If you are very lucky when you're in Hawaii, you may see a Hawaiian monk seal. I've seen several over the years I've been visiting the islands and it's no less a thrill every time.
The Hawaiian monk seal is an endangered species, with a current population estimated to be only about 1,200. It was officially designated as an endangered species on November 23, 1976 and is now protected by the Endangered Species Act and the Marine Mammal Protection Act.
Needless to say, it is illegal to kill, capture or harass a Hawaiian monk seal. This is why when a monk seal is found on a beach in Hawaii, lifeguards or other officials secure the area with police tape.
The ancient Hawaiians called the monk seal 'Ilio holo I ka uaua (dog that runs in rough water) which, when you think of it, made a lot of sense since they had never seen a seal before.
The U.S. Fish and Wildlife Service provides excellent information on Hawaiian Monk Seals:
"An adult monk seal is usually dark gray or brown with a light gray or yellow belly. Adults can weigh anywhere from 375 to 500 pounds; adult females are generally larger than males. Pups are jet black and usually weigh 25 to 30 pounds at birth and weigh up to 132 to 198 pounds within five to six weeks.
The monk seal's common name is derived from its folds of skin that look like a monk's hood, and because it spends most of its time alone or in very small groups.
They spend most of their time in the ocean but like to rest on sandy beaches, and sometimes use beach vegetation as shelter from wind and rain. Monk seals are expert swimmers and divers; one seal was recorded diving into depths in the range of 66 and 96 fathoms (396 to 576 feet). The average monk seal dives 51.2 times per day. The life span of the Hawaiian monk seal is from 25-30 years."