The Effect of Bioturbation on Roxann®, a Remote Acoustic Seabed Discrimination System

Abstract

Whilst evaluating the use of RoxAnn® for benthic biotope mapping it was noted that over certain visually similar sediments differences were observed in the acoustic signature. To assess this phenomenon a number of physical parameters were determined (mean sediment grain size, sediment sorting, sediment organic carbon content and the percentage of sand, silt and clay present in the substratum) from within a survey area in the North Minch. Investigation of the epifaunal and burrowing megainfaunal communities was also carried out using towed underwater television (TV) techniques. Generalized linear modelling showed that changes in Nephrops norvegicus burrow density could account for 94·7% of the variability in the RoxAnn® E1 signal. The model, however, appeared to be improved when both the percentage of silt present and the sorting of the sediment were also taken into account, with 984% of the variance in El being explained. Although improving the original model, the addition of these extra variables was, however, considered insignificant in terms of the variability accounted for by N. norvegicus density alone. The findings of this study are discussed in relation to possible shellfish management.