Evaluation of Inventory Procedures for Hatchery Fish. I. Estimating Weights of Fish in Raceways and Transport Trucks

Abstract Techniques and sources of error in estimating size and numbers of fish in hatchery raceways and on transport trucks were examined at three Oregon hatcheries and with three species of salmonids (Oncorhynchus spp.). The greatest source of error in determining fish size depended upon the number of individual samples taken from a raceway. Error also varied with percentage of the population sampled, but the correlation between error and percentage of population sampled was not as great as that between error and the number of samples taken. Samples of 6.4 kg did not show better precision than samples of 2.5 kg. Variability in fish size seemed to affect the minimum error associated with estimates offish size. From these studies, we suggest that errors in fish size of 2–5% are common. We recommend that seven to nine random samples be taken to attain an acceptable level of error in size estimates.