1.2.04 The sturgeon is making a comeback – repopulation of a former river resident

The sturgeon was a typical resident of North-German rivers that then disappeared from these waters. Its eradication is a symptom of the conditions of the water: migrating fish in particular find it difficult to locate suitable conditions in obstructed and contaminated rivers. An ongoing research project conducted by the BMBF and the BMU has been working since 1996 to meet the necessary requirements for the successful repopulation of the sturgeon. The scientists have already established parent stock for North Sea and Baltic Sea sturgeon and released the first set of young into the Oder and Elbe as part of an experimental stocking measure. Fish from French and Canadian rivers constitute the germ cell for the offspring.

At the end of the 19th century, sturgeon were widespread along the entire European coast and they had spawning grounds in all the major European rivers. Today, this breed of fish is threatened with global extinction. The rivers have become obstructed and contaminated, destroying their habitat, and intensive fishing has simultaneously decimated the population. Individual catches of sturgeon were registered in Germany as late as 1992. After that, the sturgeon was deemed to have died out in Germany.

It is not just the sturgeon that has suffered the destruction of its habitat; other migrating fish have also been affected, e.g. the salmon, sea trout, houting, allis shad and twait shad. The experience gained in the reintroduction of the sturgeon and possible reclamation measures is therefore also of benefit to other fish populations.

Residents of different waters

The sturgeon is a migrating fish that leaves the sea and moves far upriver in order to breed, laying over a million eggs in fast flowing water. Once the larvae have hatched and grown up among the pebbles, the offspring drift downstream to sections of the river rich in food. At the end of their first year, the fry progress to the brackish water of the river mouth and then go on to reside in the sea for the next two to four years. After 10 to 20 years, the sexually mature fish return to the river of their birth in order to breed.

Reintroduction research project

The quality of the water in rivers has improved greatly in the last 20 years – providing an opportunity to reintroduce sturgeon, which was seized by the Gesellschaft zur Rettung des Störs e. V. (society for saving sturgeon) in 1994. The federal ministries for research and the environment have given over EUR 1.8 million since 1996 to support a research project on the reintroduction of sturgeon to the feeder rivers of the North Sea and Baltic Sea. Entitled “Genetische Populationsstruktur, Zuchtplan und künstliche Vermehrung einer süßwasseradaptierten Zuchtgruppe des Europäischen Störs (Acipenser sturio) als Voraussetzung einer erfolgreichen Wiedereinbürgung” (genetic population structure, breeding plan and artificial reproduction of a freshwater-adapted breeding group of European sturgeon (Acipenser sturio) as a prerequisite for successful reintroduction), the project involves the German Federal Agency for Nature Conservation (BfN), the Berlin Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), the Landesforschungsanstalt für Landwirtschaft und Fischerei Mecklenburg-Vorpommern (Mecklenburg-Western Pomerania state research facility for agriculture and fisheries) as well as other research facilities.

Suitable sturgeon were bred

If the waterways are to be repopulated, it is essential to have sufficient numbers of fish that correspond to the former native breeds. A significant sub-project is therefore the establishment of a parent stock for producing a stock of offspring suitable for the respective habitat. The European Atlantic sturgeon (Acipenser sturio) from the Gironde in south-west France was selected for the offspring to be introduced to the North Sea and its feeder rivers. From a genetic perspective, this very small fish population is virtually identical to the fish that once lived in the North Sea. The IGB has been obtaining a few samples with the co-operation of Cemagref in France since 1996 in order to breed stocking fish for the Elbe and Rhine. As sturgeon are not sexually mature until the age of 10 to 12 at the earliest, the first offspring of fish formerly of French stock became available in 2007. The fish produced from this reproduction were marked, fitted with telemetric transmitters and released in the middle of the Elbe so that their migration could be tracked.

The sturgeon that once lived in the Baltic Sea differ from those of the North Sea both genetically and in appearance. They are the descendants of the American Atlantic sturgeon (Acipenser oxyrinchus), which migrated to this location around 1,000 years ago. A breed that is genetically very similar to the Baltic Sea sturgeon lives in the Rivers St. Lawrence and St. John in Canada. The Gesellschaft zur Rettung des Störs brought some sexually mature fish to Germany for breeding purposes in 2005 and 2006 with the aim of founding an initial parent stock. The release of offspring from controlled reproduction in Canada into the Oder river basinPart of the earth’s surface that is drained by a river and its tributaries. We distinguish between above-ground and underground basins. The drainage divide marks the boundaries of the basin. has been taking place since 2006 for telemetric examinations and to determine the use of the habitat.

Offspring from controlled reproduction were reared in order to build up parent stocks. These fish were characterised using genetic screenings, particularly via microsatellites developed by the University of Potsdam, and breeding plans were created in order to optimise genetic diversity. 2010 saw the first successful reproduction from the A. oxyrinchus parent stock in Germany, so now early live stages can also be examined.

Development of alternative fishery techniques

To ensure that the growing sturgeon population does not become a victim to fishing, the project has also driven forward the further development of gillnets for coastal fishing. The aim is to minimise the unintended catching (bycatching) of sturgeon and simultaneously to optimise the catching of zander and perch in the Szczecin Lagoon. Trials with newly developed nets have shown that the bycatching of sturgeon can be almost completely eliminated by implementing simple changes. But as the amount of target breeds entering the net was also somewhat lower, uptake within the fisheries is still rather low.

Sturgeon under observation

Once the sturgeon have been released, they remain under intense observation. Markings and transmitters are used in order to research the migration of the fish, the aim being to identify and describe suitable habitats and to determine the risks posed to them. This monitoring is to form the basis for further releases and possible reclamation measures in rivers. If the quality of the sturgeon habitats is improved, then other animals will also benefit. The sturgeon can therefore also become a precursor for the resettlement of other breeds with similar ecological requirements.

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1.3 IWRM

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1.2.03 SEDYMO research project