Monk seals are solitary, both in the water and onshore. When loose groups form on beaches, they gather because the local environment conditions are favorable. Except for mothers with pups, resting seals avoid bodily contact with each other. Monk seals vocalize from when they are young into adulthood. The bubbling resembles that of water from a jug.
Monk seals feed on fishes and invertebrates both within atoll lagoons and in deeper water offshore.
Monk seals may eat as much as ten percent of their body weight in a day. They sometimes spend many days at sea before returning to the islands where they sleep and digest their food. Monk seals, although totally protected, remain one of the most endangered of all seals. It is estimated that fewer than 1500 Hawaiian monk seals exist today. It is illegal to kill, capture or harass monk seals.