Distribution of maerl and horse mussels (Modiolus modiolus) around Shetland: findings from a directed PMF survey.

Richard L. Shelmerdine, Beth Mouat

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Horse mussel, Modiolus modiolus, and maerl beds are listed as OSPAR habitats and Annex I habitats of the EU Habitats directive. In Scotland, they are listed as Priority Marine Features (PMF) and several PMF sites have already been identified around Shetland. In 2011, the Shetland Shellfish Management Organisation (SSMO), through consultation with their members, proactively created a series of Voluntary Closed Areas around the then known PMFs in order to protect the features pending more in-depth surveys. Initial surveys of the PMFs and the Voluntary Closed Areas were carried out around Shetland during 2011
(Shelmerdine, et al., 2013). The results of the surveys allowed the SSMO to fine-tune the initial Voluntary Closed Areas to either remove them or upgrade them to Closed Areas with a final protected surface area covering 21.4 km2 (Shelmerdine, et al., 2014). During 2012, Heriot-Watt University led further survey work (Hirst, et al., 2013) taking sediment grab samples and Drop Down Video drifts within the then proposed Marine Protected Area (MPA) of “Fetlar to Haroldswick”, which has subsequently been designated as a Nature Conservation
Marine Protected Area (NCMPA). During the Heriot-Watt survey, further PMF sites were identified which were outside the initial survey area of the NAFC Marine Centre 2011 surveys.
A third location, which identified maerl at the south end of Clift Sound, was reported to the SSMO by a fisher in 2016. As a precautionary measure, until the areas could be fully surveyed using hydro-acoustics, the SSMO introduced Voluntary Closed Areas encompassing the new sites in Hascosay Sound, the area South of Unst, and southern Clift Sound. Four Closed Areas were created in June 2017, after hydro-acoustic surveys, and were located at Hascosay Sound (Area 16), South of Unst (Area 17), South of Uyea (Area 18), and Clift Sound (Area 25).
During April 2018, a further series of Closed Areas (Areas 19 to 24) were created to protect seagrass around Shetland. The total surface area of all the Closed Areas covered a sea surface area of 29.9 km2.
In May 2019, a series of DDV surveys were carried out around Shetland by SNH and funded by the European Maritime and Fisheries Fund (EMFF). The results of this EMFF survey were preliminary analysed by SNH staff and made available to the SSMO for their consideration. The preliminary analysis highlighted a series of maerl and horse mussel PMF sites around Shetland that were not within an existing SSMO Closed Area and may warrant a degree of protection, depending on their extent and abundance
Original languageEnglish
Number of pages57
Publication statusPublished - 2020


  • Marine Protected Areas
  • Shetland
  • Maerl
  • Modiolus modiolus
  • Horse mussel
  • Fisheries
  • Scallop dredging
  • Priority Marine Features
  • PMF


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