Background

The history of sturgeon (Acipenser oxyrinchus) in the Baltic Sea has been particularly tragic. This extraordinary fish species, widely known for its impressive size and black caviar, got extinct here in the last century. The main reasons for this were the deterioration of the quality of spawning rivers through migratory barriers and water pollution and overfishing. The last specimen of natural origin was caught in 1996 in Estonian waters. Baltic sturgeon is included in a list of the priority species in Annex II for the EU Habitats Directive, marked with an asterisk.
The issue of the restoration of the Baltic sturgeon population began to be addressed decades ago. The development of the HELCOM Action Plan for the Protection and Recovery of Baltic sturgeon and the adoption of the Plan in March 2019 is an important step in recovery of the sturgeon population in the Baltic Sea. The reintroduction together with the elimination of the adverse factors, is the only way for the re-establishment of the viable population of extinct A. oxyrinchus in Baltic Sea region.
This project will initiate the recovery of the sturgeon population in the North-Eastern area of the Baltic Sea. The introduction of juvenile sturgeons into the River Narva and River Pärnu, the most important historical sturgeon spawning rivers in the region, will be launched. The most important preconditions for the efficiency and sustainability of the project are met, as the main risk factors have been suppressed – the conditions of the spawning rivers have been significantly improved and fishing for this species is strictly prohibited. There are very good prospects for the successful implementation of this ambitious project, as significant preparations have been made for it.

Baltic Sea sturgeon, Acipenser oxyrinchus oxyrinchus, is an anadromous species that reproduces in fresh water and spends most of its life at sea. The species is long-lived (up to 100 years) and grows large (up to 4.5 m total length and 350 kg in weight). The life cycle is long, with a late maturation occurring at an age of 12-18 years (up to 27 years in colder climate). As such, sturgeon populations reveal a reproductive cycle of 2-7 years over a period of up to 80 years which helps to maintain the populations stable for long periods of time but also is the key factor for the high sensitivity against overharvest.

The Baltic population of A. oxyrinchus has been traced back to 500 B.C. in archaeological remains in the Baltic Sea (Stankovic et al. 2010) while retreating in the range in the North-East Altantic and North Sea where it was replaced by the European sturgeon radiating from the Mediterranean (Nikulina & Schmölcke 2016). Reproduction was described in the major rivers entering the South, East and North-Eastern Baltic Sea tributaries and the tributaries to the lakes Onega and Ladoga. In the 19th century, the Baltic sturgeon ranged throughout the Baltic Sea still.

The last recorded specimen of natural origin was caught in 1996 in the Estonian coastal waters not far from the Pärnu River mouth. The fish was 2,9 m long and weighed 136 kg. In the Gulf of Finland and Narva River, the last specimens were caught in 1941 and 1945.

In 1992, the Baltic sturgeon was included as a priority species under Annex II of the Habitat Directive, at the time the scientific name of Acipenser sturio was still applied. It was only in preparation of the remediation measures in Germany that it was uncovered that the Baltic sturgeon did not belong to A. sturio, but represented the Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus (Ludwig et al. 2002, 2008, 2009). These results were verified by other labs and the resulting conclusions of an international expert panel (Ritterhoff & Gessner 2004). Subsequently the results were adopted by the Helcom range states and in the Baltic Sea Action Plan.