Since 1998, the International Council for the Exploration of the Sea (ICES) has applied precautionary reference points as the basis for its advice, identifying which harvesting rates meet precautionary criteria. These criteria aim to ensure sustainability by keeping spawning stock biomass (SSB, the weight of mature fish) above a minimum precautionary level, Bpa (set high enough to allow a margin of error sufficient to keep SSB above a lower limit level, Blim), and keeping the fishing rate (F) below a maximum precautionary level, Fpa (set low enough to allow a margin of error sufficient to keep F below an upper limit level, Flim).
Based on advice from ICES in 2007, which evaluated stock assessments using fisheries data for years up to and including 2006, and survey data up to and including 2007, the following stocks fished by the UK have experienced unsustainable fishing levels when compared to the maximum precautionary level:
(i) North Sea
Herring since 2006
(ii) West of Scotland
Haddock since 2006
(iii) Irish Sea
Cod since the introduction of precautionary reference points in 1998, sole since 2006
(iv) Western Channel
Both plaice and sole since the introduction of precautionary reference points in 1998
(v) Widely distributed
North-east Atlantic mackerel since 2001, blue whiting since 1999
For a number of stocks it has not been possible to make a quantitative comparison because the level of F was uncertain in 2007. This includes some stocks which have shown a long-term decline, such as cod in the west of Scotland.