Figure 5.  Map showing sampling sites over acoustic-backscatter intensity in the study area.  Backscatter intensity is an acoustic measure of the hardness and roughness of the seafloor.  In general, higher values (light tones) represent rock, boulders, cobbles, gravel, and coarse sand.  Lower values (dark tones) generally represent fine sand and muddy sediment.  Tonal variations may occur across track in the sidescan-sonar data and between survey days in the multibeam echosounder data.