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

Diet composition and feeding habits of the eyespot skate, Atlantoraja cyclophora (Elasmobranchii: Arhynchobatidae), off Uruguay and northern Argentina

ABSTRACT The eyespot skate, Atlantoraja cyclophora, is an endemic species from the southwestern Atlantic, occurring from Rio de Janeiro, Brazil, to northern Patagonia, Argentina. The feeding habits of this species, from off Uruguay and north Argentina, were evaluated using a multiple hypothesis modelling approach. In general, the diet was composed mainly of decapod crustaceans, followed by teleost fishes. Molluscs, mysidaceans, amphipods, isopods, lancelets and elasmobranchs were consumed in lower proportion. The consumption of shrimps drecreased with increasing body size of A. cyclophora. On the other hand, the consumption of teleosts increased with body size. Mature individuals preyed more heavily on crabs than immature individuals. Teleosts were consumed more in the south region (34º - 38ºS) and crabs in the north region (38º - 41ºS). Shrimps were eaten more in the warm season than in the cold season. Prey size increased with increasing body size of A. cyclophora , but large individuals also consumed small teleosts and crabs. Atlantoraja cyclophora has demersal-benthic feeding habits, shifts its diet with increasing body size and in response to seasonal and regional changes in prey availability and distribution

Estimating the geographic range of a threatened shark in a data-poor region: Cetorhinus maximus in the South Atlantic Ocean

The distribution of the planktivorous basking shark Cetorhinus maximus is influenced by zooplankton abundance at small scales and temperature at medium scales in the North Atlantic. Here, we estimate the distribution of basking sharks on South Atlantic continental shelves, and the relative importance of chlorophyll concentration, as a proxy for zooplankton abundance, and temperature in determining habitat suitability for basking sharks at large scales. We used maximum entropy (MaxEnt) and maximum likelihood (MaxLike) species distribution modelling to test three hypotheses: the distribution of basking sharks is determined by (1) temperature, (2) chlorophyll concentration, or (3) both chlorophyll and temperature, while considering other factors, such as oxygen and salinity. Off South America, basking shark habitat included subtropical, temperate and cool-temperate waters between approximately 20°S and 55°S. Off Africa, basking shark habitat was limited to cool-temperate waters off Namibia and southern South Africa. MaxLike models had a better fit than MaxEnt models. The best model included minimum chlorophyll concentration, dissolved oxygen concentration, and sea surface temperature range, supporting hypothesis 3. However, of all variables included in the best model, minimum chlorophyll concentration had the highest influence on basking shark distribution. Unlike the North Atlantic distribution, the South Atlantic distribution of basking sharks includes subtropical and cool-temperate waters. This difference is explained by high minimum chlorophyll concentration off southern Brazil as compared to North Atlantic subtropical areas. Observations in other regions of the world support this conclusion. The highest habitat suitability for basking sharks is located close to nearshore areas that experience high anthropogenic impact.Fil: Lucifora, Luis Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; ArgentinaFil: Barbini, Santiago Aldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Di Giacomo, Edgardo Ernesto. Universidad Nacional del Comahue. Instituto de Biología Marina y Pesquera Almirante Storni; ArgentinaFil: Waessle, Juan A.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Figueroa, Daniel Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Blue Hake Antimora rostrata (Gadiformes: Moridae) off the Atlantic Coast of South America: an Overview on Its Distribution and Biology

