Adaptive management, rightsholder involvement and whole-ecosystem experiments are key for sustainable freshwater recreational fisheries: examples from Germany

Speaker: Dr. Robert Arlinghaus
Fisheries Professor
Leibniz Institute of Freshwater Ecology and Inland Fisheries & Humboldt-Universität zu Berlin
Integrative Institute on Transformations of Human-Environment Systems (IRI THESys)

The complexity of ecological and social relationships in coupled social-ecological systems render a reductionistic approach to learn about the outcomes of common management actions, such as fish stocking or habitat restoration, problematic. Active adaptive management (AAM) where management is treated as experimental intervention at whole-system scales is considered a suitable alternative, but the examples where AAM has worked in practice are few in number. Dr. Arlinghaus will present two large scale multi-year projects where AAM was implemented in partnership with recreational fisheries stakeholders in Germany. Using replicated whole-lake experiments and appropriate controls his team investigated whether the common practice of fish stocking generated stock enhancing impacts in multiple species with and without natural recruitment. Further, they examined whether spatially confined habitat restoration activities, specifically the creation of shallow water zones and the introduction of dead woody habitat in small lakes, could offer suitable alternatives to increase fish stocks and help biodiversity more generally. Treatment effects were measured in a before-after-control-impact design. Dr. Arlinghaus’ team found that stocking delivered additive effects on fish abundance only in exceptional cases and only for species that were not naturally recruiting. By contrast, ecosystem-based habitat rehabilitation created a sustained positive impact on fish stock abundance, even when improving only a few percent of the littoral habitat. Importantly, the replicated experiments were created in co-design and knowledge co-production settings with local rightsholders over multiple years, where practitioners were part of the hypothesis generation process and strong partners in implementing and interpreting study outcomes. Dr. Arlinghaus will end by outlining the social and governance conditions under which AAM can work in management practice.