Razor clam scientific trial: fisheries assessment
A fisheries assessment for the Scottish razor clam scientific trial extension. This report assesses the potential impact of the razor clam scientific trial with reference to priority marine features, and the conservation objectives of a variety of sites in Scotland's MPA network.
4. MPA Assessment – North East Lewis Nature Conservation MPA
4.1 MPA Protected Features
Bio-diversity: Risso’s dolphin & sandeels.
Geodiversity: Quaternary of Scotland & Marine Geomorphology of the Scottish Shelf Seabed.
Conservation Objective: The aim is to conserve these features in order to make a long-lasting contribution to the MPA network.
4.2 Proposal Details
Electrofishing for Razor Clams Scientific Trial – fishing to continue in Trial Area 1 Broad Bay until the trial ends. The fishery operates annually from the 1 February to the 31 January the following year. There is a seasonal closure from 20 April 2006 – 18 May 2026 to protect the spawning period in all trial areas.
4.3 Details of Proposed Operation (inc. location, timing, methods):
Broad Bay. The fishery operates annually from the 1 February to the 31January the following year. There is a seasonal closure from April to May to protect the spawning period.
Scientific derogations were issued after an application process and participants are bound by the terms and conditions (T&Cs) of the trial, which are subject to change. T&Cs include being subject to a daily catch limit of 450kg and an annual effort limit of 110 days at sea. In addition, all vessels require a Remote Electronic Monitoring (REM) system on board at all times, providing details of vessel position and status of the electrofishing gear. The REM system must remain switched on, including when the vessel is transiting or fishing for species other than razor clams. Lastly, the electrofishing gear must operate within the parameters specified by the Marine Directorate.
Electrofishing for razor clams (Ensis sp.) involves divers following the electrodes, which are towed behind a fishing vessel. Marketable clams are collected whilst clams below the minimum size of 100mm can re-burrow in the sediment.
Vessels have average speeds of 3 metres per minute when towing the electrofishing gear. Fishing typically occurs in the early morning.
4.3.1 Test 1: INITIAL SCREENING: Is the activity and/or development capable of affecting, other than insignificantly, the protected features of a Nature Conservation Marine Protected Area?
4.3.1.1 Risso’s Dolphin
Risso's dolphins feed on a range of benthic and diurnally migrating cephalopod species, with octopus (Eledone cirrhosa) dominating the prey identified in the stomachs of stranded animals from Scotland (MacLeod et al, 2014). The targeted removal of razor clams on should have an insignificant impact on dolphin diet.
Risso’s dolphins are nocturnal feeders and razor fishing occurs in the early morning, there should be insignificant overlap.
(Evans, Anderwald, & Baines, 2003) reported that Risso's dolphins in UK waters favoured habitat of 50–100 m depth. Razor clam fishing tends to be in shallow water of around 10 metres depth, overlap with dolphin activity is likely to be insignificant.
In Broad Bay, the majority of razor fishing occurs in the bayhead, just off of Aiginis. There is also a small pocket of fishing off Gleann Tholastaidh. Dolphin activity has been recorded at the mouth of the bay, Tiumpan Head, but predominately spread down along the east coast of Lewis (Weir, Hodgins, Dolman, & Walters, 2019). Razor vessel movement disturbance is therefore likely to be insignificant on this feature.
There is evidence that anthropogenic noise, acoustic disturbance, can cause the alteration of behaviour, consisting of avoidance of the impacted area (Wensveen, et al., 2019) but Rissos’s dolphins currently do not frequent the razor fishing areas, indicating insignificant impact.
Broad Bay has significant marine traffic in the area which will create significant marine acoustic disturbance. The main vessel traffic in Broad Bay consists primarily of local fishing vessels, inshore boats targeting shellfish like lobster, crab and scallops using creels. Broad Bay plays host to a lot of recreational and charter boats, typically offering sea angling and wildlife tours, these are typically small motorboats or RIBs. Charters and tours tend to operate seasonally. Stornoway is the largest port in the Outer Hebrides and is in close proximity to Broad Bay. Passenger and cargo ferries regularly sail between Stornoway and Ullapool. Occasionally whitefish trawlers operate in the area around the Bay but the Bay is closed to mobile gear fishing like dredging and trawling. The closest aquaculture projects are located in Loch Liurboist and in the inshore area from Cromore heading inland up the loch. Razor fishing Broad Bay would not significantly increase marine acoustic disturbance in the area.
Conclusion: no significant effect.
4.3.1.2 Sandeels
In Broad Bay, the majority of razor fishing occurs in the bayhead, just off of Aiginis. There is also a small pocket of fishing off Gleann Tholastaidh. Evidence demonstrates sandeel aggregation from the mouth of the bay and beyond into deeper water (Langton, Boulcott , & Wright, 2021). Overlap with sandeel activity is likely to be insignificant. Razor vessel movement and fishing disturbance is therefore likely to be insignificant on this feature.
Sandeels show a strong preference for sediments composed primarily of coarse to very coarse sand (0.5–2.0 mm grain size) to bury in (Henriksen, et al., 2024). While this substrate in the seabed can be associated with razor clams, this is principally the case for E.arcuatus rather than E.siliqua which are the main species targeted by this fishing trial. Razor vessel movement and fishing disturbance is therefore likely to be insignificant on this feature.
If sandeels were present in 10 metre depths the divers work at they may become incidentally temporarily stunned if they come into contact with electrodes. Our available knowledge suggests the effect on sandeel mortality would be of insignificant impact, due to the scale of the fishery and observations of stunned sandeels recovering soon after being shocked.
Towing the electrofishing gear leaves a 1cm furrow compared with a 25cm furrow of a dredge in the seabed (Murray, Copland, Boulcott, Roberston, & Bailey, 2014). Diver activity may produce some very localised silt movement. Electrofishing activity can be said to have an insignificant impact on benthic disturbance.
Conclusion: no significant effect.
4.3.1.3 Quaternary of Scotland
No razor fishing occurs in the Minch.
Conclusion: not applicable.
4.3.1.4 Marine Geomorphology of the Scottish Shelf Seabed
No razor fishing occurs in the Minch.
Conclusion: not applicable.
4.4 Monitoring and Review – North East Lewis MPA
The trial is scheduled to end in 2027. Any new information relating to the impact of razor clam fishing in this MPA will be taken into account, possibly requiring further management measures as appropriate.