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

Abstract

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.

South American Sea Lions Otaria flavescens, a good indicator of relative spatial and temporal changes in the distribution and abundance of marine resources?

“…In reference to the feeding ecology of the South American sea lions, Otaria flavescens (Shaw, 1800), its study is of utmost importance if we consider that one of the factors affecting the population fluctuations of marine mammals is the availability of food in the ocean (Crespo & Pedraza, 1991;Soto et al, 2006). The information available on the diet of O. flavescens has increased in the last two decades in different areas of its distributional range (Soto et al, 2006;Hückstädt et al, 2007;Bustos et al, 2014Bustos et al, , 2019Cárdenas-Alayza et al, 2022). These studies suggest that O. flavescens has a generalistic and opportunistic trophic behaviour, with differences in the diet between males and females, probably associated with different feeding areas (Koen Alonso et al, 2000;Naya et al, 2000;Drago et al, 2009;Crespo et al, 2012;Zenteno et al, 2015).…”

“…These studies suggest that O. flavescens has a generalistic and opportunistic trophic behaviour, with differences in the diet between males and females, probably associated with different feeding areas (Koen Alonso et al, 2000;Naya et al, 2000;Drago et al, 2009;Crespo et al, 2012;Zenteno et al, 2015). Up to date, dietary studies in the maritime coast of Río Negro province (North Patagonia) have been focused on the colonies of Punta Bermeja and Caleta de los Loros (Bustos et al, 2012(Bustos et al, , 2014(Bustos et al, , 2019. These have indicated differences in the relative proportions of the dominant prey taxa between both rookeries.…”