Embryo survival and alevin emergence of brook charr, Salvelinus fontinalis and brown trout, Salmo trutta, relative to redd gravel composition

Effects of three homogeneous gravels (2.7, 6.2 and 9.2 mm in diameter) and five heterogeneous gravel mixtures (with 0, 20, 40, 60 and 80% sand; geometric mean diameters = 14.2, 10.1, 7.2, 5.1, 3.7 mm, respectively) on embryo survival and subsequent emergence of brook charr (Salvelinus fontinalis) and brown trout (Salmo trutta) were examined in the laboratory using vertical flow incubators. Differences in survival to emergence, temporal components of emergence and developmental stage of emergents are significant among gravel types within and between species. Alevin survival, time interval to first and 50% emergence and duration of emergence period vary directly with gravel size and inversely with sand concentration. Survivals of 0 to 20% occurred in unigranular gravels 6.2 mm or finer and in multitextured gravels with 60% or more sand and rates of 60 to 96% were found in 9.2-mm gravel and gravels with 20% or less sand. Emergent survival increased from 14 to 79% in gravels of 6.2 to 9.2 mm and from 2 to 96%...