Effects of predation and discharge on habitat use by brown trout, Salmo trutta, and grayling, Thymallus thymallus, in artificial streams
Greenberg, Larry A.
Archiv für Hydrobiologie Volume 145 Number 4 (1999), p. 433 - 446
published: Jul 26, 1999
ArtNo. ESP141014504007, Price: 29.00 €
The effects of predation and discharge on habitat use by brown trout, Salmo trutta, and grayling, Thymallus thymallus, when alone and together, were studied in four indoor, artificial streams. Each stream consisted of three habitats, a riffle, a run and a pool, the latter two being further divided into shallow margins and deeper mid-regions. The experimental design differentiated between intraspecific and interspecific effects by having two densities of allopatry for each salmonid and one density of sympatry, for a total of five treatments. These five treatments were then run in the presence and absence of the piscivorous northern pike (Esox lucius) at high and low discharge. Decreasing discharge reduced the area of the run and pool margins covered by water, thereby reducing use of these areas by trout and grayling. In the absence of a predator, brown trout caused grayling to markedly reduce its use of pool mid-regions and increase its use of the shallow margins, but only at high flow. Grayling had a more modest effect on brown trout, causing brown trout to increase its use of pool mid-regions, but only at high flow. There were no effects of intraspecific effects on habitat use by either species. In the presence of pike, which occupied the pool, grayling had no effect on habitat use by brown trout, whereas brown trout caused grayling to increase its use of shallow water habitats. There were no effects of intraspecific effects on habitat use by either species when pike was present. The number of grayling or trout consumed by pike did not vary among the different treatments. The results showed that variation in flow and predation altered habitat use patterns of brown trout and grayling.