Mapping seabed biotopes using sidescan sonar in regions of heterogeneous substrata: Case study east of the Isle of Wight, English Channel

As part of a wider research programme to investigate the utility of acoustic remote sensing techniques for mapping seabed biotopes, an area of seabed to the east of the Isle of Wight, some 12 x 4 km in size, was surveyed using sidescan sonar The study site was selected due to the high degree of sediment heterogeneity within the region. A mosaic of the sidescan sonar data was produced to provide a 100% spatial coverage map of the study site, which was subsequently divided into acoustically distinct regions, and each region ground-truthed using a suite of physical sampling and optical techniques. The main sampling tools, a 0.1 m(2) Hamon grab and a drop-camera system, were used to characterise the benthic communities and sediment characteristics within each acoustically distinct region. Relationships between acoustic regions, physical habitat characteristics and assemblages were investigated using a range of statistical techniques. Results from these analyses were used to identify discrete biotopes. Statistically distinct assemblages were identified within a number of the acoustic regions, although the high degree of sediment heterogeneity proved problematic in identifying discrete boundaries to physical habitats. Problems associated with delineating the spatial distribution of biotopes over regions of seabed comprising differing degrees of habitat/sediment complexity are discussed.