Monk seal ancestors originated in the North Atlantic Ocean at a very early date. The Hawaiian monk seal became separated from the Atlantic-Caribbean members of the genus as early as 15 million years ago. Perhaps because of their primitiveness, monk seals seem far more sensitive than other phocids to human intrusion of their environment. Pregnant females and mothers with nursing young appear greatly upset when approached. These disturbances may cause increased deaths among Hawaiian monk seal pups.
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.