Citizen Science Highlights the Dispersal of Invasive Tilapias Through Rainwater Drainage Channels and Rivers on Santa Catarina Island, Southern Brazil

The spread of invasive alien species (IAS) is causing significant ecological, biological and socioeconomic impacts worldwide, making eradication efforts extremely challenging once they become established. The most effective approach is to prioritize prevention by blocking the entry of high‐risk species. However, early detection and rapid response (EDRR) is crucial when prevention fails. In the Southern Right Whale Environmental Protection Area (RWEPA) in southern Brazil, EDRR efforts included citizen science through social media. Citizen science reports from a sport fisherman were received about the high‐risk invasive species Nile tilapia ( Oreochromis niloticus ) and red‐breasted tilapia ( Coptodon rendalli ) on Santa Catarina Island (SCI), located north of the RWEPA boundary. We compared the citizen science results with scientific databases and literature. Notably, citizen science contributed significantly more records than all scientific sources combined. The data suggests that tilapias are establishing populations across the SCI, spreading through drainage channels and rivers, even reaching protected areas. This highlights the need to assess drainage systems globally when studying tilapia invasions. Urgent studies are needed in the SCI region to assess the distribution, establishment and impacts of the tilapia invasion, supporting management actions to eradicate or at least control tilapia populations and consequently conserve native species. Effective management should also improve the sanitary conditions of the SCI to reduce the success of invaders. This study demonstrates that, in understudied areas, a simple citizen science initiative in social media can provide crucial information for conservation biology, highlighting the value of this collaborative approach.