Spatial structure of coastal pelagic schools descriptors in the Mediterranean Sea

Biomass estimates during acoustic surveys rely mostly on fish accessibility which in turn depends on the spatial distribution and structure of schools . In this paper, we first investigate the spatial behaviour of schools thro ugh some of their descriptors in order to assess the interest of a study on the influence of environmental factors on this behaviour. Morphological, e nergetic and positioning descriptors of schools were measured in the Catala n and Adriatic Seas during four acoustic surveys. The spatial structure of the descriptors was studied using geostatistical methods. The variograms we re calculated on the averaged school descriptors within a sampling distance of 1 nautical mile (elementary sampling distance unit). Globally, most of the variograms are structured, depending on the type of descriptor and on t he cruise. The results are discussed according to the topography of the two studied regions, the temporal variability existing in the data, the domina nt species in the area and the possible biases due to the acoustic device u sed. (C) 2000 Elsevier Science B.V. All rights reserved.