New records of birds in stomach contents of marine apex predators from the north Atlantic ocean and Mediterranean sea

Abstract

 Predation on seabirds by sharks or other large predators is a poorly documented issue. The blue shark is a known generalist predator that feeds on seabirds, among other prey. Bluefin tuna is a well-studied species, but to date no species of seabird has been cited as being the prey of any species of Scombridae. The present study reports the first record of Atlantic bluefin tuna (Thunnus thynnus) predation on a seabird (Cory’s shearwater Calonectris borealis). We also provide three new records of blue sharks (Prionace glauca) feeding on terrestrial and seabirds in the Northeast Atlantic Ocean and in the Mediterranean Sea. Seabirds can associate with other large marine predators, especially large tunas and marine mammals, in any oceanic region for the purpose of feeding. It is known that small pelagic fish try to flee from predators by approaching the surface of the sea, which is when seabirds take advantage of this situation by attacking them from the air to feed on them. Therefore, during the fishing frenzy, an individual bluefin tuna could have fed on the shearwater. This hypothesis is consistent with our observations. However, the case of seabirds found in the stomachs of blue sharks could imply the intentional and opportunistic predation by blue sharks on seabirds floating on the surface of the sea. On the other hand, exhausted migrating terrestrial birds (non-marine birds) could fall into the sea and thus become prey.