The effect of different environmental factors on habitat selection by Salmo trutta in Karaj River

Habitat selection is an important factor in predicting the distribution and abundance of species in ecology research or fields. In fish, determination of the habitat selection, especially for endangered, rare, native species or species with discontinuous distribution and sensitive to developmental effects, is an important step in biodiversity conservation of fish and planning for land use. Habitat characteristics of Salmo trutta in Karaj River were determined by analyzing the effects of depth, current velocity, Froude number, substrate index, substrate shelter, visual coverage, combined coverage, and pool in 16 sites with data collection during the years 1395 and 1396 using software HABSEL, and the range and habitat used and selected was defined for this species by the amount of access to each variable. Based on the results, the selected habitats of brown trout in the Karaj River were at depth of 46-52, current velocity of 0.40-0.45 m/s, Froude number of 0.26-0.30, substrate index of 3.4-3.8, substrate shelter of 10-20, visual coverage of 56-64, combined coverage of 17.5-21, and pool of 21-28. Among the variables studied in the Karaj River, Froude number, current velocity, and substrate factors were the most favorable for Salmo trutta. Despite the availability of favorable conditions in some parts of the Karaj River for existing of brown trout, the absence of this species must be due to human disturbances on freshwater ecosystems or extreme climatic changes, such as floods