The statistical design of comparative fishing experiments

Experimental designs for alternate tow gear experiments are described and evaluated, considering situations with and without randomized complete blocks. Variance components relevant to the performance of these designs are identified, and a method for estimating them is presented and applied using data for the Pacific multispecies groundfishery. The aim of the Pacific experiment was to estimate the magnitude of changes in fish length for various species and total tow catch value due to changes in cod end mesh size. Alternative experimental designs are compared with regard to the sample sizes needed to reject the null hypothesis that there is no treatment effect. For the specific application examined, there is a 4-10-fold reduction in sample size when randomized complete blocks are used within a vessel trip, compared with an unblocked experimental design using only one treatment type per vessel trip.