Abstract The Franciscana dolphin is the most endangered cetacean in the Southwestern Atlantic Ocean. Knowing its biology and ecology is crucial to promote measures to prevent its bycatch, and the study of its diet contributes to the knowledge of its ecology. However, most of these studies are performed from hard remains found in stomach contents and these contents have different digestion and retention rates, which could lead to an overestimation of some prey. However, the analysis of undigested portions of the stomach content is implemented in marine predators whose diet consists in rapid digestion invertebrates. This method avoids the effect of digestion and accumulation of measurable hard remains. Consequently, an analysis of the P. blainvillei diet was performed in order to determine differences between both diet study methods, which allow to determine the effect of the differential digestion of prey and the accumulation of hard remains with taxonomic value. The study was conducted on 41 stomach contents, whose results showed great differences in the diet following both methods. Indigestible beaks of Loligo sanpaulensis and robust sagittal otoliths of Cynoscion guatucupa accumulate in the stomach, and thus, overestimate the importance of these prey. Moreover, the analysis evidence a rapid digestion of Engraulis anchoita and Trachurus lathami, which are underestimated. In turn, the results suggest changes in the characterization of trophic habits of P. blainvillei, in its nutrition, and in the degree of overlapping with the fisheries of the area. This latter one is crucial for the Franciscana dolphin because of the high accidental mortality rate in fishing nets.

Resumen El delfín franciscana (Pontoporia blainvillei) es el cetáceo más amenazado del Atlántico Sudoccidental. Conocer su biología es esencial para promover medidas medidas que permitan mitigar su captura incidental y estudiar su dieta, contribuye al conocimiento de su ecología. La mayoría de los estudios de dieta son realizados a partir de restos duros encontrados en contenidos estomacales con distintos grados de digestión y retención, llevando a sobrestimación o subestimación de presas. Sin embargo, el análisis de la fracción fresca del contenido estomacal es una metodología implementada en predadores marinos cuya dieta es dominada por invertebrados de rápida digestión, método independiente de los efectos de digestión y acumulación de restos duros cuantificables. Se realizó un análisis de dieta de Pontoporia blainvillei considerando por separado la fracción fresca y los restos duros, con el objetivo de determinar diferencias entre estos métodos que evidenciaran el efecto de la digestión diferencial y la acumulación de restos duros con valor taxonómico. El análisis de 41 contenidos estomacales, mostró diferencias entre ambos métodos de estudio, demostrando retención de mandíbulas de Loligo sanpaulensis, y otolitos sagitta de Cynoscion guatucupa, sobreestimando así su importancia; y una homogénea digestión de Engraulis anchoita . Trachurus lathami, subestimando su importancia. Este trabajo aporta evidencias de retención y digestión diferencial de presas que implican cambios en la caracterización de los hábitos tróficos de la especie, su nutrición y el grado de solapamiento con las pesquerías de la región. Siendo esto último importante en una especie con elevada tasa de mortalidad accidental en redes de pesca, como es el caso del delfín franciscana.

Benthic polychaete association and their relationship with sedimentary parameters at south of Samborombón Bay (Buenos Aires province, Argentina): The present work describes the structure of benthic polychaete association of the southermost part of Samborombón Bay and its relationship with sediment after two decades of the last study made in the same area. Three sampling stations were established: Punta Rasa, Tapera de López and Arroyo San Clemente. Four species of polychaetes were identified: Laeonereis culveri, Heteromastus similis, Alitta succinea and Polydora cornuta, being L. culveri and H. similis the most abundant. Variations between stations in terms of the association and relative abundances of polychaetes with granulometry of sediment were recognized. Punta Rasa and Tapera de López were characterized almost exclusively by fine sand, observing the four species of polychaetes with dominance of H. similis. In Arroyo San Clemente the dominant sediment was medium sand, with pelites becoming important; A. succinea was absent and L. culveri was dominant. This indicates that variation in the distribution of polychaetes would be strongly influenced by the sedimentary parameters, and that this variation can arise even at small spatial scale. Both, polychaete species richness and general density (individuals/m2) by station were lower than density annual values observed in studies in the ‘90s. This could be because this study was conducted in the early fall, after shorebirds concentration (spring-summer), that strongly fed of these benthic organisms. This kind of studies is important since it is an environment potentially affected by human activities, taking place mainly in the inner zone of the Río de la Plata estuary.

