The index of abundance calculated during the HERAS acoustic survey is one of the key components of the North Sea Herring assessment. Whilst echosounder measurements are the basis of this survey, data needs to be coupled with biological samples in order to obtain the abundance at age estimations.
Because multiple components are merged together during this process, the overall uncertainty calculation is complex. Firstly, the number of biological samples are usually limited and the way these samples are assigned to acoustic data are based on expert subjective judgment. Secondly, whilst sampling uncertainty of the acoustic measurements is accounted for, the effect of several other uncertainty sources such as instrument calibration and use of target strength- length relationship are not well known.
Recently the procedure of coupling biological data with acoustic outputs became more systematic with use of a common software StoX. Developed by IMR (Norway), StoX is a framework consisting of multiple modules. The input acoustic data, length frequency and biological measurements are converted into final estimate of abundance at age/maturity group together with uncertainties. This method however, despite being more systematic and objective compared to earlier methodologies, is different. In order to ensure the consistency in the time series, the effect of transition to StoX, as well as the other unaccounted uncertainties needs to be well understood.
Doel van dit project
Sinds kort is de procedure voor het koppelen van biologische informatie met gegevens van akoestische surveys beter gestructureerd door het gebruik van StoX software. Echter, heeft deze nieuwe methode mogelijk een effect op de continuïteit van tijdsseries. Binnen dit project worden de veroorzaakte effecten onderzocht. Daarnaast wordt de gevoeligheid van de indexberekeningen getest als gevolg van de veranderingen in analyse opzet en vastgestelde variabelen.