Barn sling
| Barn sling | ||||||||||||
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Barn skate ( Dipturus laevis ) |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Dipturus laevis | ||||||||||||
| ( Mitchill , 1818) |
The barn ray ( Dipturus laevis ) is the largest ray (Batoidea) in the north-western Atlantic and is harmless to humans. The largest specimens reach a length of 153 centimeters and a weight of 20 kilograms. As one of 5 species of rays, it is commercially important in its range and is classified as endangered by the IUCN .
features
The broad, diamond-shaped pectoral fins of the barn door are sharply angled at the corners, the front edges are concave, the dorsal fins are close together. The back of the pectoral fins are also rounded and its tail is somewhat short and quite thick. It is reddish-brown in color with dark spots and slightly lighter stripes. A special feature is a thin and dark stripe that starts at the head and runs towards the tail to the very edge of the pectoral fin. The belly side is white to gray and the muzzle is marked with dark spots.
It has no placoid scales on its tail , so you can distinguish it from almost all other species of real rays . But the tail has three rows of small thorns. Larger specimens have such thorns on their backs, and sexually mature females also on their heads and shoulders. They do not yet have young specimens.
Dipturus laevis grows slowly and becomes quite long-lived at 11 years of age. As one of the largest species of rays in the north-western Atlantic, the barn slate grows to around 150 centimeters and weighs a maximum of 18 kilograms. Unconfirmed finds even gave a length of 180 centimeters. Typically, these rays weigh between 71 and 76 centimeters and weigh 2 to 3 kilograms.
The teeth of the female as well as the young male barn sliver are very close to each other and have rounded tips. In contrast, sexually mature male rays have widely spaced pointed teeth arranged in rows. The upper jaw consists of 30 to 40 rows of teeth. The rows of teeth in the lower jaw have between 28 and 38 teeth.
Distribution and ecology
The barn ray is found along the Atlantic coast of North America. The northern limit of its range is the coast of Newfoundland and the southern part of the Gulf of St. Lawrence . To the south, its area extends to the US states of North Carolina and Florida .
In summer the ray tends to migrate to deeper sea areas, in winter to shallow ones. Because of its size, large sharks are likely its only predators.
The barn slipper can usually be found on soft, muddy, sandy or stony ground, in shallow as well as in deep waters. Its preferred sea depth is between 0 and 150 meters, with a maximum depth of 750 meters. The water temperature can vary greatly here: from just above freezing point to approx. 20 ° C. Although Dipturus laevis can also be found in brackish water, the optimal salinity of its habitat is 31–35 ‰.
Way of life
The barn stingrays usually stay close to the ground and feed on invertebrates such as mussels, octopus, lobsters, shrimp, worms and small fish. With its pointed snout, it digs for mussels in the sand.
Reproduction
This kind of ray lays eggs ; However, very little is generally known about their reproductive cycle. The animals probably reach sexual maturity between the ages of 8 and 11 years. There is a significant hug when they mate. After mating, the females carry the eggs for about 6 to 12 months. These are quite large, about 7-13 inches long, 4.5–7.5 inches wide, yellow and or greenish. They are elongated, rectangular and have small stiff horns at the tips that are used to attach them to sandy or muddy places. They are laid in both shallow and deep waters in winter. The young hatch in spring or summer. The number of young animals is quite small. They are around 180 to 190 millimeters long and resemble their parents. Young animals tend to follow large objects like their mother.
Danger
As with other ray species in this region, Dipturus laevis is threatened by the local fishery, but the barn ray is not targeted. Since 1981, the catch quotas for rays in the USA have risen steadily. This development is primarily due to the strong increase in demand for ray fins on the US export market and secondarily to the demand as bait fish for lobsters. The barn sliver is very often caught with trawls as bycatch, and this is sometimes the greatest danger for this species. A number of data on trawling show a decline in biomass and the distribution of this species. Basically, it was historically difficult to collect correct data, in the 1960s and early 1970s the population of this ray fell rapidly and data indicated that the biomass decreased approximately 96% to 99%. The population remained low until 1990, but increased again from then on. This trend could not be foreseen for the time being and petitions were even started to classify this species as endangered. According to a study published in 2002, this ray should not be classified as endangered as the biomass increases. In 2003, however, it got on the Red List of Endangered Species . The reasons for this can be traced back to slow growth, late sexual maturity, low fertility and large body size. At the moment there are no protection programs to protect this species, the populations are stable.
supporting documents
- ↑ a b c Dipturus laevis in the Red List of Threatened Species of the IUCN 2017-2. Posted by: Dulvy, NK, 2003-04-30.
- ↑ a b c d e Jennifer Basta: Dipturus laevis Barn-door skate. Museum of Zoology University of Michigan, accessed August 13, 2017 .
- ↑ a b c d e f g Mary Jane Wettstein: Barndoor Skate. Florida Museum of Natural History, accessed August 13, 2017 .
- ↑ David B. Packer, Christine A. Zetlin, and Joseph J. Vitaliano: Essential Fish Habitat Source Document: Barndoor Skate, Dipturus laevis, Life History and Habitat Characteristics NOAA Tech Memo NMFS NE 175., March 2003 ( // PDF; 5.4 MB ).
- ↑ a b c d Dipturus laevis on Fishbase.org (English)
Web links
- Barn sling on Fishbase.org (English)