The Validity of Single Vertical Hauls of the International Net in the Study of the Distribution of the Plankton

Abstract

In both the series of hauls made for the purpose of estimating the reliability of a single haul of the International Vertical Net, the possibility that the variation in the size of catch of successive hauls is due to errors of the methodique has been examined. Errors due to variations in the speed of hauling, and to the effect of light and darkness on the catch of the net can be ruled out. The enumeration error, even where the enumerated total rests on a single count, is insufficient to account for the major part of the variations found, and, having regard to the fact that such totals were derived from two, and sometimes more, separate “counts” from each sample, there is good reason to believe that the main cause of variation in the size of catch is to be sought elsewhere, the most likely being the lack of uniformity in the distribution of the organisms themselves.