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Interesting Facts about the Thornback Skate

[Phylum: Chordata] [Class: Chondrichthyes] [Order: Rajiformes] [Species: Raja clavata]

It has several common names (e.g. roker) and often called a ray. However, Raja clavata is actually a cartilaginous skate fish belonging to the family Rajidae.

This page contains information about the thornback skate, including where they live, what they eat, and how these oviparous carnivores reproduce.

Thornback Skate Habitats and Distribution

The geographical range of thornback rays is quite widespread, largely around the northeastern Atlantic and the Southwest Indian Ocean.

Nonetheless, they thrive best in the neritic coastal and offshore waters of certain marine environments, such as:

Northern Europe (e.g. Iceland, Norway, UK, Channel Islands)
The Mediterranean Sea (including Croatia, Cyprus)
South Africa (including Madagascar) and West Africa (e.g. Senegal)
The Black Sea (e.g. Bulgaria, Romania, and Turkey)

During the daylight hours, thornbacks like to bury themselves in sedimentary seabeds, anywhere between ten (10) and three hundred (300) metres deep.

Hence, they prefer to live in a habitat that has an abundance of sand, mud, or shingle substrates, such as the dive site at Chesil Cove in Dorset in the South of England.

Pro Tip: Anyone who enjoys scuba diving around the British Isles is likely to have encountered thornback skates (Raja clavata) because they are one of the most common sightings in these waters, albeit spotted less frequently at the dive sites in Scotland.

Thornback Ray Characteristics and Behaviour

Despite being part of the ray fish family, they are also closely related to the shark phylum. As a result, thornback skates also have the same kind of soft cartilage skeleton.

The distinct diamond body shape is mostly due to the oversized pectoral fins - that function similar to underwater wings.

Key takeaways:

The standout features of the thornback ray are the short snout and a row of 30 to 50 prickly backward pointing "horns" (called bucklers) scattered around their back and elongated tail.

By and large, the marbled body colouration contains various shades and hues of browns and greys. This pattern tends to blend together with pale yellow spots in smaller specimens.

The average length of the thornback skate is around 139 centimetres (54 inches) and an adult can weigh up to eighteen (18) kilograms (39 pounds).

It's common for fully matured females to display thorns on their underbelly - which is a pale white colour. Even though other species of batoids also have horns or venomous spikes (e.g. the spotted eagle ray), the thornback skate (Raja clavata) has the largest.

Interesting Fact: One of the biggest thornback rays ever recorded measured almost four (4) feet wide (wingtip to wingtip).

What Do Thornback Skates Eat?

Even though they are a typical carnivore, skate fish spend most of the daytime colonising the ocean floor. At dusk, the majority of skates feed on active bottom dwelling sea creatures by trapping them from above, such as:

Amphipods (eaten mostly by juvenile skate species)
Cephalopods
- cuttlefish
- octopus
- squid
Crustaceans
- bottom-living shrimps
- crabs
- lobsters
Mollusks
- clams
- oysters
Small, slow-moving or injured fish (especially flatfish)
Worms (Phylum annelida)

Interesting Fact: Skates and the electric ray are the only chondrichthyans with electric organs in the tail (used for communication rather than hunting). Plus, the skate is the only electrogenic fish that has paired electric organs running lengthwise through the tail.

How Do Thornback Rays Reproduce?

Unlike most ray fish and mantas, which give birth to live offspring, skates lay eggs. The leathery case that protects the eggs, known as a mermaid's purse, is a rectangular capsule that can measure up to 9 centimetres long (about 4 inches).

For the most part, the age of sexual maturity for sea skates is ten (10) years. Following a successful courtship, the gestation period of up to forty eggs can last up to twelve (12) months in some species.

Fun Fact: The egg capsule usually contains only one embryo. But, there can be up to seven (7) embryos for some species, such as the mottled skate (Beringraja pulchra).

Global Threats and Predators

Despite having an average lifespan of fifteen (15) years, the population of thornback rays is declining - mostly due to commercial fisheries and human consumption.

Besides being a valuable food source for humans, several marine species prey upon thornback rays, particularly large sharks, killer whales, tuna, and northern elephant seals.

The IUCN Red List of Threatened Species assessed the thornback skate (Raja clavata) in 2023 and highlights them as being "Near Threatened" with a current population trend of "Decreasing".