Estimating and decomposing total uncertainty for survey-based abundance estimates of Norwegian spring-spawning herring

A method is developed to quantify the uncertainty of abundance and age-specific abundance estimates of Norwegian spring-spawning herring, accounting for the combined effect of several error sources. We present an abundance estimate adjusted for vessel avoidance, acoustic shadowing, and depth-dependent target strength, and highlight the potentially dramatic combined effect of these adjustments. Uncertainty in this estimate is affected by the precision of the adjustment formulae as well as by the sampling errors in acoustic and trawl measurements. This total uncertainty is decomposed into contributions from each source. Here, the method is applied to data from surveys on the overwintering stock in the Vestfjord system and off Vesteraalen in northern Norway in November/December of the years 2001-2004.