The Jackass Penguin (Spheniscus demersus) as a pelagic predator

Abstract

Swimming and diving capabilities of Jackass Penguin Spheniscus demersus were examined. Mean maximum speed over a 10 m course in a rock pool was 12.4 km h-' for breeders, 9.5 km h-' for juveniles and 4.6 km h-' for fledglings. Theoretically fledglings could not swim fast enough to catch adult Cape Anchovies Engraulis capensis, the normal prey of adults. Fledglings probably feed on fish larvae. Moulting penguins swam at speeds comparable to fledglings and did not feed. When travelling to the foraging area, breeding penguins swam at 4.8 km h-'. Maximum theoretical foraging range is 24.2 km, but actual range was < 20 km. Mean duration of dive was 22.3 S inside Saldanha Bay and 146 S outside the bay. During long dives outside Saldanha Bay, penguins were probably foraging. At midday, when most Jackass Penguins are at sea, largest numbers were seen outside the bay in 30 to 40 m depth. Penguins fitted with depth gauges dived routinely to 30 m, but spent most time in the upper water layers. Maximum recorded depth was 130 m. There was a positive correlation between distance swum and amount of food ingested. suggests that the anchovy on which they feed formed small schools which were encountered frequently.