Midwater trawl catchability in relation to krill and possible ways of assessing gross catch
Research into midwater trawl catchability rates was carried out on the basis of data obtained from AtlantNIRO expeditions from 1983 to 1990 in the Scotia Sea. A methodology was developed for and applied to determining the rate of krill filtration through the trawl rope and netting and also the probability that krill will come into contact with various parts of the net as it passes through the trawl sides. Studies were based on the results of 250 hauls made with a 72/308 trawl. Catchability was worked out with the aid of fine-meshed chafers, hydroacoustic methods and theoretical calculations. A comparison of the experimental hydroacoustic assessment with the calculated one demonstrated that the theoretical model agreed well with the real situation. Analysis of the efficiency of midwater trawls in the krill fishery indicates that the potential exists for this efficiency to be increased.