Page 46 - Bulletin, Vol.79 No.1, February 2020

WHERE DO OUR FISH COME FROM?

Where do our fish come from? For a number of years the management of recreational
fishing has been under the control of conservation biologists, most of whom regard the
anglers, who have observed their incompetence, with a paternal, almost
condescending, eye. The time has come to make a challenge! As can be seen from the
article below by Christian Lévêque, hydrobiologist, researcher and author of a number
1
of works , notably “Quelles rivières pour demain? Refléxions sur l’écologie et la
restauration des rivières” (Ed. Quae, 2016).

If you do not believe in spontaneous regeneration and if you do not believe either that
God created the world some 7000 years ago … then you must ask yourself “where do
our fish come from?”

One thing that is certain is that aquatic life today is but an instant in the long film of the
immense evolution that has profoundly modified our climates, landscapes and
ecological systems. By consulting the work of climatologists, one learns that at the time
of the mammoths, the north of Europe was frequently subjected to cycles of glaciation.
During the last of these periods, around 20,000 years ago, the Alpes were under ice, as
were also the British Isles. In the rivers of the plains, often icy, only a few species could
survive these extreme conditions: pike, common bream, dace, chub, roach, gudgeon,
perch, and loach. Going even further back in time, in the era of the dinosaurs, there
were tropical fish in the Rhone valley, witness the fossils in the tropical lagoons of the
Cerin (Ain). In short, if, over short periods, there is the impression that nothing changes,
this is far from being the case.

An American limnologist, John Magnuson, spoke of the invisible present when
discussing the slow changes that could be observed only over long periods of time.
Lake Léman, for example, has registered over several decades a slow increase in the
temperature of the water.

In short, the aquatic fauna of northern Europe has been decimated several times over
the past million years due to the progress of the glaciers of the Pole. Compared with
tropical fauna, it is highly impoverished. The rivers of southern Europe (the south of
Spain, south of Italy) have been less affected by these glacial phenomena and a part of
their fauna has survived. It is generally agreed that the Danube River basin was the
main refuge for European aquatic fauna during these periods. How did these species
recolonize the ice-free zones from their meridional shelter? Since, in theory, a
watershed is equivalent to an island and taxonomic groups such as fish, mollusks and

1 Lévêque C. & Van der Leeuw S. 2003. Quelles natures voulons-nous ? Pour une approche
socio-écologique du champ de l’environnement, Elsevier Paris
Beisel L.N. & Lévêque C. 2010. Les introductions d’espèces dans les milieux aquatiques. Faut-il
avoir peur des invasions biologiques ? Editions QUAE. 232 PP.

42 AAFI-AFICS BULLETIN, Vol. 79 No. 1, 2020-02