Impact on Fishing and Marine Life
The first half of 2023 witnessed record-breaking sea surface temperatures around the Japanese archipelago, exceeding even the highs of 1998. This phenomenon, attributed to an abnormal flow of the Kuroshio Current, has significantly impacted marine life and fishing activities.
The Kuroshio Current, carrying warm water from the south, typically turns eastward off the coast of Choshi. However, since late 2020, it has been flowing northward along Honshu, likely due to changes in westerly wind patterns. This shift has resulted in warmer waters off Hokkaido, with surface temperatures exceeding normal levels by 2.38 degrees in the first half of the year.
The warmer waters have disrupted salmon and trout populations, making them difficult to catch later in the fishing season. Consequently, the start of the fishing season in Habomai, Hokkaido, was moved up a week this year. Additionally, the area off the eastern coast of Hokkaido to Sanriku has experienced frequent ocean heat waves, statistically rare events where high sea temperatures persist for extended periods.
These heat waves, exacerbated by the northward movement of the Kuroshio Current, prevent the southward flow of the cold Oyashio Current, creating ideal conditions for harmful algal blooms. In 2021, the eastern coast of Hokkaido experienced the worst red tide on record, triggered by an explosion of toxic phytoplankton fueled by changes in the undersea environment caused by an ocean heat wave.
Experts believe the increased frequency of ocean heat waves is linked to global warming. Compared to the early 1990s, the likelihood of these events has quadrupled in the 2020s. The rising sea temperatures pose a significant threat to marine ecosystems and the livelihoods of those who depend on them.