Harvest control rules and changing productivity: the working example of North Sea herring

Abstract

North Sea herring is managed by the EU and Norway through a harvest control rule where target fishing mortalities are changed if the estimated SSB falls below a trigger biomass million tonnes). This management agreement was adopted in December 1997, amended in November 2004. The management agreement includes target fishing mortalities both adult and juvenile fish. Initial studies to test the robustness of the rule assumed stable state of productivity, with stochastic variability in recruitment. Recruitment in North Sea herring has been relatively poor for the last 4 year classes 2003, 2004 and 2005). This sustained sequence of reduced recruitment has not observed before at current levels of stock biomass. According to a recent ICES study SGRECVAP) this serial poor recruitment has been caused by an increase in the mortality larvae over the first winter, and was not due to overexploitation of the stock. Thus, the short term, the productivity of North Sea herring has changed, whilst the management agreement currently has not. As the agreement is primarily based on target fishing mortalities, changes in productivity should not undermine the management agreements ability to stock, because the trigger points are based on biomass, nevertheless the agreement longer be optimum for sustainable exploitation. 2006, the ICES advice changed to account for the changes in the productivity of North herring. Projected catches and SSBs were estimated assuming a shift in recruitment average of the last 25 years (since the stock recovered from collapse) to the average four years to reflect the more recent low levels. The management agreement ambiguous during the recovery the SSB was taken as the assessment year, ICES advice is based on the TAC year. In addition to the less than optimal biomass points the agreement (amended in 2004) also now includes a maximum change in TAC a limit of 15% change per year, which if implemented at all levels of biomass conflict with the need to respond swiftly to changes in productivity of the stock in the sustained decline. Keywords: Herring, changing productivity, North Sea harvest control rule, advice