The network of farmed Pacific oyster movements in Scotland and routes for introduction and spread of invasive species and pathogens

Abstract Aquatic invasive species and pathogens can have negative impacts on marine biodiversity and economic activities such as aquaculture. Live animal movement networks are important in defining risk for introduction and spread and for identifying targets for surveillance. We have used Pacific oyster movement authorisation data from Scotland to create the first network of mollusc movements between sites at a national level, including both imports and exports. This is a small but well documented mollusc production industry, making it a good example for a case study. The resultant network shows a high proportion of Scottish sites are directly exposed to import movements from relatively few hatchery sources outside Scotland. Should these sources contain invasive species or pathogens their introduction into Scottish Pacific oyster aquaculture could be rapid and widespread. On the other hand, there was relatively few movements of oysters within Scotland, and so if a particular site within Scotland becomes affected by an invader, movement of live animals, as a pathway for further spread, would represent a relatively small risk. This structure shows the need for cross-border surveillance and co-operation.