Common skate (Dipturus batis)
Historically, the common skate was one of the most abundant and widespread skates in the Northeast Atlantic, but it is now locally extinct in inshore waters throughout its range due to its vulnerability to commercial trawling. The conservation status of the common skate is listed as critically endangered on the Irish Red List for cartilaginous fish and by the IUCN Red List.
Since 2010, biologists have proposed reclassifying fish historically identified as common skate into two separate but very similar and closely related species: the blue skate (Dipturus batis) and the flapper skate (Dipturus intermedius). In general, flapper skate are considerably larger than blue skate as fully grown adults, and blue skate tend to have a more offshore distribution that flapper skate. Historical catch statistics generally have not differentiated between the two species, which fisheries scientists often currently group as a common-skate species complex to make up for otherwise limited data.
The flapper skate is the largest skate in the world, reaching lengths up to 285 cm. Common skates are greyish brown in colour on its upper surface, with a pointed snout and a row of thorns along its tail. Common skates inhabit depths usually within 200 metres but occasionally down to 1000 metres. They feed on benthic animals, and they can also be active predators moving off the seabed and up through the water column in pursuit of other fish. The common skate is oviparous, with females annually laying about 40 egg cases called mermaids' purses, which are oblong and leathery, with horns projecting from each corner. Juvenile common skates gestate in the egg cases for several months before emerging at over 20 cm in length. This life strategy, with a low rate of reproduction and large size of juveniles, means that common skates are vulnerable to mortality as fisheries by-catch, even from a very young age.
The Marine Sportfish Tagging Programme tagged 1,159 common skates between 1972 and 2014 off the coast of Ireland, with 88% of taggings in the vicinity of just five sites: Clew Bay, Baltimore, Courtmacsherry, Ballycastle Bay and Tralee Bay. The programme has shown that 89% of recaptures of tagged fish occur close to their original tagging locations.
