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Evidence for temporal changes in ray and skate populationsin the Portuguese coast (1998–2003) – its implicationsin the ecosystem

Published online by Cambridge University Press:  17 May 2007

Ivone Figueiredo ,
Teresa Moura ,
Pedro Bordalo-Machado ,
Ana Neves ,
Cristina Rosa  and
Leonel Serrano Gordo
Ivone Figueiredo
Affiliation:
Departamento de Recursos Marinhos, IPIMAR, Av. Brasília, 1449-006 Lisboa, Portugal
Teresa Moura
Affiliation:
Departamento de Recursos Marinhos, IPIMAR, Av. Brasília, 1449-006 Lisboa, Portugal
Pedro Bordalo-Machado
Affiliation:
Departamento de Recursos Marinhos, IPIMAR, Av. Brasília, 1449-006 Lisboa, Portugal
Ana Neves
Affiliation:
Departamento de Biologia Animal and Instituto de Oceanografia, Faculdade de Ciências de Lisboa, Bloco C2, Campo Grande, 1749–016 Lisboa, Portugal
Cristina Rosa
Affiliation:
Direcção-Geral das Pescas e Aquicultura, Av. Brasília, 1499-030 Lisboa, Portugal
Leonel Serrano Gordo
Affiliation:
Departamento de Biologia Animal and Instituto de Oceanografia, Faculdade de Ciências de Lisboa, Bloco C2, Campo Grande, 1749–016 Lisboa, Portugal
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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.

Keywords

Chondrichthyan fishRaja spp.Associate speciesCommercial landingsSurveysCluster predictionSpecies compositionTemporal changes
Type
Research Article
Information
Aquatic Living Resources , Volume 20 , Issue 1: New developments in coastal environment research: results from the national coastal environment program , January 2007 , pp. 85 - 93
Copyright
© EDP Sciences, IFREMER, IRD, 2007

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