An investigation of optimum methods and unit sizes for the visual estimation of abundances of some coral reef organisms

Abstract

Surveys of abundances of demersal biota provide the empirical bases for assessing the biological status of the Great Barrier Reef, testing the success or failure of management strategies, investigating anthropogenic impacts on the reef, and contextualising fundamental research. The accuracy and precision of the data that arise from surveys will be at least partly a function of the survey methods. It is important, therefore, to thoroughly document the sampling characteristics of those methods. We sought to examine the relative biases and characteristics of precision of sampling several species of benthic organisms and demersal fish by visual surveys of belt (or strip) transects of a range of sizes. We also examined the biases arising from several procedures for counting organisms within transects.