Angel sharks are a type of shark in the group called Squatina. They are the only living members of the family Squatinidae and the order Squatiniformes. These sharks usually live on sandy ocean floors near a depth of about 150 meters (490 feet).

Sharks in the group Squatina and other Squatiniformes have flat bodies and wide pectoral fins, which make them look similar to rays. They are found in temperate and tropical seas around the world. Most species live in shallow, warmer or cooler ocean areas, but a few live in deeper waters, as deep as 1,300 meters (4,300 feet). Angel sharks are sometimes called monkfish, though this name is also used for sharks in the group Lophius.

Some species of angel sharks live in large areas, but most are found only in smaller regions. This limited range may be because Squatina species are ambush predators that stay near the ocean floor and do not move far. Because of this, they rarely travel across oceans, even though some species, like Squatina squatina, are known to move along coastlines.

Many angel shark species are now classified as critically endangered by the International Union for Conservation of Nature. These sharks were once common in large areas of the Northeast Atlantic, including regions near Norway, Sweden, Morocco, the Canary Islands, the Mediterranean, and the Black Seas. However, fishing has caused their populations to drop significantly.

Appearance and biology

Angel sharks can grow up to 7 feet (2.1 meters) long and weigh about 77 pounds (35 kilograms). The front part of their body is wide and flat, while the back part is more muscular, like other sharks. Their eyes and spiracles are on top of their head, and they have five gill slits on their back. Both the pectoral and pelvic fins are large and held flat. They have two dorsal fins, no anal fin, and their tail has a longer lower lobe than the upper lobe, which is unusual for sharks. Most angel sharks grow to about 1.5 meters (5 feet) long, but the Japanese angel shark can reach up to 2 meters (6.5 feet).

Some angel sharks have physical problems, such as curved spines (scoliosis), humpback curves (kyphosis), or extra or missing fins. These issues are rare and can be caused by poor nutrition, genetic factors, parasites, injuries, or stress. In 2015, two sharks were found with scoliosis and kyphosis near their pectoral fins, but these deformities did not stop them from swimming.

Spinal curvatures are more common in pelagic sharks that rely on swimming to hunt, but for angel sharks, these issues do not seem to hurt their ability to catch prey. Angel sharks hide in the sand to ambush fish, crustaceans, and mollusks. They have strong jaws that snap upward quickly and sharp, needle-like teeth. They are ovoviviparous, meaning they give birth to live young after the eggs develop inside the mother. Pacific angel shark pups are born between March and June in deep water, about 180 to 300 feet (55 to 90 meters) deep, possibly to protect them from predators.

Angel sharks usually live in water 1 to 200 meters (3.3 to 656.2 feet) deep, where they blend in with muddy or soft sea floors. They lie still and wait for prey, then quickly lunge forward to suck in food using their mouths. Members of the family Squatinidae, like angel sharks, use this unique hunting method to catch prey.

Angel sharks are often caught near coasts, where they live. In 1986, over 1,125 tonnes of Pacific angel sharks were caught, making them the most commonly landed shark species off the U.S. West Coast that year. Few attacks on humans have been reported, and most happened accidentally when people stepped on hidden newborn sharks.

Species analysis

Identifying species based on their appearance in the field can be challenging because some species look very similar. In this case, three species of sharks belong to the genus Squatina in the southern part of the western Atlantic Ocean. These species are Squatina guggenheim, Squatina occulta, and the Brazilian guitarfish Pseudobatos horkelii. All three species are listed as threatened on the IUCN Red List and are protected by Brazilian law, which makes fishing and trading them illegal. To stop the capture and sale of these endangered species in São Paulo, scientists used DNA barcoding. This method showed that people were catching and selling these protected animals.

Habitat

Angel sharks live in temperate and tropical ocean areas. They are usually found in shallow waters near coasts, at depths between 3–100 metres (9.8–328.1 ft). During the day, they dig into sandy or muddy areas to hide and remain camouflaged for weeks until they find prey to eat. At night, they become more active and move along the ocean floor. Squatina eats fish, crustaceans, and cephalopods.

Behavior

This shark lives near the ocean floor and seems harmless, but it can cause painful injuries if disturbed because of its strong jaws and sharp teeth. It may bite if a diver gets too close to its head or touches its tail.

Angelsharks have a special way of breathing that is different from most other bottom-dwelling fish. Unlike other fish, they do not push water out from their mouth and throat area. Instead, they use gill flaps under their body to move water during breathing. This method helps them stay hidden and avoid being noticed.

Commercial value

Before the late 1980s, the Pacific angel shark was considered a "junk fish." It was a product that was not wanted, often caught accidentally during commercial fishing with gillnets and used only as crab bait. In 1977, Michael Wagner, a fish processor in Santa Barbara, California, US, worked with local fishermen to create a market for angel sharks. The amount of angel sharks caught each year in 1977 was about 147 kilograms. By 1985, the amount caught along the central California coast had grown to more than 454 tonnes, or about 90,000 sharks. This caused the population to drop sharply, and rules were later put in place to protect them. Angel sharks live near the shore, which leads to many being caught accidentally. In 1991, the use of gillnets in nearshore waters of California was banned, and fishing was limited in a larger area where the sharks live. In April 2008, the UK government gave the angel shark full protection under the Wildlife and Countryside Act.

