European regional assessment: Critically Endangered Possibly Extinct (CR PEW)
EU 27 regional assessment: Critically Endangered Possibly Extinct (CR PEW)

This species has been assessed as Critically Endangered under Criteria A and D, due to there being a population decline of up to 100% within the last three generations, and the estimated population size being below 50 mature individuals. It is also listed as Possibly Extinct in the Wild.

For the natural population of the Baltic Sea subpopulation of Acipenser oxyrinchus, the last sightings date back to 1984 and 1996 with previous sightings in the late 1960s. Population Viability Analysis (PVA) and analysis of functional extinction have shown that the historical subpopulation in the Baltic might have become extinct in the 2000s (Jaric and Gessner 2013). Relatively recent catches of A. oxyrinchus in the Gulf of Biscay (2007) and the Eastern Atlantic (in Pembrokeshire in 2002) comprised adult fish of unknown origin.

Restocking and restoration efforts in the Baltic Sea range were initiated in 2006 and have resulted in increasing numbers of juvenile fish in the coastal waters of the range since then. However, no natural reproductions had been observed by2022. The first natural reproduction from introduced individuals might be possible by 2025, based on the life cycle of the species.

In Europe, this species has been recorded from a large range along the north-western seaboard of Europe (Desse-Berset et al. 2011).

Historically, A. oxyrinchus oxyrinchus spawned in the drainages of the southern tributaries to the Baltic Sea (Oder River, Vistula River, Pregel, Memel/Nemunas, Daugava, Venta, Narva, and Newa rivers, as well as the Volchow River – a tributary to Lake Ladoga; Gessner et al. 2007). Its marine feeding range, based upon bycatch in commercial fisheries, comprises the Baltic Sea including Bothnian Bay, the Kattegat and Skagerrak, the southern North Sea from Norway (Bergen) to the English Channel, and the southeastern Atlantic with the Gulf of Biscay.

Besides the rivers, where spawning sites historically were located from lower river sections to the headwaters approximately 1,000 km from the sea (Arndt et al. 2002), a peculiarity of the Baltic Sea are the forebays of the rivers to the Baltic Sea, which are characterised by low (up to 5 ppt) salinity and high productivity. These represent important juvenile feeding grounds. In the marine Baltic waters, the species ranges along the coasts in water depths between 5 and 40 m, not exceeding 80 m (Gessner et al. 2019).

The existence of a population originating from the British Isles (Scotland and Severn catchment) was suggested even in earlier days (Parnell 1831, cited in Kirsch and Fordice 1889) and was reiterated with the observation of adult fish in the Severn catchment, but their past existence is under discussion.

Recent investigations claim that the distribution of the species in northern Europe dates back approximately 3,500 years BP, being the first sturgeon species to have inhabited the North Sea and the Baltic with a later displacement by A. sturio in the North Sea (Popovich et al. 2014, Nikulina and Schmölcke 2016).

Globally, the range of the nominate subspecies (Acipenser oxyrinchus oxyrinchus) extends over the American east coast from the St. Lawrence River in Canada to the St. Johns River in Florida, with at least seven genetically identifiable subpopulations (King et al. 2001). The subspecies A. o. desotoi is described from the Gulf of Mexico, ranging from Florida to Louisiana.

The wild population of the Atlantic Sturgeon is considered “possibly extinct in the wild” in Europe, with the last documented catches dating back to 1996 in Estonia (Paaver 1996) and 1984 in Lake Ladoga (Podushka 1985). Population decline in its entire Baltic range peaked from the 1860 to 1920s, while remaining individuals were documented in the rivers Oder and Vistula until 1967.

The main drivers of their extirpation in the Baltic Sea region were overharvesting (of both adults and juveniles), river management and hydro-constructions, and pollution (Gessner et al. 2011). Effective protection of spawners was not sufficiently enforced, and supportive stocking was unsuccessful in the late 19th and early 20th century due to a lack of mature spawners and deficiencies in reproduction techniques.

Since 1996 a coordinated program for the reintroduction of A. oxyrinchus was prepared by the southern Baltic range states which focuses on a founder population originating from imports from the Saint John River (New Brunswick, Canada) to develop an ex situ stock and subsequent releases in the Oder and Vistula rivers since 2006. Since 2010, ex situ stock in Germany is reproducing and used for releases in the Oder, Vistula, Gauja, Narwa, and Nemunas rivers, as well as retaining a proportion as part of a long-term captive brood program.

