Food and feeding ecology of the Tasmanian short-tailed shearwater (Puffinus tenuirostris, Temminck): insights from three complementary methods

Maëlle CONNAN, Patrick MAYZAUD, Keith HOBSON, Henri WEIMERSKIRCH, Yves CHEREL

Abstract


The diet of seabirds is usually studied by the identification of prey items recovered from their stomachs. This method is however limited to freshly ingested prey and to non-digestible hard parts, precluding the determination of marine resources consumed by birds during long foraging trips. Thus alternative indirect approaches are necessary to assess the potential importance of digested prey from long-term foraging activity. In this project, we present three complementary techniques to determine the prey of breeding short-tailed shearwaters (Puffinus tenuirostris) when they feed for themselves during long foraging trips: (1) conventional food analysis, (2) stable isotope analysis of carbon and nitrogen signatures of plasma (δ13C and δ15N), and (3) lipid analysis of stomach oil and use of fatty acid and fatty alcohols as trophic markers (stomach oil is of dietary origin). Dietary analysis food showed that fish dominated by mass over crustaceans (82 and 18%, respectively). Euphausiids Euphausia vallentini (sub-Antarctic species) and Nyctiphanes australis (Tasmanian species), and fish postlarvae represented more than 94% of total number of food items, with myctophid fish of larger size dominating by mass. Plasmatic isotopic signature of birds suggested that shearwaters foraged in sub-Antarctic and Antarctic areas (δ13C = -23.8‰), and fed at a trophic level close to that of a myctophid-eater, the king penguin (δ15Nshort-tailed shearwater = 8.7‰, δ15Nking penguin = 9.9‰). Comparisons between fatty -acid and -alcohol patterns of stomach oil wax ester with those of potential prey also suggested a food based on myctophids (Electrona antarctica, Krefftichthys anderssoni and Gymnoscopelus braueri). To conclude, both lipid and stable isotope methods emphasized the importance of myctophids in the nutrition of short-tailed shearwaters during the chick-rearing period when adult birds feed for themselves. This study illustrates the interest of using both direct and indirect methods to determine trophic relationships between marine organisms.

Keywords


Top predator; Myctophids; Southern Ocean; Stable isotopes; Stomach content; Lipid analyses

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