More than a year has passed since the beginning of the LIFE Baltic Sturgeon project

With the support of the LIFE Baltic Sturgeon project lasting over five years, juvenile Baltic sturgeon (Acipenser oxyrinchus) of different age groups will be introduced in sturgeon’s historical distribution rivers, which in Estonia are Narva River and Pärnu River. The plan is to release at least 500,000 young sturgeons. Most are released into the rivers as newly hatched larvae in the summer immediately after being brought from Germany, a smaller number is reared to a larger size in the RMK Põlula Fish Rearing Centre. The plan is to rear and introduce a stock of at least 40,000 one-summer-old (3-4 months), 8000 two-year-old (14-15 months) and 900 two- to three-year-old Baltic sturgeons within five years. Some of the two-year-old fish are individually tagged which allows the study of growth rate and migration based on the recapture reports. Two- and three-year-olds can be tagged with modern telemetry devices that provide a detailed picture of the fish's movements.

Baltic sturgeon have been reared in Estonia to populate Narva River even before the start of the project in Riina Kalda’s fish farm Carpio in Haaslava, Tartu County and RMK Põlula Fish Rearing Centre. In Põlula, experimental work was started in 2019. From 2019 to the end of the first half of 2022, a total of 23,000 young sturgeon of different ages (including 18,100 hatched in the same summer, 1600 one-year-olds, 2900 two-year-olds and 400 three-year-olds) from Põlula were reared and stocked in the Narva River.

To successfully restore the sturgeon population, it is necessary to do tagging and research work, collect and analyse recapture data of tagged fish, and raise awareness in the media and among fishermen. These works are carried out by Eesti Loodushoiu Keskus / Wildlife Estonia.

A year and six months have now passed since the beginning of the project. Let's take a look at the progress made in the implementation of the project during this time.

Rearing and establishing the Baltic sturgeon population

The central activity of the project is rearing and release of young sturgeon hatched in the same summer and earlier. In October and November of 2022, 972 1 g sturgeon hatched in the same summer, and 1850 two-year-old sturgeon with an average individual weight of 260 grams were introduced into the Narva River. In May 2023, 346 one-year-old sturgeon with an average weight of 6.8 grams were released into Narva River; at the end of June, 200,000 newly hatched sturgeon larvae were brought directly from Germany (individual weight 10 mg) and in September-October, 14,800 specimens hatched in the same summer (à 1.7 g) and 870 two-year-old specimens (à 43.1 g) were introduced. In October, for the first time, a small batch of 60 tagged two-year-old specimens weighing 200 grams was introduced into the Pärnu River. Within two years, a total of 716 specimens of two-year-old sturgeon were tagged with individual tags. 3000 sturgeons hatched in the same summer were kept for further rearing in 2024.

Some of the few-day-old sturgeon larvae brought from Germany in plastic bags filled with oxygen and water are released directly from the bag into their new home river. Photo: Iris Tambets

In the RMK Põlula Fish Rearing Centre, water from the Lavi spring is used to rear fish. It is cold (6°C) year-round at the point of exit from the ground and is directed to fish farm buildings through pre-heating ponds, where it warms up to 12°C in summer. The water is suitable for the growth and development of cold-loving fish, e.g. salmon. The water is too cold for young sturgeon. In the wild, they live at the mouths of large rivers in the first summer, where the water temperature is around 20°C in summer. In Põlula, sturgeon larvae are reared in the tanks at the quarantine building in the first summer, where the water can be heated and reused. As the rearing options are limited there, some of the sturgeon must be introduced into the river in the same autumn at the age of about three months, weighing 1-5 grams. Young fish left for further rearing are brought to other rearing buildings for the winter. In the following spring, rearing will continue in cages placed in a shallow pond with a slow water change, where the water will warm to a temperature suitable for sturgeon.

Three-day-old sturgeon larvae are brought from the German reproduction centre to Põlula by car in plastic bags filled with water and oxygen, where the water temperature is 18-20 degrees. The journey usually takes the whole night and day. Depending on the maturing time of the roe and milt of the breeding fish in the rearing centre, the delivery may take place at the end of June, July or the beginning of August. Plastic bags with water and fish are kept from overheating. 10,000 -15,000 sturgeon larvae are placed in one plastic bag and the individual weight of them varies between 10-20 mg. During transport, the loss of sturgeon larvae untrained to feed is usually small and accounts for less than one per cent of their total number. After being brought to Estonia, some of the sturgeon larvae are released into the river immediately, the rest are placed in tanks for further rearing, where after a couple of days their feeding training will begin. The first feed is larvae hatched from the inactive dormant eggs of brine shrimp Artemia (Artemia salina). They are well suited as the primary feed for sturgeon and other small fish larvae due to their size, way of moving, and nutritional value. Artemia lives naturally in salt lakes of all continents, from where its dormant eggs have been collected and marketed as the primary feed for fish larvae since the 1920s. Special care and attention of the breeder is required at the time of training fish to feed. Water temperature and flow, as well as light and feeding regime and fish population density must be kept at an optimal level. Moreover, it is very important to create good hygienic conditions to prevent stress and bacterial diseases of the fish. When incubating the shrimp larvae from Artemia eggs, one must be careful and precise so that they hatch at the right time and stay alive. It is necessary to disinfect the eggs to prevent the transmission of possible bacterial diseases and to maintain the correct water salinity and light, temperature and oxygen regime during incubation. Artemia eggshells must be removed before feeding them to sturgeon as they can clog the digestive tract of the sturgeon larvae.

