Review of the Exploitation of the Mussel, Mytilus Edulis, in Scotland
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Review of the Exploitation of the Mussel, Myti/us edulis, in Scotland David W McKay and Sarah L Fowler No68 Review of the Exploitation of the Mussel, Mytilus edulis, in Scotland David W McKay and Sarah L Fowler 1997 The Nature Conservation Bureau Ltd 36 Kingfisher Court, Hambridge Road, Newbury, Berkshire RG14 5SJ Nominated Officer: K Duncan, Aquatic Environment Branch Report date: 1996 Report to: Scottish Natural Heritage Contract No: RASD/026/195 AEB This report should be cited as follows: McKay, D.W. and Fowler, S.L. 1997. Review of the Exploitation of the Mussel, Myti/us edulis, in Scotland. Scottish Natural Heritage Revjew. No 68 Scottish Natural Heritage Scottish Natural Heritage Publications Section Research and Advisory Services Directorate Battleby, Redgorton, Perth PH1 3EW 2 Anderson Place, Edinburgh EH6 5NP UNITED KINGDOM UNITED KINGDOM ISSN 1350-3111 Review ofthe Exploitation ofthe Mussel, Mvtilus edulis in Scotland Contents 1. Summary ............................................................................................................................................... 1 2. Introduction ........................................................................................................................................... 2 3. Methods ................................................................................................................................................ 3 3 .1. Questionnaire survey ................................................................................................................... 3 3.2. Literature review .......................................................................................................................... 3 3.3. Collation and analysis of fisheries landing data .......................................................................... .4 4. Biology .................................................................................................................................................. 5 4.1. Taxonomy .................................................................................................................................... 5 4.2. Habitat and geographic range ...................................................................................................... 5 4.3. Ecology and life-cycle ................................................................................................................. 7 4.4. Feeding ......................................................................................................................................... 9 4.5. Pollution and mussels .................................................................................................................. 2 5. The fishery .......................................................................................................................................... 12 5 .1. Market requirements .................................................................................................................. 12 5.2. Catch statistics ............................................................................................................................ 12 5.3. The Domoch Firth fishery ......................................................................................................... 14 5.4. The Montrose Basin fishery ..................... .' ......................................... :....................................... 14 5. 5. Other wild Scottish fisheries ...................................................................................................... 15 5.6. Future projections ...................................................................................................................... 16 6. Aquaculture ......................................................................................................................................... 19 7. Environmental considerations ............................................................................................................. 21 7 .1. Environmental role of mussels ................................................................................................... 21 7.2. Environmental impacts of dredging wild mussel beds and relaying seed .................................. 22 7.3. Environmental impacts of suspended mussel culture ................................................................ 25 7.4. Environmental impacts of hand collection ................................................................................. 28 8. Comparisons with elsewhere in Europe .............................................................................................. 29 8.1. England, Wales and Northern Ireland ....................................................................................... 29 8.2. Spain and Ireland ....................................................................................................................... 29 8.3. France ......................................................................................................................................... 30 8.4. Dutch, German and Danish Wadden Sea .................................................................................. .30 9. Legislation ........................................................................................................................................... 32 9 .1. Ownership of mussel fisheries ................................................................................................... 32 9.2. Public health .............................................................................................................................. 33 10. Recommendations for further research and management .................................................................. .34 10 .1. Research priorities ..................................................................................................................... 34 10.2. Management recommendations ................................................................................................. 35 Acknowledgements ..................................................................................................................................... 36 References ................................................................................................................................................... 36 Appendices ................................................................................................................................................. 41 1. Copies of questionnaires sent to SNH and SFP A offices. 2. SOAEFD records of mussels landed in Scotland, 1975-1994. 3. List of potentially relevant legislation Figures 1. Areas supporting populations of commercial-sized mussels in east Scotland ............................. 6 2. Tonnage of mussels harvested by statistical rectangle, 1975-1994 ........................................... 12 3. Landings from the Montrose Basin and Domoch Firth fisheries, 1975-1994 ........................... 13 4. Monthly pattern of landings from the Domoch Firth Fishery, 1993-1994 ................................ 14 5. Reported locations of mussel harvesting activity, Scottish Natural Heritage staff.................... 17 6. Reported locations of mussel harvesting activity, Scottish Fisheries Protection Agency staff.. 18 Tables 1. Catches of shellfish in Scotland in 1994 ...................................................................................... 2 2. Mussel harvesting data, 1974-1994, 1895-1900 and 1933-38 ................................................... 13 3. Farmed mussel production for the table by region 1993-1994 .................................................. 19 4. Farmed mussel production for all Scotland, 1986-1994 ............................................................ 19 5. Ecological effects of mussel fisheries in the Wadden Sea ......................................................... 25 6. Removal of carbon, nitrogen and phosphorous from coastal ecosystems by mussel farming ... 26 7. Faecal waste production and sedimentation from shellfish farming ......................................... 27 8. Sediment accumulation below shellfish farms .......................................................................... 27 ii Review of the Exploitation of the Mussel, Mytilus edulis. in Scotland 1. SUMMARY The common mussel (Mytilus edulis Linnaeus 1758) is widely distributed around Scotland, both on rocky shores and within sediment areas in inlets. Large, commercially exploitable stocks are generally confined to more sheltered areas, particularly where there is some freshwater influence, and make up large beds in the lower littoral and shallow sublittoral zones. These extensive mussel beds comprise an important part of the ecosystem. Long-lived stable mussel beds provide a particularly important benthic habitat which supports a wide range of associated species and may be of high marine nature conservation importance. They also provide an essential food source for invertebrate and vertebrate predators (including internationally-important populations of shorebirds and seaduck). They probably also have significant effects on coastal hydrology and chemistry, in that they can stabilise large sediment areas, are very important consumers of phytoplankton, and may play a key role in the cycle of production and breakdown of organic matter, including the stimulation of denitrification and the possible reduction of eutrophication levels. Many of the areas