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7256591 
Journal Article 
Evolution of the spawning grounds of the Arctic char in Lake Geneva from 1981 to 2005 
Rubin, JF; , 
2005 
Yes 
Archives des Sciences
ISSN: 1661-464X 
SOC PHYS HIST NATURELLE GENEVE 
GENEVA 6 
201-229 
WOS:000246169700005 
Evolution of the spawning grounds of the Arctic char in Lake Geneva from 1981 to 2005 - The capture of the Arctic Char in Lake Geneva is on the decrease since the year 2000, in spite of an important stocking effort. In the 1980's the poor quality of the water in the lake probably did not allow for a significant success in the na tural reproduction of this fish. On the other hand today Lake Geneva being under way to re-oligotrophication, the eggs laid in the deep spawning ground sites should have more chance to hatch. So that to check the evolution of the reproduction sites, the principal spawning ground sites of the Arctic Char were studied from 1981 to 2005, thanks to 69 dives (160 fours 22 minutes of observations) made by the submarine FA. Forel. In Lake Geneva there are 9 sites of which each have one or several different spawning grounds. These spawning grounds have the appearance of a great slide of gravel, stones And pebbles without any covering of sediment, which usually measure 1 to 5 cm in diameter and are mostly situated betvvet n 50 and 120 metres deep. Maps of under water areas have been drawn up, which provides the exact position and location of these spawning grounds and their evolution in the course of time. The spawning grounds are mostly due to the outco:me of the wilful immersion or not of gravel. This is the reason why many among them are situated in the lake below the quarries. Spawning grounds of strictly natural origin are rare because today the dynamic force of rivers is no longer able to drag gravel along and bring sufficient quantities of it to the depths of the lake. Certain spawning grounds seem remarkably stable in the course of time whereas others are more short-lived. Apparently 3 criteria appear fundamental to ensure the survival of a spawning ground: (1) the constant provision of gravel, (2) the presence of water currents, (3) deep sites. It is possible to re-create artificial spawning grounds by immerging gravel at certain places. This method may be very effective and the spawning grounds can be functional for several years. However without a constant supply of gravel they will become covered in silt after 3 or 4 years and the attractiveness of the surface, which draws the attention of the Arctic Char will be reduced. Consequently it is the intention to choose a few sites where, in turn, a certain quantity of clean gravel will be immersed each year in order to propose a new fish management not only based on stocking but equally on the renaturation.