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Abortive Migration in Fish

Main currents flowing around Japan

The Tsushima Warm Current is a branch of the Kuroshio Current that flows into the Sea of Japan via the Tsushima Strait. It flows out into the Pacific Ocean via the southern Hokkaido strait, and into the Bering Sea via the northern Hokkaido strait. This current brings marine creatures that generally inhabit warmer environments than the Pacific Ocean coast of Japan up to the northern parts of the Sea of Japan.

However, even though the warm current flows all year round, the temperature of the Sea of Japan drops in winter. As a result, a number of tropical and sub-tropical marine creatures which are carried along the current from the south perish because they cannot survive the winter. This phenomenon is called ‘abortive migration’. Some examples are bluespotted boxfish (Ostracion immaculatus) and pearl-spot chromis (Chromis notate) which are often seen in the sea around Oki.

Neon damselfish (Pomacentrus coelestis)

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