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

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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

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.

Basking shark map

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.

Sandy ray map

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.

Spiny dogfish map

Spiny dogfish
© 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.

Common skate map

Common skate
© 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.

Blue shark map

Blue shark
© 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.

Porbeagle shark map

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.

Portuguese dogfish map

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.

Leafscale gulper shark map

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