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

Abstract

We demonstrate how the total uncertainty of the abundance estimate and abundanceat- age estimate of Norwegian spring-spawning herring are affected by uncertainty in the parameters of vessel avoidance, shadowing and depth dependent target strength, and uncertainty from trawl hauls and spatial-temporal coverage. The total uncertainty is decomposed into the sum of the contribution from each source separately. In addition, we highlight the potentially dramatic combined effect of correcting for vessel avoidance, shadowing and depth dependent target strength on the abundance estimate. The main framework is believed to be a promising tool for focusing the effort for reducing the uncertainty in the abundance estimates. The method is applied to data from surveys on the over-wintering stock in the Vestfjord system and Vesteraalen in northern Norway in November/December in the years 2001–2004