North Sea cod should never have been labelled sustainable in the first place

Earlier this week the certificate of sustainable status for North Sea cod was suspended by the Marine Stewardship Council. And yet just two years ago cod stocks were heralded as having recovered and the coveted certificate of sustainability was awarded. How could the fortunes of this fish have changed so quickly? The simple answer is that North Sea cod had never recovered, leaving serious questions about both the science and management of the stock.

The most recent analysis of the stock by the International Council for the Exploration of the Sea (ICES) – the body that provides official scientific advice to governments – shows that cod declined almost continuously from the 1960s until the early 2000s.

A cod fishing boat in the North Sea. Shutterstock

During this period fishing removed about 40-60% of the stock each year, a removal rate that was clearly unsustainable. But this percentage dropped dramatically around 2007 and the stock began to recover. This change occurred because controls on catches improved and the number of trawlers declined.

To strengthen management of the stock, the European Commission introduced a Cod Recovery Plan that included further reductions in catches, additional controls on the number of days that cod trawlers could spend at sea, and where they could fish.

Calculating sustainability

Scientists and fishery managers judge the sustainability of a stock by its size, measured as the total weight or “biomass”, and the percentage of the stock removed by fishing each year. A limit is set on the minimum biomass of adult fish in the sea – called the “spawning stock biomass” (SSB) – that ensures enough young fish can be produced to replace those that are caught.

Managers try to keep the SSB above 150,000 tonnes, and restrict the removal rate to below 25%. The most recent assessment by ICES estimates the SSB to be barely half the minimum level, with a removal rate nearly double the maximum limit – a situation that is almost certainly not sustainable.

When the cod stock was awarded its MSC certificate of sustainability, ICES estimated the SSB in 2016 to be 161,000 tonnes with a removal rate of about 29%, so it was believed to be well above the minimum stock size with a removal rate only slightly above the maximum. At this point, in 2017, acting on ICES’ advice, the European Commission dropped the cod recovery plan, abandoning days-at-sea controls and raising limits on allowed catches which undoubtedly has contributed to the present problems.

But if we look at the latest ICES assessment of the stock, it also shows that the SSB in 2016 never rose above the minimum as was thought, but was actually 22% below it. The changed perception has arisen in retrospect because new, detailed data collected across ten cod age groups since 2016 shows there must have been fewer fish than was previously thought.

On top of this, the removal rate was well above the maximum. So now ICES has revised its earlier estimates, showing that the cod recovery plan should never have been abandoned and that the evidence on which the MSC certificate was granted was itself unreliable. The stock had never fully recovered.

Science got it wrong

When fish stocks decline it is commonplace to blame the fishing industry for greedily over-exploiting stocks or for managers to be criticised for not heeding scientific advice. The changing environment, particularly the warming of the oceans, is also cited as a cause of decline.

Over-exploitation has undoubtedly occurred and managers must take responsibility for weak action in the light of clear evidence of chronic over-exploitation. We also know that cod is a cold water species likely to suffer as a result of ocean warming resulting in fewer young fish being spawned.

But we should not lose sight of the weaknesses in the scientific evidence that led the European Commission to end the cod recovery plan. With hindsight, the earlier analysis was over-optimistic and resulted in a poor management decision which in turn has aggravated the problems for the stock.

Back in 2017, the science underpinning estimates of cod stocks in the North Sea got it wrong.

When calculating safe limits for cod and the rate at which they are fished, ICES takes into account uncertainty in the stock size estimates. What is clear from the North Sea cod experience is that the scientific analysis is far more uncertain than is believed. This means that scientists need to better understand the robustness of their assessments and that managers should be far more aware of the limitations of the technical advice they receive and act in a more precautionary manner.

The outlook for North Sea cod is poor. The typical number of young fish being produced each year is at an all-time low and will not sustain large-scale fishing in the long term. While the environment is a likely factor in its decline there is a need for all involved – fishers, managers and scientists – to raise their game and ensure a sustainable future.