Ballpoint pen and brown and black marker illustration of Squatina argentina (Argentine angelshark), dorsal view almost lateral. This representation is very schematic and artistic, and does not necessarily represent the animal's true colors. I also include the other photo with the two previous sketches I made. For this drawing, I based it on photographs by Kriss Shephard (2008), NOAA, and Gadig O.B.F. (FishBase); and on the illustration available at Fish Commercial.
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The skecthes!:
Some facts about Squatina argentina.
Attention. I wrote almost none of the following information. It's a combination of various pieces of information that weren't taken from Wikipedia. Sources at the end!
Description: This species is distinguished from its congeners by having a darker background color, ranging from dark-brown to reddish-brown (vs. light-brown to dark-brown in S. guggenheim and S. occulta), with higher number of tooth rows with 24 vertical tooth rows in both upper and lower jaws, tooth formula 12-12/12-12; (vs. 9-9 to 10-10/9-9 to 11-11 in S. occulta, and 9-9 to 11-11/9-9 to 11-11 in S. guggenheim), and with anterior half of pectoral fin margin convex (vs. anterior margin of pectoral fin straight).
Cross section: angular.
Distinguishing Characteristics. Differs from S. guggenheim and S. occulta with the interspiracular surface covered by small and homogeneous dorsal denticles, without enlarged denticles (vs. a pair of enlarged, conical and morphologically distinct dermal denticles between spiracles in S. occulta and S. guggenheim); differs from S. occulta by lacking blackish irregular small spots surrounding white spots on dorsal surface (i.e. absence of ocelli-like markings); differs further from S. guggenheim by having the dorsal midline denticles on trunk morphologically similar to other trunk denticles and barely organized in a row (vs. dorsal midline row of enlarged denticles morphologically distinct from other trunk denticles), the denticles close to origin of pectoral fin morphologically homogeneous, similar to other pectoral denticles (vs. presence of a pair, or more, enlarged and morphologically distinct denticles from other pectoral denticles, in S. guggenheim).
Coloration. It varies, but it generally has a sandy brown or brownish-gray body with lighter spots or blotches, allowing it to blend into the sandy or muddy bottom. This camouflage helps it remain hidden from both prey and potential predators.
Dentition. Tooth formula 12-12/12-12.
Biology: Found on the continental shelf and slope. Benthic. It feeds primarily on a variety of bony fishes and smaller bottom-dwelling invertebrates. They can bury themselves in the sand or mud of the seabed, effectively camouflaging themselves and remaining virtually invisible, a phenomenon known as "cryptic behavior." Only their eyes and spiracles (the openings behind the eyes that they use for breathing) remain exposed.
Parasites: Pontobdella moorei Oka, 1910 (Hirudinea).
Reproduction: Ovoviviparous, embryos feed solely on yolk. Both ovaries are functional. Argentine angelsharks reach sexual maturity at about 120 cm (3.94 ft) in length. The female's reproductive cycle lasts two to three years. The number of pups per litter can vary, but is generally between 9 and 10 (the range is from 7 to 11). When it's time to give birth, the female angelshark releases her already formed pups into the water. The pups are relatively large compared to other shark species, measuring between 30 and 40 centimeters (12 and 16 inches) in length. This size advantage at birth may increase their chances of survival. The Argentine angelshark’s reproductive cycle is thought to be biannual.
Development: After birth, young angelsharks embark on an independent life. They grow and develop through a continuous growth process, shedding their skin and developing new dermal denticles as they grow in size. Angelsharks' growth rate is influenced by factors such as prey availability, environmental conditions, and individual genetics.
Longevity: Not well documented, but it is estimated that they can live at least 15.5 years.
Habitat: It's commonly found in coastal areas, close to the shore, but is also common in offshore waters. They are also associated with estuaries, and the continental shelf and slope, where they find suitable prey and shelter. It prefers sandy or muddy substrates, where it can effectively camouflage itself among the seafloor sediments. They have also been seen, additionally, in habitats such as sandbanks, seagrass meadows, rocky bottoms, and areas with underwater canyons or reefs.
Importance to humans: The primary threat to Argentine angelsharks is overutilization by commercial fisheries, particularly the trawl and bottom gillnet fisheries in Brazil, where the species is likely most concentrated. The species is reported as a significant bycatch species in the commercial monkfish fishery, which likely contributed to a significant decline in the population in the early 2000s.
Size: 100 to 120 cm. In males: 100 cm, max. 170 cm. Pups: 30 - 40 cm.
Depth: 51 / 100 to 400 m.
Distribution: Southwest Atlantic: Brazil to southern Uruguay, including Argentina.
IUCN status: Critically Endangered (CR) (A2bd). Date assessed: 05 August 2017
References and sources:
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