In Põlula, the sturgeon larvae are placed in a quarantine building at first, where it is possible to ensure suitable conditions for sturgeon. In the photo, Kunnar Klaas, Head of the Põlula Fish Rearing Centre, introduces the possibilities of the centre to German sturgeon experts. Photo: Mart Thalfeldt

After about 15 days, when the fish have grown to a weight of 40-50 mg, they will be given additional feed in parallel with the Artemia, larvae of non-biting midges (Chironomidae). Feeding of Artemia brine shrimp stops on the 30-35th day.

By the beginning of September, the fish have grown to a weight of one gram, which means that their body weight has increased a hundredfold in two months. Then they are gradually trained to get used to dry feed specially prepared for sturgeon. It is characteristic of sturgeon to feed at the bottom. Their mouths are small, so their feed must be the right size. However, a small amount of the fish do not learn to take factory feed. They are recommended to be picked out and released into the river where they will hopefully find natural food. The feeding and light regime must be carefully monitored and the feed must be evenly distributed in the tank and available to all fish. The goal is that the sturgeon hatched in the same summer achieves the weight of 6-10 grams or more, so that they can withstand the winter water temperatures of the spring water in the farm. Winter is already difficult, as sturgeons have adapted to live in different environmental conditions in their natural habitats at the mouths of large rivers.

Sturgeon hatched in the same summer in the tanks at the fish rearing building at the beginning of winter. Photo: Arno Mikkor

Young sturgeons are characterized by a large difference in growth between different individuals. The sturgeon must be sorted often so that the smaller ones do not stop growing and that they can be given the appropriate size of feed. This is done by hand due to the peculiar body shape of the fish and to avoid injury. When rearing the larvae to age 0+, it is recommended to sort the sturgeons every 10 days. This work is very time-consuming for fish farmers. Timely sorting improves fish growth and feed availability and reduces trauma caused by fighting for feed.

When growing one-year-old sturgeon in net cages placed in the pond, they need to be sorted repeatedly during the summer. During the sorting process, they are also counted, thinned, and relocated in cages which have been scrubbed of algae. Relocation is important to prevent overcrowding and for water exchange, as the cage net can quickly become clogged during vigorous algae growth in the pond. Water exchange is also reduced by the fact that the bottoms of the cages are made of panels. The net is not suitable there, because the sturgeon looks for food on the bottom with its protrusible mouth. It also needs considerably more space than many other farmed fish species.

Two-year-old sturgeon placed in net cages at the pond in Põlula. Fish are measured and weighed before releasing. Suitably sized fish are also tagged so it’s possible to compare how much they have grown in the wild. Photo: Wildlife Estonia

During the Autumn, around the beginning of October, is a good time to release pre-reared sturgeons into the wild. Before that, the fish are checked for the presence of fish diseases and a release permit is requested from the Environmental Board. The fish to be released have been counted and weighed and some of the larger ones have also been tagged. A representative of the Environmental Board will be present at the release. Large temperature differences between the fish transport container and the river water can cause severe stress, even shock, in the fish. Therefore, the water temperatures of the river where the fish are to be stocked are monitored before the release, and a suitable releasing time is chosen accordingly. A temperature difference of up to 3°C between the river and the fish container is considered normal.

Sturgeons are transported from Põlula to the place of release in special containers. Correctness of the water temperature and oxygen conditions are carefully monitored. Photo: Jelizaveta Gross

Rearing and stocking of fish is carried out under the careful supervision of specialists. Ene Saadre and Marten Ojang keep an eye on the small sturgeon from their arrival in Põlula until they are released in the wild. Photo: Jelizaveta Gross

Larger sturgeon have to be taken to the river with a bigger vessel and they are released a little further from the shore. Photo: Jelizaveta Gross

Tagging, studies and raising awareness

Young sturgeon usually enter the sea in the same year (age 0+), but they can also stay in the river or the estuary for a year or two. After entering the sea, they initially live and feed in coastal waters, where they feed on benthic invertebrates, such as mollusks, polychaetes and crustaceans, and later on smaller fish. Due to their peculiar body shape, sturgeon could get entangled in fishermen's nets. Therefore, it is very important to raise awareness extensively and continuously among fishermen, in cooperation with officials of the Environmental Board, so that the fishermen report the findings of tagged sturgeons that have been released from traps alive, as well as those that have died in traps. As there is a ban on fishing for sturgeon, people are often afraid to report a dead sturgeon. A sturgeon that has died in a trap can be brought ashore if it has been reported to the environmental inspector before reaching the port. The fish should be put in the freezer and contacted by the scientists who get very valuable information about the sturgeon growth and nutrition.

