Norway’s Institute of Marine Research has pushed back against claims in industry media concerning management of mackerel stocks over the last couple of decades, in the light of the ICES revision of methodology for mackerel.
This led to an upwards revision of the size of the historical mackerel population, and industry entities have latched onto this to claim that the mackerel stock is significantly higher than estimated by ICES, and that far more can be fished than the maximum catch recommended by ICES.
Researchers Espen Johnsen and Are Salthaug state that the revised methodology led to an upwards revision of older population estimaes, and the main reason for this was that assumed natural mortality was increased – an adjustment to the population assessment model that was made due to more recent research results.
‘This is how the system works: The advice must necessarily be based on the information available at that time. New knowledge is acquired, the methods are revised and the model is developed. When a new method revision on mackerel is to be carried out in a few years, new, documented knowledge will be evaluated again. Then the current model will again be adjusted and improved. This is a step-by-step knowledge-based process,’ they state.
‘When ICES revised the model last year, the stock estimates back in time were adjusted upwards. There were probably more mackerel in the sea at that time – than we estimated then. But we also saw something else in the new model: It became clear that the supply of new generations, the so-called recruitment of mackerel in the last ten years was much lower than the five years before.’
The researchers state that this is the main reason for the 2013-2022 edcline in the stock – which has also been more heavily exploited than ICES has recommended.
‘Unfortunately, today the status is that the spawning stock is below the critical level, meaning that the reproductive capacity of the stock has been reduced. Fishing pressure over the past three years has also been far higher than what would have produced maximum sustainable yield (FMSY),’ Espen Johnsen and Are Salthaug state.
‘ICES’s advice for 2026 is therefore to reduce the harvest significantly so that the spawning stock quickly rises above the critical level.’
They point out that it’s important to note that the absolute level of the stock does not significantly affect quota advice because the harvest rate (FMSY) is adjusted accordingly.
‘This means that one cannot conclude that one could have fished more back in time even if the historical spawning stock level has been adjusted upwards,’ they say, commenting that the old model tended to underestimate population development, so that the estimates had to be adjusted upwards each year when new data came in, while the new model is more stable and accurate – and all the data points in the same direction as egg surveys, trawl surveys and tag-recapture data all indicate a clear decline in the mackerel population.
