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An analysis of variation in quantitative sampling of bottom fauna in lakes Northcote, Thomas Gordon

Abstract

Transformation of counts and weights of bottom fauna to either logarithims or square roots was required before application of statistical analyses. Preliminary analyses indicated that variability associated with relatively restricted sampling in a large lake prevented reliable evaluation of the bottom fauna while variability evident in extensive sampling from a large lake was not so great as to prevent reasonably precise estimation of abundance. Further analyses showed that the degree of variability was affected by regional location, depth, changes in abundance of the fauna, and qualitative composition of the fauna. Examination of factors contributing to sampling variability showed that operation of the Ekman-Birge dredge, distinction and delimitation of sampling zones in respect to depth and bottom substrate, diurnal and seasonal changes, and the size of samples all were of importance. The use of Ekman-Birge dredge with more powerful jaws in conjunction with more rigorous horizontal and vertical stratification of sampling was suggested as a means of reducing extreme variability in sampling. A 70 per cent sodium silicate solution was found to provide an effective separation of bottom organisms from certain types of substrate. Predation by fish was suggested as responsible for the significant littoral minimum evident in abundance of bottom organisms in Hatzic lake.

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