HaffStör: Unravelling Baltic sturgeon ecology in the Lower Oder River and Szczecin Lagoon to inform sustainable management

The Baltic sturgeon Acipenser oxyrinchus , once widespread in rivers draining to the Baltic Sea, was extirpated by overfishing and habitat degradation and is now the focus of a basin-wide restoration programme. Since 2006, more than seven million hatchery-reared juveniles have been released in Baltic rivers, yet the movements, habitat use and survival of stocked fish remain poorly quantified. HaffStör aims to close these knowledge gaps and to provide an operational basis for adaptive, cross-border management of the recovering population in the Oder River–Szczecin Lagoon system (Germany/Poland). The project combines movement ecology, conservation biology and social sciences in four interconnected work packages. First, we optimise rearing protocols, comparing juveniles produced under different degrees of environmental control (ambient vs. static recirculating aquaculture systems), coupled with behavioural experiments on habitat choice and anti-predator responses. Second, we release tagged juveniles in the Lower Oder and Szczecin Lagoon and track their movements using active and passive acoustic telemetry, complemented by habitat mapping and benthic sampling, to identify key migration routes, habitat utilisation and zones of overlap with human activities, mainly associated with fisheries and navigation. Third, we develop and test a standardised, cost-effective monitoring framework, based on passive gears, fishery-independent surveys and environmental DNA, aligned with Bern Convention guidelines and intended to be transferable to other Baltic catchments. Fourth, we establish cooperation with commercial fisheries through targeted outreach to initiate structured by-catch reporting, co-designed surveys and joint project activities. By integrating ecological and fishery data, HaffStör will deliver robust estimates of juvenile survival and mortality drivers, refine release and monitoring strategies and generate spatially-explicit assessments of by-catch risk. Beyond new scientific insights into Baltic sturgeon ecology, the project seeks to strengthen stewardship amongst local communities and practitioners and to support evidence-based, transnational governance for this flagship migratory species.