Okayama's Nori Farming Shaken by a Sea of Environment - Trials of the 2000s

Okayama's Nori Farming Shaken by a Sea of Environment - Trials of the 2000s

In the 2000s, the nori cultivation along the coast of Okayama Prefecture suffered a major blow. Sea water temperatures did not drop even in winter, slowing the growth and lowering the quality of the seaweed. Frequent color fading and disease outbreaks plagued the fishermen and cast a shadow over the local economy. Furthermore, although eutrophication of the Seto Inland Sea was controlled by long-standing restrictions on the total volume of water and sewage maintenance, the side effects were a shortage of nitrogen and phosphorus, which depleted the nutrients necessary for the growth of the nori. The policy of protecting the environment ironically resulted in the depletion of the productive capacity of the fishing grounds.

Against this historical background, global climate change is progressing: with the Kyoto Protocol coming into effect in 2005 and the release of the IPCC Fourth Report in 2007, the risks posed by global warming began to be widely recognized by society. The beaches of Okayama were also facing economic headwinds, such as soaring fuel oil prices and price competition with foreign products, and were indeed facing a double challenge. Fishermen were struggling against this backdrop, devising ingenious ways to manage their fishing grounds on a daily basis.

The technology introduced at the time began with improved monitoring and forecasting accuracy. Fixed-point observations of water temperature, salinity, and nutrients were made along the coast, and remote sensing using satellite imagery was used to determine the status of the sea area. Early detection of signs of red tide and anoxia led to shared decisions to accelerate harvesting and net management. At aquaculture sites, flexible measures were taken, such as raising and lowering nets to avoid high water temperatures in the surface layer and relocating fishing grounds to offshore areas with better tidal passage. They also increased the frequency of net washing to prevent attached organisms and ensure photosynthetic efficiency.

In addition, to cope with nutrient deficiencies, liquid fertilizers were sprayed to supply nitrogen. However, since excessive application of fertilizers would lead to environmental degradation, pointwise and small amounts were applied under careful rules. The operation of sluices and weirs in rivers were reviewed, and attempts were made to deliver nutrients by adjusting the timing of incoming water. It was also around this time that a strain of nori that was resistant to high water temperatures and disease was selected, and improved netting materials were introduced to make the equipment more tolerant of frequent operations. Fishermen also made efforts to maintain quality by improving processing and sanitary management, so that even if the harvest volume decreased, the value of the product on the market would not be diminished.

There were also circumstances unique to Okayama. The topography of the inner bay was not conducive to water circulation, and the high water temperature and low nutrient levels caused by stagnant seawater tended to increase the number of organisms attached to the fish. River inflows brought nutrients, but they also caused turbidity and rapid salinity fluctuations, so they had to be handled with great care. The fishery industry could not be allowed to act on its own logic, as it had to come to terms with other industries and policy goals, such as ports, tourism, and environmental protection.

The lesson of this period is that no single tool can address the vagaries of climate change. Nutrient management in nori aquaculture was not about reducing or increasing nutrients, but about maintaining an optimal balance. The situation is visualized through observation, and decisions are updated on a weekly basis to adjust the cropping season and depth. Combined with fertilizer application and river inflow management, it was necessary for the government, researchers, and fishermen to work together to face the crisis.

The predicament that befell Okayama's nori-agriculture industry was symbolic of the complex reality faced by primary industries at the intersection of climate change and human environmental policy. The effects of global warming and oligotrophication are not just a local fishery issue; they pose a universal question: How do we build harmony between nature and human activities?