Monk seal
Monk seals are earless seals of the tribe Monachini. They are the only earless seals found in tropical climates. The two genera of monk seals, Monachus and Neomonachus, comprise three species: the Mediterranean monk seal, Monachus monachus; the Hawaiian monk seal, Neomonachus schauinslandi; and the Caribbean monk seal, Neomonachus tropicalis, which became extinct in the 20th century. The two surviving species are now rare and in imminent danger of extinction. All three monk seal species were classified in genus Monachus until 2014, when the Caribbean and Hawaiian species were placed into a new genus, Neomonachus.
Monk seals have a slender body and are agile. They have a broad, flat snout with nostrils on the top. Monk seals are polygynous, and group together in harems. They feed mainly on bony fish and cephalopods, but they are opportunistic. The skin is covered in small hairs, which are generally black in males and brown or dark gray in females. Monk seals are found in the Hawaiian archipelago, certain areas in the east Atlantic and Mediterranean Sea, and formerly in the tropical areas of the west Atlantic Ocean.
All species experienced overhunting by sealers. The Hawaiian monk seal experienced population drops in the 19th century and during World War II, and the Caribbean monk seal was exploited since the 1500s until the 1850s, when populations were too low to hunt commercially. The Mediterranean monk seal has experienced both commercial and illegal hunting since the Middle Ages and has always been threatened with eradication by fishermen. As of 2022, it is estimated and agreed upon that not more than 600–700 Mediterranean monk seals remain, concentrated primarily along the coasts of Turkey, Cyprus, and Greece. The Hawaiian monk seal appears to be faring somewhat better; the 2021 monk seal population count by the National Oceanic and Atmospheric Association numbered 1,570 animals, an encouraging increase from 1,453 seals in 2019. This marked the first time the Hawaiian monk seal's population exceeded 1,500 in 20 years; their numbers have been recorded and observed to increase approximately 2% each year from 2013 to 2021. Some of this successful growth is undoubtedly due to numerous rescue-and-release operations and the relocating of weaned pups to quieter beaches, enabling more seals to mature naturally and safely.
Etymology
The name "monk seal" was suggested by naturalist Johann Hermann, who claimed that the seal was popularly known as moine in Marseille, and speculated that the seal looks from behind like a monk wearing a cape and hood.Taxonomy and evolution
Monk seals are earless seals of the tribe Monachini. The tribe was first conceived by Victor Blanchard Scheffer in his 1958 book Seals, Sea Lions, and Walruses: A Review of the Pinnipedia. The two genera of monk seals, Monachus and Neomonachus, comprise three species: the Mediterranean monk seal, the Hawaiian monk seal, and the Caribbean monk seal, which became extinct in the 20th century. All three monk seal species were classified in genus Monachus until 2014, when comparison of the species' mitochondrial cytochrome b DNA sequences led biologists to place the Caribbean and Hawaiian species in a new genus, Neomonachus.Fossils of the Mediterranean and Caribbean species are known from the Pleistocene. The time of divergence between the Hawaiian and Caribbean species, 3.7 million years ago, corresponds to the closing of the Central American Seaway by the formation of the Isthmus of Panama. The divergence between Mediterranean seals and the New World clade was dated to 6.3 Mya ago.
Fossils of a Pliocene species of monk seal, Eomonachus belegaerensis, have been found in Taranaki region of New Zealand. This could possibly place the origins of the group in the Southern Hemisphere. The only other fossil monk seal is Pliophoca etrusca, from the late Pliocene of Italy.
Habitat
The Hawaiian monk seal, as the name suggests, lives solely in the Hawaiian archipelago. Monk seals migrated to Hawaii between 4–11 Mya through an open-water passage between North and South America called the Central American Seaway. The Isthmus of Panama closed the seaway 3 Mya. The species may have evolved in the Pacific or Atlantic, but in either case, came to Hawaii long before the first Polynesians. When monk seals are not hunting or eating, they generally bask on the beaches; Hawaiian monk seals tend to bask on sandy beaches and volcanic rock of the Northwest Hawaiian Islands.The habitat of the Mediterranean monk seal has changed over the years. Prior to the 20th century, they had been known to congregate, give birth, and seek refuge on open beaches. Since sealing had ended, they have left their former habitat and now only use sea caves for such behavior. More often than not, these caves are rather inaccessible to humans due to underwater entries, and because the caves are often along remote or rugged coastlines. Scientists have confirmed this is a recent adaptation, most likely due to the rapid increase in human population, tourism, and industry, which have caused increased disturbance by humans and the destruction of the species' natural habitat. Because of these seals' shy nature and sensitivity to human disturbance, they have slowly adapted to try to avoid contact with humans completely within the last century, and perhaps, even earlier. The coastal caves are, however, dangerous for newborns, and are causes of major mortality among pups when sea storms hit the caves.
