What future for Native Oysters in Clew Bay?

Clew Bay Oyster Co-op members dredging for oysters in Clew Bay, County Mayo 22/11/2016. Photo Shay Fennelly/Aquaphoto©2016

Oysters have been a source of food for the people around Clew Bay shores from  prehistoric times. ‘Kitchen middens’ which are collections of discarded oysters shells can sometimes be seen exposed on eroded seashore banks and shows our ancestors taste for dining on shellfish picked at low tide.

Honour Sisk’s study into the islands in Clew Bay reveals the importance of the oyster beds to the island communities in the 19th century. In Clew Bay there are many natural oyster beds to be found between the islands. Handpicking and later dredging was practised at all times of the year. The oysters were sold to people on the other islands by the basket containing four hundred for 10d to 12d pence. Small in size, the oysters were of good quality and when not in season. Large quantities were reputedly sold to oyster beds on the Clare coast. In the late 1800’s up to fifty boats and two hundred people are thought to have been engaged in the public oyster fishery (First Report of the Government Commission of Inquiry into the State of the Irish Fisheries 1837). A Coastguard officer warned because the oyster beds were open to the public it would have a disastrous effect for the future of the fishery. In June 1880 a local priest was reporting to the Mansion House Relief Fund Committee there were about twenty inhabited islands in the Kilmeena parish with a population of over seventy families. They are very poor, destitute and wretched as they are also depended much on oyster dredging and fishing. For the past three years they are deprived of this means of livelihood, as the oyster beds are so impoverished, that the Board of Fisheries ordered them to be closed. (Mansion House Relief Fund Local Committee 1880) The Great Famine of 1845-1849 was the most tragic episode of Irish history. In County Mayo it struck harder and turned into a massive human tragedy. The population declined by 29 per cent: deaths and emigration accounted for the loss of 114,057 of people. Sisk (1990 The Outer Islands of Clew Bay) noted due to the islanders practising agriculture and fishing as well as other economic activities their survival rate was far superior to that of the mainland and Mayo as a whole. By 1880 the oyster fishery was destroyed because of overfishing and was closed by the Board of Fishery. The tradition of dredging had died out on Islandmore by the 20th century but began again in the early 70’s. Fishing for herring using nets took place from September to January. The fish were gutted and salted and kept for consumption over the winter.

Source. Honour Sisk (The Outer Islands of Clew Bay) Journal of the Westport Historical Society Vol10 No.1, 1990)

Oyster fishermen land flat or native flat oysters to fishing boat in Clew Bay, County Mayo 1983
Achill currach fishermen (Liam Cattigan and Christy Gallagher) haul in a heavy dredge fishing for oysters in Blacksod Bay, County Mayo. 15/03/2006
Photo Shay Fennelly/Aquaphoto©2006

The tradition of dredging for oysters in Clew Bay resumed in the 1970’s.

Mary Gavan from Clynish island measuring dredged flat oysters in Clew Bay 1983
Mary Gavan from Clynish island measures oysters in Clew Bay 1983. Photo Shay Fennelly/Aquaphoto©1983
Ostres edulis The Native Oyster Photo Shay Fennelly/Aquaphoto©
Pádraig Morgan and Didi Korner take a tea break after a days oyster fishing in Clew Bay, County Mayo 1985. Photo Shay Fennelly/Aquaphoto

What is the Impact of dredging on the seabed?

The impact of dredging is largely dependent on the gear type and the sediment type (Murawski and Serchuk, 1989). Any fishing gear which is towed over the seabed will disturb the sediment and the resident community to some degree, but the intensity of this disturbance is very much dependent on the details of the gear and the sediment type (Hall 1994). Cox noted that an oyster dredge which had caused little concern on a sandy substrate caused severe damage when it was used on the softer sediments as it dug to a deeper level. It ripped into both the mudflats and Zostera beds leaving the criss crossed furrows and shattered remains of bivalves. Anoxic and oxygenated sediments were churned up and in places the clay bedrock was brought to the surface (Cox, 1991). Dredging can have an adverse environmental impact. Unwanted organisms, such as starfish and crabs, are removed and the spat which is attached to cultch (mussel shell) or half grown shellfish are laid on the seabed. Any existing seabed community will be damaged by dredging and affected by the silt and mud released by the operation. Harvesting, by dredging, is indiscriminate in nature and can damage or destroy stocks of other food resources, such as Zostera, sand eels (Ammodytes spp.) and other molluscs (e.g. Macoma spp.) (Kirby et al., 1993).

In summary

• Dredging generally has a much greater effect on soft mud than on hard sandy
• On sandy sediment the trend seems to be loss of the older molluscs and sedentary organisms.
• On soft muddy sediment dredging changes the nature of the sediment to become more gravelly as the finer sediments get washed away in the sediment plume.
• The impact will depend on the type of dredge used.
• The habitat may take months, if not years, to recover.
• Dredging may destroy habitat and reduce juvenile recruitment.
• The impact will depend on the importance of the site e.g. if there are Zostera beds of importance to birds/fish.
• The community structure can be affected.
• Dredging can leave fauna open to predation as their environment is drastically
changed, as they are exposed immediately after dredging.
• Overfishing can lead to population crashes in predators and ultimately in the
target species itself.

