Tracing the occurrence of the Critically Endangered smalltooth sawfish Pristis pectinata at its southernmost distribution in the Southwest Atlantic Ocean

Sawfishes are the most globally threatened group of sharks, rays, and chimaeras. One of the 5 sawfish species is the Critically Endangered smalltooth sawfish Pristis pectinata. Although it is currently found in only a small portion of its historical range, this species was once distributed along tropical and subtropical coasts on both sides of the Atlantic Ocean. Its historical distribution included the Southwest Atlantic in Brazil and Argentina, with its presence in Uruguay assumed from its occurrence in neighboring countries. However, occurrence records in this region have only been compiled for Brazil. The aim of this study was to characterize the occurrence of P. pectinata in the Argentinean-Uruguayan Common Fishing Zone (AUCFZ). Quantitative sampling data revealed no sawfish specimens during 150 bottom trawl cruises and 8490 hauls (1905 in winter; 1647 in fall; 3141 in spring; 1797 in summer months) in the AUCFZ between 1981 and 2015. Nevertheless, qualitative data based on interviews (N = 275; researchers, fishing companies, fishermen, and recreational anglers) supports the occasional presence of sawfish in the AUCFZ. Five new oral reports were obtained and, although these records lack reference material, they have an associated capture year: 2 records from the 1950s, 1 record from the 1990s, and 2 records from the 2010s. Two of these records are the first for Uruguay and were reported by experienced fishermen. We conclude that the species was always a vagrant to the region, and suggest that the view of P. pectinata as extirpated from Uruguay and northern Argentina should be revisited.Fil: Cuevas, Juan Martín. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados; Argentina. Wildlife Conservation Society; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: García, Mirta Graciela. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Hozbor, Natalia. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Faria, Vicente V.. Universidade Federal Do Ceara; BrasilFil: Paesch, Laura. Dirección Nacional de Recursos Acuáticos; Urugua

Alimentación de juveniles de corvina rubia (Micropogonias furnieri) en la Laguna Costera Mar Chiquita (Buenos Aires, Argentina)

De un total muestreado de 1581 ejemplares de corvina rubia, se examinaron 475 juveniles entre 20-185 mm Ls provenientes de la laguna Mar Chiquita. El muestreo se realizó empleando una red de arrastre playera, considerando tres zonas de distinta salinidad (zonas 1, 11 y 111). Los ejemplares presentaron una distribución unimodal, siendo las tallas más frecuentes aquéllas entre 35-60 mm Ls, con un modo en 45 mm Ls. La dieta está compuesta principalmente por invertebrados bentónicos, constituyendo los poliquetos el ítem alimento principal (67%F). Le siguen en importancia los isópodos y los anfípodos gamáridos, mientras que los cangrejos, ostrácodos, copépodos y decápodos son ocasionales. El espectro trófico de esta especie varía en función de la talla, incorporándose en los individuos de mayor tamaño presas mayores, tales como peces. En la zona 1, donde predominaron las corvinas de menor talla (modo 35 mm Ls), se encontraron como alimento copépodos de agua dulce, ostrácodos y misidáceos. En la zona 11, donde las tallas intermedias (40-60 mm Ls) fueron las más representadas, se incorporaron a la dieta anfípodos gamáridos, cangrejos y restos de peces, mientras que en la zona 111, donde se encontraron las tallas más grandes (20-185 rnm Ls) se observaron anfípodos gamáridos, isópodos y poliquetos. Durante el verano y el otoño, los juveniles de corvina presentaron las mayores densidades anuales, ocupando casi la totalidad de la laguna, mientras que durante el invierno y la primavera el número de ejemplares encontrado fue muy bajo.Fil: Hozbor, Natalia M.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: García de la Rosa, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentin

Feeding habits and habitat selectivity of the shortnose guitarfish, Zapteryx brevirostris (Chondrichthyes, Rhinobatidae), off north Argentina and Uruguay

Dietary shifts with predator’s size, maturity stage and season and bottom type selection of Zapteryx brevirostris were evaluated, using generalized linear models. In terms of index of relative importance, the most important prey were amphipods (39.17%), polychaetes (22.33%) and lancelets (20.33%), followed by decapods (8.93%), cumaceans (5.41%) and isopods (3.41%). Z. brevirostris consumed mainly polychaetes and amphipods in spring and summer, ate more cumaceans in winter, consumed more lancelets in spring, and preyed more heavily on decapods and isopods in summer. As Z. brevirostris increased in size, the consumption of decapods, polychaetes and isopods was higher, but the consumption of amphipods decreased. Mature individuals of Z. brevirostris consumed more lancelets than juveniles. Z. brevirostris selected sand over other bottom types. The diet of Z. brevirostris can be influenced by the selectivity of this species for sandy bottoms. As sandy bottoms are exposed to a high intensity of bottom trawling, the positive selection of sandy bottoms increases the vulnerability of Z. brevirostris by exposing it to fishing mortality.Fil: 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; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Lucifora, Luis Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Posadas; Argentina. Administracion de Parques Nacionales. Parque Nacional "iguazu". Centro de Investigaciones Ecologicas Subtropicales; ArgentinaFil: Hozbor, Natalia M.. Instituto Nacional de Investigación y Desarrollo pesquero; Argentin

Effects of body size, age and maturity stage on diet in a large shark: Ecological and applied implications

Ontogenetic diet shifts are a widespread phenomenon among vertebrates, although their relationships with life history traits are poorly known. We analyzed the relative importance of body size, age and maturity stage as determinants of the diet of a marine top predator, the copper shark, Carcharhinus brachyurus, by examining stomach contents using a multiple-hypothesis modeling approach. Copper sharks shifted their diet as size and age increased and as they became sexually mature, incorporated larger prey as they grew, and had a discrete shift in diet with body size, with only individuals larger than ≈200 cm total length able to prey on chondrichthyans. Body size was the most important trait explaining the consumption of chondrichthyans, while age determined the consumption of pelagic teleosts. Pelagic teleosts were consumed mostly by medium-aged sharks, a result, probably, of a risk-reducing feeding strategy at young ages coupled with either a senescence-related decline in performance or a change in sensory capabilities as sharks age. Copper sharks of all sizes were able to cut prey in pieces, implying that gape limitation (i.e., the impossibility of eating prey larger than a predator's mouth) did not play a role in producing the diet shift. Our results suggest that, contrary to the current practice of setting minimum but not maximum size limits in catches, any plan to conserve or restore the ecological function of sharks, through their predatory control of large prey, should aim to maintain the largest individuals. © 2008 The Ecological Society of Japan.Fil: Lucifora, Luis Omar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Dalhousie University Halifax; CanadáFil: García, Verónica Beatriz. Dalhousie University Halifax; CanadáFil: Menni, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Escalante, Alicia Haydee. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Hozbor, Natalia M.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentin