WWW.WA S .ORG • WORLD AQUACULTURE • SEP TEMBER 2022 45 including weather interactions, it was challenging to achieve the proper height for drying. I set five nets at an angle from low to high on the poles to help determine the height that provided the best growth. We also suspended nori nets across herring weirs in Grand Manan, NB, setting the height to that of the local nori growing naturally on the herring weir poles but, given that the species were different, there was little success. The second method was to place the nets in nursery systems called ikada, frames that can be raised out of the water as needed. CPI adopted the Urano-san style ikada, designed and patented by Urano-san and now the most widely used system in Japan. Each ikada can hold up to two bundles of six nets tied on top of each other. The ikada works as a leverage system; when one pulls down the “front door”, seen off of the bow of the boat in the photo (Fig. 4), the system is leveraged up and the nets come out of the water. In parallel, ten ikada are linked to a rope and pulley system and can be raised from one position. With another ten opposite, the boat operator can raise twenty ikada without having to move. As the seedlings grow, the nets are split from 12 to 6 and then to 3 nets. During periods of prolonged fog or cloudiness, the diatoms may not be killed by air drying. The first remedy was to use a water pump to blast the nets. If this was not successful, the nets were removed and placed in a hydrochloric acid bath with a pH of 2 for 5 minutes. This killed the benthic diatoms and did little harm to the nori but was very labor intensive. ( C O N T I N U E D O N P A G E 4 6 ) (Fig. 3). The nets were made of 183-cm bar mesh of three interwoven fibers; monofilament for strength, nylon to retain moisture, and polyester for the spores to adhere to. The combined fibers have a thickness or denier (a measure of thread thickness) of 17,000, but depended on the expected weather in the culture area; high humidity and fog mean less denier to allow for faster drying, hot dry weather requires a thicker denier. The strands were examined microscopically for spore attachment, and when there were 6-10 spores per field of view at 100×, the nets were ready to be deployed in the nursery. This could take only a few minutes with a very good spore release. Several hundred nets can be seeded in one day in this manner. They were then placed in covered saltwater tanks for 24 h to allow the spores to set on the net twine. Nori is an intertidal plant, requiring daily exposure to air to grow. If kept submerged, benthic diatoms will completely cover the seedlings, suffocating them. Daily drying kills the benthic diatoms and no doubt provides beneficial physiological changes in the plants. One method to provide the proper environment was to suspend the nets horizontally between parallel poles set in the intertidal zone. The height of the nets could be adjusted depending on environmental conditions – on hot sunny days, the nets were lowered to allow longer submergence and cold wet days nets were raised to allow more drying. Close examination of the population of benthic diatoms on the nets determines the proper height. CPI had a 2-ha intertidal lease site near Mathews Island for 20 saku. With a tide ranging from 5 m to 8.5 m, depending on the moon cycle and not FIGURE 3. Net wheel with conchocelis shells for seeding nets. FIGURE 4. Ikada with nursery nets. FIGURE 5. Nori production net.
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