| Last modified: Thursday September 24th, 1999 |
Monk seals
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Appearance
Males are on average 214 cm long and weigh 172 kg. Females are
larger: 234 cm long and a weight of 270 kg. Pups are 100 cm at birth and weigh 16-18 kg.
The monk seal is dark brown to black in colour and lighter ventrally.
Distribution
These seals used to live on sandy beaches, but can only be found in
caves and on small islands. The monk seal can be found in countries around the
Mediterranean Sea, on islands in the Adriatic Sea, on the Madeira Islands, the
Canary Islands and the Atlantic ridge islands.
Feeding
The monk seal lives on local fish and octopus. The diet includes fish
species, such as eel, carp, whiting, sardine and bonito.
Population dynamics and life history
There is little information about this seal. They probably
become mature at the age of 4 and gestation lasts probably 11 months. Other
parameters are unknown.
Trophic relations
There is probably no competition and there are no natural
predators.
Interactions
Because the monk seal feeds on fish species that are commercially
exploited, there are interactions with fisheries. Monk seals get entangled in fishing
nets and are shot by fishermen, trying to protect their nets. Over-exploitation of fish
stocks severely depletes the monk seal's food supply. These seal are very sensitive
for disturbance.
Population size:
The total population size is probably no larger than 500-600 seals
and is declining. There have been some estimates made for parts of the monk seal's
range: Morocco and Algeria: 100; Greece: 150; Port Etienne: 50; Black Sea: 50;
Cyprus and Lebanon: 50; Desertas: 50; small groups of 20 seals or less on Madeira,
Canary Islands and in Turkey.
Exploitation
The monk seal is protected throughout its range. Despite the protection monk seal
are still killed by fishermen.
Threats to the population
This small population of secretive animals, that is
spread out over a large area is very vulnerable. These seals are very sensitive to
disturbance, which explains why they retreat further all the time. Additional threats
are net entanglement and incidental kill by fishermen, food supply depletion and
pollution. There have been a number of conferences on the conservation of this
species. Some of the conclusions of these meetings have been summarized by Johnson
and Lavigne (1995).
In May 1997, a sudden mass mortality struck the North-west African population. In
a month, about 150 animals died. The estimated population size before the die-off was
about 300 animals. A bloom of dinoflagellates (algae) producing saxitoxins have been
implicated in this mass mortality (Lavigne, 1997).
References
- Boulva, J. (1979)
- Mediterranean Monk Seal. in: Mammals in the Seas, volume II:
pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5,
Vol II, pp. 95-100
- Johnson, W.M. and Lavigne, D.M. (1995)
- The Mediterranean Monk Seal - Conservation Guidelines. 52pp.
International Marine Mammal Association Inc.
- Kenyon, K.W. (1981)
- Monk Seals, Monachus Fleming, 1822. in: Ridgway, S.H. and
Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 2: Seals, pp. 195-220,
Academic Press Inc., Ltd, London
- King, J.E. (1983)
- Seals of the world, 2nd edition. British Museum (Natural History),
London and Oxford University Press, Oxford, 240pp.
- Lavigne, D. (1997)
- Red tide is suspect killer. BBC Wildlife 15(7):21
- Ronald, K., Healey, P.J. (1982)
- The Monk Seal (Monachus monachus). in:
Mammals in the Seas, Volume IV: small cetaceans, seals, sirenians and otters. FAO
Fisheries Series, No. 5, vol. IV, pp. 243-252
- See also: Phil Gibbs' Mediterranean Monk Seal page
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Nomenclature
The West Indian monk seal is also referred to as the Caribbean monk seal.
Appearance
This seal is 200-220 cm long and weighs 160 kg. Pups are 85 cm
long. Pup weights are unknown. This seal is greyish brown with a yellowish ventral.
Females have a slightly darker ventral.
Distribution
The range of this species was from the Bahamas through the Florida
keys and the Yucatan peninsula into the Caribbean Sea, including Cuba and
Jamaica.
Feeding
unknown
Population dynamics
no data available.
Trophic relations
Its main predators are sharks.
