Workshop on the evaluation of NEA mackerel stock components (WKEVALMAC, outputs from 2023 meeting)

The objective of WKEVALMAC was to review information on stock identification of NEA Mackerel and develop a consensus understanding of the Atlantic mackerel population structure and key uncertainties. The data and studies covered the distribution and movements of different life-stages of mackerel, including changes over time. The evaluated data and studies centred on genetics, tagging, otolith approaches; egg and larval dispersal models; commercial landings and perceptions from the industry. The motivation was the continued consideration of the mackerel stock consisting of three ‘components’ and the advice sheet referring to separate recommendations for at least one of the ‘components’ (the North Sea). The workshop found that spatial and temporal patterns in demography (e.g. size and age) of NEA mackerel are not due to separate components but rather are primarily related to the highly migratory and dynamic nature of a single stock. Recent directed genetics, tagging, otolith chemistry investigations; ongoing surveys; catch data; fisher perspective; and preliminary modelling studies all failed to support the three-component concept for NEA mackerel. The Workshop therefore rejected the current three-component structure and accepted a single NEA mackerel stock concept to advance towards assessment, management, and advice. The workshop therefore recommends that the current ‘headline advice’ based on a single-stock assumption should continue and the advice sheet should discontinue reference to components within the Northeast Atlantic Mackerel stock. The workshop also raised a number of data gaps and uncertainties which can be addressed with future research. These included: improvements to existing survey and catch data programs to enhance our understanding of the spatial and temporal dynamics of the NEA stock, investigations in to how indeterminant spawning interacts with migration behaviours in the annual egg production estimates, and exploring assessment model sensitivity to parameter values and model configuration given the non-stationarity in this stock.