Adults are robust, with short flippers, a long fusiform body, and a moderately-sized head. The head and muzzle are wide and somewhat flat, with the eyes spaced widely apart. The mystacial pads are large, fleshy, and extend beyond the nostrils. The nostrils are in a sub-terminal position, pointed up, rather than in a terminal position facing forward, as is typical of most northern phocids. The vibrissae are smooth and not beaded like in other monk seals, Antarctic seals, and both elephant seals. Females have four retractable abdominal mammae.
Coloration is variable, with differences existing between adult males and females and between age classes. Variation also occurs within each age class, and has been proposed to be present between the now isolated sub-populations. Adult males are dark brown to black over most of the body. Most adult females are medium to dark gray above and paler below, the colors separated by either a gradual blending or a sharp demarcation. The dark coloration is made paler by light tips to the hairs. Juveniles and subadults can be a range of gray tones above, including light, chestnut, medium, and dark gray, and are paler from off-white to light gray below.
Pups are born in a brownish black long woolly lanugo coat that is molted at six to seven weeks to a youngster stage, which is comprised of a mixture of weakly developed juvenile countershaded coloration features and pup markings. Most pups have a large irregular light gray ventral patch on the abdomen that can rise up on the sides at mid-abdomen, well behind the fore flippers. In males there is an anterior extension of dark coloration into the posterior edge of the patch on the mid-line that encompasses the penile opening. Irregular spotting and blotching can mark the boundary of this light patch with the darker fur of the sides. The pale ventral patch disappears at the second molt from youngster to juvenile pelage at about 7-9 months, when the animals essentially become countershaded dark above and lighter below. This belly patch reappears in some otherwise dark adult males. Dark adult males can have a light ventral patch on the abdomen like that described for the pup and a patch of light color on the throat and chin that extends onto the sides of the neck.
Countershaded adults and juveniles show numerous variations in the extent of coverage of the neck, areas around the eyes, top of the muzzle, and sides of the head with light ventral coloration. Adults also usually have numerous lighter line and irregular markings from scars. Adult females can have a sash of pale color on the back over the abdomen, which is thought to be from the accumulation of numerous scars in this general location on the back from biting by males.
Little is known about the adult and subadult molts; however, the related Hawaiian monk seal is known for its dramatic epidermal molt, in which hair is shed attached to layers of skin.
Adults are up to 2.8 m in length, and weigh 250-400 kg. In contrast to the Hawaiian monk seal, Mediterranean monk seal males may grow to be slightly heavier and longer than females. Newborns are 80-120 cm and 15-26 kg.
The dental formula is I 2/2, C 1/1, PC 5/5.
Can be Confused With
Mediterranean monk seals do not regularly share their range with any other pinniped. The nearest occurring species are eastern Atlantic Ocean populations of the more northerly distributed harbor and gray seals. These as vagrants, along with wandering hooded and bearded seals from the Arctic, have occurred near the Mediterranean monk seal’s range. However, Mediterranean monk seals can be readily distinguished from harbor, gray, and adult hooded seals by their lack of numerous spots or blotches, distinctively wide and somewhat flattened head and muzzle, sub-terminal upward-facing nostrils, smooth vibrissae, and four mammary teats.
Bearded seals have few to no spots, and share rounded vibrissae and four abdominal nipples as features in common with Mediterranean monk seals. However, bearded seals have a proportionately smaller, domed head. The muzzle is proportionately narrower with more densely packed, longer, and predominantly downward pointing vibrissae. The short, rounded fore flipper with a short first digit is also unique to the bearded seal and gives the end of the flipper a rounded edge. Mediterranean monk seals have typically proportioned fore flippers, with the first digit longer than all other digits.
