STATISTICAL-ANALYSIS OF CATCH-AT-AGE DATA WITH CORRELATED ERRORS

We extend the statistical model used to estimate abundance from commer cial catch-at-age data for many of the major commercial fish species i n the world. The model we consider combines commercial catch-at-age da ta and research survey estimates of fish abundance; we extend the mode l to allow correlated errors among ages within a year for the survey e stimates of fish abundance. We also formulate a method for modeling th e fishing mortality on the oldest ages of the fish caught. Estimates a re obtained using maximum likelihood. We conclude that the level of co rrelation among ages is sufficiently large to produce large biases in the standard methods for some stocks. The statistical model that inclu des correlated errors greatly reduces bias and increases efficiency if the correlation in the estimation error is large.