Publication - Strategy/plan

Scotland's Marine Atlas: Information for The National Marine Plan

Published: 16 March 2011
Topic: Marine and fisheries
ISBN: 9870755982547

Scotland's Marine Atlas is an assessment of the condition of Scotland's seas, based on scientific evidence from data and analysis and supported by expert judgement.

SHARKS AND RAYS

Elasmobranchs

Elasmobranchs (sharks, skates and rays) differ from other fish in the sea by having a skeletal structure made out of cartilage as opposed to bone.

Elasmobranchs range throughout the oceans and can be found in all oceanic and coastal zones. Scotland has over 30 species of sharks, skates and rays recorded in its waters of which 25 are found in coastal waters.

All elasmobranchs share life history characteristics which make them vulnerable to overfishing and means that once depleted, populations take a long time to recover. Elasmobranchs are slow growing, late to reach maturity and typically have low fecundity, thus the number of individual fish recruited into a population on an annual basis is low. They have a variety of breeding methods:

Oviparous: Egg laying.

Ovoviviparous: Live young bearing with nutrition from yolk sac.

Viviparous: Live young bearing with maternal nutrition.

Some smaller species such as the small spotted catshark (aka lesser spotted dogfish) can mature as early as 6 years old. Larger, longer lived species such as the common skate do not mature until around 15 years old. Low fecundity can mean that each female only produces between 25-50 eggs/pups per year (some females only produce young every two years). The number of young produced is directly proportional to the size of the female, the larger, older fish producing more young than the smaller recently mature fish. The young are often fully developed and instantly capable of self nurture but they are almost instantly at danger from being taken as bycatch as they are large enough to get caught in trawl nets and dredge gear.

As many elasmobranchs tend to school in sex and age related groups, trawls can often pick up large numbers of juvenile fish in a single haul before they have had a chance to reproduce. Therefore relatively few animals actually reach breeding age, and those that do only produce large enough numbers of young later in life to help rebuild a population.

In 2009 it became compulsory for commercial fisheries to report on elasmobranch landings by species as opposed to family. Historically, skates and rays were recorded under one label, now individual species must be recorded. However, many species of skate and ray are similar in appearance and the variation in morphology within the same species can often lead to confusion and misidentification. This will give false numbers of species being landed and could lead to misrepresentation of stock levels.

Many species are also vulnerable to habitat disturbance and loss and some surface dwelling species such as the basking shark are susceptible to boat strikes and harassment.

All species of sharks and rays are on the OSPAR list of Threatened and Declining Species due to their removal as both target and non-target species.

Priority marine features Basking shark - Cetorhinus maximus Spiny dogfish - Squalus acanthias Porbeagle shark - Lamna nasus Portuguese dogfish - Centroscymnus coelolepis Leafscale gulper shark - Centrophorus squamosus Common skate - Dipturus batis complex Blue shark - Prionace glauca Sandy ray - Leucoraja circularis	Basking shark © Paul Naylor
Basking shark Cetorhinus maximus The basking shark is the second largest fish in the world and the largest in British waters, growing up to 9.8m in length. They are known to migrate over large distances in both offshore and coastal waters at depths from the surface to over 750m. They are particularly associated with tidal fronts on the continental shelf and shelf edge where they feed on plankton. They have been recorded from around the whole Scottish coast, with sightings peaking in the summer months especially at a number of hot spots on the west coast. Pressures In the past basking sharks were subject to a targeted fishery in Scottish waters and whilst this no longer exists and they are protected in British waters they are still fished elsewhere. They have suffered 50-80% population declines in recent years. Numbers remain low and they are classed as globally Vulnerable on the IUCN Red List.
Sandy ray Leucoraja circularis The sandy ray can reach 120cm in length and occurs at depths from 70-275m. It is an offshore species typically found on sandy or muddy sea beds to the north-west of Scotland but can occur elsewhere around the coast. Pressures The status of the species is unknown and while there is not a target fishery it is often taken as bycatch, leading to declines in its numbers. It is listed as Vulnerable on the IUCN Red List.
Spiny dogfish Squalus acanthias This is a small dogfish reaching 1.6m in length and is one of the most abundant shark species in the world. It is widely distributed in Scottish waters and is found just above the sea bed, typically at depths of 10-200m (but can be as deep as 900m). Pressures Most populations are at serious risk from overfishing and the species is classed as Vulnerable internationally and Critically Endangered in the north-east Atlantic, where populations are depleted, on the IUCN Red List. Both directed fishing and accidental bycatch pose threats.		© Paul Kay
Common skate Dipturus batiscomplex The common skate can grow up to 3m in length, and is found at depths down to 600m. It has been recorded from all around Scotland. It was once abundant in north-west Europe but there have been significant declines around the UK over the last century due to overfishing. Pressure The waters around the Isle of Mull and Firth of Lorn retain a relatively healthy population but it is classed as Critically Endangered on the IUCN Red List and it is prohibited to land any catch in the EU.		© James Thorburn
Blue shark Prionace glauca The blue shark can grow up to 3.8m in length and, as part of their annual migration, can be found especially off the west coast of Scotland during the summer months. It occurs at depths from the surface down to 600m. Pressures The blue shark is widely fished either through bycatch of by targeted fisheries. The North Atlantic stock status is unclear due to unreliable catch data but there appears to be a declining trend in recent years. Local legislation to protect it is likely to have only limited impact as they are highly migratory. It is currently listed as Near Threatened on the IUCN Red List.		© John Richardson, Shark Trust
Porbeagle shark Lamna nasus The porbeagle shark can reach 3.5m in length and is usually found in mid-water between 200-700m, but sometimes in shallower water close inshore. Pressure It is widely distributed around Scotland although considered rare, and is currently listed on the IUCN Red List as Critically Endangered in the north-east Atlantic and Vulnerable internationally. It is fished for human consumption and fishmeal production and is highly susceptible to overfishing. In 2010 an EU-wide zero TAC was introduced.
Portuguese dogfish Centroscymnus coelolepis This dogfish can reach 1.2m in length and is a deepwater species found between 400-2700m on the continental shelf and abyssal plain. Found off the far west and north coasts of Scotland. Pressure It is commercially valuable, susceptible to overfishing and currently classified as Near Threatened on the IUCN Red List.
Leafscale gulper shark Centrophorus squamosus The leafscale gulper shark can reach 1.6m in length and is found on the continental shelf rarely above depths of 1000m. It is found off the far west and north-west coasts of Scotland. Pressure It is commercially valuable, susceptible to overfishing and currently classified as Vulnerable on the IUCN Red List.

