IBTS otolith sampling scheme (KB-24-005-004)

Project: LNV project

Project Details


The international bottom trawl survey (IBTS) collects otoliths of fish for the determination of age-at-length keys(ALK). The current sampling scheme is under debate due to high number of otoliths required and recent studies have shown improved statistical techniques requiring smaller number of otoliths for estimating the ALK. Prior to this project it was proposed to collect the otoltihs by station rather than large spatial areas, this would allow incorporation of spatial aspects in the estimation of the ALK. Unfortunately, not all countries followed this approach making the current data unsuitable for the incorporation of spatial aspects required for reducing the number of otoliths. Without the inclusion of spatial aspects the analysis based on bootstrapping a reduced number of otoliths from the whole fish population comparing it with the current method, showed that a reduction in number of otoliths would increase the uncertainty in estimating the ALK. Therefore, a reduction in otoliths cannot be proposed at this moment. It is however proposed to continue the station-specific sampling without reducing the number of otoliths. The station-specific sampling would allow redoing the analysis incorporating spatial aspects next year. This project already provided the codes for doing the analysis within the timeframe of the regular IBTS working group.

Effective start/end date1/01/1631/12/16


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