North Sea Horse Mackerel Fisheries Management Plan

Stock Assessment and MSY

Scientific evidence

As set out in Section 3.2 of the JFS, the UK takes an evidence-based approach to fisheries management, making use of the best available scientific evidence. For the purpose of stock management and Total Allowable Catch (TAC) setting, this tends to focus on the use of advice produced by ICES, although other sources of information, including data from the fishing industry, may also be used.

ICES provides annual advice for horse mackerel in the southern and central North Sea, eastern English Channel, and in the Northeast Atlantic and adjacent waters. ICES advice is organised according to categories, ranging from 1 (the most information available) to 6 (the least). At the time of writing this draft FMP, the Western horse mackerel stock is classed as a Category 1 stock and is considered to have full age- and size-structured data on which to base an assessment, with MSY reference points available to provide a framework for advice on sustainable management.

Benchmark exercises are a process used by ICES to evaluate existing and new scientific evidence and methods and, where relevant, apply them in the stock assessment process. They are part of the continuous improvement process which ensures that ICES advice is based on the best available scientific evidence. ICES completed an assessment benchmarking process both horse mackerel stocks in 2024.

As a result of the benchmark, horse mackerel in the SCNS and eastern English Channel was upgraded to a category 1 stock and is currently assessed using an age-based model. However, it was not possible to reliably estimate MSY reference points F_MSY and MSY B_trigger and therefore they are not defined. Evidence underpinning the stock assessment is highly dependent on data from large-scale vessels that previously operated a directed fishery in 4.b-c and 7d. With the cessation of that fishery, this data stream has effectively been lost, and the quality of the scientific advice may therefore decline from Category 1.

Advice is currently being sought from ICES on options that will maintain high-quality evidence to enable MSY to continue to be assessed annually. ICES are expected to report at the end of June 2027. The policies and actions relating to this stock are therefore cognisant of these circumstances and are predicated on the need to engage with ICES and agree appropriate actions to mitigate this loss of evidence.

Assessment of evidence

The following evidence has been collated from the most recent ICES advice sheet assessment working group report (ICES, 2026)

The latest assessments in 2025 show that the fishing mortality for western horse mackerel is below F_MSY, and the spawning-stock size is above MSY B_trigger. On the other hand, the spawning stock size of the SCNS and Eastern Channel stock is below B_lim, and consequently the current catch advice for this stock is a TAC of zero. No reference points for fishing pressure have been defined for this stock. With no directed fishery for the southern North Sea and eastern Channel horse mackerel due to the poor state of the stock, and the absence of scientific surveys targeting horse mackerel in this area, the information available to track stock trends is very limited.