Diets of thornback ray (Raja clavata) and tope shark (Galeorhinus galeus) in the bottom longline fishery of the Azores, northeastern Atlantic
Tope shark (Galeorhinus galeus) and thornback ray (Rajaclavata) are the two most captured elasmobranch species by the Azorean bottom longline fishery. In order to better understand the trophic dynamics 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 feeding 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 moreheavily upon fish compared with the predation patterns described in other areas. Differences in the diet may bedue to differences in the environments (e.g. in the Azores, seamounts and oceanic islands are the major topographicfeatures, whereas in all other studies, continental shelves have been the major topographic feature). No differenceswere 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 werefound 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 illustrates that thornback rays and tope sharks are top predators in waters off the Azores.
| Main Authors: | , , , |
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| Format: | article biblioteca |
| Language: | English |
| Published: |
2003
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| Subjects: | Biology, Ecology, Fisheries, |
| Online Access: | http://hdl.handle.net/1834/31002 |
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| Summary: | Tope shark (Galeorhinus galeus) and thornback ray (Rajaclavata) are the two most captured elasmobranch species by the Azorean bottom longline fishery. In order to better understand the trophic dynamics 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 feeding 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 moreheavily upon fish compared with the predation patterns described in other areas. Differences in the diet may bedue to differences in the environments (e.g. in the Azores, seamounts and oceanic islands are the major topographicfeatures, whereas in all other studies, continental shelves have been the major topographic feature). No differenceswere 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 werefound 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 illustrates that thornback rays and tope sharks are top predators in waters off the Azores. |
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