| Sharptooth houndshark | |
|---|---|
 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Carcharhiniformes |
| Family: | Triakidae |
| Genus: | Triakis |
| Species: | T. megalopterus |
| Binomial name | |
| Triakis megalopterus (A. Smith, 1839) | |
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| Range of the sharptooth houndshark[2] | |
| Synonyms | |
Mustelus megalopterusSmith, 1839 | |
Thesharptooth houndshark orspotted gully shark (Triakis megalopterus) is aspecies ofhoundshark in thefamily Triakidae found in shallowinshore waters from southernAngola toSouth Africa. Favoring sandy areas near rockyreefs andgullies, it is an active-swimming species that usually stays close to the bottom. This robust shark reaches 2 m (6.6 ft) in length and has characteristically large, rounded fins; thepectoral fins in particular are broad and sickle-shaped in adults. It also has a short, blunt snout and long furrows around its mouth. This species is gray or bronze in color above, with variable amounts of black spotting.
Mainlyactive at night, the sharptooth houndshark feeds mostly oncrustaceans,bony fishes, andcephalopods. It has been observed gathering in groups in shallow water during summertime, possibly for reproductive purposes. This species isaplacental viviparous, meaning that the unborn young are sustained mainly byyolk. Females give birth to 6–12 pups between late May and August, on a 2- or 3-year cycle. The sharptooth houndshark is often hooked byrecreational anglers, and some are also captured on commercialbottom longlines. Because of its small range and low growth and reproductive rates, it is very vulnerable tooverfishing. TheInternational Union for Conservation of Nature has listed this species as least concern.
ScottishzoologistAndrew Smith originally described the sharptooth houndshark as a species ofMustelus in 1839, as part of his workIllustrations of the Zoology of South Africa. His account was based on two specimens caught off theCape of Good Hope,South Africa. Smith named the sharkmegalopterus, from theGreekmega ("large") andpteron ("wing"), referring to its large fins.[3][4] Anothercommon name for this shark is "sweet William".[4]
Later authors have reassigned the sharptooth houndshark to the genusTriakis, more specifically to the subgenusCazon alongside thesharpfin houndshark (T. acutipinna) and thespotted houndshark (T. maculata).[5] A 2006phylogenetic study by J. Andrés López and colleagues, based on fourprotein-codinggene sequences, found that this species did not group with theleopard shark (T. semifasciata). Instead, theflapnose houndshark (Scylliogaleus quecketti) and it formed aclade within theMustelus lineage. This result suggests that the two subgenera ofTriakis—Cazon andTriakis—may not be closely related, which would warrant a redefinition of the genus.[6]
The sharptooth houndshark is a stout-bodied species with a short, thick, and blunt snout. The nostrils are widely spaced and preceded by lobe-like flaps of skin that do not reach the mouth. The horizontally oval eyes have ridges underneath and are equipped withnictitating membranes. The large mouth bears long, deep furrows at the corners, with those on the lower jaw almost meeting in the middle. The teeth are small and tightly packed to form pavement-like surfaces. Each tooth has a rounded,molar-like base that rises to a sharp, upright central cusp; rarely, a pair of barely developed lateral cusplets may also be present. Five pairs ofgill slits are found.[4][5]
The fins are distinctively large and rounded at the tips. Thepectoral fins of adults are broad and falcate (sickle-shaped). Thedorsal fins have nearly vertical trailing margins, with the first originating over the pectoral fin rear tips. The second dorsal fin is about three-quarters as high as the first. Theanal fin is much smaller than the second dorsal fin and originates well behind it. The short, thickcaudal peduncle lacks notches at thecaudal fin origins. The caudal fin has a small but well-defined lower lobe and a longer upper lobe with a ventral notch near the tip. The skin is often loose. This species is dark gray to bronze above and white below. Young sharks are mostly unmarked, while adults vary from plain to densely covered with irregular black spots. It may reach 1.7 m (5.6 ft) in length and 40 kg (88 lb) in weight.[2][4][5] Females grow larger than males.[7]
