Hábitos alimentarios de la raya de cola corta, Bathyraja brachyurops (Chondrichthyes, Rajidae), en el Atlántico Sudoccidental

Food habits of Bathyraja brachyurops were studied based on stomach content analyses of 346 specimens collected from research cruises carried out from 2003 to 2005 on the Argentinean continental shelf (36ºS-55ºS). A total of 265 stomachs (76.6%) contained food, and thirty-five taxonomic levels of prey were identified. The most important prey were fishes followed by isopods. Trophic level analysis revealed that B. brachyurops is a tertiary consumer throughout its life history. There were no differences between sexes and regions in the diet composition, but dietary shifts with ontogeny were found. The Levins’ standardized index indicated wider niche breadth for small skates, whereas larger skate specimens showed a narrow niche breadth with a specialization in fishes.Se estudiaron los hábitos alimentarios de Bathyraja brachyurops en base al análisis de los contenidos estomacales de 346 ejemplares capturados en campañas de investigación realizadas durante el periodo 2003-2005 sobre la plataforma continental Argentina (36ºS-55ºS). Un total de 265 estómagos (76.6%) contenían alimento en los cuales se identificaron treinta y cinco ítems presa. Las presas más importantes fueron los peces, seguidos por los isópodos, ubicando a B. brachyurops como un consumidor terciario a lo largo de toda su historia de vida. No se hallaron diferencias en la composición de la dieta entre sexos y regiones, sin embargo se apreciaron cambios ontogenéticos en la alimentación. El índice de Levins’ estandarizado indicó una mayor amplitud de nicho para las rayas de menor tamaño, mientras que los ejemplares de mayor tamaño mostraron una menor amplitud de nicho trófico y una especialización ictiófaga

Reproductive biology of the cockfish, Callorhinchus callorynchus (Chondrichthyes: Callorhinchidae), in coastal waters of the northern Argentinean Sea

ABSTRACT The cockfish, Callorhinchus callorynchus, is a widely distributed holocephalan in the south-western Atlantic and an important resource for Argentinean fisheries. The reproductive characteristics of this species were studied in northern Argentinean coastal waters, where specimens arrive seasonally (winter-spring). Sexual dimorphism in maximum precaudal length (PCL) and total body mass (TM) was found, being females (PCL=630 mm; TM=3330 g; n=167) larger and heavier than males (PCL=482 mm; TM=1630 g; n=19). Maturity size for females was 466.22 mm PCL, representing 74% PCL of the largest female sampled. The mean number of ovarian follicles was 8.37 (± 4.84). The highest values of ovarian follicles diameter, gonadosomatic and oviducalsomatic indices were found in spring. A high proportion of mature females (44%) had atretic ovarian follicles, suggesting that they were in the resting stage of their reproductive cycle. The low number of mature males recorded and the absence of mature females with spermatophore masses or egg cases indicate that the study area would not be a reproductive zone. The seasonal presence of C. callorynchus in this region could be related to trophic movements. These results, obtained in an area with high fishing pressure on chondrichthyans, will be useful for implementing conservation and management measures