Ecological Aspects and Conservation Challenges of the Russian sturgeon (Acipenser gueldenstaedtii) in Romanian Waters

The Russian sturgeon (Acipenser gueldenstaedtii), a critically endangered potamodromous species, has experienced a drastic demographic decline in the Lower Danube River and the Danube Delta. This review synthesizes two decades of the scientific literature and official monitoring reports to evaluate the species' ecological status and the efficacy of conservation frameworks implemented in Romania. The results indicate that anthropogenic pressures have reached a critical threshold. The fragmentation caused by the Iron Gates I and II dams has resulted in the loss of over 80% of historical lithophilic spawning grounds, isolating populations and reducing natural recruitment by more than 90% compared to mid-20th-century levels. While the 2006 commercial fishing moratorium has reduced legal exploitation, illegal, unreported, and unregulated (IUU) fishing, alongside emerging chemical pollutants and microplastics that affect larval ontogeny, remains a primary driver of mortality. A discussion of current mitigation reveals a "survival gap": although ex situ captive breeding preserves genetic diversity, its long-term impact is marginalized by high post-release mortality and the loss of physiological cues due to insufficient river connectivity. Current measures are often fragmented and fail to address the underlying loss of lateral and longitudinal ecosystem functions. The conclusions emphasize that preventing extirpation requires a shift from passive protection to active ecological restoration. Immediate priorities must include engineering fish passages at major dams, implementing DNA-based traceability to curb poaching, and harmonizing restocking protocols at a Danube basin scale. Without integrated structural interventions to restore river connectivity, A. gueldenstaedtii faces functional extinction in the wild within the next two decades.