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

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Abstract
Effects of 3 homogeneous gravels (2.7, 6.2 and 9.2 mm in diameter) and 5 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 (S. fontinalis) and brown trout (S. 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 (P .ltoreq. 0.05) among gravel types within and between species. Alevin survival, time interval to 1st and 50% emergence, and duration of emergence period vary directly with gravel size and inversely with sand concentration. Survivals of 0-20% occurred in unigranular gravels 6.2 mm or finer and in multitextured gravels with 60% or more sand, and rates of 60-96% were found in 9.2-mm gravel and gravels with 20% or less sand. Emergent survival increased from 14-79% in gravels of 6.2-9.2 mm, and from 2-96% in sand concentrations between 60 and 20% because of reduced entrapment. Period of emergence was longest in 9.2-mm gravel (mean for charr, 381 days degrees; mean for trout, 423 days degrees) and in 0% sand-gravel mixture (mean for charr, 232 days degrees; mean for trout, 179 day degrees). Premature emergence of alevins over a shortened emergence period in finer gravels is identified as a stress response. Larger gravel and lower sand concentrations produced the largest and most advanced alevins at emergence. Ecological implications of the results are examined.

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