Remediation of Atlantic Sturgeon in the Baltic Sea: Background, Status, and Perspectives
Jörn Gessner, Gerd-Michael Arndt, Arne Ludwig, and Frank Kirschbaum
Abstract.—A century ago, sea sturgeon (Atlantic sturgeon Acipenser oxyrinchus and European sturgeon A. sturio) were prevalent in the fish communities of all major German rivers, both in the North and the Baltic Sea drainages. Since then, population sizes have decreased rapidly due to overfishing, pollution, and hydropower construction. The last catches in the Baltic drainage occurred in the late 1960s. Only individual captures of sturgeon have been reported in the last 30 years, the most recent being in Lake Ladoga (Russia) in 1984 and off the coast of Estonia in 1996, approximately 25 years after the disappearance of the species from the fishery. Today, sturgeon are considered extinct in German waters. In 1996, the Federal Agency for Nature Conservation, in cooperation with the Society to Save the Sturgeon, started the pilot phase of a remediation program involving assessment of the prerequisites for remediation. The first juvenile European sturgeon were transferred to the Leibniz-Institute of Freshwater Ecology and Inland Fisheries under a scientific cooperation agreement with the Centre d’Étude du Machinisme Agricole, du Rural, des Eaux et Forêts in May 1996. With these specimens, an ex situ measure was initiated. In addition, phylogenetic and population genetic analyses of the species were carried out using mitochondrial DNA and microsatellites. These genetic analyses of recent and historical material have proven the existence of two different species in what was previously considered the Baltic or common sturgeon. The Atlantic sturgeon has been identified as endemic in the Baltic Sea and the European sturgeon in the North Sea. According to morphological evidence based on archaeological samples, the Atlantic sturgeon invaded the Baltic Sea approximately 2,000 years ago and has been the only sturgeon species there for the last few centuries. These results led to the separation of the remediation activities in North Sea and Baltic Sea tributaries. Broodstock development using the northernmost populations of the Atlantic sturgeon is currently being carried out. Subsequent reproduction for restocking requires a sufficiently large broodstock and a genetic breeding plan based on pedigree analysis. As a further prerequisite, an evaluation of the status of critical habitat for the early life stages of Atlantic sturgeon in the Oder River has been performed in collaboration with the Institute for Inland Fisheries of Poland. Alternative fisheries techniques, based on data for the bycatch of exotic sturgeon, are being developed to reduce the fishing pressure on juvenile sturgeon upon release.