Defection from cold currents -- rising ocean temperatures and fish turnover (Spring 2007)

Defection from cold currents -- rising ocean temperatures and fish turnover (Spring 2007)

In May 2007, the Japan Meteorological Agency (JMA) released an analysis of sea surface temperatures in the waters surrounding Japan based on shipboard observation data for the past 100 years. According to the analysis, annual average sea surface temperatures have increased by up to 2.2 degrees Celsius in the central Sea of Japan, which is 1.4 to 3.2 times the global average rate of increase. This announcement brought home the reality that the abstract environmental problem of global warming is hitting Japanese dining tables and industries.

The impact is particularly noticeable in the change in water temperature during the winter season. In the Kinan region of Wakayama Prefecture, the catch of tropical sesame mackerel has been rapidly increasing, replacing the once-mainstream chub mackerel. 100m depth water temperature had been stable at 15°C until 1993, but after 1995 it rose to 16°C and reached 17°C in 2002. There was a clear correlation between this change in water temperature and the increase in sesame mackerel, and by 2005 sesame mackerel accounted for 80% of the mackerel catch. In terms of price, the price of chub mackerel is higher than that of sesamo mackerel, and this is an "ecological reversal" that clearly results in a decrease in income for the fishermen.

In the Tsugaru Straits of Aomori Prefecture, the growth of cold-water seaweeds such as kelp and kelp gouge has deteriorated due to the rise in water temperature during the winter. A phenomenon known as "isoyaki," or seafloor scorching, has also been occurring frequently, resulting in a situation where seaweed does not grow on the seafloor. As a result, the number of seaweeds that have been traded at high prices in the fishing grounds has been drastically reduced, and warm current seaweeds have emerged in their place. This is not just a change in biota, but a major blow to the local economy.

In the Seto Inland Sea, nori-nori cultivation has been devastated. An unusual phenomenon known as winter red tide was reported, and unprecedented weather patterns were hitting the fishing industry. Fishermen in Okayama and Hiroshima are no longer at the mercy of natural fluctuations, but of "human-caused waves" called climate change.

At the time, Japan's domestic policy was in a state of search, with no clear path for reducing greenhouse gas emissions after the ratification of the Kyoto Protocol; CO2 emissions reached a record high in 2005, and the balance between environmental policy and economic growth was not being achieved. Against this backdrop, the rise in sea surface temperatures sounded a strong alarm to fishermen and local residents as a phenomenon accompanied by a "real sense" of climate change.

In other words, this is not just a change in weather data. It was the beginning of a chain reaction of disruption of livelihoods: fish migrating due to changes in ocean temperatures, the collapse of aquaculture, and the disappearance of traditional local industries. Global warming" is no longer just a story about ice in a distant land, but has the power to quietly reshape the taste and lifestyle of Japan's oceans.