Participatory science to complement professional data: Towards conservation of declining native freshwater fish, the crucian carp

Abstract The participatory science approach helps to gather relevant ecological data with high coverage and reduce time and costs to solve intriguing conservation issues. However, the precision and additional value of using participatory science for monitoring freshwater fish species with similar appearances is not well understood. In this study, we aimed to evaluate the effectiveness of participatory science in distinguishing between critically endangered and invasive species within the genus Carassius , which are relatively similar in appearance. Native crucian carp ( Carassius carassius ) has encountered a sharp population decline in central Europe and is currently critically endangered in the Czech Republic, prompting conservation measures. The participatory science project ‘Save the Crucian Carp’ was launched to map its distribution and to conserve and restore the population. We aimed to analyse the effectiveness of this project which recorded the current and historical distribution of the crucian carp and the invasive gibel carp ( Carassius gibelio ), which is largely behind this decline. A total of 953 volunteers contributed information on species distribution and occurrence details. These web data were analysed to assess respondents' species identification skills, opinions about the project, and the impact of media outreach on volunteer participation. Field verification of occurrence tips revealed an accuracy of 35% for crucian carp presence. A positive correlation was identified between respondents' species identification quiz scores and the number of tips they provided. Respondents aged 31 to 50 showed greater enthusiasm for conservation efforts compared to other age groups. The increase in volunteer participation driven by media outreach underscores the critical role of raising public awareness about the freshwater biodiversity crisis to ensure conservation success through participatory science. Data collected via participatory science demonstrated greater regularity and coverage compared to the Nature Conservation Agency of the Czech Republic (NCA) data, emphasizing the importance of collaboration with the public to provide a stronger foundation for conservation decisions. Practical implication. This project demonstrates the potential of participatory science for conserving other freshwater fish species on a global scale.