Fisheries Research 81 (2006) 293–305 Differentiation of commercially important flatfish populations along the Portuguese coast: Evidence from morphology and parasitology Joana F. Marques a , C´ elia M. Teixeira a,b , Henrique N. Cabral a,c,* a Universidade de Lisboa, Faculdade de Ciˆ encias, Instituto de Oceanografia, Campo Grande, 1749-016 Lisboa, Portugal b Instituto Piaget, Unidade de Investiga¸ c˜ ao e Forma¸ c˜ ao em Ecologia Aplicada, Quinta da Arreinela de Cima, 2800-305 Almada, Portugal c Universidade de Lisboa, Faculdade de Ciˆ encias, Departamento de Biologia Animal, Campo Grande, 1749-016 Lisboa, Portugal Received 14 December 2005; received in revised form 2 May 2006; accepted 5 May 2006 Abstract The population differentiation of seven flatfish species, Citharus linguatula, Lepidorhombus boscii, Platichthys flesus, Microchirus azevia, Solea lascaris, Solea senegalensis and Solea solea, widely distributed along the eastern north Atlantic and occurring in sympatry along the Portuguese coast was studied using morphological and parasitological data. Fish were obtained from commercial fishing vessels operating in three locations along the Portuguese coast (north, centre and south) between January 2003 and June 2005. Eleven morphometric and seven meristic characters were considered in morphological analyses. Size effect was removed from morphometric measurements by principal component analysis and a multivariate discriminant analysis was performed to investigate the differences between populations using both morphometric and meristic data, separately. Individuals were examined for macroparasites infections according to standard procedures, and a multivariate discriminant analysis was also applied to investigate population differences. Analyses of both types of data (morphological and parasitological) revealed a similar pattern of a generally low differentiation evidenced by the high overlap of individuals in the ordination diagrams. However, some differentiation was found between samples from the west (north and centre) and the south Portuguese coast evidencing the existence of an ecological differentiation along the Portuguese coast. Broad scale population studies should, therefore, take into account the information provided by such data, especially with regard to fisheries’ management policies and stock definition. © 2006 Elsevier B.V. All rights reserved. Keywords: Flatfish; Portuguese coast; Population structure; Morphology; Parasites 1. Introduction Along the Portuguese coast, flatfish are a commercially important resource. During the last decade, the soles Solea lascaris (Risso, 1810), Solea senegalensis (Kaup, 1858), and Solea solea (Linnaeus, 1758) have been the most landed species of flatfish along the western coast of Portugal (more than 150 t year -1 ), whereas the bastard sole, Microchirus azevia (Capello, 1868), has been the most landed in the south coast (more that 100 t year -1 )(DGPA, 2004). The increasing fishing effort exerted upon flatfish species along the Portuguese coast, and the differences in exploitation patterns between coastal areas, demand knowledge of the stock structure and the degree of * Corresponding author. Tel.: +351 217 500 826; fax: +351 217 500 207. E-mail address: hcabral@fc.ul.pt (H.N. Cabral). mixing among populations to adequately manage these impor- tant resources. Despite the recognized small degree of population structure of several flatfish species along the northeast Atlantic (Kotoulas et al., 1995; Borsa et al., 1997; Exadactylus et al., 1998; Hoarau et al., 2004), it is known that, within a relatively small geo- graphic area, topography, oceanographic current patterns and species’ local adaptations to these features, can prevent gene flow to some extent. Located between three important biogeo- graphic areas – the cold temperate Atlantic, the warm temperate Atlantic and the Mediterranean – the Portuguese coast consti- tutes an important transition zone where marine species with boreal, temperate and subtropical affinities occur in sympatry. Due to its geomorphological characteristics, namely a narrow coastal shelf divided by two deep canyons, and different cur- rent patterns, with the Gulf Stream flowing from north to south dominating on the western coast and a flow from west to east 0165-7836/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2006.05.021