An ‘ecological corridor’ for migratory fish in the Danube basin

Migratory species of sturgeon have significantly declined in the Danube River basin over the last century. Multiple pressures including habitat loss, pollution, overfishing and the fragmentation of migratory routes have caused populations of sturgeon and other migratory fish to crash in the basin in recent years.

Last week, the MEASURES project published an ambitious new strategy to help restore migratory fish populations in the Danube basin. The Danube River Corridor Strategy states that the Danube river should be considered as an ‘ecological corridor’ along which governments should co-operate to ensure the safe passage of migratory fish.

“The Danube River Corridor Strategy proposes measures to support the populations of migratory fish species in the Danube,” say the strategy authors Gertrud Haidvogl, Cristina Munteanu and Ralf Reinartz. “It frames the Danube as an ecological corridor, and offers measures to re-establish continuity, to protect and restore habitats for different life stages of migratory fish, and to support populations, for example through establishing ex-situ facilities. In short, ‘habitat’ plus ‘connectivity’ plus ‘viable populations’ equals ‘healthy ecological corridor for migratory fish’.”

The strategy is published at a key time for sturgeon conservation. “Danube sturgeons are close to extinction, and measures to safeguard their populations are urgently needed,” the authors say. “A large proportion of the rest of the migratory Danube fish community and biodiversity is also in dire straits. It was important to propose specific measures such as ex-situ facilities as main options to safeguard Danube sturgeon populations until sufficient habitats are available and populations in the wild have recovered.”

The strategy has resulted from a long-term collaboration centred around the MEASURES project. “The publication of the strategy was a collaborative process, and the core team of authors was supported by a group of contributors and reviewers,” say the authors. “Many of the contributors were actively involved in the MEASURES project, as well as in fish and sturgeon conservation.

“The strategy is thus based on the finding of the MEASURES project to a large extent,” the authors continue. “For example, during the project, both potential and actual habitats of migratory fish species were identified and compiled. The genetic profile of Danube sterlet and Russian sturgeon populations for ex-situ measures was identified and individuals from controlled propagation were released in the Hungarian and Romanian Danube. However, information on the threatened status of species, management and conservation of rivers, fish populations, green infrastructure and climate change were also integrated.”

The strategy outlines the key technical measures needed to restore the Danube basin as an ecological corridor. It identifies four sets of priority measures. First, to restore the connectivity of migration corridors, through the removal of barriers such as dams and weirs. Second, to restore and conserve degraded habitats which are crucial for spawning and feeding.

Third, the operation of ‘ex-situ’ fish hatcheries to breed native populations of fish species for reintroduction. Fourth, to encourage better policy coordination between local and national decision-makers to ensure that migratory fish habitats are restored across the entire Danube basin.

“We hope that the ecological corridor for migratory fish concept becomes an important tool for aquatic conservation,” say the authors. “During the project, all project partners were in close contact with concerned stakeholders, in particular with those involved in river management and nature conservation.

“We hope that this exchange, and improved knowledge of the most pressing issues, will support the implementation of high priority measures, and that all the actors involved in MEASURES will continue to work towards the conservation and restoration of the Danube as an ecological corridor,” the authors conclude.

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Funded by the EU as part of the Danube Transnational Programme, MEASURES aimed to improve habitat quality and connectivity along the Danube in order to support populations of threatened sturgeon species, as well as other migratory fish and wider aquatic biodiversity in the basin.