Source – M. L. Heffernan (1999) A review of the ecological implications of mariculture and intertidal harvesting in Ireland. Irish Wildlife Manuals, No. 7.

Oyster bed restoration

Interest in the restoration of oyster beds has grown recently in the UK and Ireland. In 2017 a Native Oyster Network was formed in the UK. This is a community of academics, conservationists, oystermen and NGO’s who are working to restore self-sustaining populations of native oysters. A European network called the Native Oyster Restoration Alliance (NORA) also set up in November 2017 is aiming at reinforcement and restoration of the native European flat oyster (Ostrea edulis). Network members are representatives of governmental agencies, science, non-governmental organizations, as well as oyster growers and other private enterprises.

Why native oyster restoration now?

Stocks of the European flat oyster are classified as highly endangered all over Europe. The species is included in the OSLO-PARIS-Convention´s List of Threatened and/or Declining Species and Habitats for the North-East Atlantic. In addition, the EU Habitats Directive provides protection for oyster reefs.

The European flat oyster has important functions in the marine ecosystem. Contrary to the currently widely present Japanese oyster (Crassostrea gigas), the flat oyster (Ostrea edulis) is adapted to the deep (20-40 meters) waters of the open sea. As reef structures, flat oyster beds provide a habitat for numerous attached and mobile species around the sea floor of these deeper water. Besides, they have a large water filtering capacity. Therefore, oyster beds are considered to be biodiversity hot spots. The richness of the ecological community dependent on flat oyster reefs was already shown around the 1880’s by biologist Carl Moebius, who investigated these reefs in the German Wadden Sea.

Until about a century ago, thousands of square kilometres of flat oyster beds were present in the open North Sea. The oyster populations collapsed due to overexploitation.  As they did in the Irish Sea and on Ireland’s west coast. Habitat loss, pollution and diseases further aggravated the situation.”( https://noraeurope.eu)

Dredging for Oysters in a currach in Clew Bay 1983 Photo Shay Fennelly/Aquaphoto©1983
Clew Bay islands sunset, County Mayo

Clew Bay is a SAC or a Special Area of Conservation for its habitats and species. A term well know to Irish farmers but not to the average urban or ‘townie’ dweller or schoolgoer. SAC’s are prime wildlife conservation areas in the country, considered to be important on a European as well as an Irish level. Most Special Areas of Conservation (SACs) are in the countryside, although a few sites reach into town or city landscapes, such as Dublin Bay and Cork Harbour. Conservation management plans are available for many SACs but the public’s awareness is almost non existant. How the public can engage and help protect there local habitats and species has not been encouraged by the government. There is no conservation management plan for Clew Bay SAC. More money is spent by the government on greyhounds and horse racing than nature conservation in Ireland.

There is a stark conflict of interest between fishermen who want to dredge oysters to sell and retain a commercial fishery and the restoration of oyster beds and the conservation of habitats and species in a Special Area of Conservation. When oysters are undisturbed and allowed to grow they will in approximately 40 oyster generations increase in number and form oyster reefs which are fish nursery areas. Dredging destroys Zostera or eelgrass and merl coral beds. Brent geese migrate from Arctic Canada feed on eelgrass to winter in Clew Bay. Maerl beds are an important habitat for many smaller marine plants and animals. Animals that burrow in the maerl gravel beneath the living bed include:bivalves, urchins, sea cucumbers, anemones, and worms. Young scallops in particular seek out living maerl beds as nursery areas. Protecting maerl beds thus helps to sustain a scallop fishing industry.

Is it possible to have a commercial fishery if the oyster stocks are overfished? No its not. Increased management efforts are required if oyster stocks are to be rebuilt. It could take a decade to restore oyster stocks if people are willing to develop a management plan. 

The future for the Clew bay Oyster Co-op (CBOC)

The CBOC do not have the finance to rebuild the oyster stocks. Since the Co-ops inception in 1979 the oyster stocks in Clew Bay have gradually declined from overfishing and Bonamia disease (a parasite that causes lethal infections in oysters)The in the last 40 years. In 2019, BIM have obtained funding from the European Maritime and Fisheries Fund to set up an Irish Native Oyster Fisheries Forum to help restore native oyster (Ostrea edulis) populations in oyster fishing areas in Ireland.

To continue to fish in a Special Area of Conservation Oyster Co-ops are required to have fishery management plans. CBOC have no oyster fishery management plan for Clew Bay. The National Parks and Wildlife Service have no conservation management plan for Clew Bay.

The challenge is how to protect the special habitats and species in Clew Bay, rebuild oyster stocks and retain a commercial fishery. If the local community are not interested and fail to engage in the management of the environment.  The benefits we take for granted, will be lost before you know it.

Ian Hicks, oyster fisherman in Clew Bay, County Mayo 1983

Published by shayfennelly

Marine scientist and photographer. Interested in all marine ecology, exploration, science and technology.

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