Interactions
Very sensitive to disturbance.
Population size
The West Indian monk seal is believed to be extinct. Repeated
surveys of its former habitat have gien no indications of the presence of living seals.
This believe was confirmed by a 1984 census (LeBoeuf et al, 1987).
Exploitation
This species has been severely over-exploited in the past. Since it is
believed to be extinct, no protective measures are taken.
References
- Boulva, J. (1979)
- Caribbean Monk Seal. in: Mammals in the Seas, volume II:
pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5,
Vol II, pp. 101-103
- Kenyon, K.W. (1981)
- Monk Seals, Monachus Fleming, 1822. in: Ridgway, S.H. and
Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 2: Seals, pp. 195-220,
Academic Press Inc., Ltd, London
- King, J.E. (1983)
- Seals of the world, 2nd edition. British Museum (Natural History),
London and Oxford University Press, Oxford, 240pp.
- LeBoeuf, B.J., Kenyon, K.W., Villa-Ramirez, B. (1987)
- The Caribbean monk seal
is extinct. Mar. Mamm. Sci. 2(1): 70-72
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Appearance
Males grow upto 210 cm and can weigh 173 kg. Females can be as
long as 230 cm and weigh upto 273 kg. Pups are 100cm at birth and weigh 16-17
kg. This seal has a slate-grey dorsal side and a light silvery grey ventral.
Distribution
This seal is found on sandy beaches in the Leeward Chain of the
Hawaiian Islands: Pearl and Hermes Reef, Lisianski Island, Laysan Island, Frenah
Frigates Shoal. They used to breed on Midway and Kure Atoll, but they left there,
because of increased disturbance.
Feeding
There is little known about the diet, but it includes cephalopods, eel and
reef and bottom fish.
Population dynamics and life history
Female become sexually mature by the age of 5 years (Iwasa and Atkinson, 1996).
In the Northwest Hawaiian islands (Laysan Island and Lisianksi Island), birth rates
for all adult-sized females is 0.544 (Johanos et al, 1994). Pupping occurs in late March
and early April. Weaning occurs in May. Mating appears to occur in late May and June.
Molting occurs in July. The pupping interval for females giving birth in consecutive
years was 381 days: females that pupped in consecutive years gave birth later each season.
This seal has an aberrant mating system, in which groups of males "mob" the females,
often injuring them. The injuries are occassionally fatal.
Trophic relations
There is no competition. The main predators are sharks.
Interactions
There is no interaction with fisheries. This seal species is very
sensitive for human disturbance. There is some competition for space with humans.
Population size
In 1956-1958 the total population was estimated at 1,200 seals. In
1980 there were only 700 left.
Exploitation
There is no exploitation of this seal. The breeding area is in the
Hawaiian Islands National Wildlife Refuge (HINWR). Access to this refuge by
tourists is discouraged or even prohibited. A few rehabilitated animals are
on display at Sea Life Park, Hawaii (where the pictures on this page were taken).
Threats to the population
This small population is very sensitive for disturbance. In addition, the "mobbing"
behavior of the males causes increased mortalities among females.
References
- Brenton, C. (1979)
- Hawaiian Monk Seal. in: Mammals in the Seas, volume II:
pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5,
Vol II, pp. 104-105
- Iwasa, M. and Atkinson, S. (1996)
- Analysis of corpora lutea to estimate reproductive cycles of wild Hawaiian monk
seals (Monachus schauinslandi). Marine Mammal Science 12(2):182-198
- Johanos, T.C, Becker, B.L. and Ragen, T.J. (1994)
- Annual reproductive cycle of the female Hawaiian monk seal (Monachus schauinslandi).
Marine Mammal Science 10(1): 13-30
- Kenyon, K.W. (1981)
- Monk Seals, Monachus Fleming, 1822. in: Ridgway, S.H. and
Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 2: Seals, pp. 195-220,
Academic Press Inc., Ltd, London
- King, J.E. (1983)
- Seals of the world, 2nd edition. British Museum (Natural History),
London and Oxford University Press, Oxford, 240pp.
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