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Visual isolation, habitat complexity, and the density of stream salmonids

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Visual isolation, habitat complexity, and the density of stream salmonids

Dolinsek, Ivan J (2004) Visual isolation, habitat complexity, and the density of stream salmonids. Masters thesis, Concordia University.

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Abstract

The effect of visual isolation on the density of territorial fish such as Atlantic salmon ( Salmo salar ) was examined. Kalleberg's (1958) hypothesis that the density of salmon can be increased by adding boulders was tested for the first time in a natural stream. Eight study reaches were established in Catamaran Brook and the Little Southwest Miramichi River (New Brunswick). Each reach was divided into three sites of 3 x 2 m, and received one of three treatments: boulder-added, 36 boulders (median diameter = 0.21 m) were added to increase visual isolation; boulder-removed, where all boulders were removed; and a control, where the reach was left unchanged. A three-fold increase in the density of salmon was observed in the boulder-added treatment compared to the boulder-removed and control sites. The impact of adding boulders was more important for the young-of-the-year than for the 1+ and 2+ salmon. However, for non-salmonid fishes, no effect was found. A Geographic Information System (GIS) viewshed analysis showed that the visible area and the distance to nearest neighbour were significantly smaller in the boulder-added treatment than in the other two treatments. Although mean water velocity was reduced in the boulder-added treatments, the snout velocity of individual salmon did not differ among treatments, suggesting that the boulders were not used as a velocity refuge. The results support Kalleberg's hypothesis that visual isolation is a key factor controlling salmon density, and that it might be used as a low-cost method for increasing the density of territorial fish.

Divisions:Concordia University > Faculty of Arts and Science > Biology
Item Type:Thesis (Masters)
Authors:Dolinsek, Ivan J
Pagination:x, 85 leaves : ill. ; 29 cm.
Institution:Concordia University
Degree Name:M. Sc.
Program:Biology
Date:2004
Thesis Supervisor(s):Grant, James
ID Code:8339
Deposited By:Concordia University Libraries
Deposited On:18 Aug 2011 14:22
Last Modified:18 Aug 2011 15:35
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