Baltic GiantThe sturgeon had gone extinct in the Baltic Sea by the start of the century. The Baltic sturgeon was actively caught over a long period of time and the quality of their habitats, especially their breeding grounds in rivers, decreased. By now, there have been positive developments in the water quality and other important aspects in the Baltic Sea countries and there is interest, opportunity and a desire to restore the natural sturgeon population here.
Baltic sturgeon population restoration efforts have already begun in many Baltic Sea countries, including Estonia.
Up until recently, it was believed that the Baltic Sea was populated by Acipenser sturio (Atlantic sturgeon, also known as European sturgeon), which currently only exists in French waters and is endangered. However, genetic, morphological and archaeological studies have shown that the sturgeon that has lived in the Baltic Sea for the past few centuries is actually related to a species of sturgeon inhabiting the east coast of North-America, Acipenser oxyrinchus (Atlantic sturgeon, also known as baltic sturgeon), which appeared in the Baltic Sea around 1200 years ago and, over the course of 400 years, replaced the A. sturio that had inhabited the area for a couple of millennia.
3.2 tonnesSturgeons can grow to be very large; specimens measuring six metres and weighing a tonne have supposedly been found in the Baltic Sea. The beluga sturgeon, a relative of the Baltic sturgeon, has even been reported to have grown to 8 metres in length and 3.2 tonnes in weight. Sturgeons can live up to a hundred years. Male sturgeons become sexually mature younger and smaller in size than females. According to American data, male sturgeons do not reach sexual maturity before seven years of age and females before eight. However, most sturgeons become sexually mature at an older age – females can take 20 years and males 15.
Sturgeons breed several times during their lifetime, usually not every year: males with a one to five year gap and females with a two to five year gap. The egg of a sturgeon measures 2-3 mm in diameter and is black, dark grey or olive in colour.
Due to their size, female sturgeons are also highly fertile. The last natural sturgeon caught in Estonian waters – Maria – was 2.9 m long, weighed 136 kg and had approximately 1.5-1.7 million eggs weighing a total of 28 kg. The eggs of a 2.88 m sturgeon caught in River Narva in 1945 weighed 25 kg with approximately 1.4 million eggs. Extremely large sturgeons, such as specimens weighing 350 kg may have 7-8 kg per breeding period.
The last sturgeon caught in Estonian waters was 2.9 m long and weighed 136 kg.
Sturgeons breed in rivers. Tagging and genetic research has shown that sturgeons will use the same breeding rivers for years, returning to the river where they were born. This is notable as sturgeons can travel considerably far at sea and populations from different rivers intermingle extensively at sea. It is assumed that sturgeons find their home river primarily by smell.
They outlived the dinosaursSturgeons as a fish group are also notable for their age. They appeared 200 million years ago and have remained more or less the same since. Sturgeons have been rather resilient, surviving the extinction event 65 million years ago that killed most of their companions, including dinosaurs. It is now up to us to make sure that the long-lived fish will also survive the current man-made extinction event.
It’s not easy: sturgeons are one of the most endangered groups of animals in the world. The state of the Baltic sturgeon has been especially depressing. But recent years have taken a brighter turn. You could even say there has been a breakthrough, with reports of more than a million juvenile sturgeons being released into rivers flowing into the Baltic Sea. You may wonder how that could be possible. No sexually mature specimens have been found in the Baltic Sea and population material from France is not suitable for repopulating the Baltic Sea. Fortunately, population material is available from the border area between the United States and Canada on the east coast of North America. This is also where the breeding fishes producing population material for the Baltic Sea in a research institute in Germany come from.
No scalesThe developmental history of the Atlantic sturgeon as one of the oldest fishes is also visible in its ancient looks. Instead of the classic scales, sturgeons are covered in 5 longitudinal rows of scutes (on the back, sides and ventral) which give the sturgeon’s body a pentagonal profile. Several smaller scutes are located on the sides of the body. The scutes of a sturgeon are rough and rather sharp on juvenile fish, becoming duller as they age. The snout of a sturgeon is long and wide, with four short barbels on the underside. Older specimens have a shorter and flatter snout. There is also a rare phenotype with a short snout. The snout is triangular when viewed from the top. The sides of the head feature small eyes and the underside features a small extendable mouth, which is toothless in juvenile fish (new fish have teeth). The dorsal, anal and pectoral fins are located in the rear near the heterocercal caudal fin. The colour of the body varies: the back is bluish black to olive or greyish brown, the sides are bluish silver, the underside is silver or whitish. It has been noted that the backs of sturgeons darken to black in fresh and brackish water.
Atlantic sturgeons eat benthic organisms by sucking them into their mouths, creating a vacuum with their mouth cavity. Young sturgeons prefer to live in areas with soft bottoms where they eat invertebrates: crustaceans, molluscs and various worms. Larger fish also eat other fish. A sturgeon’s diet can vary over the course of the year. Sturgeons stop eating for the mating period.
Sturgeons at a few weeks old
The Atlantic sturgeon was spread throughout the entire Baltic coast as well as in larger rivers and their deltas. Fresh water populations were found in the Ladoga and Onega lakes. Occasional catches and/or archaeological finds have also been found in Western Europe: French rivers, British territories and the North Sea. The native Atlantic sturgeon has gone extinct in those areas. The Atlantic sturgeon went extinct in the Baltic Sea region due to the negative effects of human activity (overfishing, damming and regulation of rivers and pollution). The extinction may also have been aided by climate change.
