Home to the only known aggregation of fan mussels in UK waters, the Small Isles Marine Protected Area (MPA) encompasses waters around the islands of Canna and Rum off the west coast of Scotland. The fan mussel is one of the UK’s most threatened molluscs. It grows to between 30-48 cm in length and as the name suggests is a narrow fan shape. It lives with the pointed end buried in mixed muddy sands, with only the straight lips of the shell exposed at the sea bed so the animal can filter the sea water for food.
This MPA is designated to conserve the following biodiversity and geodiversity features:
Biodiversity:
- black guillemot
- burrowed mud
- circalittoral sand and mud communities
- fan mussel aggregations
- horse mussel beds
- northern feather star aggregations on mixed substrata
- northern sea fan and sponge communities
- shelf deeps
- white cluster anemones
Geodiversity: Quaternary of Scotland – glaciated channels/troughs, glacial lineations, meltwater channels, moraines, streamlined bedforms
[1]
A further consultation on management measures for this site is expected later this year. Save Scottish Seas campaign members assessed the Scottish Government’s proposal for management measures for this site as part of its consultation response to the first consultation on management measures for this site.
Read our response to the MCO consultation here:
LINK Marine Group welcome the proposed measures for conservation of the identified Priority Marine Features within the Small Isles MPA with two main exceptions: i) the proposed no-trawling zone excludes the part of the Sound of Canna lying immediately to the east of Canna and north of Sanday; and ii) the area of burrowed mud within the zone protected from trawling is insufficient.
The Sound of Canna contains the most diverse assemblage of features within the MPA, including horse mussel beds, northern featherstar aggregations, northern sea fan and sponge communities and, most notably, the fan mussel aggregations, the only one known in the UK. Fan mussels are primarily threatened by the use of mobile fishing gear and its current, relict distribution is believed to be largely confined to zones that are naturally protected from trawling by virtue of their topography. The Sound of Canna is one such zone. VMS data confirm that the remaining fan mussel aggregation has been subject to very low trawling pressure from 2007-2013 although the zones all around it have been subject to medium to high pressure.While the proposed no-trawl zone includes the relict fan mussel aggregation, it does little other than duplicate the protection already afforded by the topographic features in the Sound of Canna that have allowed fan mussels to persist. Crucially, the continuation of trawling pressure around the proposed no-trawl zone allows only limited expansion for the fan mussel population beyond its current distribution. In common with many other sedentary benthic invertebrates, fan mussels have a planktonic larval stage, which, amongst other benefits, ensures larval dispersal, population expansion and, most importantly, population stability. The Sound of Canna represents the only known viable source population of fan mussels in Scottish waters, which makes it highly vulnerable to disturbance and environmental change. It is for this reason that, in response to the 2013 Possible Nature Conservation Marine Protected Area consultation, we stated our support for ‘conserve’ objectives for all features other than the fan mussel (and indeed northern feather star) aggregations, for which we stated ‘recover’ objectives be set, a position we stand by. It is, therefore, essential that the amount of protected habitat suitable for fan mussels is increased within the Small Isles MPA to ensure population expansion and persistence. The nearby areas of sublittoral mud are the most suitable habitat for fan mussel recruitment and are therefore essential for the expansion and enhancement of the remaining population. For the Small Isles MPA to be effective in restoring the health of its fan mussel population, the proposed no-trawl zone should be expanded upon to include more of these important habitats.The zone to the east of Canna also contains known records of the extremely rare burrowing anemone Arachnanthus sarsi – an MPA Search Feature for which no suitable sites were identified – as well as other PMFs, most notably northern feather star, northern sea fan and mud volcano worms, all of which will be threatened by trawling within this zone. To repeat our response to the 2014/15 consultation;
“A rare example of the burrowing sea anemone (Arachnanthus sarsi) has been identified in the muddy seabed off the north east of Canna. This species is considered to be of international importance in Scottish waters as a result of declines in UK populations. It is likely that more may inhabit this area, as yet undocumented, and we think that as much of this area as possible should be closed to mobile demersal fishing activities as a precaution to ensure that this key habitat, and the biodiversity it hosts, is conserved.”LINK members are concerned that the proportion of burrowed mud habitat protected from trawling within the MPA is insufficient. The proposal indicates that only 19% of the sublittoral mud community and 55% of the recorded tall sea pens are protected from trawling. LINK members suggest that the proposed measures should do more to consider the wider ecosystem that relies on interaction with the burrowed mud habitat. “For example a large amount of recorded tall sea pen (Funiculina quadrangularis) habitat will remain open to trawling and dredging under the revised proposals, a species more sensitive to damage and less able to recover than other sea pen species5.” In addition to the importance of this habitat as a nursery zone for fan mussels, the overall protection of this feature in Scottish waters is insufficient. Given the stark difference between the abundance and diversity of benthic species in the Sound of Canna compared to the rest of the MPA, LINK members highlight the clear need to remove pressure from mobile demersal fishing gear across more of the soft sediment habitats to improve the benthic biodiversity.The Small Isles MPA exists within a newly designated Special Area of Conservation for harbour porpoise and within the proposed ncMPA for minke whales and basking sharks. Increased fishing effort using static gear and unintentional ‘edge effects’ resulting from the shifting of gear use along MPA or MCO boundaries, created by gear displacement, might be detrimental to these species. We therefore encourage a joined-up approach to MCOs and MPA management procedures, as well as wider measures to include the scope of the proposed Inshore Fisheries Bill, and seek assurance from the Scottish Government that measures to protect features in one MPA are compatible and complementary with those of adjacent or overlapping MPAs.
