West Coast of Scotland Nephrops: proposed Fisheries Management Plan

Stock Assessment and MSY

Scientific advice

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^[9] as a trigger level defining an abundance below which management measures should be implemented, and an optimal harvest rate (F_MSY^[10]).

MSY B_trigger is typically defined as the lowest historically observed stock level, although higher levels are 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 in relation to these reference points. Headline catch advice is usually given for catch for each stock corresponding to F_MSY or a reduced catch if the stock is below MSY B_trigger.

Assessment of evidence

As set out above, West of Scotland Nephrops have a high level of data available overall. On this basis, there is sufficient available scientific evidence for the relevant fisheries policy authorities to make annual MSY assessments of the stocks.

Nephrops fisheries covered by this FMP are currently being fished sustainably within MSY limits, 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 Unit (FU)

• Stock Status (2022-2024^[11]): Unknown (data limited stocks).

2. FU11 – North Minch

• Stock Status (2022-2024) Fishing pressure on the stock is below FMSY, and stock size is above MSY Btrigger.

3. FU12 – South Minch

• Stock Status (2022-2024) Fishing pressure on the stock is below FMSY, and stock size is above MSY Btrigger

4. FU13 – Firth of Clyde and Sound of Jura

• Stock Status (2022-2024): Fishing pressure is below FMSY, and stock size remains above MSY B(trigger).

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.