Below the critical limit

Wageningen Marine Research contributes to international research on mackerel stocks by collecting independent data at sea. For example, Wageningen researchers participate in mackerel egg surveys, coordinated by the International Council for the Exploration of the Sea (ICES). They also work with the fishing industry to combine scientific monitoring with data collected on board fishing boats. This collaboration provides accurate insight into the size and dynamics of the mackerel stocks. 

Other countries are conducting similar surveys on fish stocks. All data flow through to ICES. "ICES is an international scientific platform, not only for the fishing industry, but also for aquaculture, the environment and oceanography," Brunel explains. On behalf of the Netherlands, he is a member of ACOM, the ICES advisory body that draws up catch advice. Its advice shows the scientifically recommended amount of catch per species to ensure that the species can be managed sustainably.

The total allowable catch (TAC) for mackerel for 2026 is expected to be substantially reduced. This means that every EU member state must limit its own mackerel fishing quotas in line with the advice. Which is badly needed, argues Brunel: "Only stopping overfishing will bring any hope of recovery."

When Brunel started as a research associate of fish stocks at Wageningen Marine Research in 2008, mackerel stocks were low but rising rapidly. "That was due to the sudden recruitment of many young fish. We don’t know how that came about, but the environmental conditions were probably good at the time."

That increase continued until 2014. After that, the mackerel fish stocks rapidly went downhill. Overfishing by the fishing industry appeared to be the main cause. And now the total biomass of mackerel is below the limit that scientists have been warning about for some time.

According to Brunel, climate change may have contributed to the mackerel habitat expanding northwards in summer. A second cause of expansion may be that the mackerel needed more habitat in which to feed in the years when numbers increased. Now that mackerel have declined sharply in numbers, the need is no longer there. He feels that this may explain why there are hardly any mackerel in Icelandic waters these days and none near Greenland.

Reducing EU quotas alone will not help, Brunel emphasises: "Mackerel is not an ‘EU-only’ species, but is also managed by the UK, Norway, Faroe Islands, Iceland and Greenland. The EU is negotiating catch quotas with the other managers, but there is no agreement. As a result, non-EU countries unilaterally set quotas that, when added together, have far exceeded the scientifically justifiable limit for years."

Brunel feels that the lack of joint management has been leading to overfishing since 2011: 40 percent above the level that allows for sustainable management. He says the solution is simple: all countries with waters in which mackerel swim, from Portugal to Iceland, should follow the scientific advice issued by ICES. "The perception of the fishing industry often differs from ICES advice. But with all the indicators pointing to a decline in mackerel stocks, the industry in almost all countries is aware that the situation is bad." 

In fact, EU countries are very critical of non-EU countries that override the scientific advice of ICES: The French fishing industry is calling on the EU to act against overfishing by non-EU countries. "It is crucial that all countries agree on an allocation in line with ICES advice," Brunel argues: "It is in everyone's interest that mackerel have a chance to return to the level that allows for sustainable management. Without intervention, stocks will not recover to the level that makes fishing possible. But if countries follow the advice, there is every reason to expect that sustainable mackerel can be caught again in the long term."

Could the peak between 2008 and 2014 be repeated in subsequent years despite overfishing? Brunel suspects that such overfishing has had a structurally negative impact: "One hypothesis we are exploring is that of social learning: old fish showing young fish the way. If the older year classes are totally depleted, the population may lose or shift its collective migration behaviour. This could partly explain why there are far fewer mackerel near Spain these days." 

Is the ICES system flexible enough to incorporate the effects of climate change in its advice? "We still don’t fully understand the exact impact that climate change is having on mackerel. It is therefore impossible to make recommendations for sustainable management that anticipate future changes. However, ICES does not ignore the fact that the environment is changing and that this affects fish stocks. For that reason, ICES regularly reviews the management objectives for each stock to take into account recent changes in their productivity. This includes mackerel."  

Meanwhile, mackerel is still marked red in the Fishing Guide, the MSC quality label has not appeared on packaging since 2019, and supermarkets have pulled the fish from their shelves. Without more favourable years with substantial recruitment of juvenile mackerel, Brunel says we will not get back to the stock of 10 years ago. "However," he argues, "if national policy makers follow the recommended quotas, it is possible to return to the 'green' state."

It is now up to politicians, he concludes: "The ICES advice has already been significantly reduced. We will see whether the other countries also decide that things really have to change now." 

• ICES