Rare fan shells discovered

One of the UK’s rarest and most threatened marine creatures has been discovered off Scotland, providing a boost to previous known population levels.

The fan shell or fan mussel is a giant but elusive mollusc growing up to half a metre long, and is the largest shell in Scotland.

Marine Scotland scientists recorded dozens of the shells from the Inner Hebrides at a depth of 175m-220m during routine monitoring in the Small Isles, using a drop frame video camera.

Prior to this discovery only 14 live specimens around the United Kingdom, and just three from Scotland, were reported to the Marine Conservation Society, the UK lead partner for the fan shell Biodiversity Action Plan (BAP).
The fan shell is believed to have once been abundant in UK coastal waters, but its numbers are thought to have declined rapidly since the advent of industrial trawl fishing. It is now so rare that it is protected under the Nature Conservation (Scotland) Act 2004 from being intentionally or recklessly killed, injured or taken. Once encountered quite commonly in seabed trawls and ship-based surveys in the past, reports of this giant mollusc are now extremely rare.

Calum Duncan, MCS Scottish Conservation manager, said: “Fan shells had previously been reported to MCS from the Small Isles, brought up as by-catch in fishing gear, and this footage provides evidence they are on the seabed in the vicinity. However, this population is an exciting find and appears to host fairly large individuals, suggesting that the dredge spoil area hasn’t been affected by seabed disturbance, such as bottom-towed fishing gear and the dredge spoil itself, for a number of years.

“The video footage is compelling, as it shows the potential for the seabed - even in sandy and gravel areas - to host extraordinary species, if left alone from human disturbance. MCS is working with Marine Scotland to consider how we can ensure the protection of this new population using the powers contained in the Marine (Scotland) Bill.”

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