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.

Osteichthyan and chondrichthyan fish present an astonishing diversity of skeletal and dental tissues that are often difficult to classify into the standard textbook categories of bone, cartilage, dentine and enamel. To address the question of how the tissues of the dermal skeleton evolved from the ancestral situation and gave rise to the diversity actually encountered, we review previous data on the development of a number of dermal skeletal elements (odontodes, teeth and dermal denticles, cranial dermal bones, postcranial dermal plates and scutes, elasmoid and ganoid scales, and fin rays). A comparison of developmental stages at the tissue level usually allows us to identify skeletogenic cell populations as either odontogenic or osteogenic on the basis of the place of formation of their dermal papillae and of the way of deposition of their tissues. Our studies support the evolutionary affinities (1) between odontodes, teeth and denticles, (2) between the ganoid scales of polypterids and the elasmoid scales of teleosts, and (3) to a lesser degree between the different bony elements. There is now ample evidence to ascertain that the tissues of the elasmoid scale are derived from dental and not from bony tissues. This review demonstrates the advantage that can be taken from developmental studies, at the tissue level, to infer evolutionary relationships within the dermal skeleton in chondrichthyans and osteichthyans.