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Squatina aculeataSawback angel shark

By Alex Wheatley

Geographic Range

Sawback angelsharks (Squatina aculeata) are found primarily in the Mediterranean Sea and the adjoining bodies of water bordering Greece, Sicily (Italy), Turkey, and Israel. They are along the continental slope of African countries that include Tunisia, Senegal, Gambia, and Sierra Leone. Sawback angelsharks migrate from the Mediterranean Sea to deeper waters in the Atlantic Ocean during the colder months, returning to the coastal region for the warmer period of the year. (Bengil and Basusta, 2018; Ellis, et al., 2021; "Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015; ; Morey, et al., 2019; "Sharks of the world: An annotated and illustrated catalogue of shark species known to date", 1984)

Habitat

Sawback angelsharks utilize saltwater habitats in seas and coastal oceanic waters. They swim in depths from 30m to 500m, closer to the substrate of the aquatic environments because of their eating habits. They are commonly found in areas with softer sediments on the Mediterranean and Atlantic coastal waters, due to their hunting strategies. Sawback angelsharks migrate to the continental shelf of the Atlantic Ocean during the winter. ("Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015; Morey, et al., 2019)

  • Range depth
    30 to 500 m
    98.43 to 1640.42 ft

Physical Description

At birth, sawback angelsharks are 30.3cm to 35cm in length. Although some sources report that both sexes reach maturity at 124 cm, others state that mature males are 120cm to 122cm. Mature females grow larger than males, with sizes ranging from 137cm to 143cm; the largest female recorded was 188cm. Sawback angelsharks vary in weight between 1000g to 8000g, with females generally being larger than males.

As their common name suggests, they possess spines along the dorsal section of their body; these spines also exist on the nose and above the eyes. Sawback angelsharks are further defined by their vertically compressed body, which is useful for camouflaging in the sandy oceanic sediments. Sawback angelsharks are brown or occasionally black; some also have scattered white spots for further camouflage. They also have fringed nasal barbels, which resemble whiskers, and anterior nasal flaps. These angelsharks also have two large pectoral fins.

Males also have claspers, which aid in mating with females. The teeth of the sawback angelsharks are small and sharp, and in 4 rows. They have 2 rows of 9 teeth in the upper jaw and 2 rows of 10 teeth in the lower jaw. (Capapé, et al., 2005; Colonello, et al., 2007; "Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015; ; "Sharks of the world: An annotated and illustrated catalogue of shark species known to date", 1984)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range mass
    1000 to 8000 g
    35.24 to 281.94 oz
  • Range length
    120 to 188 cm
    47.24 to 74.02 in

Development

Sawback angelsharks are ovoviviparous, which means females hatch their eggs internally and give birth to live offspring. Sawback angelsharks also have a uterine-cloacal chamber, where the unborn sharks will continue to grow before birth. The chamber protects them from the external environment while supplying them with essential nutrients. However, the chamber has also been suspected to be an avenue for aborting the births if the females feel threatened.

These angelsharks have a 3-year reproductive cycle, consisting of a 12-month gestation period and a 2-year oocyte maturation period. Sawback angelshark pups are between 30.3cm and 35.0cm while weighing between 276g and 325g. These angelsharks are dimorphic, with males typically ranging in size from 120cm to 122cm, and maximum sizes of ca. 152cm. Females are larger, with ranges normally 137cm to 143cm, and maximum sizes being 188 cm. Both sexes may reach maturity at approximately 124 cm in length, while other sources suggest that females may need to reach lengths of 137 cm to be mature. Sawback angelsharks exhibit indeterminate growth. (Capapé, et al., 2005; Colonello, et al., 2007; "Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015; )

Reproduction

While little is known about sawback angelsharks' breeding seasons, it is thought that seasonal meetings would coincide with their migrational patterns. Capapé et al. (2005) suggest that these angelsharks are polygynandrous. Given evidence that males produce sperm year-round, females may mate with multiple males. There is an increase in male activity, such as biting other females, during the summer months, suggesting their breeding season might occur during this time. Males have claspers that aid in internal fertilization. Biting scars have also been noted on females, suggesting biting occurs from males latching onto females during mating. (Capapé, et al., 2005; Colonello, et al., 2007)

