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Day 7, August 7, 2005 TER daily cruise report
Day broke on a mackerel sky and a two to three feet swell out of the NE. Six permanent monitoring sites are scheduled to be visited by divers today. A number of these sites are along the northern margin of the National Park.
silt from the bottom
These sites average around 95 ft in depth and have a very fine substrate, referred to by some, as pluff mud. Visibility is generally low, 10-15 ft, unless one of the dive team disturbs the bottom causing everything to vanish in a gray cloud. Returning to monitoring stations like these year after year require very precise navigation as visibility conditions make searching for our site (marked by a steel rods driven in to the bottom and one small float) once divers are on the bottom a losing proposition. To minimize the need to search for the site we use very precise Global Positioning System (GPS) that relies on satellites, a sophisticated antennae and computer that provided precise position, direction and speed.
This system allows the dive boat to navigate to a point within three feet of the center of the sites location. As the boat intersects this “point” on the ocean we mark it by tossing out an anchor attached to a dive line and large float. Survey divers descend the line to the anchor which in theory, and often in reality, in next to our survey site marker. This ability, to return to the same spot on the bottom of the sea, is quite amazing. For those interested in the health of our ecological systems, this technology represent a critical step