Key challenges and solutions in large scale native oyster restoration
Insights from Highlands Rewilding’s 2025 Marine Engagement
By David Smyth, Marine Rewilding Lead
Native oysters (Ostrea edulis) once flourished in UK coastal waters, playing a vital role in marine ecosystems by filtering water, sequestering carbon and creating reefs that provide shelter, fish spawning grounds and nurseries. Today, the populations of native oysters in Europe have collapsed and, globally, an estimated 85% of native oyster beds have disappeared. You can read about our report of the functional extinction of oysters at Loch Sween, discovered as a result of our surveys completed last year. Huge efforts are therefore being made to restore this iconic species, recognising the importance to the health of our seas.
Highlands Rewilding Diver photographing native oyster remnants
This year, as part of the UK effort, Highlands Rewilding has taken an active role in the Celtic and Irish Sea hub, a cross-border network of stakeholders that aims to foster cooperation aligned with the Horizon Europe Mission to “Restore Our Ocean and Waters”. Highlands Rewilding is one of the selected representatives of Scottish interests in the Irish Sea and are part of a study group tasked with investigating barriers to upscaling key priority marine habitats as part of the 30x30 commitment to protect at least 30% of land and sea for nature by 2030, a key element of the UK's approach to the global "Global Biodiversity Framework" (GBF) agreed at COP15 in 2022.
Our marine team, along with other representatives, visited three different sites spanning Scotland, Wales and Ireland, to experience large-scale native oyster restoration firsthand and identify challenges practitioners were encountering during the process.
These field trips have highlighted a series of critical challenges and actionable opportunities for native oyster restoration in the UK:
Visit 1: Community-led native oyster restoration at Seawilding, Loch Craignish (February 2025)
Loch Craignish, aerial image from Seawilding’s website
Less than an hour’s drive fromTayvallich Estate, where Highlands Rewilding is conducting baseline biotope surveys, Seawilding in Loch Craignish is the UK's first community-led native oyster and seagrass restoration initiative. Founded in 2019 by Danny Renton, Seawilding has become a national model for grassroots marine restoration.
National Lottery funding in 2020 allowed Seawilding to start and scale their restoration, and within just five years, the project has:
Restored 350,000 native oysters
Planted 400,000 seagrass seeds and 18,000 rhizomes
With a goal of restoring 1 million oysters, Seawilding’s aim is wider: to restore lost biodiversity, sequester carbon, create green jobs and to mentor other community-based groups to do the same. However, the initiative is now running up against systemic challenges, particularly in sourcing disease-free, bio-secure, mature native oysters. A shortage of native oysters across Europe has led projects to use commercial juvenile stocks, causing delays in scaling up.
Many of the challenges and solutions in the table above were discussed during the site visit, with the approach implemented by Danny and the Seawilding team at Loch Craignish presenting promising solutions to address the current decline of native oysters in Loch Sween. The community are a driving force behind this project, and with well placed partnerships, government support and funding secured, more progress could be made in reestablishing the oyster habitats to the Loch.
Native oysters at Loch Craignish, from Seawilding website and 2024 Native Oyster Report.
Find out more on their website: https://www.seawilding.org/native-oyster-project.
Visit 2: Scaling up with NOAR Hatchery, Marine Centre Wales (March 2025)
The second field visit took the team to Marine Centre Wales (MCW), home to NOAR Hatchery, one of the most productive native oyster production units in Europe, aimed at addressing the primary challenge of native oyster upscaling. In 2024, the NOAR hatchery unit produced over 3 million native oyster larvae, with an impressive larval mortality rate of less than 30%.
The visit to MCW aimed to provide participants with an opportunity to learn about the procedures involved in operating and establishing a native oyster production unit. A similar facility on the west coast of Scotland could fulfil supply and biosecurity requirements for large-scale restoration efforts thereby addressing the current difficulties in native oyster habitat repair in the area.
Oysters and juvenile oyster clumps destined for restoration projects in the south of Wales
Significant investment and infrastructure would be needed to establish a hatchery like NOAR. However, with todays current shortfall of native oysters, if a Scottish unit was successful, it could be self-sustaining and within profit in a short period of time.
Visit 3: Disease management and seabed deployment, University College Cork and Rossmore Oysters Ltd (April 2025)
The final visit in the trilogy brought hub participants to University College Cork (UCC) and Rossmore Oysters Ltd, and the trip was designed to share knowledge on and methods for addressing major native oyster disease and managing high density native oyster production.
The visit was hosted by Professor Sarah Culloty, Head of the College of Science, along with Dr. Sharon Lynch, Senior Research Fellow specialising in molluscan diseases and marine habitat restoration at UCC’s Environmental Research Institute. Recognised as global leaders in their field, their expertise in the Bonamia ostrea parasite, a major disease affecting native oysters, is be invaluable for any restoration scaling efforts. Bonamia restrictions concerning oyster production and seed movement are significant impediments faced by restoration initiatives throughout the UK and Europe.
Image from University College Cork.
The second half of the visit was hosted by Rupert Hugh-Jones of Rossmore Oysters Ltd. The Rossmore oyster beds are located at Crawley near Cork, an area suitable for oyster breeding due to the warm, shallow waters and nutrient-rich flow, conditions like those found in several of the Scottish sea lochs. Rupert's experience with commercial seabed deployment aimed to provide participants insight into the challenges of large-scale seabed lays. Additionally, Rossmore's 10 hectares of land with 22 oyster breeding and spatting ponds could offer an alternative to hatchery production of seed. Ponds could also be adapted for hatchery spawned oyster grow-out prior to seabed deployment, offering a predator-free protected area for settled larvae to reach adult sizes.
Rossmore oysters commercial spatting ponds, image from website.
The visit to Cork showed that more economical alternatives to a hatchery unit were feasible, with ponds offering natural outdoor areas which do not require the costly infrastructure needed for hatchery produced oysters. Indeed, Rossmore Oysters Ltd. is a highly successful business supplying millions of native oysters throughout the world. If the real estate and infrastructure was in place a model like Rossmore’s could provide a highly profitable venture in Scotland, with commercial spatting ponds not only supplying table oysters but also restoration stock.
Native oyster restoration insights
The marine team's participation in the Irish and Celtic Sea hub has helped deepen connections and knowledge-sharing within restoration networks, and highlighted clear pathways for scaling nature restoration across the UK.
Three central insights have emerged:
Funding and infrastructure investment is critical: Establishing regional hatcheries and/or spatting ponds is essential for scaling, alongside upskilling and training for restoration practitioners and technistions.
Policy must be consistent and catch up with practice: Restoration-specific legislation is required, which meets community-led restoration expectations, is paired with regional expertise, and regional and national restoration hubs.
Nature and economy, and community can all benefit: With the right model, restoration can be profitable, while bringing both community and local economic benefits.