Squatina Duméril , 1806 : 102, 342. Type Squalus squatina Linneaus 1758 , by subsequent designation.
Rhina Rafinesque 1810 : 4. Type Squalus squatina Linneaus 1758 , type by monotypy.
Definition. Broad, flattened body with large bat-like pectoral fins. Mouth terminal, broadly arched with ornate nasal flaps and highly protrusible jaws. Spiracles large, without valves. Pectoral fins not fused to head, origin opposite gill openings. Anterior extent of pectorals triangular and covering gill openings. Five pairs of gill openings positioned between pectoral origin and base of the head. Trunk compressed dorsal-ventrally. Two dorsal fins, spineless, originating behind pelvic fin insertion on the precaudal. Anal fin absent. Furrow on ventral from dorsal origin to caudal peduncle. Caudal fin hypocercal. Total length, depending on species, generally between 1-2 m.
Squatina Dumeril, 1806 is a monotypic genus within the family Squatinidae (Bonaparte, 1838). Although morphologically similar to batoids, squatinids are distinct from true batoids in that the squatinids have lateral gill openings, pectoral fin lobes that are free lateral to the gills, and possess a lower caudal fin lobe that is longer than the upper caudal lobe. Within the genus these sharks can be difficult to distinguish due to the lack of well defined characteristics. Adding to the confusion in the literature are the inadequate original descriptions of many species.
Sixteen valid species are recognized worldwide, with four reported to occur in the western North Pacific (WNP; Compagno et al., 2005). These four species include Squatina formosa Shen and Ting, 1972 , S. japonica Bleeker, 1858 , S. nebulosa Regan, 1906 , and S. tergocellatoides Chen, 1963 . Distinctions among these four WNP species hinge upon the nasal barbel shape, interorbital and interspiracle distances, ocellus patterns, number of dermal folds about the mouth, and the presence of midback thorns (Lindberg & Legeza, 1967; Shen & Ting, 1972; Nakabo, 2002). However, specific identification is hard to assign to individuals because many of these characters are difficult to distinguish, and many characters currently used are susceptible to damage during collection or from preservation. Additionally, inadequate original descriptions for some species and confusion within the subsequent literature have further obscured definitive characters among the WNP species. Because members of this genus are frequently targeted in fisheries in an area that has sparsely recorded catch information, and congeners are particularly sensitive to fishing pressure (Gaida, 1997; Stevens et al, 2000), it is imperative that adequate descriptions are available to identify individual species.
During two field expeditions to Taiwan, one of us (DAE) observed at least four species of Squatina that were frequently landed at fish markets around Taiwan. Attempts to identify the various species were often hampered by a lack of adequate fish keys and descriptive characters for the various Squatina species observed. Furthermore, we had the opportunity to examine the holotype and three paratypes of S. formosa as well as collect additional material.
Using this information, we provide a detailed redescription of three of the species, S. formosa , S. japonica , and S. nebulosa , with new material from Japanese and Taiwanese waters. In addition, we supply a list of important key characters for distinguishing all known WNP squatinids, especially to facilitate identification of the two most similar species, S. formosa and S. nebulosa .
The main confusion among WNP squatinids lies in differentiating S. formosa and S. nebulosa from one another. The main character used in the past to differentiate these two species was the number of dermal lobes at the corners of the mouth (Chen 1963, Nakabo 2002, Compagno 2005a). Based upon our examination, this character does not appear to be robust in separating these species. Although all S. formosa individuals studied had one dermal lobe, S. nebulosa specimens had one or two lobes, invalidating this character as a method of separating the two species. Additionally, the number of dermal lobes was often difficult to determine since differentiation between lobes is often vague and these lobes are susceptible to damage during capture and or preservation of specimens. A combination of characters should be used to identify individuals of these two species, since the differences are subtle and a great deal of overlap exists among many characters. The best characters available, based on our findings, appear to be the shape of the caudal pelvic and dorsal fins, the ratio of standardized pelvic girdle distance with the standardized head length, and the shape and height of the upper lip arch. The upper lip arch appears to be of particular value as a field character. It is a feature that is not prone to damage and is easy to assess quickly in the field. More specimens are needed to assess the utility of this character but it appears to be useful for all WNP squatinids.
Based on the key characters presented herein, we provide the following key to the WNP squatinids:
Key to Western North Pacific Squatina Species
1. Pelvic fin tips do not extend to origin of first dorsal fin..............................................................................2.
- Pelvic fin tips extend to or surpass origin of first dorsal fin........................................................................3.
