Harbor seals haul out on the offshore rocks at the tip of the headland. The pupping season occurs at Yaquina Head during April and May. Gray whales, killer whales, and sea lions occasionally can be seen from the headland. To look for sea lions or seals stand on the Cobble Beach observation deck and look out towards the low flat rocky island and study it carefully. Sea lions bark.
Seals move like an inch-worm.
Sea lions are all one color. Seals have spots or blotches. Look for their round shiny heads. The marine mammals you have been observing are harbor seals. A number of them live on these protected islands year-round.