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The Northern Menai Strait mussel fishery is run by Bangor Mussel Producers Ltd.. This is an association of four businesses;  Myti Mussels Ltd., Extramussel Ltd., Ogwen Mussel Ltd., and Deep Dock Ltd. The fishery has been certified by the Marine Stewardship Council (MSC). Mussel seed is fished from Morecambe Bay and Caernarfon Bay (areas without invasive species such as the Slipper limpet, Crepidula fornicata) with a proposed area in the River Dee. The mussel seed is then laid in the Straits on “lays”. These are areas of the seabed leased to each company. It takes three years of growth before they can be harvested. Over this time they are moved from shallow intertidal waters (year one) to deeper sub tidal waters (year three) Once harvested, using a mussel dredge, they are left for 42 hours in clean water before being exported to Holland, Ireland and France. Discussions are currently underway to meet the growing demand for locally produced seafood by keeping more of these mussels in the Welsh marketplace.

Blue/Common Mussel (Mytilus edulis)

Image: Ben Lincoln –Mytlius edulis feeding

The Blue mussel is a common marine bivalve that varies in colour from purple/blue to brown, with a pearl white interior. The shell is roughly triangular but varies depending on the environmental conditions. The shell is smooth but has concentric lines running down each valve from the umbones. Their size varies from 2-20cm, but is usually 5-10cm.

Habitat & Distribution

The Blue mussel is found from the high intertidal zone to the shallow sub tidal. They attach to the substrate using byssal threads (strong, silky fibres) and often occur in high densities forming large ‘biogenic’ reefs, binding to each other and forming layers. They are found on exposed open coasts on rocks as well as in sheltered estuarine environments and are common all over the British Isles. They range from the White Sea in the North to Southern France in the NE Atlantic as well as from the Canadian Maritimes down to North Carolina in the W Atlantic. They also occur off the coasts of Chile, Argentina, The Falkland Islands, There are also several large commercial beds, for example in the Menai Straits and the Wash.

Life Cycle

Spawning occurs over a long time period in some populations with a peak in Spring and Summer. Reproduction timings vary with environmental conditions. Fertilisation is external with an individual female releasing from 7-40 million eggs depending on environmental factors and size. This can occur over a broad range of temperatures (5-22°C) and salinities (15-40psu). The eggs are released into the water column and usually take around 1 month to develop. The juvenile mussels (pediveligers) test the substrate with their sensory foot before settling, preferring uneven ground without adults. They first settle on filamentous substrate, for example ground rich in algae, bryozoan or hydroids, at a size of around 260µm. When they reach a size of 1-2mm they move to grounds where the adult mussels lie, drifting using their byssal threads. These newly settled mussels are called ‘Spat’. As a result of drifting with currents in the water column and then again to re-settle mussels can be dispersed over wide areas.

 

Publications

Caldow, R.W.G., Beadman, H.A., McGrorty, S., Kaiser, M.J., Goss-Custard, J.D., Mould, K. & Wilson, A. (2003). Effects of intertidal mussel cultivation on bird assemblages, Marine Ecology Progress Series 259: 173-183

Caldow, R.W.G., Beadman, H.A., McGrorty, S., Stillman, R.A., Goss-Custard, J.D., Durell, S.E.A. le V. dit, West, A.D., Kaiser, M.J., Mould, K. & Wilson, A. (2004). A behaviour based modelling approach to reducing shorebird-shellfish conflicts. Ecological Applications 14: 1411-1427

Beadman, H.A., Kaiser, M.J., Galanidi, M., Shucksmith, R., & Willows, R. (2004). Changes in species richness with stocking density of marine bivalves. Journal of Applied Ecology 41: 464-475

Tweddle, J.F., Simpson, J.H., & Janzen, C.D. (2005). Physical controls of food supply to benthic filter feeders in the Menai Strait, U.K. Marine Ecology Progress Series 289: 79-88

Saurel, C., Gascoigne, J.C., Palmer, M., & Kaiser, M.J. (2007). In situ mussel feeding behaviour in relation to multiple environmental factors: Regulation through food concentration and tidal conditions? Limnology and Oceanography 52: 1919-1929

Murray, L.G., Seed, R., Jones, T. (2007). Predicting the impacts of Carcinus maenas predation on cultivated Mytilus edulis beds. Journal of Shellfish Research 26: 1089-1098

Murray, L.G., Newell, C.R., & Seed, R. (2007). Changes in the biodiversity of mussel assemblages induced by two methods of cultivation, Journal of Shellfish Research 26: 153-162

Gallagher, T., Richardson, C.A., Seed, R., & Jones, T. (2008). The seasonal movement and abundance of the starfish Asteria rubens in relation to mussel farming practice: a case study from the Menai Strait, UK. Journal of Shellfish Research 27: 1209-1215

Van de Koppel, J., Gascoigne, J., Theraulaz, G., Rietkerk, M., Mooij, W.M., & Herman, P.M.J. (2008). Experimental evidence for spatial self-organisation and its emergent effects in mussel bed ecosystems. Science 322: 739-742

Reports

Beadman, H. (2003). Impacts of mussel seabed-lay bottom cultivation, with special reference to the Menai Strait and Conwy Bay candidate Special Area of Conservation. CCW Contract No. FC 73-02-257, University of Wales Bangor

Rees, E.I.S., Dare, P., Dolmer, P., & Smaal, A.C. (2003). Peer review of a CCW commissioned report: Beadman, H. (2003): Impacts of mussel seabed-lay bottom cultivation, with special reference to the Menai Strait and Conwy Bay candidate Special Area of Conservation. CCW Contract No. FC
73-02-90D, University of Wales Bangor

Saurel, C., Gascoigne,  J., & Kaiser, M.J. (June 2004). The ecology of seed mussel beds: literature review, SEAFISH

Morris, E.S., Goudge, H., & Duce, C. (2007). An introductory review of the biology and population dynamics of the green shore crab, Carcinus maenas, in the UK, with special reference to the Menai Strait. CCW Policy Research Report 07/18

North Menai Strait Mussel Fishery (Mytilus Edulis) Annual surveillance report - November 2011

PhD thesis

Murray, L.G. (2008). The impacts of Carcinus maenas on commercial mussel beds. PhD thesis, Bangor University

MSc thesis

Gregory, F.C. (2005). Predators of seed mussel beds at Caernarfon Bar and Morecambe Bay, UK. MSc Thesis, Bangor University, 82pp