Cephalopod diet of juvenile male southern elephant seals Mirounga leonina at Marion Island, South Indian Ocean

Abstract

Southern elephant seals Mirounga leonina have a circumpolar distribution and migrate across broad geographic regions. Therefore, they can provide important insights into the responses of top predators to changes in the environment, especially those effected by climate change. For this, determining trophic interactions is key, and thus it is important to investigate the diet of all populations of M. leonina in the Southern Ocean. Limited literature exists on the diet of southern elephant seals at the Prince Edward Islands in the sub-Antarctic. During August and September 1976, the stomach contents of two juvenile male southern elephant seals were opportunistically collected at Marion Island (46o54’S, 37o51’E), and later analysed. Accumulated cephalopod beaks (n = 137) representing 18 taxa in nine decapod families were found. Onychoteuthidae was numerically the most abundant (28.7%), followed by Brachioteuthidae (21.8%), Neoteuthidae (12.6%), and Histioteuthidae (9.2%). Slosarczykovia circumantarctica (Brachioteuthidae) was the most abundant species (19.5%) followed by Batoteuthis skolops (Batoteuthidae) at 12.6%. Allometric equations using lower rostral lengths showed that the southern elephant seals ingested cephalopods with mantle length between 5.2 and 39.9 cm and weighing between 0.003 and 2.62 kg. There was only one very digested crustacean, and no recognizable fish remains in the stomach contents. The continuation of the investigation relies on examination of natural mortalities and dietary items obtained by stomach lavage of individuals, complemented by, for example, stable isotope compositions captured along the length of vibrissae and within dentinal growth layer groups of teeth as proxies for the elephant seals’ trophic ecology.