2. A prominent row of thorn-like denticles extending from mid-back to caudal peduncle; no distinct ocelli on posterior lobes of the pectoral fins................................................................................................ S. japonica
- No row of thorn-like denticles extending from the mid-back to the caudal peduncle, distinct paired ocelli on the posterior lobes of the pectoral fins......................................................................... S. tergocellatoides
3. Upper lip arch semi-circular in shape (>1.5% TL in height); dorsals are lobed with a curvilinear anterior margin; pelvic girdle distance 1.4 times or less head length; caudal fin is lobed, especially dorsally, with a curvilinear postventral caudal margin........................................................................................... S. formosa
- Upper lip arch is not semi-circular in shape (<1.5% TL in height); dorsals are not lobed (angular) without a curvilinear anterior margin (straight); pelvic girdle distance greater than 1.4 times head length; caudal fin is not lobed (angular), especially dorsally, without a curvilinear postventral caudal margin (straight) ... ..................................................................................................................................................... S. nebulosa
The angelsharks are a group of sharks in the genus Squatina of the family Squatinidae. They commonly inhabit sandy seabeds close to 150 m (490 ft) in depth. Many species are now classified as critically endangered by the International Union for Conservation of Nature. Once common over large areas of the Northeast Atlantic from Norway, Sweden, Morocco and the Canary Islands, to the Mediterranean and Black Seas, fishing pressure has resulted in significant population decline.
Squatinidae are unusual in having flattened bodies and broad pectoral fins that give them a strong resemblance to rays. This genus is the only one in its family and order Squatiniformes. They occur worldwide in temperate and tropical seas. Most species inhabit shallow temperate or tropical seas, but a few species inhabit deeper water, down to 1,300 m (4,300 ft).[2] Angel sharks are sometimes called monkfish, although this name is also applied to members of the genus Lophius.
While some species occur over a wide geographic range, the majority are restricted to a smaller area. Restriction in geographic range might be as a result of the behaviour of Squatina species, which are ambush predators with a corresponding stationary bottom-dwelling habit. Thus, trans-ocean migration is extremely unlikely, even though large-scale coastal migratory patterns have been reported in species such as Squatina squatina.[3]
The angel shark has unique features that differentiates them from other sharks. They are considered as smaller sized sharks because they grow up to only 7 feet (2.1 m) and can weigh around 77 pounds (35 kg), as opposed to the whale shark that can measure up to 32 feet (9.8 m) and weigh 20,000 pounds (9,100 kg).
While the anterior part of the angel shark's body is broad and flattened, the posterior part retains a muscular appearance more typical of other sharks. The eyes and spiracles are dorsal and the five gill slits are on its back. Both the pectoral and pelvic fins are large and held horizontally. There are two dorsal fins, no anal fin and unusually for sharks, the lower lobe of the caudal fin is longer than the upper lobe. Most types grow to a length of 1.5 m (5 ft), with the Japanese angel shark, known to reach 2 m.[4] Some angel sharks have deformities that have been described in elasmobranchs. These can include skeletal deformities, as lateral spinal curvature (scoliosis), humpback curvature (khyphosis), axial spinal curvature (lordosis), missing fins, additional fins, deformed snout, and more. These abnormalities have only been found in a few sharks, but the causes of these deformities have been found to be from dietary nutritional imbalance, genetic factors, parasites, traumatic injuries, or stress in the specimen. In 2015, two sharks were captured and examined, and both showed a lateral spinal curvature (scoliosis) and also a humpback curvature. Both the animals had the curvature in the middle of their pectoral fins, but the deformity did not affect their swimming capacity.
