CPUE

Catch per unit effort (CPUE) is a widely used index of stock abundance in fisheries science. It is defined as the catch (in weight or number) divided by a standardised measure of fishing effort (e.g., number of hooks, trawl hours, vessel-days). Under assumptions of constant catchability, CPUE is proportional to stock abundance, making it a key input for stock assessment models. However, CPUE can be misleading when fishers "hyper-stable" behaviour (targeted searching in remaining habitat) maintains high catch rates even as abundance declines substantially.

CPUE indices are standardised using Generalised Linear Models (GLMs) or GLMMs to remove effects of year, season, area, vessel, and gear type.