Citizen Science and Expert Judgement: A Cost-Efficient Combination to Monitor and Assess the Invasiveness of Non-Indigenous Fish Escapees

Mapping the distribution and evaluating the impacts of marine non-indigenous species (NIS) are two fundamental tasks for management purposes, yet they are often time consuming and expensive. This case study focuses on the NIS gilthead seabream Sparus aurata escaped from offshore farms in Madeira Island in order to test an innovative, cost-efficient combined approach to risk assessment and georeferenced dispersal data collection. Species invasiveness was screened using the Aquatic Species Invasiveness Screening Kit (AS-ISK), and revealed a high invasion risk. Occurrences of S. aurata were assessed involving citizens in GIS participatory mapping and data from recreational fishing contests. A probability map showed that S. aurata is well dispersed around Madeira Island. This assessment proved to be a cost-efficient early warning method for detecting NIS dispersal, highlighting the urgent need for additional surveys that should search for sexually mature individuals and assess the direct and indirect impacts in the native ecosystem.

Automated summary

This study aims to map the distribution and assess the impacts of the non-indigenous species (NIS) gilthead seabream Sparus aurata escaped from offshore farms in Madeira Island. An innovative and cost-efficient approach using risk assessment and georeferenced dispersal data collection was tested. The invasiveness of the species was screened using the Aquatic Species Invasiveness Screening Kit (AS-ISK), revealing a high invasion risk. Occurrences of S. aurata were assessed through GIS participatory mapping and data from recreational fishing contests. A probability map showed a widespread dispersal of S. aurata around Madeira Island. This assessment proved to be a cost-efficient early warning method for detecting NIS dispersal and highlighted the need for additional surveys to evaluate the impacts on the native ecosystem.