Monachus schauinslandi
SUBFAMILY
Monachinae
TAXONOMY
Monachus schauinslandi Matschie, 1905, Laysan Island, United States.
OTHER COMMON NAMES
Spanish: Foca fraile de Hawaii.
PHYSICAL CHARACTERISTICS
Males: 6.9 ft (2.1 m); 385 lb (175 kg); Females: 7.5 ft (2.3 m); 528 lb (270 kg). Males and females are similarly colored slate gray on the upper part of their body and a light silvery gray below. Pups are born with a black natal coat.
DISTRIBUTION
This species occurs only in the Hawaiian Archipelago. Its current distribution is mainly at a chain of small, remote islands known as the northwestern Hawaiian Islands, although it has recently begun to re-inhabit the main Hawaiian Islands in small numbers. In the past, they may have occupied islands outside the Hawaiian Archipelago such as Johnston Atoll, Wake Island, and Palmyra Atoll.
HABITAT
The small islands and atolls used by monk seals for breeding, molting and resting are made up of coral sand. The parts of islands used for breeding usually have a shallow coral shelf where females and pups can cool off during the peak heat of the day and be afforded protection from large sharks that prey upon the pups. Foraging habitat appears to be primarily among the coral reef habitat although some areas of open ocean off the shelf may also be used.
BEHAVIOR
During the breeding season females haul out on islands, remaining close to the water and tend to be evenly dispersed rather than clustered. Males spend little time hauled out on these beaches with females, but periodically visit them to check their reproductive status. During molting, males and females tend to be more aggregated on land than during breeding. Seals do not migrate from their breeding or molting beaches to forage. They forage in or near the atolls or islands where they rest, molt, and breed. The subtropical latitude inhabited by monk seals requires spending time in the water daily to keep cool. As a result, few animals are hauled out during the middle part of the day when temperatures and solar radiation are at their highest levels.
FEEDING ECOLOGY AND DIET
The monk seal diet is varied and differs among the islands and the different age groups of seals. Over 40 species have been recorded from scats. The most common type of food is marine eels (Congridae, Muraenidae, and Ophicthidae), and various reef fishes such as wrass (Labridae), squirrelfish and soldierfish (Holocentridae), and triggerfish (Balistidae). Much smaller amounts of squid, octopus and lobster were also found. Recent studies using a video camera attached to a small number of free-ranging seals showed most foraging to occur at or near the bottom, and provided images of seals turning over rocks and debris on the bottom. From these camera studies and studies using dive recorders, the depths at which foraging occurs is highly variable. For some individuals it may be well under 330 ft (100 m) and for others it may be in excess of 495–990 ft (150–300 m). This is an area of study needing further effort.
REPRODUCTIVE BIOLOGY
Males are believed to be polygynous, however, mating is seen infrequently because it occurs in the water. Some evidence suggests that individual males may follow individual receptive females at sea for a period of time until mating with them, a tactic known as roving or scramble competition. More studies are necessary to gain a better understanding of mating tactics and success. The age at which males produce sperm is not well known. Females give birth for the first time from about five to six years of age. They give birth to a single young annually. Lactation is about 44 days but the milk's fat content is not known in this species. A highly unusual pattern of switching of pups occurs frequently in this species. As many as 87% of the females in a colony will switch pups during the breeding season at least once following fights between females. The reasons for this behavior are unclear, although higher-density colonies have higher rates of switching. The behavior does not appear to effect pup survival. The breeding season of monk seals is much more extended than in most other phocids, lasting six months or more.
CONSERVATION STATUS
This species is Endangered. For the past decade, the population has hovered around 1,500 seals. It is likely to decline dramatically over the next decade because of a lack of young cohorts being recruited into the breeding population. As older breeding animals die there will be few new ones at many of the colonies. Past declines may have been related to human disturbance by military installations on some of the islands, but those have been controlled or removed for some years, yet the population fails to expand. Major environmental changes, called regime shifts, may have affected the capacity of the environment to provide adequate food for this species. There may also be indirect effects from humans, too; entanglement in discard nets are known to kill monk seals and poor fisheries management (e.g., lobsters) may have helped to diminish monk seal food resources.
SIGNIFICANCE TO HUMANS
In recent times monk seals have been of no significance to humans. A current problem is arising with the increased use of the main Hawaiian Islands by monk seals. They are hauling out on major tourist beaches, and their protective status as an endangered species has resulted in the closure or restriction of the use of these beaches. Managing such situations presents a challenge so as to not turn the public against this fragile species, which could easily become extinct before the end of this century.
