Estimation of sample zooplankton abundance from Folsom splitter sub-samples

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Abstract
Procedures are described for estimating the abundance of each zooplanklon species in a sample after counting at least two sub-samples from a Folsom splitter. A multinomiai model is assumed for the splitting process. The method may be summarized as follows: two sub-samples, balanced with respect to the left — right splits, are counted. The counts for each species are tested for homogeneity using a x2 test. If the counts are homogeneous, an estimator is given which permits the estimation of the number of animals in the sample, and the variance of this estimate. If the subsample counts are heterogeneous, it is assumed that clumping has occurred. A procedure is described in which additional sub-samples are counted to locate the clump, and estimators of abundance (and variance estimators) are derived. If the splitter bias is <5%, bias of the abundance estimator is negligible compared to the binomial sampling error. Comparisons of species abundance between plankton samples is made more rigorous using the estimates of mean abundance, and the variance of this mean, provided by the methods described here.

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