about the fanshell

The UK has populations of a remarkable marine creature, and the Marine Conservation Society needs information on it! The rare fanshell (Atrina fragilis) appears to be concentrated in sheltered locations of UK waters, but we are lacking accurate population data. It is hard to find, and exists in mud, sand and gravel habitat. It is most likely to be seen by fishermen as part of the catch when hauling in nets from the sea bed, or by divers.

description

Growing to an impressive 48 cm in length, the fanshell (Atrina fragilis) (also sometimes called a fan mussel) is one of the largest of the bivalve molluscs found in Europe. It takes its English name from the delicate shell, which is triangular in shape, and tapers to a point. The valves of the shell are pale yellowish-brown to dark brown in colour, with a glossy interior. Living specimens are partly buried vertically in the sediment, with only the top portion of the valves visible. Fanshells anchor themselves into the sediment by attaching to small stones with numerous fine strands of protein known as 'byssus'. The byssus of this species is so like human hair that many fishermen believed that fanshells had fed upon drowned people. They therefore deemed this species 'unclean', and would return them to the sea if they were caught.

range

This scarce species is found around the coast of Britain and Ireland, with the densest populations occurring in Scotland and off the southwestern coast of Cornwall. It is believed that the fanshell has disappeared from many inlets in the southwest of England, where it was once common. Elsewhere its range extends as far south as the Iberian Peninsula.

The species inhabits waters from the surface down to depths of 400m, and is found in muddy, sandy and gravelly sediments.

biology

At present, relatively little is known of the biology of this species. The fanshell occurs solitarily or in small groups and feeds by filtering organic particles from the water. Fanshells reproduce by broadcast spawning and fertilisation is external, and success is affected by the proximity of other individuals as well as a range of environmental factors. Studies of annual growth rings on the shells have suggested that they grow at a rate of 3-4 cm per year. Based on this rate of growth, it is thought that the largest individuals are 10-12 years old, and possibly even older. The upper, exposed parts of the shells are often damaged, leaving sharp edges, but the shell is repaired quickly.

threats

The main cause of the decline of this species is thought to be the use of trawls and dredges in fishing, both of which disturb the seabed and damage fanshells, often removing them from the sediment. Further threats include gravel and sand extraction.

conservation

The fanshell is fully protected within 12 nm of the UK coast under Schedule 5 of the Wildlife and Countryside Act, 1981 and the Wildlife (NI) Order 1985. Atrina fragilis is also listed as a priority species under the UK Biodiversity Action Plan (UK BAP). The lack of information on the biology of this species hinders efforts to conserve it. However, recent work has shown that it may be possible to restore populations where favourable habitat remains. It has been demonstrated that live specimens are able to survive being moved and 're-planted' into the sediment. As the species is attached to the sediment, it is also possible that protected areas could be established where good populations survive. A dedicated survey of this species is needed to determine its UK distribution more accurately.

In order to promote the recording of fanshells, MCS has produced various leaflets that can be donwloaded:

Click Here for Fanshell information leaflet/recording form for the UK (pdf)

Click Here for Fanshell information leaflet/recording form for Scotland (pdf)

All too often MCS receives reports of specimens trawled up, and even picked up by divers ignorant of their protected status. Only by divers spreading the message of the endangered status of this and other marine species, are we likely to get anywhere near protecting known populations of the species in shallow waters. So, please get in touch with MCS if you hear about, or have seen a fanshell in your area, or on your dive - we may be able to help you find one of the rarest marine animals in the UK!

Please contact Jean-Luc Solandt at MCS (email - jls@mcsuk.org, tel - 01989 561 594) if you see one, or for more information and hard copies of the leaflets. Many thanks.