Mediterranean monk seals are widely-distributed in the Mediterranean Sea, as well as the Aegean, Ionian, and Black seas, and the Sea of Marmara. Historically, they occurred throughout the region, but now are only found in small widely-scattered aggregations. They occur in the eastern North Atlantic from the Strait of Gibraltar south and west to Mauritania at 19°N, with wanderers reaching Dakar, Senegal at 15°N. They are offshore at the Cape Verde Islands and at Desertas Island in the Madeira Island group. Although Mediterranean monk seals can still be seen on occasion throughout much of their former range, this is becoming increasingly rare. On land, they choose rocky coastlines, with a preference for sea caves and grottos that are generally inaccessible from land approaches, and sometimes have only submarine entrances. In West Africa, they will come ashore on open beaches.
Ecology and Behavior
This seal is considered non-migratory, with individuals spending most of their time within a very limited home range. They make extensive use of grottos and sea caves for hauling-out and breeding. The single pups are born across a wide pupping season that can last from May through at least November, and possibly January, with an October peak, but some authors speculate that pupping could occur year-round. Females are on an eleven-month cycle of copulation to birth, and then wean their pups at four months, but can allow offspring to stay with them up to four years.
Mediterranean monk seals are among the least social of pinnipeds when ashore; they are presumed to be most socially active in the water, where the only copulation ever seen was witnessed. Little information is available on diving, but most dives are thought to be shallow, less than 70 m, and short, less than 10 minutes in duration.
Feeding and Prey
The diet consists of octopus, at least one type of ray, and a large variety of coastal fishes. Large fish that cannot be swallowed whole are brought to the surface and shaken apart.
Threats and Status
The Mediterranean monk seal is the most endangered pinniped species in the world, with an estimated population of 350-450 animals. This small population is widely-scattered in isolated sub-populations from the North Atlantic to the eastern Mediterranean and Black seas, most of which are reproductively isolated from one another. There is a high risk of inbreeding depression and low genetic variability in these sub-populations, resulting from the species being so widely-distributed in small breeding groups.
The Mediterranean and adjacent North Atlantic and Black seas are heavily fished. In many areas, monk seals are viewed as a pest species, and competitors for fish resources, and in some instances have been shot. They are also susceptible to entanglement in marine debris and discarded and lost fishing nets and line. Human disturbance of animals at haul-out sites and in foraging areas could also contribute to lower reproductive success. An outbreak of a phytoplankton based paralytic toxin was the probable cause of a large-scale die-off in a colony along the Western Sahara coast. A morbillivirus may also have been a factor in this mortality event.
Gazo, M., F. Apaicio, M.A. Cedenilla, J.F. Layna and L.M. Gonzalez. 2000. Pup survival in the Mediterranean monk seal (Monachus monachus) colony at Cabo Blanco Peninsula (Western Sahara-Mauritania). Marine Mammal Science 16(1):158-168.
Gilmartin, W.G. and J. Forcada. 2002. Monk seals Monachus monachus, M. tropicalis, and M. schauinslandi. pp. 756-759 in W.F. Perrin, B. Würsig, and J.G.M. Thiewissen, eds. Encyclopedia of marine mammals. Academic Press.
Kenyon, K.W. 1981. Monk seals - Monachus Flemming, 1822. pp. 195-220 in S.H. Ridgway and R. Harrison, eds. Handbook of marine mammals, Vol. 2: Seals. Academic Press.
King, J.E. 1983. Seals of the world. Second Edition. British Museum (Natural History), Comstock Publishing Associates, and Cornell University Press. 240 pp.
Pastor, T. and A. Aguilar. 2003. Reproductive cycle of the female Mediterranean monk seal in the western Sahara. Marine Mammal Science 19(2):318-330.
Pires, R. and H.C. Neves. 2001. Mediterranean monk seal Monachus monachus conservation: a case study in the Desertas Islands. Mammalia 65(3):301-308.
Samaranch, R. and L.M. Gonzalez. 2000. Changes in morphology with age in Mediterranean monk seals (Monachus monachus). Marine Mammal Science 16(1):141-157.
Sergeant, D., K. Ronald, J. Boulva and F. Berkes. 1978. The recent status of Monachus monachus, the Mediterranean monk seal. Biological Conservation 14:259-287.