Little ray
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Little ray ( Leucoraja erinacea ) |
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| Leucoraja erinacea | ||||||||||||
| ( Mitchill , 1825) |
The little ray ( Leucoraja erinacea ), also known as hedgehog ray or little hedgehog ray , is a species from the family of real rays (Rajidae), which occurs in the northwestern Atlantic off the eastern US coast . This species is classified as Endangered by the IUCN .
features
The little ray has a very rounded snout and a rounded, diamond-shaped breast disc that is dark brown, rusty red or gray. This is covered with numerous small spots that have a diameter of about 1 to 2 centimeters. The edges of the pectoral fins are paler. On the underside it is white or light gray. Both dorsal fins are close together on the tail. The Leucoraja erinacea's slender tail stalk is about as long as its body. This species becomes a maximum of 60 centimeters long, mostly 40 to 50 centimeters. The small rays attain a width of about 1.2 times the body length and weigh about 0.3 to 1 kilogram. They usually reach an age of 5 years, a maximum of 8.
The little ray has Lorenzini ampoules , a sensory organ under the skin on the head that enables the perception of electrical fields and temperature differences. It can use it to track down its prey, which generates weak electrical fields. It is believed that he can also perceive the earth's magnetic field and that this organ functions as a compass.
The little ray has an electroplax on its tail that can generate electrical voltage. This organ is not used for hunting. It is believed that the electroplax is instead used for communication or for localizing conspecifics.
A very unusual discovery was made near Fisher's Island, south of New London : a specimen caught was hermaphrodite . The testicles were well developed on the left side of the body and juvenile ovaries were developed on the right side of the body .
The differentiation of Leucoraja ocellata is often quite difficult, because the animals have the same shape, you can only distinguish them based on the different pattern of spots. Since spots may be missing in Leucoraja ocellata , these two species are often confused.
The little ray has 38-66 rows of round teeth on plates, adapted for grinding prey.
Female specimens have small skin spines scattered on the head, snout, shoulders and sides of the tail. Most of the time, no spines can be found along the midline or the back of the shoulder girdle. Males have fewer spines than females because they lose most of them during sexual maturation. Otherwise the spines can be found in the same places as in the female specimens.
Distribution and ecology
Leucoraja erinacea lives along the eastern US coast, from the Newfoundland Bank and northeastern Newfoundland to South Carolina . Most of the specimens are found near the Scotian Shelf in Canada. In the Gulf of Maine are the most common species Roche.
In general, small rays do not migrate far, in summer they are more in the coastal area, in winter more in deep water. Whether this is really the case in all areas of distribution remains questionable, as different sources describe this migration differently and specimens have been found at other depths in some seasons.
These rays are typically found over sandy soils at depths of around 90 m. But they have also been caught at depths of 400 m. In summer they prefer a water temperature of approx. 2–13 ° C and usually stay at a depth of 11–120 m. In autumn they are found at a depth of approx. 1–400 m and at temperatures of 5–21 ° C. They only occur in salt water, the optimal salinity of the sea is 29–33 ‰.
Way of life
In general, these rays feed on invertebrates such as crabs, shrimp, worms, mussels, squid, but also on small fish and copepods . They are nocturnal and spend the day on the ground, lightly buried in the sand.
Its predators are small sharks, such as the sandbar shark , other rays and gray seals .
Because these rays live so close to the surface of the water, they can come into contact with humans. If you step on these rays or touch them, you can injure your spines. The spines do not contain poison, their electrical organ cannot harm people.
Lesser ray parasites are the protozoa Caliperia brevipes , Haemogregarina delagei , and Trypanosoma rajae . Chloromyxum leydigi and Leptotheca agilis and nematodes (such Pseudanisakis tricupola ) and copepods ( Eudactylina corrugata and Lernaeopodina longimana ).
Reproduction
This type of ray lays eggs . Along the pelvic fins, males have two long tubular clusters for the transmission of sperm. The reproduction of the species does not seem to be tied to any season, but twice a year there seem to be more pregnant specimens: from October to December and from April to May. They also lay eggs all year round, mainly October through January and June through July. The egg capsules are initially amber or golden yellow, but they turn dark green over time. They are elongated and have small stiff horns at the tips and are deposited in sandy or muddy residential areas and attached to algae there. The eggs are 4.5–6 cm long and 2.5–4.5 cm wide. about 10 to 35 eggs are laid each year. The yolk contains all of the organic materials needed for the development of the embryo. Hatching takes place in an aquarium under good conditions about 5 to 6 months after being laid; in nature this can take longer, especially in times of the year with lower temperatures. The young hatch through a transverse opening in the capsule and are about 10 cm tall. The empty black capsule can be found on the beach.
Danger
The biggest danger for the little ray comes from catching lobsters, as it is used as lobster bait. Another threat is trawling , especially bottom trawling , where it is inadvertently caught as bycatch . There is currently no protection program for this species, but one is in place should the population drop to a certain level. One can assume, however, that this value will soon be undershot, as there is intensive fishing in the relatively small distribution area. The IUCN calls for more precise information on the number of catches, more detailed research into the animal's way of life and more state studies of the population. One should also begin to develop target and limit values for stocks and catch quotas.
For these reasons, the little ray is classified as Endangered .
supporting documents
- ↑ a b c Antal Vida: 365 fish . Tandem Verlag 2006, ISBN 3-8331-2070-3 , p. 35.
- ^ Theodor CH Cole: Dictionary of animal names . Springer Spektrum Berlin Heidelberg 2015, 2nd edition, p. 379. ISBN 978-3-662-44241-8 .
- ↑ Leucoraja erinacea on Fishbase.org (English)
- ↑ a b c d Leucoraja erinacea in the Red List of Threatened Species of the IUCN 2017-1. Posted by: Sulikowski, J., Kulka, DW & Gedamke, T., 2008-12-01.
- ↑ a b c d e f g h i j Kimberly Kittle: Little Skate. Florida Museum of Natural History, accessed August 3, 2017 .
- ↑ Benjamin L. King, Ling Fang Shi, Peter Kao, William T. Clusin: Calcium activated K + channels in the electroreceptor of the skate confirmed by cloning. Details of subunits and splicing. In: Gene , 578, No. 1, 2016, pp. 63-73.
- ↑ Jayne M. Gardiner, Robert E. Hueter, Karen P. Maruska, Joseph A. Sisneros, Brandon M. Casper, David A. Mann, Leo S. Demski: Sensory physiology and behavior of elasmobranchs. In: Jeffrey C. Carrier, John A. Musick, Michael R. Heithaus (Eds.): Biology of sharks and their relatives. CRC Press, April 9, 2012, 2nd edition, Chapter 12, pp. 349-401 ( Google Books reading sample ).
- ↑ Jayne Michelle Gardiner: Multisensory integration in shark feeding behavior. Dissertation December 8, 2011, University of South Florida ( PDF ).
- ↑ a b c d David B. Packer, Christine A. Zetlin, and Joseph J. Vitaliano: Essential Fish Habitat Source Document: Little Skate, Leucoraja erinacea, Life History and Habitat Characteristics NOAA Tech Memo NMFS NE 175., March 2003 ( / / PDF; 9.9 MB ).
literature
- Antal Vida: 365 fish . Tandem Verlag 2006, ISBN 3-8331-2070-3 , p. 31.
Web links
- Little ray on Fishbase.org (English)