Sawback angelsharks mate during the summer months. Sawback angelsharks are ovoviviparous and give birth to live young. Female angelsharks have an estimated gestation period of 12 months. Litter size varies from 8 to 12 pups. Sawback angelsharks do not provide care for their young after birth. Females are thought to only breed in the summer months, although males are able to breed year-round. Sawback angelsharks are born between at lengths of 30.3cm and 35.0cm and masses of 276g to 325g. After birth, sawback angelsharks are independent. Although age of sexual maturity is not published, these sharks may attain maturity at ca. 124 cm for both sexes. Other sources suggest females are larger, ca. 137 cm, at maturity. (; "Sharks of the world: An annotated and illustrated catalogue of shark species known to date", 1984; "Status review report of 3 species of angelsharks: Squatina aculeata, S. oculata, and S. squatina", 2016)

  • Breeding interval
    Sawback angelsharks likely breed once yearly but with multiple mates
  • Breeding season
    Likely summer
  • Range number of offspring
    8 to 12
  • Average gestation period
    12 months
  • Range time to independence
    0 (low) minutes

Female sawback angelsharks are ovoviviparous, carrying the eggs inside of them until they hatch. This period lasts 12 months. After the pups are born, the female provides no additional parental care. Males provide no parental care beyond the act of mating. (Capapé, et al., 2005)

  • Parental Investment
  • no parental involvement
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The lifespan of sawback angelsharks has not been reported but others in the genus are reported to live 35 years in the wild. Their generation length is thought to be about 15 years.

There are no sawback angelsharks held in captivity. (; "Status review report of 3 species of angelsharks: Squatina aculeata, S. oculata, and S. squatina", 2016)

Behavior

Sawback angelsharks live a solitary lifestyle, only socializing during mating season. Sawback angelsharks are bottom-dwelling sharks, meaning they swim and feed on the substrate on the ocean or seafloor. Sawback angelsharks are nocturnal, more active in their hunting around sundown, with the peak of activity at midnight. This lines up with the increased number of prey items active at night. Sawback angelsharks migrate from the Atlantic to the Mediterranean seasonally to remain in warm waters.

Sawback angelsharks use tactile communication, often by biting and rubbing against one another. Female sawback angelsharks have been found with bite marks on them, suggesting males bite during mating. They also use tactile efforts to forage for prey items. ("Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015; "Status review report of 3 species of angelsharks: Squatina aculeata, S. oculata, and S. squatina", 2016)

Home Range

The home range of sawback angelsharks has not been reported. Sawback angelsharks are not territorial. ("Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015; "Status review report of 3 species of angelsharks: Squatina aculeata, S. oculata, and S. squatina", 2016)

Communication and Perception

Not much is known about the sawback angelshark's ability to communicate with others. They are electroreceptive, meaning they can utilize electric signals to find their prey. They do this by using sensory organs called the ampullae of Lorenzi. They use their sense of smell, which is the primary sense they use to hunt their prey. Sharks can see very well at closer distances, but not as well far away. Sharks also can hear very well, being extremely affected by low frequencies, down to 10 Hz.

Sharks are tactile, using their teeth in foraging and mating. They will bite objects to learn more about them, and males are thought to bite females while mating. Sawback angelsharks also have a lateral line that is used to detect movement, vibrations in the water, and the pressure of the surrounding environment. ("Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015)

Food Habits

Sawback angelsharks are ambush predators and are carnivorous. They camouflage in the sandy depths of the ocean or sea and wait for unsuspecting prey to fall victim to their trap. They tend to feed on other bony fish, crustaceans, and cephalopods like the broadtail squid (Illex coindetti). They also found a striped soldier shrimp (Plesionika edwardsii) in the stomach of one sawback angelshark. (Corsini-Foka and Zava, 2007; "Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Predation

Sawback angelsharks' camouflage and flattened body shape hide them from potential predators. Larger sharks are the primary predators of sawback angelsharks, including great hammerhead sharks (Sphyrna zygaena). Humans (Homo sapiens) are the most common predators. ("Eastern Atlantic and Mediterranean angel shark conservation strategy", 2017; "Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Sawback angelsharks are bottom-feeding predators in their ecosystem. Sawback angelsharks hunt small crustaceans and other bottom-dwelling animals. They also consume smaller sharks and other bony fish. There are few predators of these sharks, including larger sharks and humans (Homo sapiens).

