Abstract
Four flatfish species were collected between January 2003 and June 2005 from commercial fishing vessels operating with gill nets and bottom trawls along the Portuguese coast in order to examine feeding habits, age and growth and reproduction. Citharus linguatula (Linnaeus, 1758), Lepidorhombus boscii (Risso, 1810) and Microchirus azevia (de Brito Capello, 1867) fed mainly on crustaceans, whereas Platichthys flesus (Linnaeus, 1758) fed mainly on echinoderms and crustaceans. Feeding activity was highest in spring and summer; females and small individuals showed the lowest vacuity index values. For all the species, significant differences were found in the proportion of prey items according to season, sex and size class. M. azevia had the largest diet spectrum. Ages were determined from sagittal otoliths. The von Bertalanffy growth equation coefficients differed between sexes. The asymptotic length L∞ of females was higher than that of males, except in C. linguatula. The lowest growth coefficient was obtained for P. flesus (k=0.11 for males and k=0.10 for females) and M. azevia showed the highest growth coefficient estimates (k=0.40 for females and k=0.30 for males). The highest proportion of individuals at spawning stage was recorded in winter for L. boscii, P. flesus and M. azevia , and in autumn for C. linguatula .
Highlights
A large number of flatfish species occur on the Portuguese coast (e.g. Nielsen, 1986a,b,c,d; Quéro et al, 1986a,b; Cabral, 2000a)
This species richness is usually higher than that found in Northern Europe and similar to that found in the Mediterranean, since many flatfish species are at their southern or northern distribution limits along the Portuguese coast (e.g. Quéro et al, 1986a; Desoutter, 1997)
In the ordination diagram obtained for numerical data it can be seen that C. linguatula was mostly associated with Mysida and fishes
Summary
A large number of flatfish species occur on the Portuguese coast (e.g. Nielsen, 1986a,b,c,d; Quéro et al, 1986a,b; Cabral, 2000a). A large number of flatfish species occur on the Portuguese coast Nielsen, 1986a,b,c,d; Quéro et al, 1986a,b; Cabral, 2000a) This species richness is usually higher than that found in Northern Europe and similar to that found in the Mediterranean, since many flatfish species are at their southern or northern distribution limits along the Portuguese coast (e.g. Quéro et al, 1986a; Desoutter, 1997). The majority of flatfish occurring on the Portuguese coast have a high commercial value and are caught by fisheries as target or by-catch species. Flatfish catches represent 4% of all the fish biomass landed on the Portuguese coast. The importance of flatfish fisheries is considerably higher due to the high commercial value of flatfish species, which account for nearly 11% of the economical value of all landings. Flatfish landings increased from 1998 to 2005 (source: Direcção Gerald as Pescas e Aquicultura [DGPA])
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