Here, we give a summary of the technical steps involved in the innovative Scottish pelagic industry-science co-sampling and self-sampling process.

Co-sampling involves collecting frozen samples of herring, mackerel and blue whiting from each haul in a random selection of fishing trips.

Once landed, co-samples are sent to the onshore laboratories at UHI Shetland and the Marine Directorate. The co-samples are then processed to collect length, sex and maturity, and the otoliths (ear bones) are removed for age determination by the Marine Directorate.

This data is entered into the Marine Directorate database and quality checks are carried out on all data. The sample data are used to calculate estimates of the total number of fish caught, and their mean weight, by age and length for each stock, by ICES division and quarter. The required data are then submitted to the ICES assessment working groups following a strict timetable for each species.

An important element is to ensure good spatial and temporal coverage of the samples. Sampling directly from pelagic vessels at sea has enabled more trips to be sampled across the full fleet, including landings abroad, providing greater coverage of the fishery and enhancing the quality of the data used in the stock assessment.

For 2023, percentage of trips sampled for herring was 40%, autumn mackerel 39%, winter mackerel 35%, and blue whiting 35%. The aim over the coming years is to increase these figures to around 50%

For onboard self-sampling where the fish are measured and weighed by crew,  both the number of fish and the number of hauls sampled has greatly increased since the scheme first started in 2018 – for example, 7,882 herring were sampled in 2018 compared to 27,570 fish in 2023. For autumn mackerel, the figure has risen from 6,165 fish to 18,070, and for winter mackerel 4,862 to 17,439 fish.

Whilst not yet incorporated as part of the ICES assessment process, there are hopes it will be in the future, and work is being undertaken toward this aim, as the extent and scope of the sampling provides an extremely useful extra data set. In the meantime, the information collected provides valuable additional biological information.