All of the rays possess a soft cartilage skeleton and are close relatives of the sharks. They are generally flat with a body disc which may range in shape from diamond-like to almost circular. They have adapted to life on the sea-bed in a number of ways, one of the main ones is in the way that they breathe. Most fish obtain oxygen by drawing in water through their mouth and passing it over their gills, for the rays to do this would result in a large amount of sediment being inhaled. They have overcome this problem with the development of small holes (or spiracles) which are located behind the eyes, in an aquarium they can be seen to open and close in passing clean, oxygen rich water over the gills.

The Thornback Ray (Raja clevata) or Roker is generally associated with large expanses of sand and shingle banks such as those found off the Thames estuary and in the Bristol Channel, but are fairly common in all shallow waters of the UK. They are usually found lying over mixtures of sand, mud and gravel, but will also occupy sandy ground between rocky outcrops.  

Thornback Ray Shape and Colouration

Thornback ID: The thornback ray has a diamond shaped body, with the pectoral wings being drawn out into wings, the tips of which form near right angles. These fish are masters of camouflage and the colouration of their upper body, as with most flatfish and rays, is influenced by the type of sea bed that they are living over. Over gravel and mixed rock this is often dominated by sandy brown with mottling of black spots and light, yellowish spots or patches. Over sand and mud they are usually lighter, almost grey with whitish spots. The underside is off-white with greyish edges that tend to be pink in some fish. The dominant feature is obviously the series of strong sharp thorns which occur over the upper surface, which are most numerous along the tail. At times ray identification can be quite difficult, spikes are not unique to the thornback and should not automatically be used as positive i.d. However the thorns themselves are distinct, if you look closely at the larger thorns, or bucklers as they are often known, they can be seen to have a smooth, broad baseplate similar to a button or the head of a nail, which is not seen in other species.

Distinctive thorns of the Thornback Ray

Lifestyle: The distinction between male and female ray unlike most fish is very obvious, the males possess two rod-like claspers, which are located towards the base of the tail and again unlike the majority of other fish fertilisation is internal, with eggs being laid individually in leathery cases often known as mermaid’s purses. Female fish move inshore in late winter to early spring followed soon after by the males. Between March and August each female deposits about 20 egg cases, which are approximately 7.5 cm long and rectangular in shape with a long “horn” at each corner. The edges of the egg case are covered with small hairs which help attach it to rocks or weed where it will stay until the young fish emerges after 4-5 months. Sexual maturity is quite slow in coming and ranges between 7 years in males when the fish is about 60 cm in length to 9 years in females. The wings of the thornback make excellent eating, but catch and release of the smaller specimens is critical to allow development to breeding age.

Location: These fish spend the whole of their lives on or very close to the sea bed in shallow waters between 5 and 100 m. They will often submerge themselves under a thin layer of sand or mud, so that only their eyes and spiracles are exposed. Their eyesight is good and allows all-round vision, but because the mouthparts are on the underside of the fish, they rely on highly developed senses of taste and smell to locate their prey. Food consists of bottom living fish and crustaceans including crabs and prawns, although adult fish have been known to take fish swimming a few metres above the bottom. 

Facts:

Thornback Ray (Raja clavata)

Diamond shaped body with short nose
Large spines with broad base
Colour Sandy brown to grey with yellowish mottling

Shore record:             21 lb 12 oz 0 dr, 1985, Kirkcudbright
Boat record:               31 lb 7 oz 0 dr, 1981, Liverpool Bay