The CPR is a self-contained mechanical automatic sampler towed 100 m behind the ship at about 10 m depth. It is towed at normal ship�s speed and can operate in nearly all sea conditions. As the CPR is towed along, water and plankton enter a small 1.25 x 1.25 cm aperture in the nose cone, which then expands into a wider collecting tunnel, slowing down the water flow. Plankton are then trapped between two sheets of 270�m mesh silk, 6.1 m long x 15cm wide, loaded in a removable cassette. The silk and plankton �sandwich� are wound on to a take-up spool inside a formalin preservation chamber, all driven by passing water turning an external propeller. Regardless of the speed of the ship, the sheets of silk are advanced at a fixed rate of 1cm for every nautical mile travelled. Each tow lasts approximately 450 nautical miles. Cassettes can be quickly changed allowing continuous sampling over long transects. Underway oceanographic, meteorological and navigational data are recorded at the same time. The silk are processed in 5 nautical mile equivalents and all plankton counted on each sample, and coded with time, date, and position of the 5 n mile sample, plus environmental data integrated over the same 5 n miles.