Spinal scoliosis has been reported to be diverse in sharks, but mostly in pelagic sharks that depend on their swimming abilities to catch their prey. For the angel shark, specifically S. squatina, these curvatures do not seem to significantly affect its hunting capacity, which involves burying itself to ambush their prey. Right now, research is assuming most physical injuries are caused by human interactions because of the constant interference in coastal areas, where most of the sharks reside. There have been few attacks reported, and what few have occurred were due to accidental stepping on of buried newborn sharks.[5] Landings of Pacific angel shark increased through the mid-1980s and reached over 1,125 tonnes in 1986, becoming the shark species with the highest total reported landings off the US West coast that year.[6]
Angel sharks possess extensible jaws that can rapidly snap upwards to capture prey and have long, needle-like teeth. They bury themselves in loose sediment lying in wait for prey, which includes fish, crustaceans and various types of mollusks.[2] They are ovoviviparous, producing litters of up to 13 pups. Pacific angel shark pups are born from March to June in deep water; generally 180 to 300 feet (55 and 90 metres); possibly to protect the pups from predators.[7]
Angel sharks usually reside in depths of 1–200 metres (3.3–656.2 ft) and can be seen on muddy or soft benthic substrata where they can easily blend in as they lie in wait. Members of the family Squatinidae have a unique camouflage method, which relates to how they obtain their food, involving lying still on the sea floor, making rapid lunges at passing prey, and using negative pressure to capture prey by sucking it into their mouths.[8]
Morphological identification in the field can be difficult due to discontinuity and similarity of species. In this specific circumstance, the sharks' place within the genus Squatina comprises three species in the southern part of the western Atlantic. The three species observed were Squatina guggenheim, S. occulta and the Brazilian guitarfish Pseudobatos horkelii. These three species are listed in the IUCN Red List as threatened, and they are now protected under Brazilian law, which makes angling and exchange illegal. To prevent landing and trade of these endangered species along the São Paulo, DNA barcoding was used. DNA barcoding revealed fishing and trafficking of these protected species.[9]
Angel sharks inhabit temperate and tropical marine environments. They are generally found in shallow waters at depths from 3–100 metres (9.8–328.1 ft) off coasts. They are known to bury themselves in sandy or muddy environments during the day, where they remain camouflaged for weeks until a desirable prey crosses paths with them. At night, they take a more active approach and cruise on the bottom of the floor. Squatina preys on fish, crustaceans, and cephalopods.
Although this shark is a bottom-dweller and appears harmless, it can inflict painful lacerations if provoked, due to its powerful jaws and sharp teeth. It may bite if a diver approaches the head or grabs the tail.[10]
Angelsharks have a unique way of breathing compared to most other benthic fish. They do not pump out water from the oropharyngeal cavity like other fish. Instead they use gill flaps located under their body to pump out water during respiration. Doing so also allows them to be more discreet and prevent detection.[11]
Prior to the late 1980s, the Pacific angel shark was considered a "munk fish".[12] It was a byproduct of commercial gillnetting, with no commercial appeal and was used only for crab bait. In 1977, Michael Wagner, a fish processor in Santa Barbara, California, US, in cooperation with local commercial fishermen, developed the market for angel sharks.[12] The annual take of angel shark in 1977 was an estimated 147 kg.[12] By 1985, the annual take of angel shark on the central California coast had increased to more than 454 tonnes or an estimated 90,000 sharks.[12] The population declined dramatically and is now regulated. Angel sharks live very close to shore, resulting in high bycatch rates. In 1991, the use of gillnets in nearshore state waters of California was forbidden, and fishing was restricted in a larger portion of the Pacific angel shark's range.[13]
In April 2008, the UK government afforded the angel shark full protection under the Wildlife and Countryside Act.
Once considered abundant in the Atlantic Ocean, the angel shark (Squatina squatina) was classified as "Critically Endangered" in 2010, and recent studies from the IUCN in 2019 reaffirm their CR status.[14][15] Angel sharks are highly sensitive to bottom trawling and are often caught in gillnets, due to their shallow habitat range.
Angel sharks found in the Mediterranean Sea, S. aculeata, S. oculata, and S. squatina, are at a high risk of extinction, with geographic studies projecting severe population declines for the three species.[16] The Angel Shark Conservation Network, a network established by the IUCN and Shark Trust, is working with authorities from Greece and Turkey to establish conservation strategies to protect angel shark populations in the region.[17]
Currently, the 26 recognized species in this genus are:
The angelsharks are a group of sharks in the genus Squatina of the family Squatinidae. They commonly inhabit sandy seabeds close to 150 m (490 ft) in depth. Many species are now classified as critically endangered by the International Union for Conservation of Nature. Once common over large areas of the Northeast Atlantic from Norway, Sweden, Morocco and the Canary Islands, to the Mediterranean and Black Seas, fishing pressure has resulted in significant population decline.
Squatinidae are unusual in having flattened bodies and broad pectoral fins that give them a strong resemblance to rays. This genus is the only one in its family and order Squatiniformes. They occur worldwide in temperate and tropical seas. Most species inhabit shallow temperate or tropical seas, but a few species inhabit deeper water, down to 1,300 m (4,300 ft). Angel sharks are sometimes called monkfish, although this name is also applied to members of the genus Lophius.
While some species occur over a wide geographic range, the majority are restricted to a smaller area. Restriction in geographic range might be as a result of the behaviour of Squatina species, which are ambush predators with a corresponding stationary bottom-dwelling habit. Thus, trans-ocean migration is extremely unlikely, even though large-scale coastal migratory patterns have been reported in species such as Squatina squatina.
