Bruno Garcia from the Charente Maritime fishing federation answers questions from listeners/fishermen on France Bleu la Rochelle. Didier lives in Aulnay de Saintonge and was able to observe on the Boutonne a reproduction of trout in a gravel pit area. The aggregates are spread over a very small area, should the fishing association add gravel to optimize the success of this spawning ground and should we fear predation from the chub which seem to be watching for spawning around this sector?
Bruno Garcia : It’s trout spawning season and I welcome this information. This species is in so much trouble on the upstream Boutonne! It’s nice to hear that there are a few survivors who survived the lack of water.
A little word about this river
La Boutonne has its source in the department of Deux-Sèvres at Chef-Boutonne. It crosses the Charente-Maritime department to flow into the Charente on the right bank at a place called Carillon. It is also one of the main tributaries of this river. According to François 1er it was not the Charente the most beautiful river in France contrary to what one can hear, it is precisely the Boutonne. It is a watercourse that suffers enormously from the lack of water from which there is a lot of water abstraction for crop irrigation. A study, already old, by a design office BRGM (Geological and Mining Research Office) which is the French public establishment of reference in the applications of Earth sciences to manage the resources and risks of the soil and from the basement. This consultancy estimated the withdrawals from this river at more than 10 million M3 per year and concluded that for it to regain a balance, these withdrawals would have to be reduced by a third. Today this is still not the case.
These trout on the Boutonne, should we add gravel or not to facilitate their reproduction?
We don’t touch this spawning ground, at least not currently, it’s especially not the time to let things happen naturally. So later in the season why not. In September or October, for example, add additional gravel, paying close attention to the existing grain size to find an identical context, very often between 2 and 4 cm this grain size. A little extra can’t hurt.
What will be the benefit of adding gravel?
You should know that gravel is the preferred medium for the reproduction of trout. Over the course of the floods, the current disperses these aggregates and the thickness necessary for the burial of the eggs is no longer sufficient. This is the principle of trout reproduction. Male and female dig a depression on the bottom of the river, the female lays the eggs there, the male fertilizes them and the whole thing is covered during the entire incubation period. It is at the end of this incubation at the birth of the fry that the difficulties arise
How long does this incubation last?
From memory it’s around 400 degree-days. That’s about 40 days at 10 degrees or 50 days at 8 degrees
Chub predation?
We can’t do much about it. It’s not just the chub that are threatening. Eels, dace, roach too and this is what causes a lot of losses in trout fry from birth, especially since a female trout only produces a few thousand eggs a maximum of 2000 i believe, unlike other species which produce several hundred thousand. All these nuisances combined.