Animal Info - Hawaiian Monk Seal

(Other Names: Foca Fraile de Hawaii)

Monachus schauinslandi

Status: Endangered

Contents

1. Profile (Picture)
2. Tidbits
3. Status and Trends (IUCN Status, Countries Where Currently Found, Population Estimates, History of Distribution, Threats and Reasons for Decline)
4. Data on Biology and Ecology (Size and Weight, Habitat, Age to Maturity, Gestation Period, Birth Season, Birth Rate, Early Development, Maximum Age, Diet, Behavior, Social Organization, Gender Distribution, Mortality and Survival, Density)
5. References

Profile

Pictures: Hawaiian Monk Seal #1 (17 Kb JPEG) (Seal Cons. Soc.); Hawaiian Monk Seal #2 (9 Kb JPEG); Hawaiian Monk Seal #3 (66 Kb GIF) (Wild Ones/Wildl. Trust)

After the annual molt, the Hawaiian monk seal is a silvery gray color on the back, fading to cream on the throat, chest and belly. Additional light patches may also be found on the body. Eventually the coat looks brown above and yellow below. This monk seal weighs 170 - 200 kg (370 - 440 lb). This monk seal lives in ocean waters and on ocean island beaches, rocky islands, and coral reefs. The Hawaiian monk seal feeds on a variety of bottom-dwelling and shallow-water fish and invertebrates in the vicinity of coral reefs, including eels, octopus and lobsters. The Hawaiian monk seal is mainly nocturnal, spending the day hauled out on sandy beaches and often wallowing in wet sand by the waters edge. It forages at depths of up to 100 m (330‘) and is known to dive as deep as 500 m (1600‘). Except for mothers with pups, Hawaiian monk seals are predominantly solitary, both on land and in the water. However, females with young may be observed near each other due to the limited areas with the preferred habitat for pupping which are available. 

The Hawaiian monk seal occurs in the Northwestern Hawaiian Islands, a low-lying, fragmentary chain of coral atolls and rock islets that extends over 1600 km (1000 mi) northwest from the main Hawaiian Islands. During the 19th century, this seal was hunted to the extent that it was almost extinct. From 1909 on it was protected and its population slowly recovered. Following partial recovery, an additional decline of about 50 % occurred from the late 1950's to the 1970's. This decline has been at least partly attributed to human disturbance at breeding grounds. The Hawaiian monk seal has remained at or somewhat below the population level of the 1970's, although it continues to be threatened by entanglement in fishing nets and other marine debris that accumulates in these islands from vast areas of the Pacific Ocean, as well as human disturbance. 

Tidbits

*** Monk seals are the only pinnipeds that live in warm, subtropical seas. Despite this, Hawaiian monk seals have the same blubber content as their polar counterparts. (Macdonald 2001)

*** It may well be that critical intolerance of man is a characteristic of monk seals in general and explains, in part at least, why monk seals do not breed among the Main Islands of Hawaii or other Polynesian islands, why the Caribbean monk seal is extinct, and why the Mediterranean monk seal is restricted to isolated caves and beaches (Kenyon 1972).

*** Because of restrictions on the beach activities of people that were put in place in 1976, as well as an increased awareness of and concern for the plight of the Hawaiian monk seal on the part of government personnel stationed on islands in the monk seals' range beginning in 1981, the seals resumed activities such as pupping and hauling out on several of the islands (Gerrodette & Gilmartin 1990).

*** The monk seal may have gotten its common name from the fact that its round head covered with short hairs gives it a kind of "Friar Tuck" appearance, or from the fact that it lives a "monk-like" or solitary existence (Pac. Whale Found.).

Status and Trends

IUCN Status:

Countries Where the Hawaiian Monk Seal Is Currently Found:

2006: Occurs in the USA (Hawaiian Islands). (IUCN 2006)

Population Estimates:

[Note: Figures given are for wild populations only.]

History of Distribution:

The Hawaiian monk seal occurs in the Northwestern Hawaiian Islands, a low-lying, fragmentary chain of coral atolls and rock islets that extends over 1600 km (1000 mi) northwest from the main Hawaiian Islands (where a small population of Hawaiian monk seals also exists). Discovered by seal hunters at the beginning of the 19th century, the Hawaiian monk seal was hunted to the extent that it was almost extinct by the end of that century. From 1909 on it was protected and its population slowly recovered. Following partial recovery, an additional decline of about 50 % occurred from the late 1950's to the 1970's. It has remained at or somewhat below that level since. The Hawaiian monk seal still occupies its original range. The main reproductive and foraging sites are on and around the remote Northwestern Hawaiian Islands of French Frigate Shoals, Laysan Island, Lisianski Island, Pearl and Hermes Reef, Midway Atoll and Kure Atoll. (Kretzmann et al. 1997, Macdonald 2001, Arkive 2006) 

Distribution Map (8 Kb GIF) (monachus.org)

Threats and Reasons for Decline:

Prior to 1909, the Hawaiian monk seal was hunted for its meat, hides and oil. Its habitat was also disturbed by gatherers of bird guano and feathers. From 1909 on it was protected. Following partial recovery, an additional decline of about 50% occurred between the late 1950's and the 1970's. This decline has been at least partly attributed to human disturbance at breeding grounds. Recently, a lack of food resources, especially around French Frigate Shoals, has been cited as the cause of high juvenile mortality and the presence of severely emaciated individuals. In addition, entanglement in marine debris that accumulates in these islands from vast areas of the Pacific Ocean, as well as human disturbance, continue to threaten the Hawaiian monk seal. (Kretzmann et al. 1997, Arkive 2006)

Data on Biology and Ecology

Weight:

A Hawaiian monk seal weighs: female - 205 kg (450 lb); male - 170 kg (380 lb). The head-tail length is: female - 2.3 m (7.5'); male - 2.1 m (7'). (Macdonald 2001) 

Habitat:

The Hawaiian monk seal is found in ocean waters and on ocean island beaches, rocky islands and coral reefs (Rice 1964).