Sturgeons hatched in the same summer weighing a few grams before being released into the river. Photo: Jelizaveta Gross

The individual tag is a yellow plastic tube attached to the back of the fish, each having its own number. This allows identifying the fish, since the time and place of its release, age, length and weight at the time of release are known. The tag has contact information, which the fishermen can use to report information about the tag number, time and place of catching it, and, if possible, the length and weight of the fish when a fish is caught in the trap. Photos of the tag and/or whole fish are often sent, as well as videos of the fish being released at times. If the fish is alive, the most important thing is to either photograph the tag or write down the number and quickly release the fish back into the water with the tag. Length and weight can also be measured and recorded by sight. The survival of each young sturgeon is important since it could be the one who will succeed in reaching its full maturity, spawning and providing hundreds of thousands of offspring in the future. There is also a small award for the effort for the senders of recapture notifications; in addition, they receive a letter of thanks and a lure and the opportunity to participate in the lottery organised every 4-5 years.

Two-year-old sturgeons are tagged with yellow plastic tags attached to their backs, with an individual number and contact information for fish scientists. Photo: Jelizaveta Gross

Raising awareness and cooperation with fishermen has been active and effective. We are delighted with the amount of information that we have been receiving about sturgeon catches and tagged sturgeons. According to the re-catch data so far, the weight of the fish has increased tenfold in one summer. For example, a 150-gram fish weighs 1.5 kg after a year and a 50-gram fish weighs half a kilo. Since the fish have spent most of this time in the sea, we can assume that the Baltic Sea is still a suitable habitat for sturgeon. Data on recaptures have been collected from the entire coastal sea of the Gulf of Finland and beyond. The farthest places from Narva are the area around Hiiumaa in Estonian waters and the Turku archipelago on the Finnish side.

The involvement of the local population and especially people in the field of fishing is very important for sturgeon protection and everyone can contribute to making these prehistoric fish swim again in the Baltic Sea and our rivers. To raise awareness among the public of the work of restoring the sturgeon population and to have a supportive attitude towards this undertaking, the project partners Wildlife Estonia and Finnish Luonnonvarakeskus (Luke) are organizing extensive awareness-raising activities for all stakeholders. Special attention is paid to fishermen who come into contact with sturgeon the most in their daily work. They cooperate with regional fishermen's associations engaged in coastal fishing, explain current activities and plan joint initiatives, for example collecting data on the sturgeon caught. Based on recapture reports of tagged sturgeon, scientists estimate how they are growing and how far they have gone in finding new habitats. Surveys have been conducted among both Estonian and Finnish fishermen, as well as among visitors to public events.

Stocking sturgeon is an event that always makes the participants happy. Photo: Jelizaveta Gross

Public interest in the sturgeon's progress is high. Rearing and stocking of sturgeon has been covered many times in news programs of TV channels, newspapers and portals. The press even plays a role in re-organizing information on sturgeon in national registers. It has now been officially accepted that the Atlantic sturgeon (Acipenser oxyrinchus), which has inhabited the Baltic Sea for the last 3500-4000 years, should be considered the natural sturgeon species of the Baltic Sea. Previously, it was considered to be a species of sturgeon, Acipenser sturio, which was also called Atlantic sturgeon at the time. DNA studies of archaeological finds and museum specimens showed that in the last millennia, the dominant sturgeon species in the Baltic Sea was Acipenser oxyrinchus, which is also a conspecific and genetically identical to the Atlantic sturgeon inhabiting the eastern coast of the North America. When dealing with the Baltic Sea population of this species, it is recommended to use the formal name Baltic sturgeon.

Sturgeon is a very attractive fish. Hopefully, people will remain interested in the progress of the sturgeon and it will once again become a natural part of the fish population of our waters. Photo: Jelizaveta Gross

Acipenser sturio, now called European sturgeon, was once widely distributed in the coastal areas of Europe, but today, its population with breeding capacity has remained only in the Garonne basin in the western part of France.