The Baltic Sturgeon subpopulation are diadromous, bottom-oriented, large river fish.

Floodplains, chutes, sloughs, islands, sandbars, and a dynamic main channel formed the large-river ecosystem that met the habitat and life history requirements of Baltic Sturgeon. Slow adaptation to saline waters is facilitated by the forebays of the Baltic Sea that allow the fish to gradually adapt to salinities above 10 ppt. Habitat requirements for spawning are met by bedrock and coarse gravel banks mainly in glacial moraine areas in mid-river sections with sufficient flow in the interstitial in the main stem and larger tributaries. Larval Baltic Sturgeon utilise clean gravel for the external embryonic phase (Gessner et al. 2009) while young-of-the-year Baltic Sturgeon are found on productive fine sediments with high invertebrate productivity.

Baltic Sturgeon can be long-lived, reaching up to 150 years of age. Based on the data on A. oxyrinchus from the east coast of North America from comparable climatic conditions, the age at first reproduction is 14-20 years for females and approximately 10-15 years for males.

Spawning has not yet been observed in stocked fish. Under hatchery conditions, fertilised eggs hatch in approximately three to four days at 20 °C. Free embryonic development lasts for six to eight days with embryos utilising gravel substrate (Gessner et al. 2006) until external feed uptake sets in.

Outmigration from river habitats is variable and takes place at age two to five years.

Competition, predation, diseases and parasites were determined not to be limiting factors for Atlantic Sturgeon stocks. Throughout the 20th century, sturgeon reproduction habitats have been adversely impacted by dams, channel maintenance (dredging) and resulting increased sediment load and siltation as well as water pollution. Although habitat and water quality concerns still occur in several locations, the vast majority of formerly occupied habitats remain available to this species.

Renewed plans to further develop inland navigation in Poland adversely affect the habitat availability and quality, and affects the potential of rivers for sturgeon restoration by planned dam construction, dredging, channelisation, resulting in habitat impairment and increased traffic, increasing also the risk of ship strikes. Hydropower development in Poland and Lithuania is a major threat for Atlantic Sturgeon restoration, but also affects the access to spawning sites in Russia, and Latvia.

Since the 16th century, Atlantic Sturgeon were important targets for commercial fisheries in the large rivers of the southern Baltic Sea for export of cooked meat as well as for fertiliser or protein source in agriculture.

With restocking of the species in its historical range since 2006, the restocked population is subjected to bycatch and illegal trade in coastal fisheries where it is sold for ornamental purposes, consumption and trophies (dried skin).

Today, the Atlantic Sturgeon subpopulation is protected in the fisheries regulations of all Helsinki Commission (HELCOM) member states, as well as being listed on the Red Lists of HELCOM and Germany, Poland, Lithuania, Denmark, and Sweden. A conservation propagation and augmentation program is in place in Germany, Poland and Lithuania. A joint Baltic Sturgeon Action Plan (Gessner et al. 2019) is implemented by HELCOM since 2018, outlining the conservation actions in four main areas: ex situ measures, in situ protection, its enforcement through involvement of stakeholders, habitat restoration (mainly for spawning and early life phase habitat, and international collaboration). This species is also appears in the EU Habitats Directive, CITES Annex II, the EU regulation of trade of flora and fauna and the Helsinki Convention.

Based on results of genetic studies (Ludwig et al. 2002, 2008), the development of an ex situ stock started in Germany in 2002 and in Poland by 2005, using wild-caught fish and their offspring of Canadian origin as a source. Since 2010, ex situ stock in Germany is reproducing and used for releases in the Oder, Vistula, Gauja, Narwa, and Nemunas rivers, as well as retaining a proportion as part of a long-term captive brood program.

Onset of migration facilitation in the mainstem Oder and Vistula rivers are to increase the availability of historic sturgeon spawning habitat. Habitat restoration is currently envisaged in the Oder catchment, which should result in improvements of sturgeon breeding and nursery habitats. Protection of the species in fisheries is attempted with awareness raising initiatives, while the improvement of enforcement is not considered a promising approach (Gessner et al. 2011). Utilisation of alternative gear to reduce bycatch mortality has experimentally been proven successful but meets little enthusiasm in fisheries (Gessner and Arndt 2006). With releases of different life phases in the Baltic tributaries, exceeding 1.5 million individuals over the last 10 years, the current population trend for Baltic Sturgeon subpopulation is increasing.