ABSTRACT. The South American sea lion, Otaria flavescens (Shaw, 1800) population is steadily expanding along the Patagonian coast of Argentina in the last decades. However, little is known about the feeding ecology of the species in the area. The aim of this study was to analyze the food habits of O. flavescens from 91 scats collected at Río Negro province, during the winter and spring of 2005. Fish occurred in 96% of scats containing prey remains, followed by cephalopods (26%). Raneya brasiliensis (Kaup, 1856) was the most frequent and abundant species occurring in 58.6% of samples and constituting almost 50% of fish predated. Second in importance were Porichthys porosissimus (Cuvier, 1829) and Cynoscion guatucupa (Cuvier, 1830) in terms of occurrence (%FO 20.7) and numbers (29.6%) respectively. The squid Loligo gahi (d'Orbigny, 1835) was the most frequent cephalopod prey (42.1%), whereas Octopus tehuelchus (d'Orbigny, 1834) was the most abundant (77%). The higher amount and diversity of prey found in the spring in comparison with the winter season might be related to a higher feeding activity of seals or to a seasonal increase in food availability in the area. KEYWORDS.Trophic ecology, Pinnipedia, fishes, cephalopods.RESUMEN. Dieta del lobo marino de un pelo sudamericano (Otaria flavescens) en Río Negro, Patagonia, Argentina, durante el invierno y primavera. La población del lobo marino de un pelo sudamericano Otaria flavescens (Shaw, 1800) ha experimentado un crecimiento continuo en las ultimas décadas en las costas de la Patagonia Argentina. Sin embargo, poco se conoce sobre la ecología trófica de la especie en el área. El objetivo de este estudio fue analizar los hábitos alimentarios de O. flavescens a partir de 91 fecas colectadas en la provincia de Río Negro, durante el invierno y la primavera del 2005. Los peces estuvieron presentes en el 96% de las fecas que contenían remanentes presas, seguidos por los cefalópodos (26%). Raneya brasiliensis (Kaup, 1856) fue la especie mas frecuente y abundante ocurriendo en el 58.6% de las muestras y constituyendo casi el 50% de los peces predados. Le siguieron en importancia Porichthys porosissimus (Cuvier, 1829) y Cynoscion guatucupa (Cuvier, 1830) en términos de frecuencia de ocurrencia (%FO 20,7) y abundancia numérica (29,6%) respectivamente. El calamar Loligo gahi (d'Orbigny, 1835) fue el cefalópodo presa mas frecuente (42,1%), mientras que Octopus tehuelchus (d'Orbigny, 1834) fue el mas abundante (77%). La mayor cantidad y diversidad de presas observada en primavera en comparación con el periodo invernal podría estar relacionada a una mayor actividad de forrajeo de los lobos o a un incremento en la disponibilidad de presas en el área.

The South American sea lion Otaria flavescens population from northern Patagonia was under intensive commercial harvesting pressure between 1930 and 1950 and is currently increasing at a rate of nearly 6% yr −1. Food availability in the oceans is one of the most important factors influencing the survival and dynamics of marine mammal populations. The objective of the present study was to determine the summer diet of O. flavescens by faecal analysis, in order to assess its trophic behavior, determine whether there are interannual differences in diet composition, and evaluate the potential interaction between fisheries operating in the study area and the species. Present results show that O. flavescens preys mainly on fish species, with Raneya brasiliensis being the most frequent (frequency of occurrence, %FO = 65.7) and abundant (%N = 47.9) fish prey. Cephalopods were the second most important prey item in terms of %FO (42.6%), with the highest index of relative importance corresponding to the octopod Octopus tehuelches. Since these prey taxa are not targeted by the commercial fishing fleet that operates in the study area, the overlap in the use of resources by O. flavescens and fisheries may not be substantial. Given that the biomass of the prey species mentioned above is not directly affected by fishery activities during summer, a greater amount of food may be available for sea lions, with this factor possibly contributing to the population recovery in the area. KEY WORDS: Otaria flavescens · Summer diet · Scats · Patagonia · ArgentinaResale or republication not permitted without written consent of the publisher Aquat Biol 20: 235-243, 2014 Ocean) (King 1983, Bastida et al. 2007). The population inhabiting the Argentine coast dramatically declined between the 1930s and 1950s due to commercial hunting, but since 1990 it has been increasing at a rate of nearly 6% yr −1 , Grandi et al. 2010.The fisheries that operate in the San Matías Gulf, Río Negro province, target demersal and pelagicdemersal species, with the Argentine hake Merluccius hubbsi being the main species caught throughout the year (Irusta et al. 2003). A trend exists towards major diversification in landings and in creased fishing activity (Romero et al. 2011). The fact that the stock of Argentine hake in the region was reported to have collapsed in the 1990s due to over fishing (Aubone 2000), combined with the extreme reduction of the sea lion population, led to a re organization of the ecosystem (Koen Alonso & Yodzis 2005). This is now characterized by larger populations of the Magellanic penguin Spheniscus magellan icus, Argen tine short-fin squid Illex argen ti nus and Argen tine anchovy Engraulis anchoita (Koen Alonso & Yodzis 2005). Furthermore, predation on hake de creased, while predation on alternative prey, such as Squalus acanthias, increased (Koen Alonso et al. 2000).All foraging trips of the South American sea lions from Patagonia are on the continental shelf of up to 400 km in width, with males moving further from the coast...

Cephalopods are important prey in the diet of top predators, such as marine mammals and seabirds. However, detailed information on their trophic relationships in the Patagonian marine ecosystem is scarce, including those cephalopod species with commercial interest. The aims of this study were to evaluate the composition of the cephalopod component in the diet of Otaria byronia and determine the habitat use and trophic levels of their main cephalopod prey by measuring the stable isotopic signature of cephalopod beaks. Between May 2005 and February 2009, fresh faecal samples were collected from two sea lions rookeries in San Matias Gulf. Cephalopods occurred in 39.4% of the 1112 samples collected during the whole period of study. The dominant prey species was Octopus tehuelchus, which occurred in 45.8% of scats containing cephalopod remains, and represented 58.7% in terms of numerical abundance and 52.0% in mass of cephalopods consumed. The second species most consumed was the myopsid Doryteuthis gahi. The significant higher δ15N values of O. tehuelchus beaks in comparison with those of D. gahi showed that these two species have different trophic levels while occupying similar habitat (δ13C values) in neritic waters of the Patagonian shelf.

The false killer whale, Pseudorca crassidens, exhibits one of the widest and most continuous distributions among cetaceans. However, basic information about its biology is poorly known due to the low frequency of sightings and its offshore habits. Moreover, most of the knowledge on this species has been obtained from stranded animals. On 3 March 2012, in the proximity of a colony of South American sea lions (Otaria flavescens) located at Caleta de los Loros, Río Negro Province, Argentina (40o59’S, 64o14’W), a cetacean skull was found in the intertidal zone. The specimen was later identified as P. crassidens. The present note reports a new record of false killer whale in the continental shelf waters of Argentina and provides new data on the distribution and skull morphometrics of the species.