Food habits of Bathyraja brachyurops (Chondrichthyes, Rajidae) on the Argentinean continental shelf.

BELLEGGIA MAURO; MABRAGAÑA EZAQUIEL; BARBINI SANTIAGO; FIGUEROA DANIEL E.; DIAZ DE ASTARLOA JM; COUSSEAU BERTA

New Orleans

Congreso; Joint Meeting of Ichthyologists and Herpetologists; 2006

American Society of Ichthyologist and Herpertologists

The broad nose skate, Bathyraja brachyurops, inhabits southern South America  waters. Food habits of this species were studied based on analysis of stomach contents of specimens collected from research cruises carried out by Instituto Nacional de Investigación y Desarrollo Pesquero during 2003-2005 on the Argentinean continental shelf (35º S - 52º  S). Prey items were counted, weighted and identified to the lowest possible taxonomic level. Diet composition was assessed using the Index of Relative Importance expressed as percentage (%IRI). The degrees of dietary overlap between sexes and size classes were compared by Schöener Index (SI), using %IRI. Trophic level (TR) was calculated to determine the position of the broad nose skate within the food web. For this purpose prey items were assigned into five groups. A total of 346 stomachs was examined, of which 265 (76,6%) contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops  fed mostly on fish (84.42%) and crabs (8.09%) and to a lesser extent on isopods (4.89%) and squids (2.23%) suggesting that the broad nose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.82) was found, although females showed higher %IRI of fish prey than males. However,  size classes variation in diet was observed. Smaller skates consumed both fish (57.07%) and invertebrates (22.45% isopods and 17.74% crabs), whereas larger individuals fed almost exclusively on fish (91.21%). Dietary changes with the size of the predator were reported for several ichthyophagous skate species. These results presented are part of an ongoing study about ecology, biology and biodiversity of Bathyraja species on the Argentinean continental shelf.