Diet of the southern giant petrel in Patagonia: fishery-related items and natural prey

Abstract

There is an increasing interest in dietary composition of threatened seabirds as an impor- tant key to understanding their feeding ecology, population dynamics and interaction with fisheries. Several seabird species exploit discards from fisheries as their main food. The southern giant petrel Macronectes giganteus is a wide-ranging procellariform. It is considered a near-threatened species under International Union for Conservation of Nature (IUCN) criteria and has been included as a threatened species in the Appendix 2 of the Convention on the Conservation of Migratory Species of Wild Animals. The diet of Patagonian colonies of this species remains unknown, even though under- standing the relationship between southern giant petrels and fisheries may be crucial to the conserva- tion of this species in the Southwestern Atlantic. We describe the diet of the southern giant petrel from north Patagonian colonies using chick regurgitations and evaluate its relationships with the fisheries. Carrion occurred in the diets of 90.8% of birds sampled, while cephalopods occurred in the diets of 65.1%. Crustaceans were present in 43.7% of samples and fishes in 19.4%. Anthropogenic items were found in 72.7% of the samples. The presence in the petrel's diet of target and discarded species from fishery vessels, and the high incidence of marine debris, suggests an extensive use of discard over the Patagonian Shelf. The population of southern giant petrels in northern Patagonia has reached higher, stable levels. Such a population trend could be linked, at least partially, to the use of fisheries discards.