The Hawaiian monk seal is one of the species that live in both the Polynesia and Micronesia Biodiversity Hotspot (Cons. Intl.) and the Eastern Polynesian Island Marine Ecosystems Global 200 Ecoregion. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)

Age to Maturity:

Females are sexually mature at around 5 – 6 years of age (Arkive 2006).

Gestation Period:

About one year (Pac. Whale Found.).

Birth Season:

Births occur throughout the year, but are most common between February and August, with the peak occurring from March - early April (Macdonald 2001).

Birth Rate:

Females usually give birth to a single pup (Arkive 2006).

The time between birth can be either 1 or 2 years (Nowak & Paradiso 1983).

Reproductive rates, expressed as the number of live pups born per 100 adults and sub-adults, varied at each atoll from 10.3 to 21.4%. The birth rate for the population as a whole was 16.3%. (Rice 1964)

The mean annual birth rate at Laysan Island is 0.56 pups per adult female (Starfield et al. 1995).

Early Development:

A female Hawaiian monk seal does not feed while nursing. She nurses her pup for five to six weeks, and during that time she subsists entirely on energy stored in her blubber. (Pac. Whale Found.)

Maximum Age:

25 to 30 years (Pac. Whale Found.).

Diet:

The Hawaiian monk seal feeds on fishes and invertebrates. Common foods include spiny lobster, eel (except conger and moray eel), flatfish, small reef fish, larval fish and octopus. The Hawaiian monk seal is also assumed to prey on species of fish found in the open ocean, because the monk seal is known to travel long distances in the open ocean. A Hawaiian monk seal can eat as much as ten percent of its body weight in a day. (Pac. Whale Found.)

Behavior:

The Hawaiian monk seal is mainly nocturnal, spending the day hauled out on sandy beaches and often wallowing in wet sand by the waters edge (Arkive 2006).

The Hawaiian monk seal forages at depths of up to 100 m (330‘) and is known to dive as deep as 500 m (1600‘). It may travel large distances to foraging locations and remain underwater for as long as 20 minutes while foraging. It sometimes spends many days at sea before returning to the islands to sleep and digest its food. (Pac. Whale Found., Arkive 2006)

The thickness of a Hawaiian monk seal’s blubber is comparable to that of a seal living in a frigid climate. To keep cool on hot, windless days, the monk seal lies on damp sand at the water's edge, with the light fur on its belly exposed, and makes wallows into cool sand layers. Normally it doesn't stay on dry, usually hot, upper beach areas except during cool, windy or cloudy weather. The Hawaiian monk seal is also very inactive when ashore. It can also hold its breath for long periods of time, during which its heart rate is low. These behaviors result in low levels of body heat production and are excellent natural adaptations protecting the Hawaiian monk seal against heat exposure. (Pac. Whale Found.)

A female Hawaiian monk seal usually gives birth on a sandy coral beach that is backed by shrubs. It uses the shrubs for shelter during the night. Successful pupping also occurs on beaches where sheltering vegetation does not exist and, in recent years, pups have been born on rocky beaches. (Pac. Whale Found.)

Social Organization:

Except for mothers with pups, Hawaiian monk seals are predominantly solitary, both on land and in the water. However, females with young may be observed near each other due to the limited areas with the preferred habitat for pupping which are available. Monk seals are polygynous. Males become extremely aggressive during the breeding season, and groups of males sometimes kill females or juveniles during this time in what is known as ‘mobbing' behavior. (Macdonald 2001, Pac. Whale Found., Arkive 2006)

Gender Distribution:

The normal male:female ratio is 1:1 (Starfield et al. 1995).

Over the past 30 years, the adult male:female ratios in several main breeding populations have become abnormal, with as many as three males for each adult female (Reijnders et al. 1993).

Mortality and Survival:

Mortality rates in adult monk seals appear to be low. Only 1 dead adult was found during the 1957 - 58 season (Rice 1960).

The annual survival rates for pups at Laysan Island are 0.82 for males and 0.87 for females. (Starfield et al. 1995).

Survival in the Hawaiian monk seal can be quite high: 80 - 90% in the first year and 85 - 98% for young seals over age 1 (Kretzmann et al. 1997).

Survival to age 5 is approximately 50% (Reijnders et al. 1993).

Density:

Data revealed no correlation between population density (seals/area of shoal water (inside the 10 fathom (60'/18 m) line around each atoll)) and reproductive rate, mortality rate, or the net annual population increment (Rice 1960).

References

Arkive 2006, Burton & Pearson 1987, Cons. Intl., Curry-Lindahl 1972, Endangered Life, Gerrodette & Gilmartin 1990, IUCN 1967, IUCN 1994, IUCN 1996, IUCN 2000, IUCN 2003a, IUCN 2004, IUCN 2006, Kenyon 1972, Kretzmann et al. 1997, Kretzmann et al. 2001, Macdonald 1984, Macdonald 2001, monachus.org, NOAA Photos, Nowak & Paradiso 1983, Olson & Dinerstein 1998, Olson & Dinerstein 1999, Oryx 1974f, Oryx 1991a, Pac. Whale Found., Reijnders et al. 1993, Rice 1960, Rice 1964, Seal Cons. Soc., Starfield et al. 1995, WCMC/WWF, Wild Ones/Wildl. Trust

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