Dai Roberts, David Smyth & Lynn Browne, Queen’s University, Belfast

1. Pros and cons of small-scale native oyster (Ostrea edulis) restoration programmes: experiences gained in Strangford Lough Northern Ireland Dai Roberts, David Smyth & Lynn Browne, Queen’s University, Belfast

2. Oysters: • component of human diets since prehistoric times • Cultured - in Europe during Roman times - in Japan during 17th century • Complex legislation failed - stocks collapsed in many parts of the world by the early 1900s due to pollution, disease, over-fishing and habitat loss • Early restoration attempts - introduction of non-native species and the co-transfer of pests and diseases which further exacerbated impacts on native species • 1960s, hatchery-based aquaculture (mainly Crassostrea gigas) developed worldwide to meet global demand - now accounts for about 75% of total world production

3. Ostrea edulis: • Natural Range - Norway to Morocco and into the Mediterranean Sea (Alcaraz and Dominguez 1985). • self-sustaining populations due to introductions in Australia (Morton et al. 2003) • is cultivated in many other parts of the world such as Australia, Japan, New Zealand and North America (Hidu and Lavoie, 1991; Gardiner and Elliott 2001). • Natural beds are now rare in Europe (Gardner & Elliott, 2001). • Listed in UK Biodiversity Action Plan as a species which should be maintained and expanded (Gardner & Elliott, 2001).

4. History of exploitation of oysters in Strangford Lough • Mesolithic shell middens with large numbers of O. edulis at several locations (McErlean et al. 2002) • Oysters dredged in great numbers from deep water as well as being gathered along the shore (Montgomery, 1683) • Oyster beds commercially exploited with a peak in the 19th century (Brown, 1818). • Oyster fishery collapses about 1903 (government report – Browne, 1903) • Culture of Crassostrea gigas starts in 1970s (Parsons, 1974; Briggs, 1978) • 1998 – Ostrea edulis restoration project starts (Kennedy & Roberts, 1999)

5. The present paper reviews : • the historical decline of Ostrea edulis in Strangford Lough • the outcome of restoration attempts • the need to reconcile ecological restoration and sustainable species exploitation

6. Figure 1: Study site Strangford Lough N Ireland 4 km

8. Study site: Strangford Lough, Northern Ireland: • Multi use: over 16 stakeholder organisations represented on Strangford Lough Management Committee [SLMC] • Approximately 60,000 people live around the lough and a further 1 million are within a one hour’s drive • Strangford Lough is currently on the UK designation list as a Special Area of Conservation (SAC) under the European Commission (EC) Habitats Directive (92/43/EEC) the aim of which is to conserve certain habitats and species within the EC.

9. The Historic Fishery Newtownards • Kircubbin Dredging area 19th century Portaferry

10. Oyster landings in Strangford Lough over a 60 year period during the 19th century in comparison with licensed dredgers. Decadal average annual landings per boat of Ostrea edulis from Strangford Lough1820-1880 160 50 45 140 40 120 35 100 30 No. of licensed dredgers Kg (x103) 80 25 20 60 15 40 10 20 5 0 0 1820s 1830s 1840s 1850s 1860s 1870s Landings DATE No. Dredgers

11. Cuan Oysters, Strangford Lough, Northern Ireland(http://www.cuanoysters.com/seafood/index/html): • the major producer of oysters in the lough - established 1974 • played an important role in the development of oyster aquaculture in the United Kingdom by pioneering culture methods for very small hatchery-reared seed • now one of the main producers in the UK, handling over 400 tonnes of oyster (C. gigas; O. edulis)per annum

12. Restoration project 1997-1999 Newtownards Portaferry Main oyster aquaculture areas 1990s

13. Restoration 1997-99 • Spreading 70-75 tonnes cultch (mainly C.gigas and scallop shells) to form the basis for new beds • Concentrating broodstock on new beds • Seeding with 250,000 O. edulis spat

