Reducing uncertainties in Baltic herring and sprat abundance estimates: Alternative approach to acoustic analyses

Hydroacoustic studies using acoustic measurements combined with biological data obtained from trawl hauls remain a challenging task. The main purpose of the present study is to identify sources of uncertainty and compare the calculation methods for a mixed pelagic fish community of Baltic Sea. Most of the calculation methodologies use conventional statistical borders to split the study area, ignoring the possible natural population distribution areas. We compared the proposed “nearest haul” and the “subdivision average” with the conventional “rectangle average” on the Estonian regular acoustic surveys in the northeast Baltic Sea. The abundance estimates of the target species – European sprat Sprattus sprattus (Linnaeus 1758) and Baltic herring Clupea harengus membras (Linnaeus 1758) – with the “nearest haul” were significantly different from the currently used method, which indicates a strong effect of the allocation method. Our results indicate a need for a large scale comparative study to consider alternative calculation methodologies.