Analysis and Interpretation of Freshwater Fisheries Data

7: Relative Abundance and Catch per Unit Effort

Wayne A. Hubert and Mary C. Fabrizio


Knowledge of the abundance of fish in a stock is a component of the information used in management of fisheries (Ney 1999). Abundance estimates are used along with data on age and length composition and weight–length relations to make judgments regarding the status of fish stocks. Many methods have been developed to estimate the numerical abundance of fish in a stock including counts within isolated segments of a water body, mark and recapture, and removal methods (Chapter 8; Van Den Avyle and Hayward 1999). However, in many freshwater fisheries these methods require more time and money than can be allocated to the assessment. In these cases, fisheries managers use indices of abundance to estimate relative abundance of fishes (Fabrizio and Richards 1996; Hubert 1996; Ney 1999).

The most common indices of relative abundance are computed from catch per unit effort (C/f ) data for samples from a fish stock (Fabrizio and Richards 1996; Hubert 1996; Ney 1999). A C/f index is defined mathematically as.