A new quantitative plankton net

Abstract

The apparatus described in this paper was constructed for the purpose of sampling the zooplankton standing crop in the ocean in a quantitative manner.A meter is described, which will record both the depth and amount of water which a net filters as it is hauled vertically through the water. The meter records on a smoked glass cylinder.The meter is mounted in a brass drum which is positioned in front of the silk filtering section of the net. In front of the meter a long canvas sleeve carries the throttling rope which closes the net by the Nansen method.Calibration of the meter for depth is done by using reversing thermometers and lowering to a series of suitable depths. Flow calibration is easily accomplished in the field by towing the canvas sleeve and meter without the silk net.The method of smoking the glass cylinders and taking photographic records of them is described.From the records it is possible to study the complete behaviour of the net below water—what depth range it has fished, how much clogging occurred, the depth of closure, etc