Spatio-temporal simulations for assessing the optimality of the Heras survey design and calculation methods (KB-36-002-038)

The survey results depends on the design and selected methods. While it is very important to maintain consistency over the long time series  it is also necessary to revise these factors periodically and ensure that the most relevant properties of the fish stocks are well represented in the survey design and calculation methods. This project will focus on the HERAS, the North Sea Herring survey, for improvements in the accuracy and precision. Target strength, being length-dependent specie-specific acoustic value, maybe affected by the depth-dependent compression of the swim bladder. Even though the results of such studies indicate some significant changes, this effect generally disregarded within the routine survey calculations to avoid complexity. The aim of this project is to understand and account for the target strength variability of the North Sea herring stock focusing on the fact that larger/older fish move northwards/ deeper waters.