Diet of the South American sea lion Otaria flavescens during the summer season at Río Negro, Patagonia, Argentina

Abstract

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...

South American sea lions Otaria byronia as biological samplers of local cephalopod fauna in the Patagonian shelf marine ecosystem

“…In order to understand the ecological role of this otarid species in the local marine food webs, several dietary studies have already been performed using traditional methods (scats and stomach content analysis) or measuring the stable isotopic values from different tissues (e.g. bones, muscle, vibrissae) of SSL (George-Nascimento et al ., 1985; Thompson et al ., 1998; Naya et al ., 2000; Koen Alonso et al ., 2000; Drago et al ., 2009, 2010; Bustos et al ., 2012, 2014). These studies have indicated that fish, cephalopods and, to a lesser extent, crustaceans, constitute their most important prey.…”

Morphological and morphometric changes ofsagittaeotoliths related to fish growth in three Mugilidae species

“…Different methods are usually employed to identify dietary items such as stable isotopes, or recognition of structures like bones and otoliths (Boecklen, Yarnes, Cook, & James ; Jansen et al., ; Volpedo & Echeverría, ). To analyze feeding habits in marine mammals, birds and fishes the study of stomach contents provides information for recently ingested prey (Bustos, Daneri, Volpedo, Harrington, & Varela , ; Pierce & Boyle, ).…”

“…These inert structures record life history stage transitions of fishes (Brothers & McFarland, 1981) and may have a substantial importance when working in trophic studies and paleoecology. Identifying otolith morphology and morphometry found in fossils or in diet remains can determine not only species but also specimen size (Barrett et al, 2007;Bustos et al, 2012Bustos et al, , 2014Reichenbacher, Sienknecht, Küchenhoff, & Fenske 2007;Riet-Sapriza et al, 2013;Scartascini & Volpedo, 2013;Tuset, Parisi-Baradad, & Lombarte 2013;Tuset et al, 2015;Veen, Mullié, & Veen 2012). Even though otolith erosion, caused by digestion, is expected to decrease its length, otolith features are still a good approximation for trophic studies on species that are difficult to collect (Harvey, Loughlin, Perez, & Oxman 2000).…”

Aplicación de los otolitos en el estudio de la interconectividad de stocks pesqueros de mugílidos de zonas costeras de la provincia de Buenos Aires, Argentina y de la costa Valenciana, España.

“…Usualmente se utilizan diferentes métodos para identificarítems dietarios como el análisis de isótopos estables o el reconocimiento de estructuras como huesos u otolitos, entre otros Boecklen et al, 2011;Jansen et al, 2012). Estas metodologías se aplican en el estudio del comportamiento alimenticio de mamíferos marinos, aves y peces, proporcionando información sobre las presas recientemente ingeridas (Pierce y Boyle, 1991;Bustos et al, 2012;Bustos et al, 2014).…”

“…Como se mencionó en el capítulo anterior, los otolitos son estructuras cuya morfología es especieespecífica (Hecht, 1987;Volpedo y Echeverría, 2001;Campana, 2004;Tuset et al, 2008;Avigliano et al, 2015a), por lo que se consideran estructuras valiosas para analizar cadenas tróficas en diferentes ecosistemas acuáticos tanto en el pasado como en la actualidad. La identificación de la morfología y morfometría de otolitos fósiles o en contenidos estomacales puede determinar no solo la especie, sino también el tamaño de las presas (Barrett et al, 2007;Reichenbacher et al, 2007;Bustos et al, 2012;Veen et al, 2012;Riet-Sapriza et al, 2013;Scartascini y Volpedo, 2013;Tuset et al, 2013;Bustos et al, 2014;Tuset et al, 2015).…”