The Estimation of Demersal Fish Densities in Biological Surveys Using Underwater Television Systems

The raw abundances of many species of demersal and benthic fishes can be estimated easily in situ by surveying transects with underwater television systems and videotape recorders. However, to determine densities (number per unit area) requires an accurate assessment of the area surveyed, which can vary with water clarity and camera altitude. This paper presents a technique for improving density estimates from underwater video transects, by 1) controlling camera altitude; 2) using two parallel-mounted cameras to determine visibility at various points along the route, thus defining the width of the transect; and 3) analyzing videotapes in detail to permit the accurate calculation of fish densities within habitats or other functional subdivisions.