Squatina aculeata

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.

• Biogeographic Regions
• atlantic ocean atlantic ocean
  • native native
• mediterranean sea
  • native native

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.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

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.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes shaped differently

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.

• Development - Life Cycle
• indeterminate growth indeterminate growth

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.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • internal internal
• ovoviviparous ovoviviparous

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.

• 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.

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.

• Key Behaviors
• natatorial natatorial
• nocturnal nocturnal
• motile motile
• migratory migratory
• solitary solitary

Home Range

The home range of sawback angelsharks has not been reported. Sawback angelsharks are not territorial.

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.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical
• electric electric

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical
• electric electric

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.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods
  • molluscivore molluscivore

• 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.

• Anti-predator Adaptations
• cryptic 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.

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.

• Positive Impacts
• food 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.

Additional Links

Encyclopedia of Life

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.

References

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