The story of our project and Baltic sturgeon published in Finland's largest daily newspaper Helsingin Sanomat led to changes in Finland's official list of species. In the past, the name sturgeon (sampi in Finnish) was used for the European sturgeon (A. sturio) and blue sturgeon or sinisampi was the name of the Atlantic sturgeon. A journalist who learned about the project in Estonia was interested in why this is so, as the sturgeon of the Baltic Sea is not blue. Then the committee of the Finnish species names decided to start using euroopansampi (European sturgeon) and atlantinsampi (Atlantic sturgeon) as the official names.

The Baltic Marine Environment Protection Commission (HELCOM) is keeping an eye on the implementation of the 2019-2027 Action Plan for the Protection and Recovery of Baltic Sturgeon. Work progress is discussed, and experiences are shared in the working group of HELCOM Baltic sturgeon experts. At the beginning of the project, an annual meeting of the expert group was held in Estonia, where our work was introduced, and representatives of other countries were encouraged to move forward with the restoration of the sturgeon population. Swedish representatives of the expert group organized a visit of nature filmmakers to Estonia in October 2023 to make a film on the work being done to restore and protect the sturgeon population in Estonia to introduce it to the Swedish public. The footage was taken of the stocking of tagged sturgeon into Narva and Pärnu rivers.

The project has been presented at several local and foreign conferences and congresses. In addition to the HELCOM expert group, the experiences and results gained in sturgeon rearing and stocking have been presented to the Pan-European working group on the protection of sturgeon, in which Meelis Tambets participates as the representative of Estonia. Employees of the RMK Põlula fish rearing department and the employees of the Baltic sturgeon breeding centre of the Mecklenburg-Vorpommern Research Centre for Agriculture and Fisheries have made mutual visits to exchange experiences.

Sturgeon rearing institutions kindly share their knowledge. Põlula's specialists visited the Institute in Germany, where stocking material for Baltic sturgeon is reared for both their own and other countries. Photo: Küllike Eder

Background of the project

The objective of the LIFE Baltic Sturgeon project, which will last from 1 September 2022 to 31 December 2027, is to create an opportunity for the re-establishment of a viable natural population of Baltic sturgeon (Acipenser oxyrinchus) in Estonian waters. The project implements the Action Plan for the Protection and Recovery of Baltic Sturgeon approved by the Baltic Marine Environment Protection Commission (HELCOM) in 2020 and its implementers are the State Forest Management Centre (RMK), the Wildlife Estonia and the Luonnonvarakeskus in Finland. The project is coordinated by RMK.

The Baltic sturgeon belongs to category III protected species in Estonia, category 0 in the Estonian Red Data Book (extinct or likely extinct); annexes II and IV of the EU Habitats Directive and category RE (regionally extinct) in the HELCOM Red Data Book.

The natural sustainable population of sturgeon, which inhabited the Baltic Sea for 3500-4000 years, disappeared in this sea in the last century. The reasons for the extinction are the blocking of large spawning rivers in the Baltic Sea basin, pollution, and overfishing. The spontaneous recovery of a viable sturgeon population is no longer possible. What is positive is that the same species, the Atlantic sturgeon, which is genetically identical to the sturgeon that lived in the Baltic Sea, still lives in the waters of the western Atlantic Ocean on the east coast of North America. Propagation material for the Baltic Sea is brought from there.
Restoring self-sustaining natural populations of Baltic sturgeon is a common goal of the Baltic Sea countries. Our project is part of the action plan adopted to achieve this goal.

Breeding stock of sturgeon from the Saint John River in Canada has been formed at the breeding center of the Mecklenburg-Vorpommern Research Centre for Agriculture and Fisheries near Born, Germany, from which the reproductive stock is obtained. Sturgeon are long-lived, very large and fertile fish. One female fish can produce a couple hundred thousand to a couple million eggs in one season, depending on the body weight. It takes a long time for sturgeon to reach sexual maturity – male fish become sexually mature at the age of 7-9 years, and female fish at the age of 8-14 years and later. In more northern areas, they reach sexual maturity even later. For example, in the Saint Lawrence River at the border of the USA and Canada, sturgeons become sexually mature at the age of 27-28 years. So, it isn’t practical to create a breeding stock in every country. The German research centre produces newly hatched larvae for introduction in water bodies or for further rearing in other countries as well.

Creating a self-reproductive sturgeon population in Estonian waters is a nature conservation activity that takes many years, given the longevity of the fish, and is not related to commercial interests. The project supported by EU LIFE funds lasts for five years, but its activities need continued support by state funds after the end of the project until the objective is achieved.
Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Climate, Infrastructure and Environment Executive Agency (CINEA). Neither the European Union nor the CINEA can be held responsible for them.

The Project “ Bringing back the extinct sturgeon into the North-Eastern Baltic Sea” (LIFE21-NAT-EE-LIFE Baltic Sturgeon) is implemented with the financial support of the LIFE Programme of the European Union and Project implementers.