ABILITY OF INSTREAM FLOW INCREMENTAL METH ODOLOGY TO PREDICT BROWN TROUT SPAWNING HABITAT

The Instream Flow Incremental Method was applied to brown trout reprod uction, in 205 morphodynamic units of 6 Pyrenees mountain streams. The correlation between Weighted Usable Area (WUA) and redd density was h igher when using a local habitat suitability curve, instead of the sta ndard curve of BOVEE (1978). However, WUA was high in some units with low redd density. This was due to an over-estimation of the WUA in som e types of unit where the gravel taken into account in WUA calculation was scattered between coarse material and thus unusable for trout spa wning. This study underlines the importance of using an aggregation cr iterion when describing the substratum for spawning salmonids.