Application of the Rayleigh distribution to size selectivity of small prawn pots for the oriental river prawn, Macrobrachium nipponense

The design feature of pot entrance may affect the number and size distribution of trapped prawns. The selection process of the entrance was studied. To identify how the design feature of the funnel affects the selection process for the body length (BL), a series of tests was carried out using model pots without bait in the south-basin fishing ground of Lake Biwa, Japan. The size of trapped prawns fits a Rayleigh type distribution. The mean value of the top one third of all the individuals BL1/3 when arranged in ascending order could be used as the principal index to evaluate the selectivity of the entrance.The results suggest that in a small pot used here, the selectivity seems likely controlled by both the pot neck height and opening diameter. (C) 1998 Elsevier Science B.V. All rights reserved.