Guest blog: Risks to North Sea fish stocks and wildlife if post-Brexit fisheries negotiations go awry

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This guest blog from Prof Michael Heath and Dr Robin Cook from the University of Strathclyde summarises a report on modelling the consequences for the North Sea of post-Brexit fisheries negotiations failing to reach agreement. It is part of a series of guest blogs exploring issues related to the recent SPICe briefing ‘UK-EU Future Relationship Negotiations: Fisheries’.

As with all guest blogs, what follows are the views of the authors, not those of SPICe or indeed the Scottish Parliament.


The principles of ‘Relative Stability’ and ‘equal access’ are central to the EU Common Fisheries Policy (CFP). Relative Stability is the formula by which the Total Allowable Catch (TAC) for each fish stock is shared between EU Member States as ‘quota’ allocations. TACs may fluctuate from year to year based on scientific advice, but the proportion assigned to each state stays the same, subject to a degree of horse-trading. The principle of equal access is that all EU registered fishing vessels are allowed to fish throughout all EU waters, at least beyond 12 miles from the coast, and subject to vessel’s owning a landing quota for any given species.

The departure of the UK from the EU may throw the principles of Relative Stability into disarray. In some cases, other Member States, and third countries like Norway who have access agreements with the EU, have relied heavily on being able to fish in UK waters to sustain their catch rates. In addition, Relative Stability awards only a small fraction of the TAC for some species to the UK, while a high proportion of the TAC that is landed comes from UK waters. Unless agreed otherwise, Member States’ automatic right of access will cease at the end of the transition period on 31 December 2020.

The UK Government has indicated that regaining control over UK waters and obtaining a greater share of the TACs are red lines in the transition negotiations. Conversely, the EU has linked access to UK waters with securing a tariff-free trade deal. As a result, there is a reasonable prospect that the UK and EU will not be able to reach an agreement, even on a procedure for agreeing quotas, by the end of June 2020, which is the time-scale set by the ‘Political Declaration‘. In that case, the next deadline is in December 2020, when TACs are routinely agreed for the following year.

The United Nations Convention on the Law of the Sea (UNCLOS) requires coastal states to cooperate in the management of shared fish stocks. However, it does not prevent states from unilaterally setting catch limits within their own Exclusive Economic Zone (EEZ) if no agreement is reached – provided these are consistent with ensuring that stocks as a whole are protected from overexploitation.

The problem is that the UK and EU are not disputing the TACs, but rather the Relative Stability share assigned to each state; in other words, the UK generally does not disagree with the decision-making process for the overall amount that can be caught for each stock, but is concerned with how this total is divided between the countries. Allocations based on Relative Stability are based on historic shares of landings. In contrast, the UK maintains that ‘zonal attachment’ is a fairer basis for sharing the resource – zonal attachment is a measure of the proportion of stock biomass which resides in a given EEZ and is estimated from scientific surveys. 

In the event that the UK and the EU cannot reach an agreement on the principle for dividing shares among states, a scenario could emerge where the UK sets catch limits within its waters based on zonal attachment and excludes EU vessels from fishing there, while the EU Member States maintain their right to catch their existing Relative Stability share but from their own waters. In this scenario, if neither party yields or no compromise is reached, stocks face being over exploited. There is a clear precedent for this scenario in an ongoing dispute between states involved in the North East Atlantic mackerel fishery (see SPICe briefing on mackerel).

Modelling the consequences of unilateral quota setting

In our recently published report (with an extended technical version available here) we describe plausible story-lines for unilateral quota-setting by the EU and Norway on the one hand, and the UK on the other, based on zonal attachment estimates for fish stocks in the North Sea. The narratives indicate a 4-fold increase in UK expectations for North Sea herring catch, 3-fold for saithe and sole, and smaller expectations for other species.

These translate into a 70% increase in international herring catch over and above the recommended TAC, and a 60% increase in pelagic trawling activity. Corresponding increases in international catches of demersal fish (cod, haddock, whiting) and demersal trawling activity of up to 10% are anticipated.

Two completely different mathematical models were then used to simulate the consequences of the above scenarios for fish stocks and the marine food web following the onset of the unilateral approach to deciding fisheries quota described above.

Model 1

The first model was a single species stock projection model. It calculated the probability of the total weight of fish in a given stock (‘spawning stock biomass’) falling below the precautionary reference level (referred to as ‘Bpa’) for seven key stocks (herring, cod, haddock, whiting, saithe, plaice, sole) (see chart below).

Stock biomass falling below Bpa is a warning signal which triggers the International Council for the Exploration of the Sea (ICES) to recommend reductions in fishing in order to conserve the stock (see SPICe Blog – How are fishing quotas set? Stage 1: Scientific advice).

Model 2

The second model simulated the whole food web in the North Sea, from bacteria to whales, but as aggregated groups of similar types of microbes, plants and animals rather than as individual species.

The two modelling approaches produced similar conclusions on the likely risks associated with unilateralism. They both showed that the greatest risk is to stocks of plankton-eating pelagic fish, especially herring. Risks to demersal fish as a whole are smaller, but within this group there is a significant risk to cod stocks.

Among the indirect consequences of unilateralism are declines in cetaceans (whales, dolphins and porpoises) and seabirds as a combined consequence of reductions in their main food supply (pelagic fish) and increased fish mortality due to by-catch in fishing gear (nets and other fishing equipment).


The report is not a prediction of exactly what will happen if talks fail to reach an agreement. Rather it indicates the direction in which fish stocks and the ecosystem may move if unilateralism takes over from cooperation. It identifies the features which are most at risk in the North Sea, and which negotiators need to be aware of in their deliberations.

Prof Michael Heath and Dr Robin Cook

Department of Mathematics and Statistics, University of Strathclyde

Title image by Tony Tang on Unsplash