How the Data are Used
Analysis of the scrutinised acoustic data is standardised, with the same target strength conversion factors being applied (for example TS = 20 log length (in cm) -71.2 for herring). The estimates are split up according to age and maturity using appropriate local age/maturity length keys derived from the trawl samples. Biomass is obtained by applying length-weight relationships also derived from the trawl samples.
Where the Results are Used
The results from the individual acoustic surveys are reported to the ICES Planning Group for Herring Surveys in a standard form, namely abundance in numbers at age, mean weight at age and total biomass. The individual surveys are then combined to produce a total combined estimate which takes into account any survey overlaps.
The combined estimate of numbers at age and mean weight at age are then reported to the ICES Herring Assessment Working Group which use the data to tune the Integrated Catch at Age model which ultimately produces the biomass estimates for the stock.