Harvest control rules for a sustainable orange roughy fishery

Some of the best described examples of unsustainable deep-sea fisheries have been for the orange roughy, Hoplostethus atlanticus. Nevertheless, fisheries for orange roughy around New Zealand have persisted for more than 30 years, and some stocks that were overfished and substantially depleted now appear to be recovering. Scientific advice on the status of New Zealand orange roughy stocks has historically used population models fitted to various observational data, but this approach has proved problematic, largely due to uncertainty in recruitment, to the extent that from 2008 these models were replaced by a simple harvest control rule (HCR). The catches taken under this HCR were a fixed proportion of the weight of the mature stock, estimated principally from acoustic surveys. We test the performance of the current HCR, and some alternative HCRs, using a simulation model. The model simulates long-term single-species orange roughy stock dynamics, stock monitoring surveys, and management decisions. We allow for uncertainty in model parameters, but focus on the effects of changes in mean recruitment and recruitment variability, because the latter have been considered the primary source of uncertainty in future stock status. Results show that the current HCR is likely to lead to a sustainable fishery. Nevertheless, there are alternative HCRs that could out-perform the existing HCR. With a reliable series of biomass estimates from acoustic surveys, good knowledge of biological parameters (natural mortality in particular), some revision of a HCR to control catch, and spatial management to control habitat damage, it appears that an orange roughy fishery might achieve best-practice sustainability and environmental standards.