Dark smooth shark
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Dark Smooth Shark ( Mustelus canis ) |
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The dark smooth shark ( Mustelus canis ) is a species of the genus Mustelus within the family of the smooth shark . It lives near the coast in the western Atlantic and is classified as potentially endangered by the IUCN . Within this species there is a further subspecies in addition to the nominate form with Mustelus canis insularis .
features
The smooth shark is a medium-sized, relatively narrow shark with an elongated body. Its maximum body length is about 1.5 meters; the shark reaches them at the age of 7 to 8 years. On average, however, it is about 1.2 meters long. It weighs around 12.2 kilograms and life expectancy is 10 years for males and 16 years for females. It has large, feline eyes and a fairly long, narrowing blunt muzzle. The body of the animals is uniformly gray on the back, becomes lighter, whitish and yellowish towards the belly. The darkness of the color changes depending on the shark's habitat. Specimens that live in sandy waters where the subsurface is lighter are lighter gray than sharks from dark habitats. Young dark sharks have light edges on their dorsal fins and tail fin, which are still dark, but they fade after a while. This species has two dorsal fins, the first dorsal fin being slightly larger than the second. The rounded dorsal fins are characteristic of this species. The second dorsal fin is found slightly in front of the anal fin, which is half the size of the second dorsal fin. The tail fin of the shark has two lobes, the upper one is round and short, the rear lobe is deeply indented near the tip of the fin.
In general, it is difficult to distinguish the dark smooth shark from other Mustelus species, so it is often confused. In contrast to other shark species, the Mustelus species has many blunt teeth arranged in different rows. The smooth shark has just as many small teeth in the upper and lower jaw, which are arranged asymmetrically in 8 to 10 rows. The animals use these teeth to grind and chew their prey and not tear it apart.
jaw
The teeth on the upper jaw
Way of life
Mustelus canis can be found near the coast and inhabits continental shelves and bays there. It prefers shallow waters with muddy or sandy bottoms that are around 20 meters deep, but can also be found at a depth of 200 to rarely 650 meters; Coral reefs are avoided. The subspecies Mustelus canis insularis , on the other hand, is found at depths of approx. 800 meters and seems to prefer rocky soils. Individual specimens have also been spotted in fresh water; however, it is questionable whether this shark can survive in freshwater for long periods of time.
The smooth shark swims in small groups or schools and has no territory. It is a nocturnal predator and feeds primarily on crustaceans such as lobsters, shrimp and crabs, but also eats octopus, other small fish, and occasionally rubbish and carrion. Young animals also eat worms, small shrimps and crabs. The smooth shark itself is prey of larger shark species.
The North Atlantic population migrates seasonally, reacting to changes in water temperature. In winter he wanders to the area between Chesapeake Bay and South Carolina , in summer he comes back north and spends this season between Delaware Bay and Cape Cod .
Reproduction
The North Atlantic population has a seasonal reproduction cycle, mating usually takes place from May to July. Females are able to store living sperm throughout the year, although it is not certain whether they will be able to use this sperm for fertilization after a while. It is a viviparous species with a yolk sac placenta . The gestation period is about 10 months and the birth takes place in early May to mid-July. Between 3 and 20 animals are born, this varies depending on the size of the mother animal. The newborns are around 28 to 39 centimeters tall and then grow up in their place of birth, in shallow estuaries and swamps. For sharks, this species grows relatively quickly, after 2 to 3 years the males reach sexual maturity and a length of approx. 70 to 90 centimeters. Female dark sharks only reach sexual maturity after 4 to 5 years and at this point they are around 70 to 130 centimeters long.
Systematics
Mustelus canis is a species of the genus Mustelus within the smooth shark family . Within the species, in addition to the nominate form Mustelus canis canis, another subspecies called Mustelus canis insularis is listed . This has a slightly higher dorsal fin, a longer caudal fin and more vertebrae than Mustelus canis canis . In addition, young animals have even more conspicuous white fin edges.
Furthermore, the species Mustelus norrisi is almost indistinguishable from the dark smooth shark . The IUCN doubts whether Mustelus norrisi is really an independent species .
distribution
Dark sharks live in the western Atlantic along the east coast of North America and South America . It comes from Massachusetts via Florida, the northern Gulf of Mexico, Cuba, Jamaica, Barbados, Bermuda, to the Bahamas and from southern Brazil to northern Argentina. The subspecies Mustelus canis insularis is native to several Caribbean islands.
Dark smooth shark and humans
The IUCN classifies the population of the dark shark as potentially endangered . This means that stocks will soon drop to a critical point. This is due to increased interest in commercial fishing of this species. Fish is fished commercially, particularly along the east coast of the United States . One uses longlines or trawls to fish it. Its meat is edible and sold. As a result, the population of female specimens has shrunk and there is currently no plan to protect the species.
With its size and blunt teeth, the smooth dark shark does not pose a threat to humans.
literature
- Antal Vida: 365 fish , illustrated by Tamás Kótai, translated by Balázs Farkas, Könemann bei Tandem, Königswinter 2006, ISBN 978-3-8331-2070-1 , p. 28.
supporting documents
- ↑ a b c d Antal Vida: 365 fish . Tandem Verlag 2006, ISBN 3-8331-2070-3 , p. 28.
- ↑ a b c d e Mustelus canis in the Red List of Threatened Species of the IUCN 2017-1. Posted by: Conrath, C., 2006-01-31.
- ↑ a b c Mustelus canis on Fishbase.org (English)
- ↑ a b c d e f g Dusky smoothhound (Mustelus canis). (No longer available online.) Wildscreen Arkive, archived from the original on July 13, 2017 ; accessed on July 26, 2017 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ a b c d e f g Cathleen Bester: Smooth Dogfishes, Mustelus canis. Florida Museum of Natural History, accessed July 26, 2017 .
- ↑ a b c d e Smooth Dogfishes, Mustelus canis. (No longer available online.) MarineBio.org, archived from the original on October 10, 2016 ; accessed on July 26, 2017 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Mustelus norrisi in the IUCN 2017-1 Red List of Threatened Species . Posted by: Jones, LM, Kyne, PM & Carlisle, AB, 2008-12-01.
Web links
- Dark Smooth Shark on Fishbase.org (English)
- Mustelus canis inthe IUCN 2017-1 Red List of Threatened Species . Posted by: Conrath, C., 2005-10-01.