Species of cartilaginous fish
The bottlenose skate, spearnose skate, or white skate (Rostroraja alba) is a species of
endangered
.
Distribution and habitat
The bottlenose skate is found along the
continental slope. Du Buit (1974) reported that it is more prevalent in rocky habitats.
[1]
Description
Most bottlenose skates are 60–150 cm long,orbit and 16–30 mid-dorsal and 17–29 lateral thorns on the tail. The
skin is rough in adults except for a smooth patch in the center of the disc; the underside is prickly except for smooth patches on the snout. The young are entirely smooth, except for on the snout. Large juveniles and adults are greyish or bluish with or without numerous small white spots above, white below with brown to black disc margins. Hatchlings are plain reddish-brown above, often with blue spots, and white below with broad dusky disc margins.
[3][4][5]
Biology and ecology
The bottlenose skate is a benthic
gestation period of 15 months. The
egg cases are oblong in shape, with stiff pointed horns at each corners and the larger horns flattened. They are deposited in sandy or muddy flats in the
spring. The capsules measure 12.5-18.3 cm long and 10.0-13.9 cm wide.
[3][5] This species is estimated to mature at 130 cm for males and 120 cm for females.
[1]
Relationship to humans
In the 17th century, the bottlenose skate was prized by the
fisheries. Anecdotal data suggests that there has been a substantial decline in the abundance and geographical range of this species in the north Atlantic and Mediterranean. In the north Atlantic, populations of bottlenose skates have declined severely or disappeared from the
Bay of Biscay and the
Irish Sea; there are no longer targeted fisheries in these regions due to localized population collapses in the 1960s. There are also no recent records of this species in the waters off the
United Kingdom, where it historically occurred. The bottlenose ray still persists along the coast of the
Iberian Peninsula, though the population data is uncertain due to confusion with the
shagreen ray (
Leucoraja fullonica) and the
sandy ray (
L. circularis).
[1]
In the Mediterranean, bottlenose skates of most size classes down to egg cases are taken as
by-catch in multi-species
trawling fisheries. Historically, it was caught frequently off the coasts of
Tunisia and
Morocco in the 1970s and was described as more or less frequent in the northwestern Mediterranean from the 1950s to the 1970s. The MEDITS trawl surveys, begun in 1985 and carried out six times a year in four geographic regions, indicates that the bottlenose skate is now very rare in the Mediterranean and that it has been reduced to a small fraction of its former range. The
Italian National Group for Demersal Resource Evaluation (GRUND) survey captured this species infrequently in the
Adriatic Sea. The species is assessed globally as Endangered in the
IUCN Red List, and Critically Endangered in the northeast Atlantic.
[6] However, its status will require re-evaluation once data from its African range is available.
[1] In 2010, Greenpeace International added the bottlenose skate to its Seafood Red List, which includes commonly marketed species that "have a very high risk of being sourced from unsustainable fisheries".
[7]
References