APPLICATION OF THE RAYLEIGH DISTRIBUTION TO SIZE-SELECTIVITY OF SMALLPRAWN POTS FOR THE ORIENTAL RIVER PRAWN, MACROBRACHIUM-NIPPONENSE

The design feature of pot entrance may affect the number and size dist ribution 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 carr ied out using model pots without bait in the south-basin fishing groun d 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 individu als BL1/3 when arranged in ascending order could be used as the princi pal index to evaluate the selectivity of the entrance.The results sugg est that in a small pot used here, the selectivity seems likely contro lled by both the pot neck height and opening diameter. (C) 1998 Elsevi er Science B.V. All rights reserved.