FATTY-ACID EVIDENCE FOR THE IMPORTANCE OF MYCTOPHID FISHES IN THE DIET OF KING PENGUINS, APTENODYTES-PATAGONICUS

We tested the usefulness of the fatty acid signature-method in investi gating the diet of seabirds in conjunction with the conventional techn ique of stomach-content analysis. We compared the fatty acid compositi on of subcutaneous white adipose tissue (SWAT) of king penguin chicks (Aptenodytes patagonicus) during fattening periods to that of total li pids from their food. In both spring and autumn, the fatty acid compos ition of chick SWAT was identical to that of the dietary lipids. Becau se the diet of adult king penguins feeding for self-maintenance (i.e. not for their chicks) was essentially unknown, we subsequently analyse d their SWAT fatty acid patterns after premolting and prebreeding fora ging trips (during which they build up large energy reserves). The fat ty acid composition of SWAT from adults was identical to that of chick adipose tissue and food. King penguin diet and SWAT were characterize d by high levels of very long-chain mono-unsaturated fatty acids (20 t o 24 carbon atoms, 16 to 23% by mass) and (n-3) poly-unsaturated fatty acids (19 to 27%); these consisted mainly of 20:1n-9 (5 to 8%) and 22 :1n-11 (5 to 8%), and 22:6n-3 (10 to 13%) and 20:5n-3 (3 to 9%), respe ctively. Prey items identified from chick stomach contents indicated t hat the bulk of the food was oceanic myctophid fishes, mainly Electron a carlbergi, Krefftichthys anderssoni and Protomyctophum tenisoni. The fatty acid composition of four other species of myctophid fishes was similar to that of penguin diet and SWAT, but markedly different from that measured for a squid species and that reported for crustaceans. T hese findings indicate that adult king penguins prey on myctophid fish not only to feed their chicks but also for their own nutrition. The f atty acid signature-technique is therefore a reliable method to gain i nformation on the food and feeding ecology of seabirds when more conve ntional techniques are of limited value. Such information is important to the understanding of trophic relationships between key species of the ecosystems, and also to provide insight into the nature of avian a daptations to the marine environment.