Since the porpoises and whales are air-breathing mammals, they periodically come to the surface to inhale and exhale. In the process, a portion of the back, including the blow hole and dorsal fin are exposed above the surface of the water, and this approach to the surface, and rolling dive in which the back is exposed, is indicative of porpoises. They usually travel in small groups, which also serves to distinguish them from sharks. The migration begins in late fall when the whales traveling singly or in small groups can be seen off the coast adjacent to the Reserve, traveling at slow speeds. When they arrive at the large shallow lagoons of Baja California the females give birth to their young, nurse them, and rest in anticipation of the return to the north.
Breeding takes place before the migration back to the Alaskan waters begins.
January finds the whales moving back north again accompanied by the small babies which swim with the mothers. The Harbor Seal reaches a length of about 6 feet and weighs less than 300 pounds. It can be identified by the grayish-yellow blotches which form a mottled pattern over a darker ground color. There are no external ears. The hind flippers always are extended directly out from the body, they cannot be brought forward, as they can in sealions.