The "manta tow" technique consists in towing an observer behind a boat at slow speed. The observer clutches to a large wooden slate linked tot the boat by a rope. The observer writes the coral cover down on a sheet of paper on the slate along the (every 2 minutes).
The coral cover is estimated through 5 surface categories occupied by live corals: 0 - 10 - 30 - 50 -75 - 100 %. The records are taken for 4 sections of 500 m, 2 on each side of the Photo-quadrat coral transect.
Comparing those two methods (photo-quadrat and manta tow) showed that the quadrats are a very good estimates of the kilometer of reef surrounding them. Until 2002, the "manta tow" technique were used on a regular basis. Since then, it is only used in case of major environmental change like biological proliferation (such as the crown of thorn starfish or Acanthaster planci).