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Laboratory studies have not duplicated the structure and composition of egg pocket centrums in redds of large salmonids, and thus have not accurately modeled survival of embryos and alevins in natural egg pockets. Field studies of capped natural redds have related survival to conditions in the redds or surrounding areas but not demonstrably in egg pockets. These data probably do not accurately reflect conditions faced by embryos or emerging alevins. The few data on egg pocket characteristics indicate that geometric mean particle diameter, fredle index, and permeability are higher in gravel surrounding the embryos than elsewhere, Survival to alevin emergence usually regresses positively on each of these factors separately and on dissolved oxygen in intragravel water. Survival to emergence usually relates negatively to percentages of small fines. Quantitative predictors depend upon careful definition of egg pocket structure through field surveying of egg pocket centrum locations and on intensive study of pocket conditions. Laboratory duplication of egg pocket structure and physical variables will permit more accurate modeling of effects of fines on survival to emergence. Redd capping in natural redds can provide estimates of survival to emergence, which one may relate to average egg pocket conditions and to variates in the redd. After appropriate modeling, it may become possible to relate conditions outside of the egg pocket to the environment within it and to survival-to-emergence.
D. W. Chapman (Fri,) studied this question.