Conservation

The angel shark (Squatina squatina) was once common in the Atlantic Ocean but was listed as "Critically Endangered" in 2010. Studies by the IUCN in 2019 confirmed this status. Angel sharks are easily harmed by bottom trawling and often become accidentally caught in gillnets because they live in shallow waters.

In the Mediterranean Sea, angel sharks such as S. aculeata, S. oculata, and S. squatina face a high risk of extinction. Research suggests their populations may decline sharply. The Angel Shark Conservation Network, created by the IUCN and Shark Trust, is working with officials in Greece and Turkey to develop plans to protect these sharks in the region.

Evolution

The earliest known members of the Squatiniformes are found in the Late Jurassic period, which was about 160 million years ago, in Europe. These early members belonged to the genus Pseudorhina. Fossils of Pseudorhina that show complete bodies look very similar to those of modern Squatina species. The earliest confirmed records of the modern genus are found in the Early Cretaceous (Aptian) period in England.

Species

At present, the 26 officially identified species in this genus are:

• Squatina aculeata G. Cuvier, 1829 (sawback angelshark)
• Squatina africana Regan, 1908 (African angelshark)
• Squatina albipunctata Last & W. T. White, 2008 (eastern angelshark)
• Squatina argentina (Marini, 1930) (Argentine angelshark)
• Squatina armata (Philippi {Krumweide}, 1887) (Chilean angelshark)
• Squatina australis Regan, 1906 (Australian angelshark)
• Squatina caillieti J. H. Walsh, Ebert & Compagno, 2011 (Philippines angelshark)
• Squatina californica Ayres, 1859 (Pacific angelshark)
• Squatina david Acero P, Tavera Vargas, Anguila-Gómez & Hernández-Beracasa, 2016 (David's angelshark)
• Squatina dumeril Lesueur, 1818 (sand devil)
• Squatina formosa S. C. Shen & W. H. Ting, 1972 (Taiwan angelshark)
• Squatina guggenheim Marini, 1936 (angular angelshark)
• Squatina heteroptera Castro-Aguirre, Espinoza-Pérez & Huidobro-Campos, 2007 (disparate angelshark)
• Squatina japonica Bleeker, 1858 (Japanese angelshark)
• Squatina leae Weigmann, Vaz, Akhilesh, Leeney & Naylor, 2023 (Lea's angelshark)
• Squatina legnota Last & W. T. White, 2008 (Indonesian angelshark)
• Squatina mapama Long, Ebert, Tavera, Acero P., and Robertson, 2021 (Small-crested angelshark)
• Squatina mexicana Castro-Aguirre, Espinoza-Pérez & Huidobro-Campos, 2007 (Mexican angelshark)
• Squatina nebulosa Regan, 1906 (clouded angelshark)
• Squatina occulta Vooren & K. G. da Silva, 1991 (hidden angelshark)
• Squatina oculata Bonaparte, 1840 (smoothback angelshark)
• Squatina pseudocellata Last & W. T. White, 2008 (western angelshark)
• Squatina squatina (Linnaeus, 1758) (angelshark)
• Squatina tergocellata McCulloch, 1914 (ornate angelshark)
• Squatina tergocellatoides J. S. T. F. Chen, 1963 (ocellated angelshark)
• Squatina varii Vaz & Carvalho, 2018 (Brazilian angelshark)

The following extinct species are known:

• † Squatina angeloides Storms, 1894
• † Squatina baumbergensis von der Marck, 1885
• † Squatina beyrichi Noetling, 1885
• † Squatina carinata Giebel, 1848
• † Squatina cranei Woodward, 1888 (also classified in Cretascyllium)
• † Squatina crassa Daimeries, 1889
• † Squatina danconai Daimeries, 1889
• † Squatina decipiens Dalinkevicius, 1935
• † Squatina fortemedeo Siversson, Cook, Cederström & Ryan, 2016
• † Squatina gigantea Ameghino, 1906
• † Squatina lerichei Jordan & Beal, 1913
• † Squatina lundegreni Siversson, Cook, Cederström & Ryan, 2016
• † Squatina minor Eastman, 1911
• † Squatina moelleri Klprijanov, 1881
• † Squatina occidentalis Eastman, 1904
• † Squatina prima (Winkler, 1874)
• † Squatina subserrata (Münster, 1846)

Most of these species are known only from single teeth, but S. cranei and S. baumbergensis are known from well-preserved remains of their bodies.

• Squatina australis
• Squatina californica
• Squatina dumeril
• Squatina japonica
• Squatina squatina