A reassessment of the North-East Atlantic mackerel stock going back more than a decade indicates that mackerel has not been significantly overfished – as has been claimed – now that past stock assessments have been revised significantly upward.
ICES states that its 2025 benchmarking has ‘resulted in an upward revision in the estimated stock size and downward revision in fishing mortality, mostly because of the new natural mortality assumption, and a corresponding revision to biomass (upwards) and fishing mortality (downwards) reference points.’
Compared to the figures from the 2023 assessment, this would indicate that the extent of the mackerel stock has been systematically underestimated by many millions of tonnes.
‘In a nutshell, this means that the stock has been much larger than had previously been believed,’ points out Icelandic MP and biologist Sigurjón Thórðarson.
‘This doesn’t come as a surprise to those who have been following the ICES advice over the past years. The stock assessment has a weak basis, including counts at intervals of several years. This assessment has been severely criticised for decades by respected scientists such as Jens Christian Holst in Norway.’
He makes the point that the mackerel stock was not over-exploited, as had been claimed, and in fact has been under-exploited at its peak by as much as 1.4 million tonnes. He also points out that the stock declined rapidly from 2014 onwards, despite this under-exploitation – indicating that the effects of fishing on the mackerel stock have been substantially over-estimated.
‘Now that a mackerel treaty is being agreed, surely this should include a proviso that advice is the basis of allocated catch levels. This is clearly based on guesswork, and the basis of advice is being constantly re-appraised,’ Sigurjón Thórðarson said.
‘It’s essential that the government makes itself aware of this regular retrospective ‘re-examination’. More attention should be paid to the condition of fish, including weight, in formulating advice instead of relying almost exlusively on calculation of the number of indivudual fish. Such assessments are highly uncertain and are based largely on guesswork.’
