EVALUATION OF INVENTORY PROCEDURES FOR HATCHERY FISH .1. ESTIMATING WEIGHTS OF FISH IN RACEWAYS AND TRANSPORT TRUCKS

Techniques and sources of error in estimating size and numbers of fish in hatchery raceways and on transport trucks were examined at three O regon hatcheries and with three species of salmonids (Oncorhynchus spp .). The greatest source of error in determining fish size depended upo n the number of individual samples taken from a raceway. Error also va ried with percentage of the population sampled, but the correlation be tween error and percentage of population sampled was not as great as t hat between error and the number of samples taken. Samples of 6.4 kg d id not show better precision than samples of 2.5 kg. Variability in fi sh size seemed to affect the minimum error associated with estimates o f fish size. From these studies, we suggest that errors in fish size o f 2-5% are common. We recommend that seven to nine random samples be t aken to attain an acceptable level of error in size estimates.