The diet of the South American sea lion (Otaria flavescens) at Río Negro, Patagonia, Argentina, during the winter-spring period

Raimundo L Bustos,Alejandra V Volpedo,Esperanza A Varela,Gustavo A Daneri,Ana Harrington

doi:10.1590/s0073-47212012000400005

Raimundo L Bustos, Alejandra V Volpedo + Show 3 more

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https://doi.org/10.1590/s0073-47212012000400005

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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.

Highlights

To estimate the number of individuals we considered the otoliths that were present in greater number, and in the case of cephalopods the number of lower beaks
Raneya brasiliensis was the most frequent and abundant fish species consumed by O. flavescens throughout the whole study period
This prey is a key link in the Southwestern Patagonian higher level food web and has been reported as a common prey item in the diet of marine mammals, marine birds and fishes (Gosztonyi et al, 2007)

Summary

Introduction

Since the food availability in the ocean is one the major factors that may influence the marine mammals population fluctuations, the study of the feeding ecology of the South American sea lion is extremely important. In this regard, Crespo & Pedraza (1991), attributed the very slow recovery in recent years of the population of O. flavescens in the Patagonian coast to diverse factors such as the expansion of fishing activities in the area, as well as the partial overlapping of spatial and trophic niche with other predator species, e.g. little cetaceans [vg. Recent studies using stable isotope analyses have indicated that M. leonina and O flavescens have similar isotopic profiles, which would indicate that both species include in their diet prey taxa of relatively similar trophic level (Lewis et al, 2006)

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