CPUE

CPUE stands for catch per unit effort and is a standard metric in fisheries science used to gauge the abundance of a target species. It is defined as the amount of catch divided by the fishing effort applied to obtain that catch. The calculation depends on the chosen effort measure, which may be days at sea, hours fished, nets deployed, hooks set, or other units describing fishing activity. Because effort definitions vary and fishing efficiency changes, raw CPUE is often standardized to remove non-biological variability.

CPUE is typically treated as a relative indicator rather than an exact population size. Researchers standardize CPUE by modeling catch as a function of effort plus covariates such as location, season, depth, gear type, vessel, and environmental conditions. The resulting index reflects relative abundance or catchability adjusted for known sources of variation.

CPUE informs stock assessments, harvest control rules, and management decisions, and can be used to track trends over time, evaluate management performance, and calibrate other abundance indices. It is particularly useful when direct biomass estimates are difficult to obtain.

Limitations include changes in catchability due to gear improvements, targeting shifts, or behavioral changes that decouple CPUE from true abundance. Rapid changes in fleet structure, price incentives, regulations, or spatial distribution can bias trends. In multi-gear fleets or mixed-species catches, CPUE may be misleading unless carefully standardized.

Data sources for CPUE include fishery logbooks, scientific observers, electronic monitoring, and fishery-independent surveys. Common methods to derive standardized indices involve statistical techniques such as generalized linear models, generalized additive models, or delta-lognormal approaches, incorporating covariates to separate abundance trends from non-biological variation. CPUE remains a practical, widely used tool in fisheries science, interpreted with appropriate caveats.