Megalofonou et al.: Incidental catch and estimated discards of pelagic sharks in the Mediterranean Sea 633 



Table 1 1 



Comparison of shark catch rates (CPUE in number offish/1000 hooks) in longline fisheries during investigations in the Mediter- 

 ranean Sea and the Atlantic Ocean. SWO-LL= swordfish longline; Tuna-LL=tuna longline gear. 



Author 



De Metrio et al. (1984)' 

 Filantietal.(1986l 

 DeZioetal. (2000) 

 DiNatale(1998) 

 Buencuerpo et al. ( 1998 1 

 Present study 

 Present study 

 Present study 

 Present study 

 Buencuerpo et al. ( 1998 ) 

 Stone and Dixon (2001) 

 Hazinetal. (1998) 



Area 



Period 



Ionian Sea 



Ionian Sea 



Adriatic Sea 



Tyrrhenian Sea, Strait of Sicily 



Gibraltar Strait 



Ionian Sea 



Adriatic Sea 



Strait of Sicily 



Alboran Sea 



E. Atlantic 



NW Atlantic 



W. Atlantic 



1984 



1978-85 



1984-98 



1991-92 



1991-92 



1998-99 



1998-99 



1998-99 



1998-99 



1991-92 



1999 



1983-97 



t ;<\u 



SWO-LL 

 SWO-LL 

 SWO-LL 

 SWO-LL 

 SWO-LL 

 SWO-LL 

 SWO-LL 

 SWO-LL 

 SWO-LL 

 SWO-LL 

 SWO-LL 

 Tuna-LL 



CPUE 



0.9-2.2 



1.5-3.0 



2.4 



0.4 



24.2 



0.5 



1.0 



0.2 



3.8 



9.9-37.J 



43.8 



16.8 



Blue shark catch rates only. 



fin makos may be one of the most over-fished pelagic 

 sharks in the Mediterranean Sea. 



Our low catch rates for common thresher shark in the 

 Mediterranean were almost identical with the findings 

 of Buencuerpo et al. (1998) for the Gibraltar Strait re- 

 gion. However, the abundance of this species supports 

 directed fisheries in some areas. Such a case occurred 

 off California waters during 1977-85, when thresher 

 shark CPUE in the driftnet fishery ranged from 0.13 to 

 1.92 fish/fishing set (Holts et al., 1998). In our study, 

 one third of the specimens caught came from the Io- 

 nian driftnet fishery but the largest individual was 

 captured in the Levantine basin (514 cm TL) with the 

 swordfish longline. Pacific females mature at 315 cm 

 TL (Strasburg, 1958) and males mature at about 333 

 cm TL (Cailliet and Bedford, 1983), and we calculated 

 that 40% of the female common thresher sharks caught 

 were below 315 cm and 50% of the males were below 

 333 cm. Although the above data indicate that most 

 were caught as immature sharks, there are no data on 

 the first maturity of common thresher sharks in the 

 Mediterranean Sea. There is doubt, however, that fe- 

 males mature at a smaller size than males in the same 

 region and we therefore deduced that fishing pressure 

 was very intense on juvenile and subadult groups. 



The low capture numbers for other shark species could 

 be due either to the scarcity of these species in the Medi- 

 terranean Sea or to the "fished-down" condition of shark 

 populations, or both could be causes. Another reason 

 could be the low capture efficiency of the gears used. 



The high proportion of sharks that were alive on cap- 

 ture agrees with Kotas et al. 2 , who reported that 97% 

 of blue sharks and 78% of shortfin makos were alive 

 when landed on deck. These high survival rates are en- 

 couraging and could become the basis for conservation 

 measures in the future, such as releasing immature fish 

 or enforcing catch quotas. 



Our study provides a reference point for the present 

 status of pelagic sharks in the Mediterranean Sea, the 

 effect of fisheries on them, and a baseline for future 

 monitoring. Fishing for swordfish and tunas affects 

 much of the pelagic ecosystem by taking predators of 

 swordfish and tunas (large pelagic sharks), their prey 

 (small tunas), and their competitors, such as other elas- 

 mobranchs, billfishes, and tunas. Up to now, there has 

 been little documentation and understanding of fishing 

 effects on the wider ecosystem. To strengthen manage- 

 ment for large pelagic fishes such as sharks, a multi- 

 species assessment with an ecosystem approach should 

 be adopted. To achieve this goal, long-term monitoring 

 programs should be established and exploitation strat- 

 egies should be linked to conservation plans for shark 

 species in the Mediterranean Sea. 



Acknowledgments 



We thank the Greek, Italian, and Spanish fishermen 

 who collaborated during sampling procedures. We thank 

 also the two anonymous reviewers who improved the 

 manuscript with their valuable suggestions. This study 

 was performed under the financial aid of the Commis- 

 sion of the European Communities (Project no. 97/50 

 DG XIV) and does not necessarily reflect the views of 

 the European Commission and in no way anticipates the 

 Commission's future policy in this area. 



Literature cited 



Amorim de, A. F., C. A. Arfelli, and L. Fagundes. 



1998. Pelagic elasmobranchs caught by longliners off 

 southern Brazil during 1974-97: an overview. Mar. 

 Freshw. Res. 49(71:621-632. 