The parasites of sawback angelsharks are not well known, but an external parasitic copepod, Eudactylina complexa, has been reported for these sharks. (Bengil and Basusta, 2018; ; Morey, et al., 2019; Raibaut, et al., 1998)

Commensal/Parasitic Species
  • copepod Eudactylina complexa

Economic Importance for Humans: Positive

Sawback angelsharks sold in fish markets around the Mediterranean coast and western Africa. These and other angelsharks are collectively caught and retained as bycatch, though identification beyond genus level makes estimates of bycatch difficult to assess. It is likely utilized for meat in West Africa and possibly elsewhere. ("Eastern Atlantic and Mediterranean angel shark conservation strategy", 2017; "Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015; Morey, et al., 2019)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known adverse effects of sawback angelsharks on humans.

Conservation Status

Sawback angelsharks are listed as a species that is "Critically Endangered" by the IUCN. The federal list has placed the sawback angelshark as "Endangered." CITES has categorized them under Appendix I, which means global trade of angelsharks is not permitted. The species is not listed on the state of Michigan list.

The largest threat to the declining population of sawback angelsharks is overfishing. Sawback angelsharks have been captured in an unregulated manner, and most reports of angelshark catches stop at the genus level. Therefore, reliable data along the African coast and in the Mediterranean are not being collected. These angelsharks have been captured as bycatch across their range, and they are believed to be consumed in western Africa. Continued harvests have meant that range-wide populations are down 80% from historical levels (over the last 45 years).

Conservation sites have been established to protect sawback angelshark populations. These areas protect about 1%-10% of the remaining population. It has also become illegal since 2010 to catch and not return any sawback angelsharks in the waters of the European Union. There are laws in Turkey, Spain, and Israel prohibiting or limiting amgelshark harvests, though the laws are not always enforced.

Before 2020, maps showing where sawback angelsharks were known to reside were inaccurate, and range maps leave about half the range with unknown status. More accurate maps were created in 2020 to help with conservation efforts. Conservation sites have been established with many Mediterranean countries. Conservation efforts have been centered around prohibiting fishing and selling of sawback angelsharks. Goals of the Mediterranean conservation programs include ending current fishing efforts for these angelsharks, setting aside critical habatats (once identified) , and minimizing any other human impacts outside of fishing. Because 3 species of angelsharks are in peril, the establishment of the Angel Shark Conservation Network is another step to collectively protect all species. ("Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act", 2015; Lawson, et al., 2020; Morey, et al., 2019; "Status review report of 3 species of angelsharks: Squatina aculeata, S. oculata, and S. squatina", 2016)

Contributors

Alex Wheatley (author), Radford University, Sierra Felty (editor), Radford University, Bianca Plowman (editor), Radford University, Karen Powers (editor), Radford University, Victoria Raulerson (editor), Radford University, Christopher Wozniak (editor), Radford University, Genevieve Barnett (editor), Colorado State University.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

electric

uses electric signals to communicate

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

IUCN: International Union for Conservation of Nature. Eastern Atlantic and Mediterranean angel shark conservation strategy. None. UK: The Shark Trust. 2017. Accessed April 26, 2022 at Retrieved from https://policycommons.net/artifacts/1368788/eastern-atlantic-and-mediterranean-angel-shark-conservation-strategy/1982956/ CID: 20.500.12592/zptdwz..

National Oceanic and Atmospheric Administration. Endangered and threatened wildlife and plants; 12-Month finding and proposed rule to list three angelshark species as endangered under the endangered species act. 150506424-5424-01. Silver Spring Maryland: National Oceanic and Atmospheric Administration. 2015.

FAO. Sharks of the world: An annotated and illustrated catalogue of shark species known to date. Fisheries Synopsis No. 125, Volume 4, Part 1. Rome, Italy: FAO. 1984.

National Marine Fisheries Service. Status review report of 3 species of angelsharks: Squatina aculeata, S. oculata, and S. squatina. None. Silver Spring, MD: National Oceanic and Atmospheric Administration. 2016.

Basusta, N. 2002. Occurrence of a sawback angelshark (Squatina aculeata Cuvier, 1829) off the eastern Mediterranean coast of Turkey. Turkish Journal of Veterinary and Animal Sciences, 26/5: 1177-1179.

Bengil, E., N. Basusta. 2018. Chondrichthyan species as by-catch: A review on species inhabiting Turkish waters. Journal of the Black Sea / Mediterranean Environment, 24/3: 288-305.

Capapé, C., D. Youssouph, S. Amadou Abdoulaye, G. Olivier, B. Jamila, Z. Jeanne. 2005. Reproduction of the sawback angelshark Squatina aculeata (Chondrichthyes: Squatinidae) off Senegal and Tunisia. Cybium, 29/2: 147-157.