The range of the sharptooth houndshark is limited to the coastal waters ofsouthern Africa, from southernAngola to theEastern Cape (or rarelyKwaZulu-Natal) in South Africa.[5] This locally common species inhabits sandyhabitats such asbays; it can be found from thesurf zone to a depth of 50 m (160 ft), but the majority are found no deeper than 10 m (33 ft).[4][8] It generally swims just barely above the bottom, favoring flat areas near rockyreefs or gullies, and seldom rises into open water.[1][4]
The sharptooth houndshark is a highly active species, though it can sometimes be found resting inside rocky crevices.[5][9] It mainly hunts at night and has been known to pursue prey almost onto the shore.[8][10] The pointed cusps of its teeth allow it to grasp slippery prey, while their broad bases allow it to crush hard-shelled prey.[4] This shark feeds on a variety ofcrustaceans (crabs,slipper lobsters, andspiny lobsters),bony fishes (includingmorwongs,sea catfishes,drums, andporgies), andcephalopods (in particularOctopus vulgaris).Sharks and rays (includingcatsharks andguitarfishes) and theiregg capsules are a minor food source for larger individuals. Off South Africa, the most important prey species is thecrabPlagusia chabrus. Its dietary composition changes with age; young sharks under 1.0 m (3.3 ft) long subsist almost completely on crabs, while larger sharks consume more bony fishes and cephalopods, as well as a greater variety of prey overall.[8] This shark has been observed deviating from its nocturnal habits to feed onchokka squid (Loligo reynaudii) during their mass spawnings.[11] Thebroadnose sevengill shark (Notorynchus cepedianus) is known to prey on this species.[12]
During the summer, the sharptooth houndshark formsgroups in shallow water. These aggregations are particularly well-documented inFalse Bay and may be related to reproduction, given the presence of many pregnant females.[5] It isaplacental viviparous, with the developingembryos nourished mainly byyolk. Mature females have a single functionalovary and two functionaluteri. Litters of 6–12 pups are birthed between late May and August, following agestation period of some 20 months. Larger females tend to produce larger litters.[8] The length at birth has been variously estimated as 30–32 cm (12–13 in) and 42–44 cm (17–17 in) by different sources; pups within a single litter may vary in size by up to 30%.[5][8] Females apparently reproduce either every two or three years, depending on whether she has ovarian eggs developing during the pregnancy that would allow her to mate again within a few months of giving birth. The sharptooth houndshark is a slow-growing species, with both sexes following a similar growth pattern. Malesmature sexually at 1.2–1.4 m (3.9–4.6 ft) long and 11–13 years of age, while females mature sexually at 1.3–1.5 m (4.3–4.9 ft) long and 15–16 years of age. Themaximum lifespan is at least 25 years.[7][13]
Harmless to humans,[14] the sharptooth houndshark adapts well to captivity and has been displayed inpublic aquariums. It is frequently caught byrecreational anglers from shore or ski-boats; it is edible but rarely eaten.[5] Small numbers are alsocaught incidentally by a commercialdemersal longlinefishery targeting theschool shark (Galeorhinus galeus) in theGansbaai and False Bay region. The meat from sharks caught in the fishery is either made intobiltong orjerky and sold locally, or exported fresh or frozen toItaly andTaiwan.[1] Although in South Africa, the sharptooth houndshark is listed as a noncommercial species, thus cannot be harvested commercially, it is often mistaken for thecommon smooth-hound (Mustelus mustelus) by fishers.[7] TheInternational Union for Conservation of Nature has assessed the sharptooth houndshark as least concern.[1] This species is highly susceptible to even moderate levels of fishing pressure, due to its restricted range, slow growth rate, and lowfecundity. The fact that most sharks caught by fishers are immature is an additional source of concern.[7]