Long-term data on spatial and bathymetric distributions, preferred bottom temperatures, length and weight of blue hake Antimora rostrata caught off the Atlantic coast of South America are presented based on published and unpublished materials. The species frequently occurred in waters of southern Argentina where catches were considerably higher as compared with Brazilian waters. The blue hake were captured at depths from 97 to 2162 m (average depth 1279 m). Most of the specimens (65.1%) were collected at depths from 700 to 1300 m, similar to depths in other parts of the species’ range. Bottom temperatures at sites of blue hake captures in Brazilian waters were 2.18–4.20°C (average 2.93°C). Specimens in bottom trawl catches were 9–61 cm in total length, averaging 34.84 cm. The bulk of the catches (85.5% of individuals) were fish of 25–45 cm. Body weight ranged from 70 to 1380 g (average 437.5 g). Frequency of occurrence decreased from southern Argentina to northern Brazil; complete absence of records in the Central Western Atlantic might relate to different means by which the blue hake colonized the Pacific and Atlantic coasts of South America.Fil: Orlov, A. M.. Russian Federal Research Institute of Fisheries and Oceanography; Rusia. Tomsk State University; RusiaFil: Sytov, A. M.. Russian Federal Research Institute of Fisheries and Oceanography; RusiaFil: Marí, N.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Figueroa, Daniel Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Barbini, Santiago Aldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Costa, P. A. S.. Universidade Federal do Rio de Janeiro; BrasilFil: Marin, Y. H.. Dirección Nacional de Recursos Acuáticos; UruguayFil: Mincarone, M. M.. Universidade Federal do Rio de Janeiro; Brasi

Decline or stability of obligate freshwater elasmobranchs following high fishing pressure

Despite elasmobranchs are a predominantly marine taxon, several species of sharks and rays are regularly found in fresh water. Although there is ample evidence of declining elasmobranch populations around the world, this evidence comes exclusively from marine and euryhaline species; the ecology and conservation status of obligate freshwater elasmobranchs is far from being understood. River stingrays (Potamotrygoninae, 32 species) live exclusively in South American rivers and represent the overwhelming majority of freshwater elasmobranch diversity. Here, we present evidence of a decline in the abundance of river stingrays in the middle and lower Paraná River, an extensive wetland mosaic of approximately 35,000 km2. By taking advantage of a stingray manipulation procedure widespread among South American fishermen, we were able to estimate spatial differences in relative fishing pressure and found that the observed decline is related to fishing pressure. The highest fishing effort and lowest relative abundance occurred in areas where fisheries operate on the riverfloodplain. The lowest fishing effort and highest relative abundances occurred in areas where fisheries operate in the main channel. The only species with a stable trend was Potamotrygon motoro. This evidence confirms the long-presumed vulnerability of obligate freshwater elasmobranchs and suggests that some species, e.g. P. motoro, can be exploited sustainably. Our results also indicate that negative effects on freshwater elasmobranchs can be minimized by adjusting fishing grounds.Fil: Lucifora, Luis Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; ArgentinaFil: Balboni, Leandro. Ministerio de Agricultura, Ganaderia, Pesca y Alimento; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Scarabotti, Pablo Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Alonso, Francisco A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Sabadin, David Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Solari, Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; ArgentinaFil: Vargas, Facundo. Dirección de Fauna y Áreas Naturales Protegidas; ArgentinaFil: Barbini, Santiago Aldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Mabragaña, Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Feeding habits of a large endangered skate from the south-west Atlantic: the spotback skate, Atlantoraja castelnaui

Elasmobranch predation has important effects on marine ecosystems. Identifying the main correlates of the feeding habits of skates is of paramount importance for determining their ecological role. We tested the hypotheses that the diet of the spotback skate, Atlantoraja castelnaui, off Uruguay and northern Argentina, changes with increasing body size, between seasons and regions and that prey size increased with predator's size using a multiple-hypothesis modelling approach. A. castelnaui preyed mainly on teleosts, followed by cephalopods, elasmobranchs and decapods. Small individuals of A. castelnaui consumed decapods and large individuals ate elasmobranchs and cephalopods. The consumption of teleosts was constant along the ontogeny but differed between seasons; more demersal-benthic teleosts were consumed in the cold season, whereas more benthic teleosts were eaten in the warm season. Also, A. castelnaui consumed more cephalopods in the warm season than in the cold season. Benthic teleosts were consumed more in the south region, whereas decapods were eaten more in the north region. A. castelnaui is able to consume larger teleosts as it grows. We conclude that A. castelnaui is a versatile, mainly piscivorous, consumer that shifts its diet with increasing body size and in response to seasonal and regional changes in prey abundance or distribution.Fil: Barbini, Santiago Aldo. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lucifora, Luis Omar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Misiones; Argentin