Identifying and reducing climate uncertainty in fisheries management reference points

Abstract

Modelling has predicted that reductions in ocean pH and increases in temperature will reduce vital rates (survival and growth) of North Pacific crab stocks and hence the target levels of fishing mortality consistent with sustainable harvesting. However, these predictions have been based on the best estimates of the effects of changes in ocean pH and temperature on vital rates from laboratory experiments. We quantified the effects of several climate and market sources of variability in Alaskan red king and southern Tanner crab fisheries on predicted optimal fishing mortality rates, including changes in ocean chemistry and temperature on vital rates, non-linear relationships between prices, costs and catch, and the uncertainty in population dynamics models. The declines in survival consistently lead to predictions of a reduction in productivity and hence the optimal level of fishing intensity over time, but the extent of change is uncertain. Uncertainty related to the effects of ocean pH and temperature on vital rates and variability among Earth System Models and future emission scenarios are the dominant sources of uncertainty, although potential fluctuations in prices and costs are also consequential. Further, simulations are used to explore the relationship between changes in ocean pH or temperature and vital rates (additional experimental replicates and a wider range of levels of ocean pH in experiments) and hence identify approaches to reduce the uncertainty in estimates of future projections of target fishing mortality rates. Importantly, we demonstrate that optimal approaches to reducing uncertainty depend on life stage (juvenile growth for red king crab and larval survival for southern Tanner crab), and the optimal experiment depends on species (increasing the range of pH levels for red king crab vs increasing sample sizes for southern Tanner crab). The results of this study can inform priorities for future ocean acidification-related laboratory experiments and provide a basis for evaluating “investment in research” more broadly.