History of this MPA
Save Scottish Seas campaign members assessed the Scottish Government’s MPA proposal for this site as part of its consultation response to the MPA network consultation.
Read our response to the MPA network consultation here:
LINK support the designation of the Small Isles possible Nature Conservation MPA to protect black guillemot, burrowed mud, circalittoral sand and mud communities, fan mussel aggregations, horse mussel beds, northern feather star aggregations on mixed substrata, northern sea fan and sponge communities, shelf deeps and white cluster anemones, and geodiversity features – quaternary of Scotland. The boundary and area of Small Isles possible MPA is fully supported. We also recommend that the future designation should include the Basking Shark Minke Whale as protected features. We note this possible MPA overlaps with two designated SPAs and management will need to refer to, and align with, the objectives of the SPAs.We support the setting of conservation objectives for the protected features within the Small Isles possible MPA to ‘conserve’ for all features other than the fan mussel and northern feather star aggregations. The latter are both scarce in Scottish waters, and the fan mussel aggregation possibly unique pending any further aggregation find, and the opportunity should be taken to enhance these features. In particular, fan mussel status throughout Scotland’s seas is plainly critical, since this is the only known aggregation, and the Small Isles population should therefore be enhanced in order to provide scope to assess the potential to re-seed the historic range of this fragile giant mollusc and ecosystem engineer. The status for both fan mussel aggregations and northern feather star aggregations should therefore be set to ‘recover’.
Management Options:
We support and encourage designation of large zones in the Sound of Canna prohibiting all forms of disturbance by mobile and static fishing gear, anchors, moorings and expansion of new aquaculture ventures, to ensure sizable proportions of sensitive communities are fully protected from disturbance and have opportunity for future enhancement, particularly fan mussel aggregations, northern sea star, feather star, sponge communities, horse mussel and array of burrowed mud community PMFs. For the Sound of Canna, we also recommend that the licensed dredge spoil sites be rescinded.
In the absence of detailed information relating to the impacts of aquaculture on proposed protected features within an MPA it is imperative that the precautionary approach be applied. Discussions with finfish farming interests cannot be used as a proxy for specific, detailed information and where doubt exists management measures must be precautionary.Socioeconomic Assessment:
LINK acknowledges the enormously important contribution of Small Isles Community Council to bringing this possible MPA to the consultation stage. This contribution is an outstanding demonstration of the high value that local communities place on the integrity of their marine environment.
The involvement of the local community in this MPA proposal is an excellent example of the existence of the non-use value of MPAs that has been largely omitted from the economic assessments. The socioeconomic impact data presented in the BRIA indicates the costs of designation (less than £0.42 million pa GVA) and restricting damaging activities will be outweighed by the medium to long term benefit of protecting the ecological integrity of the possible MPA so it can continue to provide ecosystem services to Scotland’s inshore waters.
The potential value of the Small Isles possible MPA to divers and sea anglers has been estimated at £7.3 to £15.3 million based on willingness-to-pay measures (Kenter et al., 2013) . Kenter et al. also found important emotional and well-being benefits associated with the Small Isles possible MPA, with interviewed local users and visitors scoring >4 (out of a maximum score of 5) for engagement, identity, spiritual, therapeutic, transformative and social wellbeing indicator.The Small Isles possible MPA is the only representative site of burrowed mud communities outside sea lochs on the west coast of Scotland, and considered by marine biodiversity specialists as the most significant relic deep water mud habitat in Scotland. Rich and unique mosaic of habitats associated in one area due to the setting of geological seascapes. Existing aquaculture ventures will need to ensure they are compliant with updated or revised Environmental Management Systems to ensure operations minimise local and diffuse cumulative impacts, particularly with respect to water quality, erosion, sedimentation and disease. Proposed future aquaculture ventures will need to be rigorously assessed for potential impact, particularly with respect to water quality, erosion, sedimentation and disease. It is likely that there will be little or no potential for installations throughout large parts of the area. There is limited information presented on wild fish populations in terms and possible contribution of the MPAs to fish populations and benefit to sustainable recreational fishing.
Further surveys in the peripheral deep basins adjacent to the Sound of Canna are needed in order to identify relict deep mud features and assess the potential for expansion of sensitive species such as the fan mussel.
As this is the best remaining area of deep burrowed mud in inshore waters it is essential to set up a monitoring programme that allows assessment of the expansion and recovery of the species and habitats in areas adjacent to the core zone
Harbour porpoise are known to use this site and under Guideline 1b of the selection criteria for PMFs on the OSPAR T&D list should be protected in the MPA and considered in the management options, as well as consideration of designation as part of the Natura 2000 SAC network.
Download the Small Isles MPA site summary document
Check out the official documents relating to the Small Isles MPA on the Scottish Natural Heritage website.
[1] Small Isles MPA site summary document, SNH