Thursday, 17 November 2011

Electric Fishing at La Celle-Guénand

We read with interest in La Nouvelle République of 16th November of an exercise to measure water quality on the Rémillon just north of its junction with the Aigronne, about 2.5 km upstream of us. This is a further part of the first tranche of the planned works launched by the Community of Communes of Southern Touraine earlier this year in the restoration of the watercourses comprising the Claise basin. What follows is my best attempt at a translation of the article. I claim no responsibility for the science!

An electric fishing exercise took place at the end of October at La Gachère, in La Celle-Guénand with the aim of getting to know the fish population of these watercourses but also to judge the effect of the works on the fish.

Copyright La Nouvelle Republique
The principle is as follows: a generator produces a continuous rectified current of between 300 and 600 volts (400 in this case). The negative pole is placed in the water at a fixed spot; the positive pole is connected to an insulating handle with a metal ring on the end from which the current flows. Once the positive pole is lowered into the water, an electric field is created and the fish swim at first towards the source of the current. This is called "forced swimming". Swimming directly up to the researchers, they are easily caught in a landing net for they are semi-conscious. They quickly recover and do not take any lasting harm.
The species of the specimens captured is determined and they are then weighed, measured and released undamaged. Each species of fish is characteristic of a type of environment. For example, brown trout (Salmo trutta fario, truite fario) prefer cool, swift-flowing and well-oxygenated waters, whereas freshwater bream (Abramis brama, brème) prefer slower, warmer flows. The objective is to check whether a watercourse described as "salmonicole" (rapid, cool and oxygenated water) is degraded or not by studying its fish population. If the fishing exercise reveals a large number of fish characteristic of slow warm waters, it can be ascertained that the watercourse is very degraded.
The results of late October's fishing exercises in the Rémillon at La Celle-Guénand shows a quite well preserved site with the presence of brown trout and species characteristic of salmonicole watercourses:
  • chabot, (Cottus gobio), [Miller's Thumb or Bullhead or Sculpin]
  • lamproie de planer (Lampetra planeri) [Brook Lamphrey]
  • loche franche (Barbatula barbatula) [Stone Loach]
At the Sauvaget site, at Bossay sur Claise, the location is very silty. Only one trout and some sticklebacks (Pungitius spp, épinochettes) show that the watercourse is very degraded in this sector but nevertheless retains the capacity to support trout.

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