A Meta-Analysis of Nonlinearity in the Relationship Between CPUE and Abundance for Orange Roughy Fisheries

Catch-rate data are commonly used as an index of abundance when assessing a stock, and can be derived from fishery-dependent or fishery-independent (survey) data.  Commercial catch and effort data are commonly compiled into a relative index of abundance called catch-per-unit-effort (CPUE) and are often assumed to be proportional to abundance. However, fish behavior, fishing behavior, or improper analysis methods may cause a departure from a proportional relationship.  This study used fishery catch-rate data from four orange roughy fisheries in a hierarchical state-space model to estimate the hyperparameters of a distribution for a nonlinearity parameter in the relationship between CPUE and abundance.  A prior distribution for the nonlinear parameter of an unknown stock was developed from these results and showed that hyperdepletion (CPUE declines faster than abundance) was more probable than hyperstability (CPUE declines slower than abundance).  Although hyperdepletion was unexpected for an aggregating species, explanations include depletion of localized aggregations, natural variation in the size of spawning aggregations, and/or disruption due to fishing. The prior distribution developed here may be used to improve assessments of orange roughy and other similar species where fishery-dependent catch-rates are an important data source.