Squatiniformes

(Angelsharks)

Class Chondrichthyes

Order Squatiniformes

Number of families 1

Evolution and systematics

Angelsharks are an ancient lineage, first appearing in the fossil record about 150 million years ago during the late Jurassic period. The remains of articulated angelsharks are known from the marine deposits of Solnhofen, southern Germany (genus Pseudorhina); these are well-preserved specimens that resemble modern angelsharks in most morphological details. Most fossil angelshark species, however, are known from isolated teeth reported from the late Jurassic to the Pliocene epoch (some 5 million years ago) of many localities, including Europe, North America, Greenland, Japan, and Africa.

The evolutionary relationships of angelsharks have been intensely debated since their discovery. They are presently classified in a large group with the cow and frilled sharks (Hexanchiformes), the dogfishes and allies (Squaliformes), the sawsharks (Pristiophoriformes), and the rays (also known as batoids). Together, these groups comprise the Squalea, as all members have complete hemal arches (ventral projections arising from the vertebral column) in the trunk region anterior to the tail, among other anatomical innovations. Within the Squalea, the angelsharks are most closely related to a group that includes the sawsharks and the rays. Angelsharks have traditionally been thought to be closely related to rays, but rays are actually more closely related to sawsharks. Almost nothing is known about the phylogenetic relationships among angelshark species. All living angelsharks are classified together in one family, the Squatinidae.

Fifteen living species of angelsharks are currently recognized, all placed in the single genus Squatina. There may also be two undescribed species living off southern Australia. Most living species of angelsharks have not been very well characterized, and critical taxonomic studies are still needed. Much is yet to be learned about their population dynamics and reproductive patterns, which are essential because some species are of commercial importance locally (for example, in Australia).

Physical characteristics

Angelsharks are among the most distinctive living sharks, strongly resembling rays in being dorsoventrally flattened, with enlarged pectoral fins reminiscent of the batoid disc. The head of angelsharks, however, is not fused to the pectoral fins as it is in rays (where it forms the disc). Their pectoral fins have a unique anterior lobe that mostly conceals the five gill slits. The gill slits are laterally situated, but extend ventrally as well (contrasting to the exclusively ventral gill slits of rays). The head is exceptionally wide and depressed, entirely anterior to the pectoral fins, and with a very wide, terminal mouth. The eyes and spiracles are dorsally situated, close to the front margin of the head, and the spiracles are somewhat transverse. The anterior nasal flaps are wide and fringed, and the pattern of fringes is sometimes useful in identification. Angelsharks have two spineless dorsal fins posterior to the pectoral and pelvic fins, a rather slender, short tail that is abruptly demarcated from the trunk, a caudal fin that is unique in having a greatly elongated lower lobe (longer than upper lobe), and no anal fin.

Coloration is diagnostic for many angelshark species. Some have a relatively light background color, but others are darker, and most are marked with various spots, ocelli (eyelike spots), and blotches, sometimes of varying color and size. Squatina tergocellata from Australia has three pairs of characteristic dark ocelli on its back and pectoral fins, and S. tergocellatoides from Taiwan has similar spots dorsally, but not quite forming ocelli. Squatina australis is unique in presenting dark spots on the lower lobe of its caudal fin, with creamy white and darker spots dorsally. Squatina japonica is reddish dorsally (as is S. squatina) with darker red blotches over the trunk. The southwestern Atlantic species are similar to each other in coloration, composed of a dark or light tan background with yellowish and brownish spots and diffused blotches.

Angelsharks are mostly of medium size, reaching about 5 ft (1.5 m) long, but occasionally larger individuals, up to 6.6 ft (2 m), may occur. For most species, males mature when between 29.5–43.3 in (75–110 cm), and females at slightly larger sizes. Size at birth varies from 9.8–13.8 in (25–35 cm).

Distribution

Angelsharks occur almost worldwide, but most species are geographically restricted. Squatina californica occurs in the eastern Pacific; three species are Mediterranean (S. squatina, S. oculata, and S. aculeata), also occurring along the western African coast (the latter two down to Namibia); four species are found in the western Atlantic (S. dumeril, S. argentina, S. guggenheim, and S. occulta); S. africana occurs in the Indian Ocean; S. tergocellata and S. australis occur off southern Australia; and four species are western Pacific (S. tergocellatoides, S. nebulosa, S. japonica, and S. formosa).

Habitat

Angelsharks occupy the continental shelf and upper slope regions, in depths ranging from just several feet (1.5 m to 150m) down to about 4,265 ft (1,300 m), but most species are found inshore. They usually occur on sand, mud, and gravel substrates.

