Estimating Population Size from Relative Abundance Data Measured with Error

Abstract

A modified DeLury method to estimate fish population size from relative abundance data was developed. The method may be applied either with or without knowledge of the age composition of catch. In addition to estimating catchability coefficients, the technique accounts for error in the measurement of relative abundance. A general-purpose nonlinear regression subroutine was used to fit the model. The technique is demonstrated using Northeast Fisheries Center bottom trawl survey data as a measure of relative abundance. Fitting was carried out for four fish populations: Georges Bank and Southern New England yellowtail flounder (Limanda ferruginea); Georges Bank and NAFO SA 4X haddock (Melanogrammus aeglefinus). Catchability coefficients calculated in this manner are consistent with prior estimates. In addition, the technique smooths the survey data by filtering measurement error from true fluctuations in population size. Population size estimates for haddock derived by this method agree closely with virtual population analysis (VPA) estimates.