Prerequisites for the Restoration of the European Atlantic Sturgeon, Acipenser sturio and the Baltic Sturgeon (A. oxyrinchus × A. sturio) in Germany

Acipenser sturio was once a prevalent fish species in all the major rivers of Northern Germany. From the end of the nineteenth century, the population sizes have decreased rapidly. The last large population was observed in the River Eider, where the last specimen was caught in 1969. Under a cooperation agreement with the French Cemagref, the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin received juvenile A. sturio of Gironde origin in 1996 and initiated an ex-situ measure. The main scientific results found since then have been: (1) first gonad maturation occurred in 11-year-old A. sturio (110 to 140 cm total length) kept in freshwater at 20°C under a natural photoperiod; (2) during vitellogenesis the growth factor insulin-growth-like factor (IGF-I) plays an important role as a paracrine modulator, as observed in the model species A. ruthenus; (3) analysis of recent and historical material revealed the presence of the A. oxyrinchus mitochondrial haplotype A in the Baltic. Investigation of the MHC (Major Histocompatibility Complex) nuclear gene, however, showed that these fish carrying this haplotype represent a hybrid population (A. oxyrinchus × A. sturio). The current restoration strategy concerning the Baltic (restocking with A. oxyrinchus) therefore needs to be reconsidered. The mtDNA studies in addition demonstrated the genetic similarity of the Gironde and the North Sea population; (4) A. sturio-specific microsatellites were established for brood stock management of the German and French brood stocks; (5) Evaluation of historical spawning grounds in the River Oder drainage in collaboration with Polish scientists showed intact spawning grounds in the Drawa River.