Behavior

Angelsharks frequently bury themselves in sandy or muddy bottoms, as do many rays, in order to ambush their prey or to rest during the day (they are primarily nocturnal). Burial is accomplished by a vigorous "flapping" of the pectoral fins, which raises the sediment. Dorsal eyes and spiracles allow angelsharks to breathe regularly while waiting for their prey to pass by, as water may reach the gills through the enlarged spiracles. The top of the head and trunk are frequently left exposed. Angelsharks are ambush predators. As prey items have to be of the right size, angelsharks may remain concealed in an immobile state for long periods, waiting for the proper prey to pass close to their mouths. Capture of prey is done in a very swift, high-speed maneuver, in which the anterior part of the body is abruptly uplifted; the prey is ingested whole after being properly adjusted in the mouth.

Feeding ecology and diet

Angelsharks eat a wide variety of invertebrates and fishes. Their capacious mouths allow them to ingest prey items of substantial size. Crustaceans, cephalopods, bivalves, and bony fishes are commonly consumed, as well as other sharks and rays; one specimen was observed to spit out a newly born bullhead shark immediately after ingesting it, probably because of its finspines.

Reproductive biology

All angelsharks are ovoviviparous (aplacentally viviparous; giving birth to live young), and have internal fertilization, as do all sharks, rays, and chimaeroids (Chondrichthyes). Gestation periods are mostly unknown, but appear to be about 10 months for one species, S. californica. Litter sizes vary between one and 20 pups per gestation, and the young measure around 9.8 in (25 cm) when born. Southwestern Atlantic angelsharks employ cloacal gestation, in which the fully developed fetus remains, prior to birth, in a small chamber (posterior to the uterus) that opens into the cloaca; this occurs during the second half of the gestation period and lasts for several months.

Conservation status

Five species of angelsharks are listed by the IUCN. S. occulta is Endangered; the Brazilian subpopulation of S. guggenheim is listed as Endangered, while the rest of the species is Vulnerable; S. squatina is Vulnerable; S. californica is Lower Risk/Near Threatened; and S. argentina is Data Deficient.

Significance to humans

Angelsharks pose little direct threat, because of their size, habits, and vertical distribution. However, caution is necessary, as angelsharks have sharp teeth and strong jaws and have been known to defend themselves if provoked. They are consumed on a regular basis as food (fresh, frozen, or salt-dried), especially in the western Pacific (S. japonica), Australia (mainly S. australis), and in the eastern Pacific (S. californica). Their skin is also used for polishing wood surfaces and as sharkskin leather (consisting of the dried skin with denticles). They are caught as bycatch in bottom trawls.

Species accounts

List of Species

Pacific angelshark

Squatina californica

family

Squatinidae

taxonomy

Squatina californica Ayres, 1859, California.

other common names

English: California angelshark; Spanish: Pez ángel del Pacífico.

physical characteristics

Pacific angelsharks present rather simple, spatulate, nasal flaps (not intensely fringed), and a light-brown background with small dark brown spots and blotches, mostly smaller than spiracle-diameter, scattered over the trunk and tail. There is a row of small denticles along the back and tail, and also in between the dorsal and caudal fins, and small spines are also present on the snout and around eyes.

distribution

These sharks occur from Alaska to the Gulf of California, and from Ecuador to Chile. South American occurrences may refer to a distinct species, presently not recognized. They are abundant close to the Channel Islands (California).

habitat

Pacific angelsharks inhabit shallow, nearshore waters, down to 164 ft (50 m) off the California coast, but to about 590.5 ft

(180 m) in the Gulf of California, over rocky, muddy, and sandy bottoms, and near kelp forests.

behavior

Pacific angelsharks are sluggish and mostly nocturnal. Adults are somewhat nomadic, spending brief periods in restricted areas of about 1 sq mi (2.6 sq km) before moving to a new region several miles distant. Although these sharks are mostly solitary, small aggregations have been observed.

feeding ecology and diet

These sharks eat fishes (croakers, blacksmith, and halibut), shrimp, squid, and squid egg cases. They also feed on the peppered catshark (Galeus piperatus) in the Gulf of California.

reproductive biology

Male Pacific angelsharks mature at about 29.5–31.5 in (75–80 cm), females at slightly greater sizes. Pups are born at about 7.9–13.8 in (20–25 cm). Litter size ranges from a single offspring to 13, and the gestation period is reported to last 10 months. Birth occurs in March and June.

conservation status

California angelsharks are listed as Lower Risk/Near Threatened by the IUCN.

significance to humans

These sharks are consumed fresh or frozen in California, and especially in areas near the Gulf of California. They are also consumed off western South America. Not usually kept in aquaria, Pacific angelsharks are one of the most commonly observed angelsharks in the wild.

