Experimental study of young grayling (Thymallus thymallus) physical habitat selection factors in an artificial stream
Sempeski, P.; Gaudin, P.; Herouin, E.
Archiv für Hydrobiologie Volume 141 Number 3 (1998), p. 321 - 332
published: Mar 9, 1998
ArtNo. ESP141014103004, Price: 29.00 €
We investigated the importance of the shape (slope, depth) of dead zones for their selection by young grayling (l5-40 mm). Our hypothesis, drawn from field observations, was that (1) larval grayling are sensitive to the shape of the dead zone they occupy and (2) they search for different habitat conditions by day and by night. Dead zones of the same dimensions (50 x 50 cm) but with different slopes and depths were placed along one bank of a 1-m wide experimental stream. Four shapes of dead zone were proposed to young grayling, from the combination of slope (gentle or steep) and water depth (shallow or deep). Habitat selection was studied over three weeks, both by day and by night. Results showed that by day, young grayling preferentially selected dead zones with the greatest depth, while by night they were mainly observed in dead zones having a flat bottom. The use of a 3D hydraulic model corroborated the following biological explanation: by day, while feeding, grayling select dead zones with the maximum density of drifting prey, while by night, they select dead zones with low bottom velocity. This study indicates the importance of the structure and thus the functioning of dead zones for young stages of grayling.