Thornback ray
size:
maximum 1 meter
weight:
maximum 18 kilograms
color:
yellowish brown with scattered dark and light spots
lifespan:
maximum 15 years
food:
worms, small crustaceans, small sea snails and small benthic fish
threats:
beam trawl fisheries
reproduction:
lays eggs with internal fertilization
number: 52-170 eggs per year
- Dut: Stekelrog (Doornrog, Driestaart, Rode rog)
- Lat: Raja clavata
- Eng: Thornback ray (roker)
- Ger: Nagelrochen
- Dan: Sømrokke
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- Thornback ray (roker), Ecomare
Thornback ray
The thornback ray owes its name to the numerous thorns on its back and tail. Nevertheless, the animal is not dangerous because the thorns are not poisonous. In order to catch its food, it hides under a layer of sand on the sea floor. Together with the spots on its back, it is well camouflaged. Any worms, crustaceans, sea snails or small benthic fish that happen to swim past are caught from its ambush. Thornbacks have rows of strong blunt teeth. When a tooth is worn down, the next one in line appears. Adult thornback rays have 36 to 44 rows of teeth.
- Reproduction
- Egg capsule of the thornback ray, Ecomare
Female thornback rays are sexually mature between 9 and 12 years old, males between 7 and 12 years. This means there is a good chance that the thornback ray is caught (while fishing for flatfish with a beam trawler) before it is able to reproduce. The eggs are laid in the spring. After four to five months, the narrow end between the protrusions breaks open and the barely 12 centimeter-long thornback ray crawls out of the egg. The protrusions serve to attach the egg capsule to a hard surface as well as to provide oxygen for the embryo.
- Distribution and habitat
- Distribution of the thornback ray., Ecomare
Thornback rays used to be very common in the North Sea, even close to the coast and in the Wadden Sea. Around 1900, thornback rays were the most common ray species in the southern North Sea. In those days, fishermen from Den Helder fished these rays commercially. Around 1960, the ray disappeared from the Wadden Sea and the Dutch part of the North Sea and by 1970, from the Zeeland delta and Dutch coastal waters. Presently they are rarely found in the coastal waters and tidal regions. It seems that the thornback ray prefers the (more southern) rocky areas of the sea floor, where one hardly if ever fishes for other benthic fish. Thornbacks are still found in the English North Sea.
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