Winter rays
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Winter rays ( Leucoraja ocellata ) |
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| Scientific name | ||||||||||||
| Leucoraja ocellata | ||||||||||||
| ( Mitchill , 1815) |
The winter ray ( Leucoraja ocellata ) is a ray from the family of real rays (Rajidae) that occurs in the northwestern Atlantic off the eastern US coast . The IUCN classifies this species as critically endangered .
features
The winter ray is nocturnal and has a rather blunt and rounded snout. Its pectoral fin tips are rounded and concave towards the snout, in contrast to this they are slightly convex towards the tail. Its tail is moderately slender and a little longer than its body. Usually this ray is about 105 centimeters long and 7 kilograms. The largest and oldest specimens, with a maximum size of 107 centimeters and a maximum age of 20.5 years, live on the eastern US coast . Males reach sexual maturity at a length of approx. 70 centimeters at an age of 11 years and females at approx. 75 centimeters at the age of 11 to 12 years. The average lifespan of such a ray is 19 years. The size and maximum age can vary from region to region.
| Dispersion area | Maximum body length (in centimeters) | Maximum age (in years) | Body length at which sexual maturity is reached (in centimeters) | Age at which sexual maturity is reached (in years) |
|---|---|---|---|---|
| eastern US coast | 107 | 20.5 | 76 (for female specimens) | 12.5 (for female specimens) |
| Gulf of Maine | 94 | 19th | 73.0 (for males)
76.0 (for female specimens) |
11.0 (for males)
12.0 (for female specimens) |
| eastern Scotian Shelf | 92.5 | 19th | 75.9 (for males)
77.0 (for female specimens) |
11.3 (for male specimens)
13.4 (for female specimens) |
In general, the winter ray is very similar to the small ray , especially if the body length of the animals is less than 35 centimeters. A distinguishing feature would be the drawing of the animals, winter rays usually have 1 to 4 dark spots with white borders on the back, near the back of the chest muscles. The teeth are blunt cusps, the winter ray has 72 to 110, in contrast, the small ray has 38 to 66. Female specimens have more blunt teeth, male conical cusps which are more pronounced, the number of teeth varies according to the size of the animals. Another distinguishing feature is the number of rows of teeth in the upper jaw. Winter rays have 63 or more rows, while small rays have only 30 to 62 rows. Winter rays also have a gently curved mouth, which is usually more curved and wider than that of the small ray. Small female small rays also have small spines very close to the cloaca , in female winter rays these are on the outer edge of the pelvic fins. Male winter rays have thorns at the basin, but male small rays do not have any at this point. Young winter rays have three to four larger thorns on each shoulder and near the eyes, along the muzzle as well. A row of 12 to 16 thorns runs along its back and ends in a row of 16 to 18 thorns along the tail. Adults have two to three irregular rows of thorns on each side of the center line. An irregular triangular group of spines lies in the neck and shoulder area. There is also a row of thorns along the chest girdle and there may be smaller thorns in other parts of your body. With increasing age, the thorns along the shoulder area and eyes in male specimens decrease, while in female specimens larger spines develop in the rear area of the pectoral fins.
coloring
The male winter ray is light brown in color and has dark spots on its trunk, pelvic fins and tail. Sometimes there are 1 to 4 dark spots on the back of each pectoral fin that are bordered in white. On each side of the muzzle there is a whitish translucent area in front of the eyes. The underside is white, with irregular light brown spots on the rear pectoral fin and along the tail.
Distribution and habitat
These rays live in the northwestern Atlantic off the eastern US coast from the Newfoundland Bank and the Gulf of St. Lawrence to North Carolina . There seem to be four regions where these rays are common, in the southern Gulf of St. Lawrence, the Scotian Shelf , a continental shelf southwest of the Canadian province of Nova Scotia , in the southern Gulf of Maine and in the waters off Massachusetts to North Carolina. The range is slightly larger than that of the little ray, which is not found in the Gulf of St. Lawrence and in the northern part of the Scotian Shelf.
Usually winter rays occur in shallow waters up to a depth of 90 meters. They usually stay over sandy or gravelly soils, less often over muddy and stony soils, and are most active at night. However, near the Gulf of Saint Lawrence, one specimen was caught at a depth of 370 meters. They stay in a water temperature of −1.2 to 19 ° C, typically in a temperature of 9 to 15 ° C. In the southern dispersal areas, these rays have been observed to move to deeper colder waters during the summer months, indicating that they prefer cooler temperatures. It can also be seen that the type of substrate over which they move determines where they are rather than the depth.
Way of life
Winter rays mainly eat flea and poly-bristle , but also fish such as sand eels , decapods , woodlice and clams . The bigger these rays get, the bigger their prey becomes. Although the winter rays are very similar to the small rays and the range is almost identical, they do not compete with each other when searching for food. Winter rays tend to eat the infauna , small rays the epifauna .
Reproduction
This type of ray lays eggs . The egg capsules are quite small with a length of 55 to 66 and a width of 24 to 45 millimeters. They are elongated and have small stiff horns at the tips, the front ones being longer than the rear ones. Winter rays in the Gulf of Maine exhibit a partially defined reproductive cycle, with most mating in July and maximum oviposition in September to November. Males produce mature sperm throughout the year and most of the time there are females capable of reproduction. There is no such defined reproductive cycle in the Scotain Shelf as fewer reproductive females live in this region. Each female lays around 40 eggs per year, each containing one embryo. The egg capsules are placed on rocky ground by the female in coastal waters. Little is known about the hunters of the winter stingray, they are eaten by sharks, gray seals and other rays. Parasites that attack these rays are protozoa . When hatching, the young are about 11.2 to 12.7 centimeters long.
Danger
As with other ray species, the life cycle of the winter ray is long, late sexual maturity, low fertility and slow population growth are the reasons for this, which means that excessive fishing can have serious consequences for the population. However, this species is not specifically caught. The primary threat is trawling , especially bottom trawling , where it is inadvertently caught as bycatch . In its Canadian range, the status of the populations differs depending on the area and intensity of fishing. In the eastern Scotian Shelf and the southern Gulf of Saint Lawrence, animals have been reported to have decreased by 90 to 98% compared to the early 1970s. This strong decrease can probably be explained by the unsustainable and excessive catch and bycatch quota and will continue. In contrast, populations in the southernmost part of the Canadian range, such as the Western Scotian Shelf or the Georges Bank , appear to be relatively stable over the period for which data are available. Ray fins obtained from the animals are consumed in the USA and Canada, but mostly exported to Europe or Asia. Young specimens are also likely to be used as bait fish.
For these reasons, the winter ray is classified as endangered .
supporting documents
- ↑ Winter rays on Fishbase.org (English)
- ↑ a b c d e f Leucoraja ocellata in the Red List of Threatened Species of the IUCN 2017-3. Posted by: Kulka, DW, Sulikowski, J. & Gedamke, T., 2004-06-15.
- ↑ a b c d e David A. Ebert, Matthias FW Stehmann: SHARKS, BATOIDS AND CHIMAERAS OF THE NORTH ATLANTIC ; Food and agriculture organization of the united nations, Rome 2013, ISBN 978-92-5-107466-4 ( // PDF ) pp. 340–342.
- ↑ a b c d e f g h i Winter Skate. Fisheries and Oceans Canada (DFO), accessed February 13, 2017 .
- ↑ a b c d e f Cathleen Bester: Leucoraja ocellata. Florida Museum of Natural History, accessed March 19, 2018 .
