 was discontinuous and not very revealing because of 

 the small number of sharks sampled (Fig. 4). Specimens 

 ranged from 75 to 514 cm TL (mean value of 316.8 cm 

 and SD 86.4 cm). No statistically significant differences 

 were observed (Kruskall-Wallis, test statistic=0.638, 

 P=0.73>0.05) in average size of specimens by fishing 

 gear (Fig. 5). Larger specimens were reported from 

 the Levantine basin area and a smaller one was re- 

 ported from the Balearic Sea (Fig. 6). Out of 27 common 

 thresher shark sexed, 15 were males and 12 females. 

 Sex ratio was 1.25 male:l female. The TL-FL and TL- 

 dressed weight relationships are given below: 



TL = 20. 2 +1.707 FL 

 TL = 69.7 DW° 35i 



[7^ = 0.95, n=24] 

 [^=0.99, n=18]. 



The remaining nine shark species observed accounted 

 for only 0.87% of the total shark catches. In total, 26 

 tope sharks were measured (ranging from 35 to 190 cm), 



15 porbeagles (ranging from 87 to 277 cm), 7 bigeyed 

 thresher sharks (ranging from 146 to 353 cm) and 4 

 smooth hammerheads (ranging from 277 to 300 cm TL). 

 Only three bluntnose sixgill sharks (mean weight of 

 10.7 kg), two sandbar sharks (mean weight of 17 kg), two 

 longnose spurdogs (mean weight of 1.7 kg), two basking 

 sharks, and one smoothhound were reported, but no 

 length measurements were available for these species. 



A total of 571 specimens were examined for life condi- 

 tion on capture. The majority were very active follow- 

 ing capture and their physical condition was especially 

 good. Only 5.1% of the specimens brought onboard were 

 dead (Table 10). 



Discussion 



Our results show that most of the sharks caught by the 

 swordfish and tuna fisheries in the Mediterranean Sea 

 are typically pelagic or coastal-pelagic species of wide- 

 spread distribution in temperate and tropical waters 

 throughout the world. However, some sporadic catches of 

 poorly known, deepwater species of the families Hexan- 

 chidae and Alopiidae were also observed. The most 

 plausible reason for these catches is that the deepwater 

 species ascend close to the surface at night where they 

 may be taken by longlines targeting swordfish (Castro 

 et al., 1999). 



