Hawaiian monk seals are found throughout the entire Hawaiian archipelago, a distance of 1,549 miles from Kure Atoll in the northwest to Hawaiʻi Island in the southeast. The majority of Hawaiian monk seals (about 1,100 individuals) live in the Northwestern Hawaiian Islands, and a much smaller population (about 300) lives in the main Hawaiian Islands. There have also been rare sightings of Hawaiian monk seals, as well as a single birth, at Johnston Atoll, the closest atoll southwest of the Hawaiian Islands. Monk seals do not migrate seasonally, but some seals have traveled hundreds of miles in the open ocean. Individual seals often frequent the same beaches over and over, but they do not defend territories.
Hawaiian monk seals are "generalist" feeders, which means they eat a wide variety of foods depending on what's available. They eat many types of common fishes, squids, octopuses, eels, and crustaceans (crabs, shrimps, and lobsters). Diet studies indicate that they forage at or near the seafloor and prefer prey that hide in the sand or under rocks. They do not target most of the locally popular gamefish species such as ulua (giant trevally), pāpio (baby ulua), and ‘ō‘io (bonefish). Monk seals generally hunt for food outside of the immediate shoreline areas in waters 60-300 feet (18-90 m) deep.
Monk seals live in warm, subtropical waters and spend two-thirds of their time at sea. They use the waters surrounding atolls and islands and areas farther offshore on reefs and submerged banks; they also use deepwater coral beds as foraging habitat. They can hold their breath for up to 20 minutes and dive more than 1,800 feet; however, they usually dive an average of 6 minutes at shallow depths to forage at the seafloor. When on land, monk seals breed and haul-out to rest, give birth, and molt on sand, corals, and volcanic rock shorelines. They prefer sandy, protected beaches surrounded by shallow waters for pupping. They usually sleep on beaches, sometimes for days at a time, and they occasionally sleep in small underwater caves.
Threats to the Hawaiian monk seals include food limitation, shark predation, entanglement, male seal aggresion, habitat loss, fishery interactions, disease, human-seal interactions, and intentional killing. A prolonged decline of the Hawaiian monk seal population in the NWHI occurred after the late 1950s, lasting until very recently. The decline that occurred in the NWHI has been attributed to a number of factors at various regions and time periods. However, low juvenile survival, likely related to inadequate prey availability, has been the primary driver of the decline during the past 25 years.