North Sea Nephrops: proposed Fisheries Management Plan

Stock assessment and MSY

Scientific evidence

Assessments for each Nephrops FU are carried out using an underwater television camera mounted on a sledge, which is towed across the seabed by research vessels. The abundance of Nephrops is estimated from the number of occupied burrows per unit area as counted in images, raised up to the area of Nephrops habitat in the FU. Nephrops catch (including estimated dead discards) is divided by the abundance of Nephrops estimated by the survey to calculate the harvest rate for the FU.

To provide management advice, scientists define reference points for harvesting of Nephrops stocks. The two key reference points used are MSY B_trigger^[8] – a biomass (B) threshold below which management measures or action may be needed, and an optimal harvest rate (F_MSY^[9]).

MSY B_trigger is typically defined as the lowest historically observed stock level, however for Nephrops this trigger is typically set at a level representing the lower bound of natural stock fluctuations around the biomass that would produce maximum sustainable yield (BMSY). Higher trigger levels are however set if the stock has shown signs of stress at this level of abundance. The optimal harvest rate reference point (F_MSY) is derived taking into consideration biological characteristics such as growth, size at maturity, burrow density, variability in stock size, and historical fishing levels.

Scientific advice is published by ICES on the size and status of the individual Nephrops stocks or FUs in relation to these reference points. The recommended catch advice for each stock is usually given based on fishing at F_MSY.r. If a stock falls below MSY Btrigger, ICES advises a reduced catch to promote rebuilding and with the aim of returning the stock to sustainable levels.

Assessment of evidence

As set out above, North Sea Nephrops generally have a high level of data available, although some individual Nephrops stocks in the North Sea are data limited. Overall, there is sufficient available scientific evidence for the relevant fisheries policy authorities to make annual MSY assessments for the most economically and socially critical FUs.

Overall, the North Sea Nephrops fisheries covered by this FMP are currently being fished sustainably, with assessed FUs showing stock health above MSY biomass reference points and fishing pressure mostly below MSY fishing mortality reference points.

The advice for each FU is detailed below:

1. Outside Functional Units

• Stock status: Unknown (data limited stock)

2. FU7 - Fladen Ground

• Stock status (for 2026): Fishing pressure on the stock is below FMSY, and stock size is above MSY Btrigger.

3. FU9 - Moray Firth

• Stock status (for 2026): Fishing pressure on the stock is below FMSY, and stock size is above MSY Btrigger.

4. FU10 - Noup

• Stock status: Unknown (data limited stock)

5. FU6 - Farn Deeps

• Stock status (for 2026) Fishing pressure on the stock is above FMSY, and stock size is above MSY Btrigger. (note the condition of this FU has improved since 2023-24)

6. FU8 - Firth of Fourth

• Stock status (for 2026): Fishing pressure on the stock is below FMSY, and stock size is above MSY Btrigger.

7. FU34 - Devils Hole

• Stock status (2023, 2024): Unknown (data limited stock)

8. FU5 – Botney Gut / Silver Pit

• Stock status (for 2026): Unknown (data limited stock)

Stock advice summaries provided are based on the most recent available information at time of writing, therefore providing important context for the development of this FMP and retaining consistency with the data provided in this document and annexes. Please refer to the most up to date ICES scientific advice, which is available through the ICES Advice Explorer.