Click on figures for larger images

Figure 19. Sidescan-sonar imagery from National Oceanic and Atmospheric Administration survey H11445.

Figure 20. Detailed sidescan-sonar image of sand waves and boulders in the study area.

Figure 21. Photograph of the sea floor at station PI12 showing a boulder encrusted with sponges, anemones, and hydrozoans.

Figure 22. Photograph of the sea floor at station PI10 showing a gravelly environment.

Figure 23. Photograph of the sea floor at station PI7 showing a sandy environment and a spider crab.

The sidescan-sonar image only covers part of the study area. Areas of higher backscatter appear as lighter tones and are interpreted as consisting of coarser grained material capable of reflecting large amounts of sonar waves. Areas of lower backscatter appear as darker tones and are interpreted as consisting of finer grained materials (fig. 19).

Individual objects of high backscatter with low-backscatter shadows are interpreted as boulders. Tiger-striped patterns of high and low backscatter are produced by sand-wave fields (fig. 20). Both of these features are also visible in the bathymetric imagery and they are further discussed in the Bathymetry section of this report. In the study area, higher backscatter occurs where there is gravel or gravelly sediment on the sea floor, such as at stations 12 and 10 (figs. 21 and 22). Lower backscatter occurs where sand is present, such as at station 7 (fig. 23). High backscatter tends to dominate the survey area, especially near the shore. Low backscatter regions are located north of Orient Point and on the shoal north of the eastern end of Plum Island.