The distribution of salmonids in upland streams in relation to depth and gradient

Abstract

The distribution of various age classes of salmon and trout was assessed in upland streams by electrofishing. Water depths and site gradients were measured and correlated to fish densities. The fry of both species were significantly more abundant in shallow water; up to 75.3% of salmon fry and 72.2% of trout fry were captured in sites of mean depth < 20 cm.Older trout were found mainly in the deeper areas, with a maximum of 7.4% captured in sites < 20 cm mean depth. Yearling fish were found in all the depth-ranges sampled, but with a tendency for higher numbers in mid-range depths. There were similar correlations in the abundance of each age class with the actual areas of shallow, mid-range and deep water habitat available within sites. Correlations of fish density with gradient indicated that trout were limited in their distribution to areas of lower flow, whereas salmon were not. Since depth and gradient were significantly negatively correlated, there was an apparent preference oftrout for slightly deeper habitats than the equivalent year classes ofsalmon. The observed habitat segregation is discussed in terms ofcompetition and selection.

Daytime habitat selection for juvenile parr brown trout (Salmo trutta) in small lowland streams

“…Previous studies have illustrated the key importance of water depth in determining juvenile brown trout habitat use (Bohlin, 1977;Bagliniere and Champigneulle, 1982;Egglishaw and Shackley, 1982;Kennedy and Strange, 1982;Heggenes, 1988c, d), including Danish small lowland streams (Hermansen and Krog, 1984). All of the above studies and others have shown that there is a positive correlation between fish size and water depth, and that the larger the trout, the deeper water it prefers (Greenberg et al, 1996;Heggenes et al, 1999;Maki-Petays et al, 1997).…”

“…There is little knowledge on physical habitat requirements in small lowland streams that can be used to evaluate the effects of different water management actions such as water abstraction or stream restoration activities aimed at increasing stream flow and improving physical habitat conditions Conallin et al, 2010a;Nislow and Armstrong, 2012). Four habitat variables are known to affect the habitat selection of salmonids and carrying capacity in streams (Vezza et al, 2012); water depth (Kennedy and Strange, 1982;Heggenes, 1988aHeggenes, , 2002, water velocity (Heggenes and Traaen, 1988;Heggenes et al, 1999;Heggenes and Dokk, 2001), bed substrate (Heggenes, 1988b;Knapp and Preisler, 1999;Kondolf, 2000), and cover (Hubert et al, 1994;Bovee et al, 1998). However, differences in stream characteristics can influence the importance of these variables on brown trout habitat selection, i.e.…”

Le développement des modèles d'habitat pour les salmonidés d'eau courante et leur application à la gestion piscicole

“…It has been suggested that habitat needs may alter with the life-stage, size and species concerned (MILNER et al, 1981 ;KENNEDY and STRANGE, 1982 ;MORANTZ et al, 1987). It is likely, therefore, that the dérivation of successfui models may, in part, be a resuit of their specificity.…”

Variabilité des populations de salmonidés en eau courante : étude de la variance liée à différentes échelles spatiales ou temporelles et implications pour les modèles d'habitat

“…Within a stream at any one time, local features are demonstrably important (e.g. LEWIS, 1969 ;GORDON and MACCRIMMON, 1982 ;KENNEDY and STRANGE, 1982), but over time they may explain only small proportions of overall variance, particularly if random factors keep the population below levels where habitat is limiting. Thus, caution should be applied to model performance expressed in this way which disregards the temporal variability, some of which will be synchronous and some of which will be contained as site-year interaction within the error variance.…”