Evaluation of the design and efficiency of the Norwegian self-sampling purse-seine reference fleet

Abstract

A self-sampling reference fleet is employed by the Institute of Marine Research to estimate the characteristics of the Norwegian commercial catch for a number of species. The reference fleet is composed of commercial fishing vessels that are paid to measure a subsample of fish from selected catches and, less frequently, to take and preserve otolith, stomach, and genetic samples. In this study, the sampling design for monitoring the catches of herring, mackerel, and blue whiting used by the recently established purse-seine segment of the reference fleet is evaluated. The precision of the estimated mean lengths, and hence that of the estimated length distributions of the entire commercial catch, was bounded by the number of boats in the purse-seine reference fleet. Therefore, the only way to improve survey precision significantly is to increase the number of boats in the reference fleet. In addition, the effective sample sizes were much smaller than the total number of fish measured, from which it followed that too many fish were measured in each selected catch. Based on this analysis, the prescribed number of fish sampled from each selected catch has been reduced by more than 50%. © 2011 International Council for the Exploration of the Sea.