The Wales Native Oyster Restoration Project

The Wales Native Oyster Restoration Project (WNORP) led by Natural Resources Wales was an initial four-year (2019-2023) European Maritime and Fisheries Fund project, administered by the Welsh Government, that investigated questions surrounding the approach and feasibility of restoring the native oyster (Ostrea edulis) in the Milford Haven waterway.

The main focus of the project was the establishment and monitoring of a series of restoration plots with the aim of addressing fundamental site-specific questions relating to survivability, recruitment, density effects, the oyster disease Bonamia and non-native species. The project documented in-plot observations related to habitat enhancement and increases in biodiversity. A range of intertidal and subtidal trial restoration sites were set up in 2020 and approximately 11,000 juvenile native oyster, Ostrea edulis, were subsequently introduced. Monitoring of the plots took place in 2021 and 2022.

Additionally, 13 tonnes of cockle shell cultch was deployed into each of two subtidal plots (each 20 m x 30 m), to test the feasibility and methodology around large scale and relatively low-cost oyster habitat restoration approaches. Approximately 3,500 juvenile oysters and 500 adult broodstock oysters were deployed onto the cultch at each restoration plot.

Summary of results

• Introduced hatchery reared native oysters were observed to survive and grow in the Milford Haven waterway. High mortality and displacement from the restoration site was also apparent.  Plots with lower stocking density (<10m²) showed slightly better success rates.
• Monitoring of the restoration sites revealed evidence of new native oyster settlement/recruitment.
• Aquaculture cage approach to restoration not suitable for growing juveniles without considerable husbandry.
• Increased occurrence of Crepidula fornicata may have contributed to lower survival and/or lack of new oyster settlement in some areas. Therefore, micro-siting of oyster broodstock areas is key to success.

The outputs of the work by contractors ABPmer fed into the production of a series of recommendations outlining the approach and feasibility of wider-scale native oyster restoration in Wales.  These actions have been summarised in the Wales Native Oyster Restoration Action Plan (West V, Woolmer A, Syvret M, Hull S, Wray B. 2025). This plan was produced with additional engagement from key stakeholders including NGOs, Government Agencies, Universities and oyster restoration practitioners and drew upon outputs from other ongoing native oyster restoration projects to identify the existing knowledge and current best practice techniques for restoration and to discuss limitations and lessons learned from existing restoration techniques. These actions are categorised under six goals:

• Collaboration;
• Priority locations for restoration;
• Establish best practice;
• Legislation and policy;
• Sourcing and supply; and
• Communities, fisheries and aquaculture.