A very endangered speciesThe Atlantic sturgeon was a commercially important species in the Baltic Sea until the consistent decline of the sturgeon population (starting at the end of the 19th century). Sturgeons have been caught in the Baltic Sea for a very long time. Sturgeons moving up to rivers to breed were an easy catch for people as early as in the early stone age. Archaeological data shows that sturgeon fishing intensified as the human population grew. References to a drop in the sturgeon population in medieval times (from the 7th century) have been found in Poland and near Lake Ladoga. Atlantic sturgeon was still caught in considerable numbers at the start of the 20th century. By the end of the 1920s, the sturgeon population had dropped to the point where catches where no longer measured in tonnes but by counting specimens. The population held out longer in the eastern parts of the Baltic Sea. There was still a fresh water population of Atlantic sturgeon in Lake Ladoga in the mid-1980s (last catch in 1984). The last Atlantic sturgeon in Vistula was caught in 1972. That same year, the second-to-last specimen was caught in Estonia. The last native specimen was caught in 1996.
According to IUCN, sturgeons are a highly endangered group in the world. Out of 25 species in the sturgeon family, 21 are endangered, 16 of which are critically endangered. 20 species have a declining population. There are 8 species of sturgeon in Europe, 7 of which are critically endangered. The unfavourable situation is caused by similar traits and risk factors among the species.
The unique traits of Atlantic sturgeons such as long lifespan, large size, late maturity and need for different types of habitats make them very vulnerable to human activity. Atlantic sturgeons are influenced the most by high pollution and the damming of mating rivers as well as the modification of habitats and overfishing. The impact of different negative factors varies by river and coastal area.
The situation could improveThe critical state of European sturgeon species has been acknowledged for a while and recent years have seen several action plans coming to life to improve the situation. In 2018, the Bern convention accepted the European action plan for the protection of sturgeons. The Baltic Marine Environment Protection Commission (HELCOM) confirmed the protection plan for Baltic Sturgeons in 2019 (Action Plan for the Protection and Recovery of the Baltic Sturgeon, BSSAP).
The aim of the plan is to fulfil the goals set out in the Bern and Bonn conventions and the biological diversity convention as well as the duties established with the habitat directive in EU member states and to provide a practical guide for the restoration of the species to fulfil the aims of the HELCOM Baltic Sea action plan. The BSSAP aims to fulfil ex situ and in situ protection programmes, to start a population and habitat survey programme and to use its results to form a habitat protection and restoration programme. The HELCOM action plan dictates that the release of sturgeons must be done in numerous groups of different ages for several consecutive years.
The restoration of the Baltic sturgeon population is taken seriously in Estonia. The sturgeon is included in strategic development and action plans as a priority species and genuine population restoration efforts are supported.
“The general goal of the fish rearing action plan is to use rearing to improve the state of endangered and protected fish species and to increase their population, also creating broader opportunities for fishing valuable species in Estonia. The Estonian nature conservation development plan dictates that the restoration of Atlantic sturgeon stocks through rearing must be ensured until the natural reproduction of the populations is sufficient. The sturgeon is also a priority species listed in the Estonian NATURA 2000 Prioritised Action Framework. The capacity for breeding juvenile sturgeons in the RMK Põlula Fish Rearing Centre has grown considerably in recent years.
It is also necessary to advocate among environmental protection services and fishers.
The protection status of the Atlantic sturgeon is strict: Category III protected species in Estonia, category 0 in the Estonian red book (extinct or likely extinct); annexes II and IV of the EU nature directive; category RE (regionally extinct) in the HELCOM red book. Sturgeon fishing is strictly prohibited in Estonia.
The aim of the LIFE Baltic Sturgeon project is to restore the Atlantic sturgeon population in the north-eastern part of the Baltic Sea. An inevitable measure for this is the restocking of sturgeons. Breeding strong population material is crucial for creating new sturgeon populations. Fishes released and reared in Estonia are received and transported here from the State Research Institute for Agriculture and Fisheries of Mecklenburg-Vorpommern (LFA MV) in Germany.
Sturgeon juveniles are reared by the RMK Põlula Fish Rearing Centre (sturgeons in other developmental stages to be added later). The rearing of juveniles received in the first summer, and later of older sturgeons, is done in special breeding tanks. The sturgeons start out external feeding with live feed (Artemia), then frozen chironomids, and older specimens will be receiving special sturgeon breeding food. Groups of 2-3 year old fish are kept for tagging and migration studies.
To optimise survival and the homing effect, sturgeons are released at different ages (fry, 3-month-olds and one-year-old specimens). The releases are planned to be carried out in the Narva and Pärnu rivers. The best experiences and guidelines and international communication (incl. workshops) are used to increase the effectiveness of the restoration efforts. The well-being of released sturgeons is monitored in older specimens, first in river habitats (summer, autumn) and later in the sea. Young sturgeons are faced with high predation which ensures high adaptability in their new habitat as well as a high death rate. This as well as economic considerations (breeding larger sturgeons is more expensive) make it more optimal to release sturgeons periodically and in a dispersed manner.
15-month-old tagged sturgeon. Upon catching, we expect data about the length and weight of the specimen and the tag number for tagged specimens
Sturgeons released in River Narva are by now spread in the Gulf of Finland. Catches have been registered by Estonian, Russian as well as Finnish coastal fishers. The fish have been in great condition and the fishers have released the fish after registering the catch. Although the repopulated numbers of fish are still relatively low and the restoration period so far has been short, studies conducted in the Baltic Sea countries, including Estonia, show that the young sturgeons are adapting well to the natural environment.
The initial results of the restoration efforts in Estonia and other Baltic Sea countries show that the restocking of sturgeon in the Baltic Sea is viable and efforts should continue and numbers should be increased. To restore the sturgeon populations, i.e. creating self-reproducing populations in rivers, restoration efforts need to be consistent and long-term (around 15 years). It is deemed necessary to focus efforts on suitable rivers that the Baltic sturgeon has used for breeding before. This requires cooperation both internationally as well as domestically between different interest groups.