Coastal species of skates, rays and sharks not listed as Priority Marine Features

Scientific name/Common name	Depth range	Habitat	Reproductive strategy	Abundance	Status
Skates and rays
Amblyraja hyperborea Arctic skate	250 - 2500m	Demersal, soft substrate	Oviparous every two years	A rare visitor.	Least concern no target fishery.
Amblyraja radiate Starry skate	18 - 1400m	Demersal various substrates	Oviparous every two years	One of most abundant in North Sea, also north-east Atlantic.	Least concern no target fishery.
Dasyatis pastinaca Common stingray	Shallows - 200m	Soft substrates	Viviparous annual	Sparsely distributed in North Sea.	Near threatened no target fishery.
Dipturus oxyrinchus Long-nose skate	15 - 900m	Soft substrates	Oviparous every two years	Widely distributed low numbers western Scotland, occasional visitor North Sea.	Near threatened no target fishery.
Dipturus nidarosiensis Black skate	120 - ~1000m	Soft substrates	Oviparous annual	Low abundance, slightly higher numbers in deeper water.	Threatened no current target fishery.
Leucoraja fullonica Shagreen ray	30 - 600m	Rough substrates	Oviparous No data on frequency	Rare species, most common off north-west coast.	Near threatened no target fishery.
Leucoraja naevus Cuckoo ray	20 - 500m	Various substrates	Oviparous annual	Comparatively common throughout.	Least concern no target fishery.
Raja brachyuran Blonde ray	10 - 900m	Soft substrates	Oviparous annual	Found throughout, more common in northern and western regions.	Near threatened no known target fishery.
Raja clavata Thornback ray	10 - 300m	Various substrates	Oviparous annual	One of most abundant throughout, more common in western and northern regions.	Near threatened target fishery within Europe.
Raja montagui Spotted ray	Shallows - 530m	Soft substrates	Oviparous annual	Widespread around northern and western coasts, rare in North Sea.	Endangered no current target fishery.
Sharks
Alopias vulpinus Thresher shark	Surface - >330m	Epipelagic, Typically 40-75 miles offshore	Ovoviviparous annual	Rare in Scottish waters, mature fish mainly offshore.	Near threatened no target fishery but taken as bycatch.
Galeorhinus galeus Tope	Surface - 550m	Demersal off continental shelf	Ovoviviparous every 2-3 years	Highly migratory throughout Scottish waters, rarer on east.	Classed as Vulnerable on the IUCN Red List, target fishery in England and Wales but not Scotland.
Mustelus asterias Starry smoothhound	Shallow 0 - 100m	Demersal sand and gravel bottom	Annual	Widespread throughout Scotland.	Least concern, unimportant bycatch in multispecies trawls.
Scyliorhinus canicula Small spotted catshark	Shallows - 400m	Demersal coastal and shelf waters	Oviparous annual	Abundant throughout Scottish waters.	Least concern. No target fishery but larger specimens kept for human consumption.
Scyliorhinus stellaris Nursehound	Shallows - 125m	Demersal rough rocky bottom	Oviparous annual	Common throughout coastal and shelf waters, high abundance in places.	Near threatened. Some target fishery.
Somniosus microcephalus Greenland shark	Shallows - >2000m	Demersal	Ovoviviparous unknown	Low abundance, mainly off north-west coast.	Near threatened. No target fishery but taken as bycatch.
Galeus melastomus Blackmouth shark	55 - 1200m	Demersal continental shelf	Oviparous likely annual	Throughout Scottish waters but more abundant in deeper offshore waters.	Least concern. Zero TAC in EU waters.
Hexanchus griseus Bluntnose sixgill	Shallows - >2000m	Semi-pelagic	Ovoviviparous unknown	Patchy abundance, mostly from north and west coast waters.	Near threatened. No target fishery but caught as bycatch in deep water trawls, retained for human consumption.
Squatina squatina Angelshark	5 - 150m	Largely benthic	Ovoviviparous annual	Very rare in Scottish waters, extinct in North Sea.	Critically endangered. Prohibition on retention in All ICES areas.

In addition to the Portuguese dogfish and leafscale gulper shark which are both priority marine features, there are a number of other deep water species of shark that occasionally visit Scottish waters, they mostly occur beyond the continental shelf and are only known due to their occurrence in deep water fisheries.

Little is known about their population numbers or abundance:

Demon catsharks(Apristurus spp .)
Black dogfish(Centrophorus fabricii)
Longnose velvet dogfish(Centroselachus crepidater)
Frilled shark(Chlamydoselachus anguineus)
Kitefin shark(Dlarias licha)
Birdbeak dogfish(Deania calcea)
Great lantern shark(Etmopterus princeps)
Velvet belly laternshark(Etmopterus spinax)
Knifetooth dogfish(Scymnoden ringens)

Starry smoothhound shark - Mustelus asterias

Starry smoothhound shark - Mustelus asterias

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