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As a general rule, sharks and rays play an important role in the energy exchanges among higher trophic levels of the marine food chain and some of them, with an important impact as piscivorous predators. Squalus acanthias (Squalidae) and Raja flavirostris (=Dipturus chilensis )(Rajidae), are two elasmobranchs with high apparition frequencies in the SW Atlantic, in the coastal and demersal fishing trawls, co-existing and predating on the principal stocks of bony fish there located, especially the Argentine hake (Merluccius hubbsi). Both species could be transformed into alternative fishing resources, even though they are not currently commercially developed as such. The knowledge on their biology, given in great detail, will provide information for a better conservation and management, since their own elasmobranch characteristics (slow growth, late first maturity and reduced number of pups of great size), make them highly vulnerable to intensive fisheries. Information was taken from 19 research cruises, held by the R/Vs of the National Institute of Fisheries Research and Development (INIDEP, Mar del Plata, Argentina) during 1985 and 1998 in the area between 34°and 56°S. The geographical and seasonal distribution by size of S.acanthias and R.flavirostris is analyzed during an annual cycle, in relation with the environmental factors. Comments on its reproductive characteristics and a synthesis on the evolution of their fisheries in the Argentine Sea are made.Trophic spectrum, interspecific trophic relationships and predation on Argentine hake are studied considering three zones, 1) Argentine-Uruguyan Common Fishing Area including southern Buenos Aires (34°-41°S); 2) northern Patagonia (41°-48°S); and 3) southern Patagonia (48°-56°S). All these topics are developed in five chapters: I, Geographical distribution, abundance and size structure of the spiny dogfish S.acanthias (Squalidae); II, Feeding ecology of S.acanthias ; III, Geographical distribution, abundance and size structure of the ray R.flavirostris (Dipturus chilensis ) (Rajidae); IV, Feeding ecologyof R.flavirostris (Dipturus chilensis ); and V, Comparison of the diet of S.acanthias and R.flavirostris (Dipturus chilensis ) with otherpiscivorous predators.
Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales.
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