A new method of determining the efficiency of towed plankton samplers

In recent years interest has increased concerning the accuracy with which collections made with plankton samplers describe the size and species composition of zooplanktonic communities. The indications are that errors arising from the avoidance of sampling devices by zooplankton may be important, especially when precise data are required. A model is proposed to describe the processes by which zooplanktonic organisms escape or avoid a sampler in terms of the radius of the mouth of the sampler, the speed at which it is towed, the effective speed the organisms can attain in order to escape, and the distance at which the organisms can detect the sampler. The model is capable of being fitted to field data to provide a curve of percentage catch plotted against speed of towing. The results presented indicate that the model gives a good representation of the processes of biological escapement. Implications of the results are embodied in recommendations respecting the design of plankton samplers.Science, Faculty ofZoology, Department ofGraduat