Change-in-Ratio Estimators for Habitat Usage and Relative Population Size

New change-in-ratio methods are developed for estimating the proportion of a population in each of several defined regions. The procedures assume population closure so that an observed decline in catch rate in one region must be balanced by increased catch rates elsewhere. Sampling gear catchability can be unknown and variable among regions. The method was used to estimate the proportion of a population of juvenile striped bass occurring in a river region slated for filling. Formulas are also given for constructing an index of abundance and for estimating the relative efficiencies of the sampling gears in the different regions.