14. Surveys • Intertidal • - 30 coastal sites • - 8 Island sites • Spat Collection - 13 collectors • Subtidal -15 dive sites • Plankton sampling • -over tidal flux

15. Newtownards Sites surveyed 2002-2004 Castleaverry Ballyreagh Newtownards Sailing Club Island Hill Mount Stewart Chapel Island N Grey Abbey Castle Espie Herring Bay Horse Island E Paddy’s Point W Kircubbin Nendrum Whiterock Horse Island Ringhaddy Simmy Island Marlfield S Island sites Killyleagh Ballyhenry Nickey’s Point Portaferry Shore surveys Castle Island Granagh Bay Castleward Bay Spat collectors Barr Hall Bay

16. Estimates of standing stocks The total number of inter-tidal and sub-tidal O.edulis in the North, West, East and South were estimated using the following formula adapted from Gunderson (1993). h _ P= ∑ ﴾Ri .F ﴿ C i I=1 a Where; P= Total population resident in full survey area. Ri= Area of region I in m2 . a= Area sampled within a single sampling unit. F= Correction factor estimating substrate types. _ Ci= Mean number of oysters observed per sampling unit in the region based i on n samples. h= Number of regions composing the survey.

17. Estimates of standing stocks: Intertidal surveys • Proportionally weighted correction factors were applied to account for the amount of suitable substratum present. • Drop due to unregulated harvesting

18. Estimates of standing stocks: Sub-tidal surveys • Proportionally weighted correction factors were applied to account for the amount of suitable substratum present.

19. Estimates of total standing stocks

20. Estimates of unregulated harvesting • no formal records of the levels of regulated or unregulated shellfish harvesting by hand for Strangford Lough • used the following approximation: Total removal per month = nos of collectors X removal rate X nos suitable low tides per month • Estimates based on the approximation above were compared to changes in estimates of standing stocks over Christmas (November - January), the most intense harvesting time when shellfish are at a premium in Europe.

21. Impacts of unregulated harvesting on standing stocks • no formal records of the levels of either regulated or unregulated shellfish harvesting by hand for Strangford Lough • used the following approximation: Total removal per month = 12 X (nos) 92k X 8 = 8,832 kg = 17,664 kg (November – January) • Estimated change in standing stocks November – January = 278x103 (24,464 kg) September – April = 1112x103 (97,856 kg)

22. Impacts of unregulated harvesting on coastal populations UNFISHED FISHED

23. Impacts of unregulated harvesting on island populations FISHED ND FISHED ND

24. Further consequences of harvesting • Decrease in suitable cultch for larval settlement • Anthropogenic disturbance of intertidal habitats within a SAC

25. Summary • >95% Increases in the densities of native oysters in Strangford Lough between 1998 and 2003 in Northern basin • due to over-summering of commercial oysters initially, hydrographical conditions and restoration efforts • is unlikely to be due to recruitment from wild stock • Restoration of O. edulis will increase biodiversity within Strangford Lough,

26. Summary • Increase in standing stocks since 1998 has resulted in the first significant harvests from Strangford Lough for over 100 years. • However, harvests have resulted in the removal of an estimated 25% of the total intertidal oyster population and are unregulated • Annual removal estimated at 97 tonnes which is nearly twice the levels at which the fishery collapsed (52 tonnes) in the 19th century and is unlikely to be sustainable • Dredging is currently banned • Until these issues are resolved, the very promising recovery of oysters in Strangford Lough with the tangible potential to reconcile ecological and harvest goals of restoration will not be realised.

27. Should restoration of Ostrea edulis be continued in Strangford Lough? Yes- because: • the restoration of O. edulis assemblages have the potential to increase biodiversity within Strangford Lough. • the Lough has suitable regions where local circulation will promote larval retention (Kennedy & Roberts,1999) • Strangford Lough oysters largely disease free

28. Acknowledgements • The Worshipful Company of Fishmongers • Strangford Lough Fishermen’s Co-operative • Department of Agriculture and Rural Development for Northern Ireland • Richard Kennedy