AN ASSESSMENT OF THE ACOUSTIC SURVEY TECHNIQUE, ROXANN, AS A MEANS OFMAPPING SEABED HABITAT

RoxAnn acoustic surveys of the inner Moray Firth, undertaken in Septem ber/October 1995 and January 1996, were used to map seabed habitat on the basis of two sediment characteristics, ''roughness'' (El) and ''ha rdness'' (E2). The traditional analytical method of fitting a ''box pa ttern'' to El vs. E2 scatter plots was compared with a more objective method using False Colour Composite Image (FCCI) and cluster analysis. Although both methods produced similar maps, the latter provided grea ter between survey consistency. Six to seven sediment types were indic ated by RoxAnn, however ordination analysis of sediment samples indica ted that some of the FCCI clusters could not be separated on the basis of their particle size distributions. This may have been due to a deg ree of depth sensitivity, but it is also possible that RoxAnn was resp onding to other physical or biotic seabed features other than just par ticle size. After combining RoxAnn FCCI clusters where ground-truthing grab samples had shown the particle size distributions to be similar, it was evident that RoxAnn could distinguish three main sediment habi tats with certainty. On this basis, the RoxAnn derived maps compared w ell with maps obtained from British Geological Survey data. Finally we examined the distributions of four flatfish species to determine whet her these were in any way related to the different sediment habitats i dentified by RoxAnn.