Communicating uncertainty in quota advice: a case for confidence interval harvest control rules (CI-HCRs) for fisheries

Abstract

Multi-annual management plans are important tactical arrangements to support upper-level marine resource policies in many countries. The newly reformed Common Fisheries Policy in the EU reiterates the role of management plans, supported by the development of harvest algorithms, commonly called harvest control rules (HCRs). Current HCRs for most commercially important fish stocks in Europe and Norway depend on point estimates of the size of the spawning stock biomass (SSB) and level of fishing mortality (F) to dictate the scientifically recommended total allowable catch (TAC). When annual TAC advice from the ICES Advisory Committee, for example, is based on a point estimate for SSB, the propagation of uncertainties (assessment models of varying complexity, variable data sources, and variable degrees and structures of random and systematic errors) and subjective expert decisions is contained, at best, in an annex of the official ICES advice document. TAC advice given as an exact number (sometimes specified to the kilogram) often occurs when clients (who commission the advice or ministerial or other government authority) expect more of science than science can deliver. We outline an alternative formulation of the HCR that reflects the knowledge base through confidence intervals (CIs) dictated by the quality of input data from multistage sample surveys and model uncertainties. Our CI-HCR determines the TAC advice given the range of SSB and F assessed and performs more robustly in the face of uncertainties than the standard HCR formulation. The advantage of CI-HCR is that the advised quota will depend on the quality of the assessments. Also, the adequate level of monitoring for advice support can be determined based on what science can actually provide.