Skates

Fishery

Skates are an important by-catch in otter trawl, beam trawl and gill net fisheries all around the UK. There are also some directed skate fisheries (e.g. gill net, tangle nets and long line) in some coastal areas, including in the Thames Estuary, and off the coasts of Norfolk, Cornwall, Devon and Wales. These directed fisheries may be seasonal, targeting skates during the spring and early summer when they may aggregate in inshore areas for spawning. Skates are also important target species in some recreational and charter boat fisheries. Currently, skates are landed either gutted or as skinned or unskinned wings. Though some fisheries may target certain species, landing statistics do not currently differentiate between the various species.

Biology

Over 20 species of skate occur on the UK shelf in the surrounding deep-water areas, though several deep-water species are only known from a few specimens. Skates are long-lived, slow growing, and are oviparous, with females laying egg cases (mermaids purses) on the sea floor. Fecundity varies between species, though is less than 100 eggs per year. The embryos develop over the following months, and then hatch at lengths of 10–20 cm, depending on the species. Many species are relatively large, growing to about 1 m in length, with the largest species (e.g. common skate Dipturus batis and white skate Rostroraja alba) growing to over 2 m, and the smaller species (e.g. blue pygmy skate Neoraja caeruleai) growing to about 30 cm.

Juvenile and small-bodied skates tend to feed predominantly on small crustaceans (e.g. amphipods, shrimps and small crabs), with larger skates feeding on either large crustaceans or fish. Some skate species, such as the cuckoo skate Leucoraja naevus develop sharply pointed teeth as they grow and then feed on fish, whilst other species, such as spotted skate Raja montagui, tend to retain their molar-like teeth and feed mainly on shrimps and crabs.

Several species of skate have been tagged and released. Juveniles tend to be recaptured quite close to the release position, which would indicate that they have a restricted home range, though larger fish may move more widely, which has also been observed in studies using electronic tags. More targeted tagging experiments could usefully be undertaken to clarify the nature of skate stocks.

Within inshore waters, the most abundant skates are thornback skate Raja clavata, spotted skate R. montagui and blonde skate Raja brachyura, and these species may occur around much of the British Isles. Some species have a more restricted distribution, with smalleyed skate Raja microocellata most abundant in the Bristol Channel and English Channel, and undulate skate Raja undulata observed most regularly in the English Channel. Further offshore, cuckoo skate L. naevus are common in the North, Irish and Celtic Seas and off North-west Scotland. The related shagreen skate Leucoraja fullonica and sandy skate Leucoraja circularis also prefer offshore grounds, occurring along the edge of the continental shelf. Starry skate Amblyraja radiata is one of the more common skate species in the North Sea.

Some skates have declined in European seas. For example, common skate is now observed only occasionally in the Irish Sea, southern North Sea and other inshore waters where it was once encountered regularly, though it is still caught on offshore fishing grounds. Historically, white skate was targeted in coastal fisheries in southern and western areas, though there are few recent records of this species.

Management and Advice

Since 1999, the various species of skate in the North Sea (ICES sub-area IV) and EC waters of the Norwegian Sea (ICES Division IIa) have been managed under a single TAC for "skates and rays". ACFM also provides advice on skates in this area