Sawback Angelsharks, Squatina aculeata
Taxonomy Animalia Chordata Elasmobranchii Squatiniformes Squatinidae Squatina aculeata
Description & Behavior
Sawback angelsharks, Squatina aculeata (Cuvier, 1829), aka monkfishes, spiny angelsharks, and sawback angel sharks, measure up to 1.88 m in length. This species is named for their large pectoral fins that resemble wings. Their flat body and gray coloring with olive blotches helps them camouflage themselves on muddy/sandy ocean bottoms where they spends much of their time buried, lying motionless, in some cases for as long as several weeks, until prey comes within striking range.
Most species in the Squatiniformes family reach maximum lengths around 1.5 m, with the exception of Japanese angelsharks, Squatina japonica, and Mediterranean angelsharks, Squatina squatina, that are reported to reach at least 2 m.
World Range & Habitat
Sawback angelsharks, Squatina aculeata, are a subtropical species found between 43°N-19°S, 18°W-17°E in the eastern Atlantic, western Mediterranean, and off the coasts of Morocco, Senegal, Guinea, Nigeria, Gabon, and Angola. They are thought to inhabit the intertidal zone down to 1,390 m. Some angelshark species are reported to be migratory.
Feeding Behavior (Ecology)
Sawback angelsharks, Squatina aculeata, feed on small sharks and fishes such as jacks, and benthic crustaceans. As mentioned above, angelsharks ambush their prey from their hiding places in muddy or sandy bottoms.
Ovoviviparous: eggs hatch and the babies develop inside the female's body but there is no placenta to nourish the pups.
Population doubling time: the number of years required for the population of a given species to double its present size, given the current rate of population growth, used to measure a specie's resilience to fishing pressure or other environmental stressors.
Conservation Status & Comments
Sawback angelsharks, Squatina aculeata, are not dangerous to humans if left unprovoked. They are currently listed as Critically Endangered (CR A2bcd+3cd+4cd) by the IUCN Red List of Threatened Species:
"Major Threat(s): Angel sharks are highly susceptible to bycatch in trawls as they lie on the bottom. Benthic trawl effort has increased in both intensity and efficiency on the shelf and slope area Mediterranean over the last 50 years. The species is also bycaught in trammel nets and bottom longlines throughout its range. Human disturbance by habitat degradation and tourism are also possible threats to its preferred sandy nearshore habitat.
There is evidence for dramatic declines from historic data from a tuna trap operating in the Northern Tyrrhenian Sea with catches of the genus Squatina reported at an average of 134 specimens from 1898 to 1905, down to 15 from 1914 to 1922 (Vacchi et al. 2002). This early decline probably marks the beginning of trawling activity in the area, to which angel sharks are highly susceptible. A low rate of exchange between Squatina populations makes them prone to local depletion and means that recolonisation will be extremely low.
Mediterranean countries that report 'angelsharks' to FAO with this species as part of the catch include Albania, Turkey, Malta and France.
Squatina aculeata has virtually disappeared from most of its former Mediterranean range where its habitat over the outer continental shelf and uppermost slope (30 to 500 m depth), is subject to intense demersal fisheries, especially off the northern coasts. Declines have also been reported from studies off the Balearic Islands where this species, previously common, may now be absent. A type of fishing net for capturing Angel sharks previously existed in the Balearics called ?escatera' (?escat' meaning angel shark in Catalan), suggesting that the species used to be common in the area. Anecdotal evidence from interviews with fishermen in the Balearics indicates that in the last 20 years all species of Squatina have diminished drastically (G. Morey pers. comm.). There are only very few records from the Island of Menorca, where an intensive lobster gillnet fishery exists. Demersal fishing pressure is very high in this area, with bottom trawls operating from very shallow waters to about 800 m for shrimp (G. Morey pers comm).
Despite the scarcity of ancient numerical data, the species seems to have experienced a dramatic decline in most of its range of distribution, becoming extremely rare in the northern part of the Mediterranean.
Along the West African coasts, there are no directed fisheries for this species but it is taken as bycatch of major international industrial demersal trawl fisheries and inshore bottom set gillnets.
Portuguese landings data from the fleet operating off Morocco and Mauritania, aggregated for S. aculeata, S. oculata and S. squatina combined indicates a 95% decline in CPUE from 1990-1998, but nothing is known of the level of fishing effort associated with these landings. Landings increased to a peak of 35 t in 1990 and when the fishery was closed in 1998 the total landings were 1.7 t. This represents a decline of 95% in landings in 8 years, however nothing is known of the pattern of effort associated with these landings.
This species was previously reported as common in Russian surveys in this region during the 1970s and 1980s (F. Litvinov pers. comm. 2006). Artisanal Senegalese fishermen also remember this species as common and frequently caught by lines and gillnet 30 years ago; however it is appears to have been strongly depleted to the point where it has almost disappeared, now occurring very rarely (M. Ducrocq pers. comm. 2006). Catches are now very rare according to both artisanal fishermen and observers of the industrial demersal trawl fleets (M. Ducrocq pers. comm. 2006).
In Sierra Leone, Squatina species were periodically caught by demersal trawlers in the 1980s, but are now caught very infrequently in Sierra Leone (M. Seisay pers comm. 2006). Few individuals (19) have been caught in FIAS research surveys (FIAS unpub. data), and none have been captured since 1998. Only one specimen was caught in Guinea (year unknown) and one individual caught in Gambia in 1998. In Senegal at total of 13 individuals were caught from 1970 to 1998 and none have been seen in recent FIAS surveys (FIAS unpub. data). In Mauritania four were caught between 1988 and 1989, and none have been caught since.
Conservation Actions: The genus Squatina is protected within six Balearic Island marine reserves, where fishing for these species is forbidden and accidental captures must be released. There are no known specific conservation measures for this species throughout the rest of its range."
CRITICALLY ENDANGERED (CR)
A taxon is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered (see Section V), and it is therefore considered to be facing an extremely high risk of extinction in the wild.
References & Further Research
Research Squatina aculeata » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SCIRIS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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