1. Fish stocking constitutes a widespread management tool for freshwater fisheries, butdepending on configuration can be economically wasteful, ecologically harmful and lead toirreversible biodiversity loss. We conducted a large-scale controlled experiment of a lectureintervention to understand whether communication of neutrally worded scientific informationabout sustainable fish stocking might alter anglers’ ecological knowledge and cognitions (e.g.functional beliefs and attitudes) about the benefits and potential costs of fish stocking.
2. Seventeen angler clubs from Germany who engage in self-organized fish stocking wererandomly assigned to receive either a stocking lecture or a control lecture (on general fishmanagement). From each club, self-selected anglers including water-body managers(N = 201) completed a questionnaire on ecological knowledge and cognitions about stockingbefore the lecture, immediately after the lecture and 10 months later to assess long-termretention. Data were analysed using Before-After-Control-Impact analysis with club-level randomeffects.
3. Compared to the control group (n = 86), anglers in the treatment (n = 115) showed asignificant post-lecture increase in knowledge in all six topics taught about the biologicalnuances of stocking and potential risks. However, there were no changes in stocking-relatedattitudes or personal norms towards future stocking.
4. Only one knowledge domain was retained long-term (10 months): the understanding thatstocking does not always have additive fishery effects (P < 005). There were also trends indicatinglong-term knowledge gains related to the genetic risks of stocking and the advantagesof local adaptation, and a decreased functional belief in stocking efficacy (P < 008). Theseresults suggest that participants may engage more cautiously in fish stocking in the future.
5. Synthesis and applications. Lectures will continue to be a dominant mode of environmentaleducation due to convenience and familiarity, particularly for stakeholders participating duringleisure time and in contexts where training lectures are legally required. Our results showthat lectures can effectively communicate complex ecological topics and lead to knowledgegain. Lectures on natural resource management will be most effective when addressing issuesof high relevance to stakeholder’s interests and modifying current practices, but changes inbasic cognitions may require a more active learning environment.