Cape trident shark

The Scottish zoologist Andrew Smith for the first time scientifically described this species and attributed it to the genus of common marten sharks ^[2] . His description related to two specimens caught at Cape of Good Hope , South Africa . The specific name megalopterus consists of two Greek words Greek. mega - "huge" and Greek. pteron - “wing”, because these sharks have large fins ^[3] . In English, these sharks are called "sweet William" ^[3] .

Later authors attributed this species to the genus of trident sharks and grouped together with the Ecuadorian trident shark into the subgenus Cazon ^[4] . In the course of 2005 phylogenetic studies based on the analysis of the genetic code, it was found that these species are not grouped with the California trident shark . On the contrary, together with the longhorn shark, they form a treasure inside the genus of common marten sharks . These data suggest that two subgenus of tripod sharks - Cazon and Triakis - may not have a close relationship, which serves as the basis for the redefinition of the genus ^[5] .

Cape tripod sharks live in the southwestern part of the Atlantic Ocean off the southern coast of Africa from Angola to the Eastern Cape Province (they are rarely found off the coast of KwaZulu-Natal ^[4] . They can be found in sandy bays from the surf zone to a depth of 50 m, more often only no deeper than 10 m ^{[3] [6]} . These bottom fish stay close to rocky reefs and rarely go out into the open sea ^{[7] [3]} .

Cape tripod sharks have a short, thick, rounded muzzle and a dense body. The nostrils are removed from each other, they are framed by lobed rags of the skin that do not reach the mouth. Oval eyes are elongated horizontally and equipped with a blinking membrane . There are projections under the eyes. At the corners of the large mouth are long labial furrows. The teeth are small, pointed, located very closely, forming a kind of “grater”. The base of the teeth is rounded, it goes into the central tip, sometimes there are 1 or 2 lateral teeth. Cape tripod sharks have 5 pairs of gill slits .

The fins are quite large, with rounded tips. In adult sharks, pectoral fins are wide, sickle-shaped. The caudal margins of the dorsal fins are located almost vertically. The base of the first dorsal fin lies between the bases of the pectoral and ventral fins. The second dorsal fin is slightly inferior in size to the first. The second half of its base is located above the base of the anal fin. The anal fin is significantly smaller than both dorsal fins. The caudal peduncle is thick and short. The lower lobe of the caudal fin is short, but well developed. At the tip of the upper lobe of the caudal fin there is a ventral notch. The number of vertebrae ranges from 162 to 166. The color is from dark gray to brown, the belly is light. Young sharks have no markings, while numerous dark spots of irregular shape can cover the back and sides of adults. The maximum fixed size is 1.7 m and the weight is 40 kg ^{[8] [3] [4]} . Females are larger than males ^[9] .

Cape tripod sharks are active predators, although sometimes they can be found by resting inside rocky crevices ^{[4] [10]} . They hunt mainly at night and, pursuing the victim, can swim to the shore itself ^{[6] [11]} . Sharp teeth allow them to capture slippery prey, while the wide base of the teeth makes it possible to crush a strong shell ^[3] . These sharks prey on various crustaceans ( crabs , lobsters ), bony fishes , including morvongs , sea ​​catfish , croakers and crucians , as well as cephalopods . Sharks and stingrays , including cat sharks and fish-guitars , and their eggs play a secondary role in the diet of large Cape tripod sharks. Off the coast of South Africa, these sharks prey mainly on the crab Plagusia chabrus . The composition of the diet varies with age. Young growth, not reaching 1 m in length, feeds mainly on crabs, while large sharks consume relatively more bony fish and cephalopods, their diet as a whole is more diverse ^[6] . Sometimes Cape tripod sharks change their nocturnal lifestyle and hunt day by day for the squid Loligo reynaudii during the season of their mass breeding ^[12] .

At the same time, these sharks may fall prey to the flat- headed seven-gill shark Notorynchus cepedianus ^[13] .

In spring, Cape tripod sharks gather in shallow flocks. Such clusters are observed in Falls Bay , probably, their formation is associated with reproduction, which confirms the presence of a large number of pregnant females ^[4] . These sharks breed by placental live birth, the embryo feeds mainly on the yolk . Adult females have one functional ovary and two functional oviducts. In the litter of 6-12 newborns. Childbirth lasts from late May to August. Pregnancy lasts about 20 months. Large females bring more numerous offspring ^[6] . The length of the newborn is 30–32 cm (according to other sources, 42–44 cm); the size of newborns in one litter can vary by 30% ^{[4] [6]} . Females give birth every 2 or 3 years, depending on whether they had ovulation during pregnancy, which allows them to become pregnant again a few months after giving birth. Cape tripod sharks grow slowly. Males reach puberty with a length of 1.2-1.4 m, which corresponds to the age of 11-13 years, and females mature at a length of 1.3-1.5 m at the age of 15-16 years. The maximum recorded life expectancy is 25 years ^{[14] [15]} .

Sharks of this species do not pose a danger to humans ^[16] . They get along well in captivity, they are often kept in public aquariums. They are the object of sport fishing: they are caught on a hook from the shore or from a boat, while the meat of caught sharks is rarely eaten, despite the fact that it is edible ^[4] . As by- catch, Cape tripod sharks sometimes end up in commercial bottom tiers placed on soup sharks ( Galeorhinus galeus ) in Gansbaai and Falls Bay. Meat from sharks is dried and sold in local markets, or they are exported fresh or frozen to Italy and Taiwan ^[7] . Although Cape tripod sharks are not considered a commercial species in South Africa, fishermen often confuse them with common marten sharks ^[14] . The International Union for Conservation of Nature has assigned this species the status of “Close to Vulnerability” ^[7] . This species is very sensitive to catching even medium intensity, as it has a limited range, slow growth rate and low fecundity. An additional concern is the fact that immature sharks are often caught ^[14] .