Colonello, J., L. Lucifora, A. Massa. 2007. Reproduction of the angular angel shark (Squatina guggenheim): Geographic differences, reproductive cycle, and sexual dimorphism. ICES Journal of Marine Science, 64/1: 131-140.

Corsini-Foka, M., B. Zava. 2007. Recent capture of Squatina oculata and Squatina aculeata from Dodecanese Islands (SE Aegean Sea, Eastern Mediterranean). Biologia Marina Mediterranea, 14/2: 352-353.

Ellis, J., J. Barker, S. Phillips, E. Meyers, M. Heupel. 2021. Angel sharks (Squatinidae): A review of biological knowledge and exploitation. Journal of Fish Biology, 98/3: 592-621.

Erglener, A., F. Turan, C. Turan. 2020. Occurrence of a sawback angelshark (Squatina aculeata Cuvier, 1829) from the Iskenderun Bay, north-eastern Mediterranean coast of Turkey. Biharean Biologist, 14/1: 57-59.

Gordon, C., A. Hood, S. Al Mabruk, J. Barker, A. Bartolí, S. Ben Abdelhamid, M. Bradai, N. Dulvy, T. Fortibuoni, I. Giovos, D. Jimenez Alvarado, E. Meyers, G. Morey, S. Niedermuller, A. Pauly, F. Serena, M. Vacchi. 2019. Mediterranean Angel Sharks: Regional Action Plan. United Kingdom: The Shark Trust.

Halit, F., E. Irmak, S. Mater. 2005. Occurence of Squatina aculeata Cuvier, 1829 (Elasmobranchii, Squatinidae) from the Aegean Sea, Turkey. Ege Journal of Fisheries and Aquatic Sciences, 22/3-4: 451-452.

Kabasakal, H. 2021. Chapter from the life story of common angel shark, Squatina squatina, from Turkish waters: A historical, ethnoichthyological and contemporary approach to a little-known shark species. Journal of the Black Sea / Mediterranean Environment, 27/3: 317-341.

Lawson, J., R. Pollom, C. Gordon, J. Barker, E. Meyers, H. Zidowitz, J. Ellis, Á. Bartolí, G. Morey, S. Fowler, D. Alvarado, S. Fordham, R. Sharp, A. Hood, N. Dulvy. 2020. Extinction risk and conservation of critically endangered angel sharks in the Eastern Atlantic and Mediterranean Sea. ICES Journal of Marine Science, 77/1: 1-26.

Morey, G., J. Barker, A. Bartoli, C. Gordon, D. Jiménez, E. Meyers, A. Hood. 2019. "Squatina aculeata" (On-line). The IUCN Red List of Threatened Species 2019: e.T61417A116768915. Accessed January 29, 2022 at https://dx.doi.org/10.2305/IUCN.UK.2019-1.RLTS.T61417A116768915.en.

Quigley, D. 2006. Angelshark (Squatina squatina) in Irish waters. Sherkin Comment, 41: 5.

Raibaut, A., C. Combes, F. Benoit. 1998. Analysis of the parasitic copepod species richness among Mediterranean fish. Journal of Marine Systems, 15: 185-206.

Serena, F., I. Giovos, D. Katsada, A. Anastasiadis, A. Barash, C. Charilaou, J. Hall-Spencer, F. Crocetta, A. Kaminas, D. Kletou, M. Maximiadi, M. Vasileios, D. Moutopoulos, R. Aga-Spyridopoulou, I. Thasitis, K. Periklis. 2021. Integrating Literature, Biodiversity Databases, and Citizen-Science to reconstruct the checklist of Chondrichthyans in Cyprus (Eastern Mediterranean Sea). Fishes., 6/3: 1-18.

Yığın, C., A. İşmen, B. Daban, K. Cabbar, U. Önal. 2019. Recent findings of rare sharks, Squatina oculata Bonaparte, 1840 and Squatina squatina (Linnaeus, 1758) from Gökçeada Island, Northern Aegean Sea, Turkey. Journal of the Black Sea / Mediterranean Environment, 25/3: 305-314.

Zava, B., G. Insacco, M. Corsini-Foka, F. Serena. 2020. Updating records of Squatina aculeata (Elasmobranchii: Squantiniformes: Squatinidae) in the Mediterranean Sea. Acta Ichthyologica et Piscatoria, 50/4: 401-411.

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