The European sturgeon combines the particular characteristics of both:

-  migratory fish that depend largely on the quality and connectivity of the milieus in which it lives or through which it travels in order to fulfil their life cycle.  The reproductive adults very probably seek to reproduce in the basin from where they originated.

-  the "giants", those large animals characterised by reproduction late in their lifecycle and a feeding strategy that forces them to consume large quantities of food and therefore to find  food-rich areas in which to gather together.

These ecological characteristics make them vulnerable to certain human activities (Rochard et al., 1990).  A collective summary (Williot et al., 2002) attempted to identify the causes that could explain the spectacular decline in sturgeon catches.  The dangers with which the populations in the wild have been confronted during the last two centuries and the threats still faced today are numerous :

- the European species has had to pay a heavy price for the deterioration of its essential habitats and their connectivity (spawning grounds,  rearing  areas).   This corresponds to the physical alterations imposed on aquatic milieus (man-made alterations and damming of rivers, the destruction of spawning grounds, etc), the deterioration of habitat quality (pollution, eutrophication, etc.) and the accumulated effects of these impacts;

- commercial harvesting, which is today banned in France and in Europe as a whole, considerably developed at the beginning of the 20th century and this activity spread throughout the species’ range, especially with the development of the caviar market.  Overharvesting in estuaries and coastal areas accelerated the phenomenon of the species’ decline;

- poaching, denounced since the statutory protection of the species in 1982, was one of the direct supplementary reasons behind the rarity of the species (Guth & Laurent, 2004). Massive mortality rates at sea of 1994 and 1995 cohorts are probably due to poaching;

- by-catches of the species made while fishing for other commercially-viable coastal species is today one of the major threats for this migratory fish.  Trapped sturgeon that are robust generally withstand these catches, and most of them can be released back into the sea.  The involvement  of  commercial fishermen in the protection of this species  is therefore of prime importance (Lepage et al., 2002) ;

- the bioaccumulation of  toxic substances (heavy metals, dioxins, hormones, etc.) diffused throughout the milieu, provokes in certain species of fish a notable impact on reproductive capacity and the viability of offspring.  Even though this indirect threat has not been described in depth for the European sturgeon, it can not be discounted  (Maury-Brachet et al., 2008);

- other factors for which the real impacts on populations in the wild have not yet been demonstrated should nevertheless be mentioned: these are the possibility of hybridisation and the risks of competition with other sturgeon species from breeding farms that are accidentally present in open waters.   To be added to these two factors is the Allee effect, or the phenomenon of depensation, which may arise when the density of the breeding population in the spawning grounds has so decreased that reproduction is increasingly difficult due to the reduced likelihood of finding a mate.  Even in the absence of any other source of mortality, the population is no longer able to sustain itself.