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- Title
Evidence for temporal changes in ray and skate populations in the Portuguese coast (1998?2003) ? its implications in the ecosystem.
- Authors
Ivone Figueiredo; Teresa Moura; Pedro Bordalo-Machado; Ana Neves; Cristina Rosa; Leonel Serrano Gordo
- Abstract
In mainland Portugal, rays constitute an important by-catch of multi-gear shelf fisheries. However and despite their economical importance, landing information discriminated by species is scarce. The relative stability in Portuguese annual landings of rays and skates can be misinterpreted as no evidence for species declines. The present concern on the overexploitation of individual species arises from both theoretical considerations about biological and ecological traits and for historical reasons. This work constitutes an approach for a retrospective analysis of ray landings in mainland Portugal. Data from research surveys carried along the Portuguese coast was used to infer possible changes in species composition on Portuguese landings. Clusters were determined based on data collected during surveys from species composition for three time-periods, 1989-1991, 1995-1997 and 2001-2003. The relative importance of the associate species within clusters was the input data to define discriminating rules posteriorly used to assign clusters to landings from each commercial vessel. The results show an increase of species relative importance and changes on species abundance: Raja brachyura and Raja clavata decreased, whilst Leucoraja naevus, increased. Furthermore, it was observed a decrease on the mean weight of the two first species and a relative stability in the last one. Such results reflect the importance of specieslife-history characteristics in particular, on the response to fishing impact. Au Portugal, les raies constitutent d''importantes prises accessoires des p?cheries multi-m?tiers. Cependant, et en d?pit de leur importance ?conomique, les informations sur leur d?barquement, distingu? par esp?ce, sont rares. La relative stabilit? d''une ann?e ? l''autre des d?barquements portugais de raies peut ?tre mal interpr?t?e car il n''y a pas d?vidence de d?clin des esp?ces. L''int?r?t actuel port? ? la surexploitation des esp?ces prises individuellement vient de consid?rations th?oriques ? propos de caract?ristiques biologiques et ?cologiques, et pour des raisons historiques. Ce travail constitue une approche d''une analyse r?trospective des d?barquements de raies au Portugal. Des donn?es de campagnes de p?che ont ?t? utilis?es pour en d?duire des changements ?ventuels dans la composition des esp?ces dans les d?barquements commerciaux portugais. Des groupes ont ?t? d?termin?s, bas?s sur des donn?es de composition des captures de 3 p?riodes de campagnes de p?che, 1989-1991, 1995-1997 et 2001-2003. L''importance relative des esp?ces associ?es, ? l''int?rieur de chaque groupe, a servi de donn?es d''entr?e pour d?finir des r?gles permettant de distinguer ces groupes ult?rieurement, dans les d?barquements de chaque chalutier de la p?che commerciale. Les r?sultats montrent une diminution d''esp?ces importantes commercialement telles que Raja brachyura et Raja clavata, tandis que les d?barquements de Leucoraja naevus augmentent. De plus, il a ?t? observ? une diminution du poids moyen des deux premi?res esp?ces, mais celui de L. naevus est stable. De tels r?sultats refl?tent l''importance des caract?ristiques biologiques, mettant en ?vidence une sensibilit? diff?rente ? l''impact de la p?che de chacune des esp?ces de raies.
- Subjects
PORTUGAL; SKATES (Fishes); RAYS (Fishes); RAJIFORMES
- Publication
Aquatic Living Resources, 2007, Vol 20, Issue 1, p85
- ISSN
0990-7440
- Publication type
Article
- DOI
10.1051/alr:2007019