Lessons from a decade of surveillance in Shetland can improve future strategic monitoring

The Shetland Islands, northern Scotland, support a diverse array of maritime activities which connect Shetland to international ports and harbours and represent a vector for non-native species (NNS) but are also sectors vulnerable to potential impacts of marine invasive NNS. A risk-based monitoring program has been in place since 2014 as part of the Shetland Biosecurity Plan, using settlement panels in eight high-risk sites to detect target NNS. This study aimed to review the effectiveness of the monitoring program and determine the most appropriate methods for surveillance over the next decade. In 2022 additional visual, panel and eDNA surveys were carried out in a wider range of marina and harbour sites. Analysis of records from 2012-2022 show that no new NNS have been detected but several NNS have increased their range within Shetland. Invasive NNS present in mainland Scotland and Norway have yet to be detected, but the current program could be improved by incorporating additional methods to detect spread of a broader range of taxa and working to increase reporting by marine users. The lessons and experience of adjusting methods to fit monitoring objectives at a local level could also contribute to guiding establishment of national strategic monitoring.