The map below shows areas that are likely to be unsuitable for native oyster (Ostrea edulis) based on refined thresholds of depth, current speed, silt content of the seabed substrate and two temperature thresholds 13°C and 15°C.
The refined thresholds are:
| Depth | Maximum Temperature | Current speed | Silt content | |
|---|---|---|---|---|
| Unsuitable Range | > 80 m | < 13°C and > 30°C | > 0.45 m s-1 | > 75% |
| < 15°C and > 30°C |
Coloured areas on the map are the areas likely to be unsuitable based on each variable, and grey areas are those areas with no available data for that variable. So locations where the basemap is visible are those that are within the extent of the dataset and the tolerances for the environmental variables which are turned on.
With the tool it is possible to consider the extent of likely unsuitable areas at a Scotland scale, but also to zoom into specific locations that might be of interest for restoration projects. The layers can be turned on and off as required. The opacity of the different layers can be changed using the slide bars.
The Scotland wide analysis was performed at a resolution of 1 km.
The tool allows for greater interrogation of the potential suitability of locations of interest and the identification of environmental variables that could limit success of native oyster restoration projects in those areas. The extent of suitable area is highly sensitive to temperature conditions thought to be required to trigger spawning. If the results of this analysis suggest that a proposed restoration site is unsuitable under temperature requirements of 15°C, but is suitable under 13°C, comparison with any known records or local field surveys into the temperature regime might be warranted. Similarly, if the analysis indicates that a location is unsuitable solely due to sediment type, options for providing artificial sediment substrate could be investigated.
The map below shows areas that are likely to be unsuitable for native oyster in the Orkney region. The variables included are depth, current speed and temperature assuming a threshold of 15°C.
There was no evidence to suggest that anywhere in the Orkney region had unsuitable proportion of silt in the seabed substrate.
The results from the Scotland wide analysis were highly sensitive to the temperature threshold required to trigger spawning; 13°C or 15°C. Applying a threshold of 15°C at the national scale with 1 km resolution may be overly restrictive. However a temperature of 15°C to trigger spawning has been observed in most populations throughout the species range (Bromley et al. 2016) and the resulting extent of potentially suitable habitat does reflect historic distribution maps of the UK (Olsen, 1883; Stechele et al.2023) and available occurrence records. In addition, using a threshold of 13°C in the Pentland Firth and Orkney Waters region indicate that none of the region has an unsuitable temperature and so is not informative for refining unsuitable habitat. Therefore only the unsuitable habitat based on the 15°C threshold is displayed.
The data layers used the analysis were kept at their original resolution.
Again, areas where the basemap is visible are the locations that are potentially suitable.
Bromley, C., McGonigle, C., Ashton, E. C., & Roberts, D. (2016). Bad moves: Pros and cons of moving oysters – A case study of global translocations of Ostrea edulis Linnaeus, 1758 (Mollusca: Bivalvia). Ocean & Coastal Management, 122, 103–115. https://doi.org/10.1016/j.ocecoaman.2015.12.012
Olsen, O. T. (1883). The piscatorial atlas of the North Sea, English Channel, and St. George’s Channels: Illustrating the fishing ports, boats, gear, species of fish (how, where, and when caught), and other information concerning fish and fisheries. https://iiif.wellcomecollection.org/pdf/b30759845
Stechele, B., Hughes, A., Degraer, S., Bossier, P., & Nevejan, N. (2023). Northern Europe’s suitability for offshore European flat oyster (Ostrea edulis) habitat restoration: A mechanistic niche modelling approach. Aquatic Conservation: Marine and Freshwater Ecosystems, 33(7), 696–707. https://doi.org/10.1002/aqc.3947