| Situation of the population in captivity |
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The European sturgeon is now one of the most seriously threatened species of fish in the world. Hopes of restoring its population, weakened throughout its range, today relies essentially on the success of ex-situ conservation projects. Indeed, protection measures taken to reduce the threats with which the natural population is faced, although indispensible in the long term, will not alone slow the decline of the species. Actions to support the population in the wild (release of alevin produced from captive stock), thanks to the mastery of artificial reproduction techniques, seem to be the only alternative that is capable of reversing the situation in the long run and saving this species from extinction.
In France, 6 groups of animals are conserved in basins at the Cemagref institute in Bordeaux:
- 2 groups of wild specimens (8 fish born before 1994 and recovered through by-catch + 32 fish born in the wild and taken as juvenile samples, probably brothers-sisters);
- 1 group of 38 individuals obtained from a first artificial reproduction in 1995 from a mating pair of sturgeons caught in their natural environment that have today provided 78 specimens;
- 1 group of 700 fish obtained from a first artificial reproduction in 2007. The success of this reproduction was the reward for the long wait while a female, born in 1994, and males from different generations reached their sexual maturity at the same time. A significant number were kept in captivity given the deformities observed in fish from the 1995 reproduction. After two years with no symptom being observed, the decision was taken to release 400 fish into the Gironde Estuary in September 2009;
- 1 group of 400 fish from 2 new artificial reproductions successively in May and June 2008;
- 1 group of 300 fish from artificial reproduction in June 2009.
Researchers at Cemagref know how to make individuals, which have been caught in optimal conditions in the wild, reproduce, even though oogenesis does not take place every year. The technique has already led to the success of an experimental programme of species strengthening in the Gironde basin in 1995, 2007 and 2008. On the other hand, we are still not certain of the optimal rearing conditions to provide these animals in order that they may develop a normal sexual cycle and supply good quality products. Indeed, difficulties in obtaining individual male and female specimens in the wild at the same time and in the right conditions of maturity to reproduce have formed a major constraint to the improvement of artificial reproduction techniques and larvae rearing.
In Berlin, Germany, 17 fish from artificial reproduction in 1995 and 500 fish from artificial reproduction in 2007 and 2008 carried out by Cemagref in Bordeaux are kept at the IGB (Leibnitz Institute of Freshwater Ecology and Inland Fisheries). This laboratory principally concentrates its work on the improvement of reproduction conditions in freshwater, the study of the effects of temperature variation and the exchange of biological material with the Cemagref for genetic, histological and ecotoxicological studies. This work should lead to future species strengthening in the Elbe and Rhine rivers. Indeed, it seems that today there is a good opportunity to restore the species in Germany, given the progress made in fighting pollution and the measures that are possible in order to limit the effects of by-catch and waterway planning.
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| Last Updated on Saturday, 07 November 2009 19:58 |