NONPARAMETRIC MAXIMUM-LIKELIHOOD-ESTIMATION OF MESH SIZE-SELECTIVITY

A nonparametric model for estimating mesh size selectivity is presente d based on a multinomial likelihood for sampling from a mixture of dis crete size classes. No functional form for the selectivity curve is as sumed when comparing the relative selectivity of standard and experime ntal mesh codends. Auxiliary information from the size distribution of fish gilled in the experimental mesh codend is used to identify when the selectivity approaches 1. Analysis is illustrated for Dover sole ( Microstomus pacificus) caught in an alternate haul study. Parametric m ethods of estimating selective curves based on logistic functions show ed tendencies for systematic bias in the tail regions as well. as poss ible errors in the mid-range (approximately 50%) of selectivity.