Catch Per Unit Effort (CPUE)

Catch per unit effort divides catch by a measure of fishing effort (hooks set, trawl hours, or days at sea) to give a relative index of abundance over time. Assessments lean on standardized CPUE series because direct biomass surveys are expensive, but raw CPUE can mislead: hyperstability, where catch rates stay high as a stock declines because fish concentrate, has masked collapses such as northern cod. Statistical standardization removes gear, vessel, and seasonal effects before the index enters a model.