In early April, drift-net fishing boats in Habomai, Nemuro, Hokkaido set out for salmon and trout fishing as the Pacific Ocean off Japan's coast experienced record high sea surface temperatures in the first half of the year, with the average temperature being notably warmer compared to previous years. The abnormal warmth of the waters has been attributed to the unusual movement of the Kuroshio Current, which carries heat from the southern ocean and has been observed to move northward along Japan's main island of Honshu since the fall of 2020.
The warmer sea temperatures have had significant impacts on fishing activities, prompting changes like starting the fishing season earlier than usual as salmon and trout have become harder to catch towards the end of the season due to rising sea temperatures. The abnormal oceanic conditions have also led to occurrences of ocean heat waves in certain areas, affecting marine life and causing phenomena like the worst red tide ever recorded off the eastern coast of Hokkaido in the fall of 2021, which was linked to highly toxic phytoplankton blooms triggered by ocean heat waves in the summer of the same year. Experts warn that such ocean heat waves have been increasing in frequency around Japan's waters, making it more challenging for marine ecosystems and fishing industries.