of the net income made the nori cultivation the 

 most profitable fishery. This was followed also by 

 the rapid expansion of the industry throughout 

 Japan, making strong demands on the advances of 

 culture techniques. 



3) Expansion of the nori grounds. Increase of 

 population, fertilization of rice fields, and the 

 progress of industry made the coastal waters 

 richer in nutrients, making cultivation possible to 

 spread away from areas adjacent to river mouths 

 where nori often suffers from declining salinity 

 during rainy weather. 



Under these circumstances, the following culture 

 techniques were pushed forward at a rapid advance: 



1) Techniques to find new grounds suitable for 

 nori culture. Conditions required are a) sufficient 

 exchange of water by currents and waves, b) suffi- 

 cient supply of nutrients, and c) protection from 

 freshwater inflows and strong surf. 



2) Improvement of collectors. Old collectors 

 were replaced by a net made of palm fiber string 

 and then of synthetic fiber string of 2-3 mm in 

 diameter. The strings are netted in a mesh of about 

 20 cm, and the standard size of a net is 18.2 x 1.3 

 m-. The nets are set stretched horizontally into the 

 sea and are tied to bamboo poles set in two rows on 

 the shallow sea. The net collector has many ad- 

 vantages over the old ones in rearing nori. It is far 

 easierto deal with, surf resistant and more produc- 

 tive. The replacement made possible a wider cul- 

 ture, spreading from the limited waters near the 

 mouth of rivers to deeper waters of rougher wave 

 action, as the waters became more nutritious. 



The net collector made possible the 

 cultivator's control on the growth of nori. Elevat- 

 ing the net a little from its standard level slows the 

 growth of nori but controls the growth of weeds, 

 such as Enteroinorpha and diatoms which may 

 overcome the nori and decrease the harvest. Low- 

 ering the net accelerates the nori growth, but the 

 nori often becomes weak by disease; Enter- 

 oinorpha and diatoms grow vigorously on 

 the net, displacing the cultured nori, if the weather 

 in winter is calm and not too cold. Nori cultivators 

 can then control the net level height as well as the 

 nori growth, protecting against diseases and in- 

 jurious ueeds. 



3) Seed control. Soon after the findings of K. M. 

 Drew on the ■"Conchocelis phase" in the life his- 

 tory of Porphyra. its whole history was made clear 



in Japan, being followed by the artificial control of 

 nori spores. In 19.S.*i-60, nori producers cultured a 

 necessary amount of Conchocelis for themselves 

 through the summer and produced nori spores to 

 start its culture. The technique removed the short- 

 age of natural spores which had limited the 

 growth of the cultivation especially in the western 

 Japan. 



It can be said, that the replacement of old collec- 

 tors by net doubled the production of pre- World War 

 II time, also doubling the seed control. 



It should be mentioned that a change of species in 

 nori occurred with the change of culture techniques. 

 P. yezoensis became dominate in place of P. tenerci, 

 the former seems to adapt more readily to higher 

 salinities and to easier cultivation of spores. The 

 change increased the harvest but produced a low- 

 grade product with decreased odor and hardening 

 when tasted. 



General View of Actual Nori Cultivation 



At present, nori is cultivated in most bays and 

 inland seas along the Pacific coast of Japan. Nori 

 grounds are about 60,000 hectares in area, produc- 

 ing about 5-6 billion sheets of nori a year worth 70-80 

 billion yen. Fishermen's cooperative unions obtain 

 prefectural government sanction to set nori grounds 

 and manage them. About 60,000 fishermen set their 

 own collectors, harvest grown nori on them, and 

 produce dried paperlike products. The products are 

 sold through the cooperative unions to the dealers. 



Coastal waters of 0-5 m in depth are available for 

 nori grounds of classic net systems, setting the nets 

 by spreading them between two rows of bamboo 

 poles. By the actual development of the new floating 

 net system, cultivators have been able to turn waters 

 20-m deep into profitable grounds. 



Usually a net, in a cultivating set, has a spread of 

 18.2 m X 1.3 m. Now 5 million sets are prepared for 

 all the grounds. About 10 million nets are used per 

 year, i.e., in a set two nets are spread one after 

 another during a harvesting season, from November 

 to next March or April. 



Every fisherman has equipment for harvesting 

 nori plants and also for manufacturing them into 

 paperlike products. Generally the cooperative un- 

 ions prepare cold storage for preserving nets with 

 young buds in living condition. These unions some- 

 times have equipment for culturing Conchocelis and 

 also for manufacturing nori products. 



Paperlike products are gathered by unions and 



