When crossing the Channel and sailing in Britanny, quite often we encountered the northern gannet (Basstölpel, Morus bassanus) far away from land. It is native to the coasts of the Atlantic Ocean and breeding in Western Europe. They search for food during the day, generally by diving at high speed into the sea. Birds that are feeding young have been recorded searching for food up to 320 km from their nest. They dive for fish from between 11 and 60 m. (see https://en.wikipedia.org/wiki/Northern_gannet)
The common tern (Fluseeschwalbe, Sterna hirundo) we observed at the river Odet at Marina Benodet, South Brittany. They fed by plunge-diving for fish in the river. When seeking fish, they flied head-down. They circled or hoverd before diving.