Caribbean monk seals were found in warm temperate, subtropical, and tropical waters of the Caribbean Sea, Gulf of Mexico, and the west Atlantic Ocean. They probably preferred to haul out at sites on isolated and secluded atolls and islands, but occasionally visited the mainland coasts and deeper waters offshore. This species may have fed in shallow lagoons and reefs.
Description
Monk seals are part of the family Phocidae, the members of which are characterized by their lack of external ears, the inability to rotate the hind flippers under the body, and shed their hair and the outer layer of their skin in an annual molt. Monk seals as a whole vary minutely in size, with all adults measuring on average and. They exhibit sexual dimorphism, in that male Mediterranean monk seals are slightly larger than females, while in Hawaiian monk seals, females are larger. Its white belly, gray coat, and slender physique distinguish it from the harbor seal, another earless seal.The Mediterranean monk seal has a short, broad, and flat snout, with very pronounced, long nostrils that face upwards. The flippers are relatively short, with small, slender claws. The monk seal's physique is ideally suited for hunting its prey: fish, octopus, lobster, and squid in deep-water coral beds. The fur coats of males is generally black, and brown or dark gray in females. Pups are about long and weigh around, their skin being covered by fur, usually dark brown or black. On their bellies, a white stripe occurs, which differs in color between the two sexes. This hair is replaced after 6–8 weeks by the usual short hair adults carry.
The Hawaiian monk seal has a short, broad, and flat snout, with long nostrils that face forward. It has a relatively small, flat head with large, black eyes, eight pairs of teeth, and a short snout with the nostrils on top of the snout and vibrissae on each side. The nostrils are small, vertical slits, which close when the seal dives under water. Additionally, their slender, torpedo-shaped body and hind flippers allow them to be very agile swimmers. Adult males are in weight and in length, while adult females tend to be, typically, slightly larger, at and in length. When monk seal pups are born, they weigh and are in length. As they nurse for about 6 weeks, they grow considerably, eventually weighing between by the time they are weaned, while the mother loses up to.
Caribbean monk seals had a relatively large, long, robust body, and could grow to nearly in length and weighed. Males were probably slightly larger than females, which is similar to Mediterranean monk seals. Like other monk seals, this species had a distinctive head and face. The head was rounded with an extended, broad muzzle. The face had relatively large, wide-spaced eyes, upward-opening nostrils, and fairly big whisker pads with long, light-colored, and smooth whiskers. When compared to the body, the animal's foreflippers were relatively short with little claws and the hindflippers were slender. Their coloration was brownish and/or grayish, with the underside lighter than the dorsal area. Adults were darker than the paler and more yellowish younger seals. Caribbean monk seals were also known to have algae growing on their pelages, giving them a slightly greenish appearance, which is similar to Hawaiian monk seals.
Behavior
Diet and predation
Hawaiian monk seals mainly prey on reef-dwelling bony fish, but they also prey on cephalopods and crustaceans. Juveniles and subadults prey more on smaller octopus species, such as Octopus leteus and O. hawaiiensis, and eels than do adult Hawaiian monk seals. Adult seals feed mostly on larger octopus species such as O. cyanea. Hawaiian monk seals have a broad and diverse diet due to foraging plasticity, which allows them to be opportunistic predators that feed on a wide variety of available prey. Tiger sharks, great white sharks, and Galapagos sharks are all predators of the Hawaiian monk seal.Mediterranean monk seals are diurnal and feed on a variety of fish and mollusks, primarily octopus, squid, and eels, up to per day. They are known to forage mostly at depths of, but some have been observed by NOAA submersibles at a depth of. They prefer hunting in wide-open spaces, enabling them to use their speed more effectively. They are successful bottom-feeding hunters; some have even been observed lifting slabs of rock in search of prey. They have no natural predators.