Mapping areas likely to be unsuitable for Native oyster (Ostrea edulis) restoration at multiple spatial scales

Target 2 of the Kunming-Montreal Global Biodiversity Framework specifies that 30% of degraded habitats need to be under effective restoration by 2030. This has resulted in increased interest in active marine restoration projects. However, the efficacy of restoration activities depends on them being appropriately located. Spatial datasets of key environmental variables for European native oyster ( Ostrea edulis ) restoration were sourced for the whole of Scotland and Orkney region. Initial thresholds of environmental tolerances were taken from the literature and used to map areas considered unsuitable for oysters at a national scale. Areas predicted to be unsuitable were compared with occurrence records for oyster to refine these thresholds where necessary. The refined thresholds were also applied to Orkney using higher resolution and more localised environmental datasets, indicating that the approach can be used at any spatial scale. The distribution of likely unsuitable habitat was predominantly influenced by the temperature required to trigger spawning. The national distribution of areas not predicted to be unsuitable reflected historic distributions of native oyster. The areas that were not predicted to be unsuitable in Orkney were restricted to bays around Mainland, e.g. Bay of Firth which was historically a productive oyster fishery, and Hoy. This work shows the success of a pragmatic approach, which uses existing knowledge about biological thresholds and available distribution data, in situations where poor data availability inhibits statistical modelling. The outputs facilitate better spatial management decision making, improving the chances of restoration aspirations being met, both at a national and local scale.