Deterioration of the natural environment PDF Print E-mail
The European sturgeon has to grow for some 10 to 16 years before it is able to reproduce.  During this juvenile phase of its life, the European sturgeon lives in different aquatic environments (rivers, estuaries, coastal waters) in areas that are subjected to intensive pressure from development and especially from pollution.  It must therefore adapt itself to extremely strong constraints in order to complete its biological life cycle. 
 
The first phase of rarefaction of this migratory species goes back to the Middle Ages and is linked to the work carried out to protect riverbanks and to the deforestation of the alluvial plains (Hoffmann, 1996 & 2005). During the 19th and 20th centuries, constraints imposed by humans on the species’ essential habitats became even stronger and were, along with fishing, the origin of its disappearance from the previously frequented European basins.
 
  • Obstacles to migration and artificialisation of rivers
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With the beginning of industrialisation, nearly all the fluvial hydro-systems in Europe were modified by hydroelectric dams and other large scale hydraulic constructions that prevented anadromous fish from reaching their spawning grounds: partial or total breakdown of ecological continuity, reduction or suppression of accessible spawning grounds, engineering works for river navigation, land filling and wet land draining, river bank development, etc.

The impossibility of reaching spawning grounds has led to the disappearance of several populations of Acipenser sturio since the beginning of the 20th century (e.g.: River Guadalquivir in Spain, since the construction of the Alcala de Rio dam).  Besides, regulated river flow in spawning areas has given rise to considerable fluctuations in the hydrological processes and water levels, making access to spawning grounds more difficult (e.g. : the River Rhone) or reducing the reproductive success of the species.
  • Deforestation of alluvial plains and the impact of intensive farming
;;;;;;; The development of farming in all the countries throughout the species’ range during the 20th century meant that trees were felled in the alluvial areas and this affected the flow rates of rivers (increased water run off, pumping river water to supply irrigation systems, etc.), and the destruction of spawning grounds (increase in the organic content of the waters, the clogging of habitats, etc.).
  • Dredging for sand and gravel extraction: destruction of essential habitats
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The extraction of sand, gravel and other material from these spawning grounds has had a particularly devastating effect in the Rivers Danube, Guadalquivir and Garonne.  These sites have been transformed and no longer have the hydrodynamic characteristics required by the species for reproduction.  This activity has reduced the benthic biomass In the rearing grounds that comprises the main food supply for the sturgeon.
  • Direct threats of pollution
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Pollution peaks of agricultural, industrial or domestic origin give rise to anoxia, increased water temperatures, eutrophication, etc.
  • Accumulative and indirect effects on the species
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Modifications to water course regimes (dams, diversions, etc.) and the different impacts on habitats (suppression, reduction, clogging) and the benthic fauna have had a devastating impact on the European sturgeon, which has been deprived of nearly all the natural spawning grounds in the rivers where the fish was commonly found in the past.  

All these observations lead to numerous questions that today remain largely unanswered:

-Are habitat modifications due to migration obstacles and the destruction or deterioration of spawning and rearing grounds reversible?
- Is the reproduction and development of the sturgeon affected to a worrying degree by the deterioration of the quality and flow of fresh water linked to water usage (irrigation, etc.), hydraulic works and chemical and thermal pollution in most of the basins where the sturgeon might be present, as well as by the development and commodification of estuary environments?
- What is the possible influence of global warming?  It is supposed that global warming does not have a profound effect insofar as the species used to live in Mediterranean basins and that it adapts to major temperature differences.  However, what indirect effect is possible due to the modification of water regime and pollution cycle, the modification of food resources, etc. 
Last Updated on Saturday, 07 November 2009 20:39