Climate change opening new habitat to Japanese eels

Japanese eels have been discovered inhabiting several rivers in Hokkaido, the most northern prefecture in the country and an area previously thought to be beyond the species’ range.

The Tohoku region, consisting of northeastern Honshu Island, was formerly thought to be the northern limit of the Japanese eel’s range. Scientists are speculating that a change in currents or warmer water temperatures caused by climate change have allowed them to colonize new habitat.

This may be beneficial for the endangered species, since habitat loss is one of the major causes of their decline. Many rivers on the Pacific coast of Japan have been dammed and contained in concrete flood-control channels, and estuaries have been eliminated by land reclamation.

The discovery of juvenile Japanese eels was made by a research group from the University of Tokyo and Hokkaido University. The group plans to continue to investigate the possibility that the habitat of eels is moving northward due to climate change or other factors.

In 2021, the research group found nine juvenile eels in a river in southwestern Hokkaido, as well as larger eels up to 20 centimeters long. In May 2022, they found 16 juvenile Japanese eels of about six centimeters in length. This is the first time that eels in the early stages of growth have been found in Hokkaido. Then, in this month's survey, juveniles were also found in other rivers in the southwestern part of Hokkaido.

Two members of the Tokyo University research group appeared on a news program about the find on Japan’s national public broadcaster NHK. Kentaro Morita of the Atmosphere and Ocean Research Institute and Mari Kuroki with the Interfaculty Initiative in Information Studies, both the authors of a 2020 paper, reported on a search for eels in rivers on the Pacific coast of the island, with a particular focus on the Yufutsu River, near the city of Tomakamai.

The research group believes that Hokkaido, which was not previously considered a habitat for eels, may have become a new habitat due to climate change or changes in the strength of the currents they ride to return to freshwater. Although there are a few records of mature eels being caught in Hokkaido in the past, it was not known whether they were natural eels or not, since eels used to be released into the sea from hatcheries.  

Photo courtesy of Wikimedia