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ISRA FACTSHEETS

EUROPEAN ATLANTIC

ISRA FACTSHEETS

EUROPEAN ATLANTIC

Celtic Deep ISRA

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Celtic Deep ISRA

Celtic Deep

Summary

Celtic Deep is a deep basin in the Celtic Sea, located within the waters of the United Kingdom of Great Britain and Northern Ireland. The area is characterised by muddy and sandy substrates. It is influenced by shelf tidal fronts, variations in phytoplankton biomass, mixing of different currents, and seasonal upwelling. Within this area there are: threatened species and reproductive areas (Common Blue Skate Dipturus batis).

Celtic Deep

Celtic Deep

DESCRIPTION OF HABITAT

Celtic Deep is located within the United Kingdom of Great Britain and Northern Ireland. It is situated outside of the Bristol Channel, between Ireland and the United Kingdom of Great Britain and Northern Ireland in the Celtic Sea. The area is characterised by muddy and sandy substrates (Aldridge et al. 2017). It overlaps with a relatively deep basin on an otherwise shallow shelf.

The area is influenced by shelf tidal fronts, variations in phytoplankton biomass, and mixing of different currents (Pingree et al. 1982), including the exchange of water from the Atlantic Ocean (via St. George’s Channel) and the Irish Sea. It is also influenced by seasonal upwelling.

This Important Shark and Ray Area is benthic, pelagic, and subsurface and is delineated from 10–160 m based on the depth range of Qualifying Species in the area.

CRITERION A

VULNERABILITY

One Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occurs in the area. This is the Critically Endangered Common Blue Skate (Ellis et al. 2024).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Celtic Sea is an important reproductive area for one ray species.

Early life stage Common Blue Skates are regularly and predictably observed in this area, in larger numbers compared to adjacent areas (ICES 2025). Data from the International Beam Trawl Survey (IBTS) (2010–2025), operating inside and outside of this area (in the broader Celtic and Irish seas) were analysed. These data indicate that Common Blue Skates were caught in February, March, April, and September. Overall, 247 neonate/young-of-the-year (YOY) Common Blue Skates were caught inside and outside of this area. These measured =< 38 cm total length (TL), and the size-at-birth for this species is 21 cm TL (Last et al. 2016). Nearly one quarter of the neonate/YOY Common Blue Skates (n = 46; 18.6%) were caught within this area. The animals were caught in 2016 (n = 1), 2017 (n = 4), 2018 (n = 2), 2019 (n = 7), 2022 (n = 1), 2024 (n = 17), and 2025 (n = 14). Included in these numbers were 18 neonate Common Blue Skates measuring =< 21 cm TL caught in 2017 (n = 2), 2024 (n = 9), and 2025 (n = 7). This area is nationally important as it is one of only two remaining hotspots where early life stages of the species are regularly and predictably observed.

Celtic Deep

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