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

BELLEGIA, M.; MABRAGAÑA, E.; SCENNA, L. B; BARBINI, S. A.; FIGUEROA, D. E.; DÍAZ DE ASTARLOA, J. M.; COUSSEAU, M. B.

New Orleans (USA)

Congreso; 2006 Joint meeting of the American Society of Ichthyologists and Herpetologists; 2006

The broadnose 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 Argentinenan continental shelf (35°S−52°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 broadnose skate within the food web. For this purpose prey items were assigned into five groups. A total of 265 stomachs was examined, of which 75,5% contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops fed mostly on fish (75.4%) and crabs (14.7%) and to a lesser extent on isopods (8.2%) and squids (0.97%) suggesting that the broadnose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.71) 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 (46.2%) and invertebrates (28.8% isopods and 23.6% crabs), whereas larger individuals fed almost exclusively on fish (86%). 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 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 broadnose skate within the food web. For this purpose prey items were assigned into five groups. A total of 265 stomachs was examined, of which 75,5% contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops fed mostly on fish (75.4%) and crabs (14.7%) and to a lesser extent on isopods (8.2%) and squids (0.97%) suggesting that the broadnose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.71) 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 (46.2%) and invertebrates (28.8% isopods and 23.6% crabs), whereas larger individuals fed almost exclusively on fish (86%). 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 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 Argentinenan continental shelf (35°S−52°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 broadnose skate within the food web. For this purpose prey items were assigned into five groups. A total of 265 stomachs was examined, of which 75,5% contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops fed mostly on fish (75.4%) and crabs (14.7%) and to a lesser extent on isopods (8.2%) and squids (0.97%) suggesting that the broadnose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.71) 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 (46.2%) and invertebrates (28.8% isopods and 23.6% crabs), whereas larger individuals fed almost exclusively on fish (86%). 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 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 broadnose skate within the food web. For this purpose prey items were assigned into five groups. A total of 265 stomachs was examined, of which 75,5% contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops fed mostly on fish (75.4%) and crabs (14.7%) and to a lesser extent on isopods (8.2%) and squids (0.97%) suggesting that the broadnose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.71) 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 (46.2%) and invertebrates (28.8% isopods and 23.6% crabs), whereas larger individuals fed almost exclusively on fish (86%). 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 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 Argentinenan continental shelf (35°S−52°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 broadnose skate within the food web. For this purpose prey items were assigned into five groups. A total of 265 stomachs was examined, of which 75,5% contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops fed mostly on fish (75.4%) and crabs (14.7%) and to a lesser extent on isopods (8.2%) and squids (0.97%) suggesting that the broadnose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.71) 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 (46.2%) and invertebrates (28.8% isopods and 23.6% crabs), whereas larger individuals fed almost exclusively on fish (86%). 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 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 broadnose skate within the food web. For this purpose prey items were assigned into five groups. A total of 265 stomachs was examined, of which 75,5% contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops fed mostly on fish (75.4%) and crabs (14.7%) and to a lesser extent on isopods (8.2%) and squids (0.97%) suggesting that the broadnose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.71) 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 (46.2%) and invertebrates (28.8% isopods and 23.6% crabs), whereas larger individuals fed almost exclusively on fish (86%). 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 −52°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 broadnose skate within the food web. For this purpose prey items were assigned into five groups. A total of 265 stomachs was examined, of which 75,5% contained food. Twenty-nine prey taxa were identified in the stomach contents. B. brachyurops fed mostly on fish (75.4%) and crabs (14.7%) and to a lesser extent on isopods (8.2%) and squids (0.97%) suggesting that the broadnose skate is a tertiary consumer (Trophic level = 4.04). A high degree of dietary overlap between sexes (SI= 0.71) 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 (46.2%) and invertebrates (28.8% isopods and 23.6% crabs), whereas larger individuals fed almost exclusively on fish (86%). 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.species on the Argentinean continental shelf.