| Abstract: | Examination of daily catch–per–unit–effort (CPUE) information on Pacific halibut revealed sharp declines that could not be explained by natural and fishing mortality. Catchability may have decreased during a fishing period because of local depletions of fish, changes in fish behavior, and other causes. Mathematical models of CPUE with a short–term catchability function of time or effort were based on a generalization of the DeLury method. A method of standardization was developed to account for the length of a fishing period and to correct for catchability. The effort model was best for Pacific halibut data and the application showed that standardization of CPUE is necessary to have a valid index of abundance when short–term changes in catchability occur. |
