590 



Abstract— Tope shark iGaleorhi- 

 nus galeus) and thornback ray {Raja 

 clavata) are the two most captured 

 elasmobranch species by the Azorean 

 bottom longline fishery. In order to 

 better understand the trophic dynam- 

 ics of these species in the Azores, the 

 diets of thornback ray and tope shark 

 caught in this area during 1996 and 

 1997 were analyzed to describe feed- 

 ing patterns and to investigate the 

 effect of sex, size, and depth and area 

 of capture on diet. Thornback rays fed 

 mainly upon fishes and reptants, but 

 also upon polychaetes, mysids, natant 

 crustaceans, isopods, and cephalopods. 

 In the Azores, this species preyed more 

 heavily upon fish compared with the 

 predation patterns described in other 

 areas. Differences in the diet may be 

 due to differences in the environments 

 (e.g. in the Azores, seamounts and oce- 

 anic islands are the major topographic 

 features, whereas in all other studies, 

 continental shelves have been the 

 major topographic feature). No differ- 

 ences were observed in the major prey 

 consumed between the sexes or between 

 size classes (49-60, 61-70, 71-80, and 

 81-93 cm TL). Our study indicates that 

 rays inhabiting different depths and 

 areas (coastal or offshore banks) prey 

 upon different resources. This appears 

 to be related to the relative abundance 

 of prey with habitat. Tope sharks were 

 found to prey almost exclusively upon 

 teleost fish: small shoaling fish, mainly 

 boarfish (Capros aper) and snipefish 

 {Macroramphosus scolopax), were the 

 most frequent prey. This study illus- 

 trates that thornback rays and tope 

 sharks are top predators in waters off 

 the Azores. 



Diets of thornback ray {Raja clavata) and tope shark 

 iGaleorhinus galeus) in the bottom longline fishery 

 of the Azores, northeastern Atlantic 



Telmo Morato 



Encarnacion Sola 



Maria P. Gros 



Gui Menezes 



Departamento de Oceanografia e Pescas 

 Universidade dos A(;ores 

 PT-9901-862 Horta, Portugal 

 E-mail address: telmo@noles horta uac pt 



Manuscript approved for publication 

 19 February 2003 by Scientific Editor 



Manuscript received 4 April 2003 at 

 NMFS Scientific Publications Office. 



Fish. Bull. 101:590-602 (2003). 



The thornback ray {Raja clavata L.), is 

 a shallow water bottom-living elasmo- 

 branch found in the Atlantic from Ice- 

 land and Norway southwards to South 

 Africa, including Madeira and Azores 

 islands. This species is also found in the 

 Mediterranean, western Black Sea, and 

 southwestern Indian Ocean (Stehmann 

 and Burkel, 1984). The thornback ray 

 is commercially exploited in several 

 countries. In the Azores it is a bycatch 

 of the bottom longline fishery directed 

 toward demersal and deepwater teleost 

 species. Food and feeding habits of the 

 thornback ray have been intensively 

 studied since the end of the 19'^^ century 

 (e.g. Day, 1880-84) and more recently 

 (e.g. Smale and Cowley, 1992; Ellis et 

 al., 1996; Daan et al.'l. However, only 

 two studies have been conducted on 

 the thornback ray off Portuguese conti- 

 nental waters (Marques and Re, 1978; 

 Cunha et al., 1986), and none exists for 

 populations inhabiting waters around 

 the oceanic islands or seamounts in the 

 northeastern Atlantic. 



The tope shark {Galeorhinus galeus 

 (L.)), is a cosmopolitan species that 

 can be found from about 70°N to about 

 55"S. Distribution of this species in- 

 cludes the Atlantic, Pacific and Indian 

 Oceans (Compagno, 1984). Tope shark 

 is also commercially exploited by sev- 

 eral countries around the world, includ- 

 ing the Azores, where it is a bycatch of 

 the bottom longline fishery. Clompagno 

 (1984) and Olsen (1984) reviewed the 

 biology of this shark; however, there 

 have been relatively few studies on 

 their feeding habits. The diet of tope 

 shark was described by Ford (1921) for 



individuals landed at Plymouth U.K., by 

 Olsen ( 1954 ) in southeastern Australia, 

 and by Ellis et al. (1996) in the north- 

 eastern Atlantic Ocean. 



Elasmobranchs are among the top 

 predators in marine environments ( Ellis 

 et al., 1996); thus they affect the popu- 

 lations of both fish and invertebrates 

 at lower trophic levels. However, feed- 

 ing studies of elasmobranches in the 

 Azores have been limited to the blue 

 shark (Prionace glaiica) (Clarke et al., 

 1996). Tope shark and thornback ray 

 are the two most abundant elasmo- 

 branch species landed by the Azorean 

 bottom longline fishery. Information on 

 the feeding habits of these two species 

 contributes to a better understanding 

 of trophic dynamics and food webs — in- 

 formation which is needed as fisheries 

 scientists advance ecosystem principles 

 to fisheries management (Pauly et al., 

 2000; Pitcher, 2000; Whipple et al., 

 2000). The purpose of this study was 

 to examine the diet of thornback ray 

 and tope shark, to describe their feed- 

 ing patterns and the effect of sex, size, 

 depth, and location on their diet. 



Materials and methods 



Thornback rays and tope sharks were 

 collected between March and May 

 (spring) of 1996 and 1997 during a 



' Daan, N., B. Johnson, J. R. Larsen and 

 H. Sparholt. 1993. Analysis of the ray 

 [Raja spec.) samples collected during the 

 1991 international stomach sampling 

 project. ICESC.M. 1993/0:15,17 p. 



