Large-scale Seaweed mariculture is carried out only in Asia, where there is a very high demand for seaweed products and burgeoning populations to create market growth.
The criterion for selecting harvest time must take into consideration the highest per-unit area production rate and the lowest wet-to-dry ratio.
Formerly, the only way to collect the seaweeds was to pick them one by one from the nets, a cold, tedious, and slow job. Today, petrol-driven rotary cutters are used which resemble an inverted lawnmower in construction. One or two men pull the nets over the cutter while another manages the boat. The harvesters tie and untie the nets as they pass. The process can be adjusted so as to select only the larger fronds and within a fortnight the remaining fronds and frond stumps will have grown sufficiently to allow a further crop to be cut. As a rule, nets are harvested 3-4 times but the crop gets progressively smaller each time. At the end of the harvesting season, the nets are carefully cleaned with freshwater, dried and stored for the next season. Some harvesters use another type of mowing machine with a vacuum pump incorporated to collect the cut plants.
In harvesting the kelp ropes are detached from the floating line, and collected in small boats, many of which are towed in a long line by a motor boat. When the boats reach the wharf or shore, the plants are transported to land and dried under the sun.
See the following sections in Cultivation of Algae in Marine environment: