Common skate

The common skate (Dipturus batis), also known as the blue skate, is the largest skate in the world, attaining a length of up to 2.85 m (9.4 ft). Historically, it was one of the most abundant skates in the northeast Atlantic Ocean and the Mediterranean Sea. Despite its name, today it appears to be absent from much of this range. Where previously abundant, fisheries directly targeted this skate and elsewhere it is caught incidentally as bycatch. The species was uplisted to critically endangered on the IUCN Red List in 2006 and it is protected within the EU. Research published in 2009 and 2010 showed that the species should be split into two, the smaller southern D. cf. flossada (blue skate), and the larger northern D. cf. intermedius (flapper skate). Under this taxonomic arrangement, the name D. batis is discarded. Alternatively, the scientific name D. batis (with flossada as a synonym) is retained for the blue skate and D. intermedius for the flapper skate. The common skate can reach up to 2.85 m (9.4 ft) in length, 2 m (6.6 ft) in width, and 113 kg (249 lb) in weight, making it the largest skate in the world. Overall shape features a pointed snout and rhombic shape, with a row of spines or thorns along the tail. The top surface is generally coloured olive-grey to brown, often with a pattern of spots, and the underside is lighter blue-grey. It can be confused with several other skates in its range, such as D. nidarosiensis, D. oxyrinchus, and Rostroraja alba. The common skate is native to the northeast Atlantic and Mediterranean Sea. Historically, the species ranged from Iceland and northern Norway to Madeira and northern Morocco. It is a bottom dwelling species mainly found at depths of 100–200 m (330–660 ft), but it can occur as shallow as 30 m (98 ft) and as deep as 1,000 m (3,300 ft). They are found in those depths at the waters off northwestern Scotland and in Celtic Sea, and along the edge of the continental shelf. At the start of the twentieth century common skates had a wide range around the British Isles. Now, their population and range are severely depleted and fragmented, with disappearances being reported on several places. The common skate can reach an estimated age of 50–100 years and maturity is reached when about 11 years old. The size where they reach maturity depend on sex and population. In D. cf. flossada (blue skate) males reach maturity when about 1.15 m (3.8 ft) long and females when about 1.23 m (4.0 ft) long. In D. cf. intermedia (flapper skate), males reach maturity when about 1.86 m (6.1 ft) long and females when about 1.98 m (6.5 ft) long. The sex ratio is 1:1, but this can vary depending on geography and season. When hatching, juveniles measure up to 22.3 cm (8.8 in) long. Once they have reached sexual maturity, they only reproduce every other year. They mate in the spring, and during the summer, females lay about 40 egg cases in sandy or muddy flats. The eggs develop for 2–5 months before hatching. Egg cases measure up to 25 cm (10 in) long, excluding the horns, and 15 cm (6 in) wide. They are covered in close-felted fibers and often wash up on the shore. Egg case hunts have been done throughout the general distribution of the common skate. In the British Isles, egg cases were only found in northern Scotland and the north of Ireland. In the 19th and 20th centuries, egg cases were seen along the entire British coastline in high numbers, but now they are only found in a few areas. Like other skates, the common skate is a bottom feeder. Its diet consists of crustaceans, clams, oysters, snails, bristle worms, cephalopods, and small to medium-sized fish (such as sand eel, flatfish, monkfish, catsharks, spurdog, and other skates). The size of the individual can affect its diet. Larger ones eat larger things like fish. The bigger the skate is, the more food will be needed to sustain its large body size. The activity level determines how much it eats; the more active it is, the more it eats. The common skate does not only feed on creatures at the bottom of the ocean, as some do ascend to feed on mackerel, herring, and other pelagic fish, which are caught by rapidly moving up from the seabed to grab the prey.