Abundance estimation of Northeast Atlantic mackerel based on tag recapture data—A useful tool for stock assessment?

In the present study we utilize tag recapture data to estimate year class abundance and spawning stock biomass of mackerel (Scomber scombrus L.) in the Northeast Atlantic for the period 1986–2008. On average 20,000 jigged mackerel have been tagged annually with internal steel tags in the spawning area west of Ireland and the British Isles, and the tags have been recaptured in commercial catches screened through metal detectors. The spawning stock biomass estimates derived from two different tag-based models were highly variable but were on average 2 and 2.3 times higher than the ICES official estimate. The official estimate is considered uncertain and most likely an underestimate of the actual biomass, due to unregistered mortality in the fisheries and lack of fishery-independent, age-disaggregated data. Hence, tag-based estimates could potentially improve the current assessment if included in the ICES stock assessment on a regular basis. These estimates also involve some uncertainty that needs consideration, especially related to variable tagging mortality, detector efficiency and migrations of the stock.

Research highlights▶ Tag recapture data indicate a substantially larger SSB than the ICES assessment. ▶ Uncertainty due to unreliable catch data is avoided in one of the tag models. ▶ Main uncertainties are tagging survival rate and detector efficiency. ▶ The estimates could be of great value and maybe included in the stock assessment.