Character of temporal variability in stock productivity influences the utility of dynamic reference points

Abstract

Abstract Reference points identify benchmarks, thresholds, or decision points for fisheries management, and are commonly defined by stock status indicators that presume equilibrium population conditions in the absence of fishing (e.g., equilibrium biomass, B0). However, equilibrium population biomass may be an inappropriate reference level when stock productivity is influenced by environmental change, predator-prey dynamics, ecosystem thresholds, and myriad other factors. Simulations were conducted to compare equilibrium-based (static B0) and non-equilibrium based (dynamic B0) indicators of stock status under alternative states of nature driven by time-varying recruitment dynamics (productivity regime), fishing dynamics (mortality regime), and species life history. Using dynamic B0 often implied a different state of the stock under directional productivity regime shifts, but was more similar to static B0 reference points under cyclic or white noise productivity scenarios. Uncertainty in stock status arising from incorrectly identifying changes in system productivity generally outweighed the uncertainty associated with initial equilibrium conditions. Empirical results across 18 U.S. West Coast groundfish stock assessments indicated predominantly small differences (