Abstract
This paper proposes a method for estimating a relative index of stock abundance using age compositions in the catch and estimates of fishing and natural mortality coefficients. The relative indices of the stock size and catch are defined by the ratio of these to the total catch in the first year of estimation. Using the indices a backward equation similar to that of Virtual Population Analysis (VPA) was obtained. Values of parameters are estimated by the least squares approach with estimates of mortality coefficients. Results of simple simulations using artificial data showed that the trends of the estimated relative indices of stock size were close to those of the true values, except under scenarios of existing bias in mortality estimates. Application of the method to data for the red sea bream, Pagrus major, in the eastern Seto Inland Sea indicated that the trends from the method and VPA were similar to each other. The problems in application were discussed.
