Performance of precautionary reference points in providing management advice on North Sea fish stocks

Abstract

Abstract For 17 stocks in the North Sea, the performance and effectiveness of management advice using precautionary reference points was evaluated. Three criteria were used to identify whether a stock was within safe biological limits: SSB < Bpa, F > Fpa, or SSB < Bpa and F > Fpa. Four scenarios were considered, comparing the advice in the assessment year with what is retrospectively (2002 assessment) known to be the status of the stock at that time: (1) stock outside safe biological limits, advice to reduce fishing; (2) stock outside safe biological limits, advice for status quo harvesting; (3) stock within safe biological limits, advice to reduce fishing; and (4) stock within safe biological limits, advice for status quo (or increased) harvesting. Signal Detection Theory was applied to these scenarios, and the proportion of Hits (1 and 4), Misses (2), and False Alarms (3) were determined for each year as the proportion of the stocks for which the respective scenarios applied. Using both Bpa and Fpa was deemed the approach with the lowest error rate, and it resulted in about the same proportion of Hits in management advice as when Bpa alone was used (62%), but the proportion of Misses was slightly lower (24% vs. 26%). Therefore, the suggested EcoQ element would be the proportion of commercial fish stocks within safe biological limits (i.e. SSB > Bpa, F < Fpa), and the Ecological Quality Objective (EcoQO) should be that this EcoQ should be at or above a desired level. This desired level is a societal/political decision relative to the EcoQ reference level (i.e. where the anthropogenic influence on the ecological system is minimal), which by definition is 100%. At present, probably <10% of North Sea fish stocks are within safe biological limits, despite the relatively high Hit rate of >60%. A possible explanation is that most of these stocks (e.g. flatfish and roundfish) are caught in a mixed fishery, for which TAC management is less effective.