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ISRA FACTSHEETS

EUROPEAN ATLANTIC

ISRA FACTSHEETS

EUROPEAN ATLANTIC

Firth of Clyde ISRA

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Firth of Clyde ISRA

Firth of Clyde

Summary

Firth of Clyde is located on the west coast of Scotland in the United Kingdom of Great Britain and Northern Ireland. It is an estuarine system that is characterised by muddy and sandy substrates. It is influenced by freshwater input and a boreal spring increase in phytoplankton. Within this area there are: threatened species and undefined aggregations (Basking Shark Cetorhinus maximus).

Firth of Clyde

Firth of Clyde

DESCRIPTION OF HABITAT

Firth of Clyde is located on the west coast of Scotland in the United Kingdom of Great Britain and Northern Ireland. The area is located within the lower Firth of Clyde estuarine system. It encompasses the area around Kintyre Peninsula, between the Isle of Arran, the Isle of Bute, and up to Great Cumbrae, and the waters surrounding Holy Island. It is characterised by muddy and sandy substrates, and some of the deepest coastal waters in the United Kingdom of Great Britain and Northern Ireland (Field Studies Council Millport 2025).

This area is influenced by the Scottish Coastal Current (Simpson & Hill 1986). It is also influenced by freshwater input and a boreal spring increase in phytoplankton in March (Scottish Government 2025).

This Important Shark and Ray Area is pelagic and is delineated from inshore and surface waters (0 m) to 100 m based on the bathymetry of 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 Endangered Basking Shark (Rigby et al. 2021).

CRITERION C

SUB-CRITERION C5 – UNDEFINED AGGREGATIONS

Firth of Clyde is an important area for undefined aggregations of one shark species.

Opportunistic land-based and vessel-based sightings reported by citizen scientists to the Shark Trust Basking Shark Project are collated into a dedicated database, with records since 1987. Observations of three or more individuals reported at one time were extracted, and duplicate records were removed. Between 2010–2018, a total of 260 Basking Sharks were observed from 48 aggregations (Shark Trust unpubl. data 2025). The mean number of aggregations per year in this period was 3, comprising an average of 5 individuals (maximum = 22 individuals). Aggregations were reported from this area in 2010 (n = 6 aggregations; 29 individuals), 2011 (n = 6 aggregations; 31 individuals), 2012 (n = 3 aggregation; 20 individuals), 2013 (n = 15 aggregations; 77 individuals), 2014 (n = 1 aggregation; 3 individuals), 2015 (n = 14 aggregations; 89 individuals), 2016 (n = 2 aggregations; 6 individuals), and 2018 (n = 1 aggregation; 5 individuals). This is one of the locations in the United Kingdom of Great Britain and Northern Ireland with the highest number of contemporary known citizen science reports of Basking Shark aggregations. This species may be aggregating in this area for feeding purposes based on direct observations by citizen scientists of animals feeding at the surface (Shark Trust unpubl. data 2025). Further information is required to determine the nature and function of these aggregations.

Firth of Clyde

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