Estimating confidence intervals for fish stock abundance estimates from trawl surveys

A method is developed for calculating asymptotic confidence intervals for trawl surveys using the swept area method, using likelihood ratios from Aitchison's delta distribution. Simulation tests of the method show that unbiassed estimates of the density and biomass can be obtained and that the estimated confidence intervals have close to the nominal coverage probability. Performance deteriorates in cases where few of the hauls contain fish, and the coefficient of variation is high. The lower confidence bound appears to be more reliable than the upper.