This information is just as important as actual cetacean sightings, as it helps to build up a picture of where cetaceans are seen and when. On most occasions, these vessels travel to different areas each time they put to sea and the observations are on more of a casual basis. Reports are made only if cetaceans are actually sighted. For this reason, we are monitoring the movement of vessels in local waters to assess any possible impact that boats may have on populations and movements of both dolphins and porpoises. There has always been a large volume of boat traffic in this area, but there appears to have been an increase from previous years.
Motor vessels are the greatest threat to dolphins.
Sailing yachts present little impact on dolphins, although the larger vessels sometimes use an engine when leaving port, or when there is insufficient wind. It is difficult to assess whether these large congregations of yachts have any impact on the dolphins. They are likely to detect the presence of the yachts and avoid the area in advance. At Worthing, Southern Water have been working on a 2 mile long sewage discharge pipeline. Noise produced during the dredging and from chains, cables and anchors could have cause the dolphins to avoid this area.