Angelshark

Squatina squatina

family

Squatinidae

taxonomy

Squalus squatina Linnaeus, 1758, Mediterranean Sea ("Oceano Europaeo").

other common names

English: Common angelshark; French: Ange de mer commun, Spanish: Angelote.

physical characteristics

Squatina squatina is distinguished by having a long tentacle on its spatulate, unfringed nasal flap, and a dorsal coloration composed of a gray, yellow, or light-brown background, mottled in dark, minute spots. There are few denticles scattered along the midline, as well as on the snout and around the eyes.

distribution

Mediterranean, eastern Atlantic, bordering the United Kingdom to Scandinavia, also in the Shetland Islands, and south to Morocco and the Canary Islands.

habitat

These sharks inhabit shallow inshore waters, from 5 ft (1.5 m) down to 492 ft (150 m). Found on rocky, gravely, muddy, and sandy bottoms.

behavior

Squatina squatina is mostly nocturnal. Adults are known to migrate northward in the summer in northern parts of the distribution.

feeding ecology and diet

Eats fishes (hake, argentines, flatfishes, and skates), crabs, shrimp, and mollusks.

reproductive biology

Female angelsharks mature at about 49.2 in (125 cm), males at slightly smaller sizes. Pups are born at about 9.4–11.8 in (24–30 cm). Litter size ranges from seven to 25, depending on the size of the mother. Females give birth in the summer months in the colder part of the range, but during the winter in the Mediterranean.

conservation status

Listed as Vulnerable by the IUCN.

significance to humans

Angelsharks are consumed fresh, frozen, or salt-dried; and are possibly utilized for fish oil and fishmeal.

Resources

Books

Bigelow, H. B., and W. C. Schroeder. Fishes of the Northwestern Atlantic. Part I, Lancelets, Cyclostomes, and Sharks. New Haven: Sears Foundation for Marine Research, 1948.

Cappetta, H. Chondrichthyes II, Mesozoic and Cenozoic Elasmobranchii. Stuttgart: Gustav Fischer Verlag, 1987.

Compagno, L. J. V. Sharks of the World. An Annotated and Illustrated Catalogue of Shark Species Down to Date. Vol. 2, Bullhead, Mackerel and Carpet Sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Rome: Food and Agriculture Organization of the United Nations, 2001.

Hennemann, R. M. Sharks and Rays, Elasmobranch Guide of the World. Frankfurt: Ikan, 2001.

Last, P. R., and J. D. Stevens. Sharks and Rays of Australia. Melbourne, Australia: CSIRO, 1994.

Nelson, J. Fishes of the World. 3rd ed. New York: John Wiley & Sons, 1994.

Springer, V. G., and J. P. Gold. Sharks in Question: The Smithsonian Answer Book. Washington, DC: Smithsonian Institution Press, 1989.

Whitley, G. P. The Fishes of Australia. Part 1, The Sharks, Rays, Devil-fish, and Other Primitive Fishes of Australia and New Zealand. Sydney, Australia: Royal Zoological Society of New South Wales, 1940.

Periodicals

Compagno, L. J. V. "Phyletic Relationships of Living Sharks and Rays." American Zoologist 17 (1977): 303–322.

Luer, C. A., and P. W. Gilbert. "Elasmobranch Fish. Oviparous, Viviparous, and Ovoviviparous." Oceanus Magazine 34, no. 3 (1991): 47–53.

Natanson, L. J., and G. M. Caillet. "Reproduction and Development of the Pacific Angel Shark." Copeia 1986, no. 4 (1986): 987–994.

Shirai, S. "Phylogenetic Relationships of the Angel Sharks, with Comments on Elasmobranch Phylogeny." Copeia 1992, no. 2 (1992): 505–518.

Sunye, P. S., and C. M. Vooren. "On Cloacal Gestation in Angel Sharks from Southern Brazil." Journal of Fish Biology 50 (1997): 86–94.

Organizations

American Elasmobranch Society, Florida Museum of Natural History. Gainesville, FL 32611 USA. Web site: http://www.flmnh.ufl.edu/fish/Organizations/aes/aes.htm

Other

FishBase. August 8, 2002 (cited October 10, 2002). <http://www.fishbase.org/search.cfm>

The Catalog of Fishes On-Line. February 15, 2002 (cited October 17, 2002). <http://www.calacademy.org/research/ichthyology/catalog/fishcatsearch.html>

Marcelo Carvalho, PhD