How are fishing quotas set? Stage 1: Scientific advice

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The arrival of Autumn sees the start of the annual cycle for negotiating and setting quotas for fish stocks. This process will determine how much fish the Scottish fleet can catch in 2019. To shed some light on the process, SPICe will be publishing a series of blogs explaining the process, focussing on key stocks important to the Scottish fleet. These steps are summarised in the image below. This post begins with the role of scientific advice.


Who provides scientific advice and why?

The International Council for the Exploration of the Sea (ICES) is the main organisation responsible for issuing scientific advice on fish stocks in the North Atlantic region. ICES was established in 1902 and is the world’s oldest intergovernmental marine science organisation.

Scientific advice is provided to underpin several international agreements and policies regarding the management of the exploitation of living marine resources. This includes the Common Fisheries Policy under which UK fisheries are currently governed. The United Nations Convention on the Law of the Sea (UNCLOS), also calls for a Maximum Sustainable Yield approach to managing fisheries (Article 119).

How is the Maximum Sustainable Yield determined?

ICES define its interpretation of Maximum Sustainable Yield as “maximizing the average long-term yield from a given stock while maintaining productive fish stocks within healthy marine ecosystems.”

In practice, the process of determining the Maximum Sustainable Yield (MSY) is challenging due to dynamic nature of marine ecosystems and pressure on stocks from fishing activity. Stock assessments use a range of data feeding into models to take into account a wide range of factors such as growth rates, historic stock and recruitment relationships, fishing and natural mortality patterns.

The first step ICES take in formulating advice is to calculate each stock’s spawning stock biomass, which is the combined weight of all individuals in a fish stock that are capable of reproducing. ICES also use surveys to estimate recruitment, which is the number of juvenile fish reaching a size or age to be caught. Another important component is the death rate of each species from both fishing and natural mortality.

ICES then calculate stock specific biomass reference points which act as “signposts” alerting fisheries managers as to whether a given stock is in good or bad health.

A key reference point is the MSY Btrigger. If the spawning stock biomass falls below this reference point, ICES advises fishing less than the Maximum Sustainable Yield. This aims to keep stocks at a level that will support maximum sustainable yield for future generations.

For a more detailed summary, ICES provide a full description of its process and approach to setting advice on the principle of Maximum Sustainable Yield.

Case study: 2019 advice on mackerel

Scientific advice on catch limits can sometimes be controversial, particularly for high value stocks such as mackerel. Mackerel is the most valuable stock to the Scottish fleet, accounting for 29% (£162m) of the total value of Scottish landings last year.

On 28 September, ICES published its latest advice for Northeast Atlantic mackerel. It advised that catches in 2019 should be no more than 318,403 tonnes, a 42% reduction on the previous year’s advice (550,984 tonnes).

ICES state that the reason for the reduction is due to “downward revision of the spawning stock biomass (SSB) compared to last year’s assessment due to high fishing pressure and below average recruitments”. The SSB was assessed as being below MSY Btrigger, prompting ICES to advise a catch limit below Maximum Sustainable Yield.

The ICES advice acknowledges uncertainty in its assessment of stock size due to the inclusion of new tagging data and because data on recruitment was not available in 2016 and 2017.

A response to the advice issued by the Scottish Pelagic Fisherman’s Association (SPFA) indicates that the advice may be taken with a pinch of salt:

“There is considerable uncertainty over the accuracy of this year’s scientific assessment due to a number of factors, including concerns over how the assessment model uses data from tagged mackerel, which has pulled down the calculated Spawning Stock Biomass figure.

Tagged mackerel data has only been used in the assessment process in recent times, and because its data shows a much higher biomass reduction, it is at odds from other data in the scientific process and throws doubt on the overall stock assessment. The ICES perception of the stock is also contrary to that witnessed by fishermen on the fishing grounds.”

However, the SPFA also state the industry’s commitment to ensuring a sustainable fishery:

“As a responsible industry, we are committed to ensuring a sustainable fishery, and we will be working with our partners in the EU, Norway and Faroes on how we can all work closely together to aid this process of ensuring the best possible science when assessing the stock. We are also committed to working with Scottish and UK Governments and Coastal States fisheries managers to find an acceptable solution to managing the 2019 fishery.”

Do coastal states have to abide by scientific advice?

The short answer is no. Scientific advice on catches provided by ICES and other organisations is not legally binding. Sometimes advice is followed, but it is often the case that the final catch limits agreed by Coastal States exceed scientific advice. For example, between 2016 and 2018 the Total Allowable Catch agreed for mackerel among the EU, Norway and the Faroe Islands was on average 28% above scientific advice.


Ultimately the setting of the Total Allowable Catch is a political decision and fisheries ministers have to balance the short-medium term economic interests of its fishing industries with the long-term sustainability of stocks.

Decisions on the 2019 Total Allowable Catch for mackerel will be made in the upcoming meeting of the Northeast Atlantic Fisheries Commission from 8-9 October. More information on this will be provided in the next blog in this series on Coastal State negotiations.

Damon Davies, Researcher, Brexit, Environment and Rural Affairs