El presente estudio describe la estructura de las asociaciones de poliquetos bentónicos del extremo sur de la Bahía de Samborombón, y su relación con los sedimentos, dos décadas después del último estudio realizado en la zona. Se establecieron tres estaciones de muestreo: Punta Rasa, Tapera de López y Arroyo San Clemente. En las mismas fueron identificadas cuatro especies de poliquetos: Laeonereis culveri, Heteromastus similis, Alitta succinea y Polydora cornuta, de las cuales L. culveri y H. similis resultaron las más abundantes. Se detectaron variaciones estacionales en la asociación y la abundancia de poliquetos en relación a la granulometría del sedimento. Punta Rasa y Tapera de López estuvieron caracterizadas casi exclusivamente por arena fina; allí se observaron las cuatro especies de poliquetos, siendo H. similis el dominante. En el Arroyo San Clemente, el sedimento dominante fue la arena media, adquiriendo gran importancia las pelitas. Alitta succinea estuvo ausente y Laeonereis culveri fue dominante. Estos resultados sugieren que los parámetros sedimentarios influirían sobre la variación en la distribución de poliquetos y que dicha variación se puede presentar aun en una escala espacial pequeña. Tanto la riqueza específica de poliquetos como la densidad general (individuos/m2) por estación fueron menores a los valores anuales observados en los estudios efectuados en la década del noventa. Esto podría deberse a que el presente trabajo fue realizado a principio de otoño, luego de la concentración de aves playeras (primavera-verano), que depredan con intensidad a estos organismos bentónicos. Este tipo de estudios resulta importante al tratarse de un ambiente potencialmente afectado por las actividades antrópicas que tienen lugar en la zona interna del estuario del Río de la Plata.

The present study provides information about the diet composition of franciscana dolphin, Pontoporia blainvillei, from southern Buenos Aires coast, Argentina. From 2003 to 2011 we collected 66 franciscana dolphins that were incidentally entangled in artisanal fishing nets. We analyzed the stomach contents and estimated the prey size in order to evaluate the diet composition and the overlapping with fisheries. We identified 11 prey species in the stomach contents; only two of them were important in the diet, the striped weakfish, Cynoscion guatucupa, and the squid, Loligo sanpaulensis. Almost all the prey found in the diet of franciscana dolphins are of commercial interest. The overlapping of target species and prey that are subject to overfishing could enhance the vulnerability of franciscana by reducing food availability.

The aim of this paper is to describe and evaluate the use of the hair discoloration method in South American sea lions, with an emphasis on its advantages and its potential use in future studies. For marking, stamp removable letters and numbers were used, connected to an extensible rod. The bleached marks obtained had a maximum duration of 347 days perfectly visible and, because of the combination of low cost and application simplicity, this technique is considered suitable for both short and long term non-invasive studies in pinnipeds.

El presente trabajo tuvo como objetivo describir y evaluar el método de marcado de lobos marinos comunes por decoloración del pelo, señalando ventajas y posibilidades de aplicación futuras. Para el marcado se utilizó un sello compuesto por letras y números desmontables donde se coloca el decolorante, conectado a una vara extensible que permite la correcta aplicación de la marca. Con esta metodología las marcas obtenidas tuvieron una duración máxima de 347 días perfectamente visibles, motivo por el cual y sumado al bajo costo y sencillez de aplicación, se sugiere que esta técnica es recomendable para estudios no invasivos en pinnípedos a corto y mediano plazo.

Na Argentina, a toninha é um dos cetáceos mais vulneráveis devido às capturas por rede de pesca artesanal. O presente estudo teve como objetivo estimar as capturas acidentais no sul da província de Buenos Aires, através de entrevistas aos capitães de barcos de pesca artesanal, entre os anos 2006-2009. As capturas foram reportadas para redes de emalhe e de camarão; com as mais altas frequências entre outubro e fevereiro, a 5 km da costa e 10-20 m de profundidade. A mortalidade acidental média anual estimada foi de 107 golfinhos (IC 95% = 87-129), 92 em redes de emalhe (IC 95% = 73-112) e 15 em redes de camarão (IC 95% = 8-25), com uma captura de 0,029 golfinhos/km de rede de emalhe (IC 95% = 0,023-0,036) e 0,024/rede de camarão (IC 95% = 0,012-0,035). As flutuações anuais responderam principalmente às diferenças nos dias de pesca. Considerando o último levantamento estimativo feito para o norte costeiro da província, estima-se uma mortalidade entre 360-539 golfinhos/ano em toda a província de Buenos Aires. Esses valores correspondem de 2,5-3,7% da abundância populacional da Argentina; o que traria como consequência um declínio populacional da espécie, tornando-se fundamental encontrar alternativas de pesca para a área.

In Argentina, the franciscana dolphin is one of the most vulnerable cetaceans regularly entangled in coastal artisanal fishery nets. The aim of this paper is to estimate the species' incidental mortality on the Southern coast of Buenos Aires province through interviews with the captains of artisanal fishing vessels, in the period 2006-2009. Franciscana bycatch was reported for gillnets and shrimper gear all year round but it occurred more frequently between October and February, at 5 km offshore and 10-20 m depth. The estimated mean annual incidental mortality was 107 dolphins (CI 95% = 87-129), 92 caught in gillnets (CI 95% = 73-112) and 15 in shrimpers' gear (CI 95% = 8-25) with a capture per unit effort of 0.029 dolphins per km of gillnet (CI 95% = 0.023-0.036) and 0.022 per shrimpe r's net (CI 95% = 0.012-0.035). Annual fluctuations were due to differences in the number of gillnetting fishing days. If mortality estimates for the Northern coast are also taken into account, values attain a maximum of 360-539 dolphins bycaught in the entire Buenos Aires province, representing 2.5-3.7% of the species' abundance in Argentina. This will inevitably lead to the decline of franciscana dolphin populations in the near future unless alternative fishing grounds are identified and alternative gearadopted.