Eastern rockhopper penguins Eudyptes filholi as biological samplers of juvenile and sub-adult cephalopods around Campbell Island, New Zealand
Résumé
Early life-history stages of cephalopods are known to play an important role as prey in food webs of the Southern Ocean, but
little information is available about their biology and availability to predators. Top predators, such as penguins, are known
to feed regularly on coastal juvenile/sub-adult cephalopods. Using eastern rockhopper penguins Eudyptes filholi as coastal
biological samplers, we examined in detail the cephalopod component of their diet in Campbell Island (New Zealand) during
two consecutive breeding seasons in order to evaluate (1) the relative importance of cephalopods (by frequency of occurrence,
by number and by mass) to the diet of both adult and chick penguins, (2) the habitat and trophic levels of the cephalopods
in the region and (3) the status of the juvenile/sub-adult cephalopod community in the waters around Campbell Island. Our
results show that eastern rockhopper penguins feed on eight species of juvenile and sub-adult cephalopods, with Onykia
ingens, Martialia hyadesi and Octopus campbelli being the most important species by frequency of occurrence, number and
mass. Differences between the diets of adult and chick penguins and between breeding seasons were found. Habitat (δ13C)
and trophic level (δ15N) information also showed that all cephalopod species (and all studied stages) occupy similar habitat
on the Campbell shelf, with M. hyadesi showing lower δ15N values than O. ingens and O. campbelli. This study indicates
that eastern rockhopper penguins can be valuable biological samplers of local juvenile/sub-adult cephalopods (including
poorly known cephalopod species) around Campbell Island when breeding, that these cephalopods were likely to be caught
naturally (not from fisheries), providing relevant information for the conservation of these penguins.