Short-nosed dogfish
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Short-nosed dogfish ( Squalus megalops ), juvenile with yolk sac |
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| Squalus megalops | ||||||||||||
| ( Macleay , 1881) |
The short-nosed dogfish ( Squalus megalops ) is a type of shark and belongs to the order of the dogfish-like (Squaliformes). It reaches a maximum body length of about 77 centimeters and is distributed in the eastern Atlantic off the coasts of Europe, Africa and the Mediterranean , on the coasts of sub-Saharan Africa and around Madagascar and in the western Pacific off the coasts of East Asia and Australia.
Appearance and characteristics
The short-nosed dogfish is a comparatively small shark with a maximum body length of around 77 centimeters. The young are born with a length of 23 to 25 centimeters; the males reach sexual maturity with 34 to 51 centimeters and the females with 37 to 62 centimeters of body length. It is a slim shark with the typical body shape of a dogfish. It is colored gray-brown to dark brown on top and has no white markings or spots. The ventral side is white. The upper tips of the dorsal fins and the upper and lower tips of the caudal fin are dark gray to black in color, the pectoral and pelvic fins are white at the rear edge. Rare cases of albinism have been demonstrated.
The head is broad with a long and wide muzzle. The nasal valves, which partially cover the nostrils, have a short median barb . Viewed from the ventral side, the mouth is almost straight and forms only a slight curve, the labial folds are long. Like all species in the family, the animals have five gill slits , which are all in front of the pectoral fins, and have an injection hole behind the eye. The eyes and the injection holes are comparatively large. The shark has two dorsal fins with the typical spines in front of them, but no anal fin . The first dorsal fin is larger than the second and begins above the inner edge of the pectoral fins. The thorns in front of the dorsal fins are comparatively short to medium-long. The pectoral fins are relatively large, the free rear end is pointed. The rear edge of the pelvic fins is concave. The tail keels are short and there is no tail notch. The upper lobis of the caudal fin is relatively long, the lower comparatively short.
The sharks have 11 to 13 teeth in both the upper and lower jaw, behind which, as with almost all sharks, there are further teeth. The teeth of the upper jaw are comparatively small. They sit diagonally, almost horizontally, in the upper jaw and have a point and sawn edges. They are overlapping and form a kind of " saw blade ". The teeth of the lower jaw are built and arranged similarly.
distribution
The range of the short-nosed dogfish includes numerous marine regions of the Atlantic, Indian and Pacific oceans. It has been found in the eastern Atlantic off the coasts of Europe and Africa, in the Mediterranean Sea , on the coasts of sub-Saharan Africa and around Madagascar, and in the western Pacific off the coasts of East Asia, Australia, New Caledonia and around the New Hebrides . It occurs only rarely in the Mediterranean and only in the western part. Officially, it is only recorded there with two specimens, of which a male was caught in 1894 off Melilla , Morocco , and a female in 1900 off the coast of Formentera . Occasional animals probably migrate through the Strait of Gibraltar ; reproduction in the Mediterranean has not been proven.
Way of life
The short-nosed dogfish live near the coast in the area of the continental shelf and on the ocean floor of the upper continental slopes at depths of up to 730 meters. The animals are social and often form larger schools, which can be mixed-sex or single-sex; however, they can also occur individually. They are active but slow swimmers and feed on smaller bony fish and sharks of smaller species, cephalopods, crustaceans, bristle worms, and other invertebrates.
The animals are ovoviviparous , so they give birth to living offspring that develop in the womb from eggs without a placenta (aplacental viviparous). The length of gestation is unknown; it is estimated to be two years. Adult females appear to be continuously reproductive with no gap between gestation periods. The births probably take place over the whole year, at least in African populations no seasonality has been proven. During development in the uterus they feed on a yolk sac , which they still have at birth and which later degrades. The juvenile sharks are born in shallow shelf areas; a female gives birth to one to six, usually two to four, young animals. After birth, the young live pelagically in the area of the birth area. The males reach sexual maturity at around 15 years of age, the females at around 22 years of age.
Systematics
The short-nosed dogfish is an independent species within the dogfish of the genus Squalus . It was scientifically described in 1881 by the zoologist William John Macleay . Part, it is assumed that as the currently Squalus megalops recognized populations from various marine areas more are very closely related species of a different species complex and, accordingly, do not belong to a single species.
Hazard and protection
The short-nosed dogfish is not classified in a hazard category in the IUCN Red List and is listed as "data deficient" due to the data situation. It is caught in relatively large quantities with bottom trawls and also with lines and mesh nets, partly as bycatch and partly for commercial purposes. Its distribution area includes some heavily fished areas, for example off Southeast Australia. However, no significant declines have been documented so far and it is relatively numerous and common in this area. There are also large areas around South Australia that are not fishing for the species, including a large area off the north west coast that is closed to shark fishing. As a result, the species is considered to be harmless in Australia; however, local fishing pressure can affect stocks.
supporting documents
- ↑ a b c d e f g Leonard Compagno , Marc Dando, Sarah Fowler: Sharks of the World. Princeton Field Guides, Princeton University Press , Princeton and Oxford 2005; P. 76. ISBN 978-0-691-12072-0
- ↑ a b c d e f g h i j Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean , Franckh-Kosmos Verlags-GmbH, Stuttgart 2005; Pp. 100-101. ISBN 3-440-10458-3
- ↑ a b Short-nosed dogfish on Fishbase.org (English)
- ↑ a b c d e f g Squalus megalops in the endangered Red List species the IUCN 2003. Posted by: RD Cavanagh, TJ Lisney, 2009. Retrieved on 17 May 2020th
literature
- Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean , Franckh-Kosmos Verlags-GmbH, Stuttgart 2005; Pp. 100-101. ISBN 3-440-10458-3
- Leonard Compagno , Marc Dando, Sarah Fowler: Sharks of the World. Princeton Field Guides, Princeton University Press , Princeton and Oxford 2005; P. 76. ISBN 978-0-691-12072-0
Web links
- Short-nosed dogfish on Fishbase.org (English)