Productivity of a seaweed farm is measured by the number of harvests a year and the biomass increase in weight (yield). Some seaweeds are harvested fully, meaning the entire biomass is removed from the site, while others are harvested partially, with some biomass remaining for further grow out. Yield is often stated in kilogram (kg) per metre (m) line, since metric tonne (MT) per hectare (ha) is not always a common measure among farmers.
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For Pyropia, multiple harvests can be taken from a single seeded net in short intervals throughout the winter months.
In Japan, the first harvest takes place after 30 days, usually at the end of November. For the next month the nets are harvested every four to five days. Then, the nets will be replaced with frozen ones which can be harvested from January to the end of March. The harvesting takes place in the early morning hours in order to process the harvested biomass within one day.
In South Korea, the core harvesting takes place between December and April. Sometimes harvesting starts as early as late October and continues all the way until early May. The harvest is done in the early morning hours when it is still dark and only lasts for a few hours. The harvesting boat then returns to a port where the auction of the fishery cooperative takes place every morning.
Specially designed harvesting boats drive beneath the cultivation net and cut off the hanging Pyropia blades underneath. They are typically 10-15 cm long at the point of harvest. In Japan and China, farmers only harvest the amount that can be processed on that day since farming and primary processing is done by the same entity.
Farmers report that pyropia harvesting technology has become more efficient and improved significantly. The main challenges are processing capacity and price.
In South Korea, the harvested Pyropia is typically sold immediately since the primary processing is done by other companies. Therefore in peak season between January and March, a lot of Pyropia biomass is harvested and needs to be sold immediately. This causes strong fluctuation in price. Because of this, some farmers say they would only harvest when the price is reasonable. In Japan and China, only the amount that can be processed on the day will be harvested.