Kuroshio Current

The Kuroshio Current is the second-largest ocean current in the world. It flows in the western Pacific from the east coast of Taiwan island, northwards to Japan, and then beyond Hokkaido past the Kuril Islands, where it merges with the North Pacific Current. In many ways, it is similar to the Gulf Stream in the Atlantic Ocean, which also carries warm tropical waters toward the polar region. The Japanese call it the Kuroshio Current, with some early English geographers translating this to the Black Stream, the name coming from the deep blue of the water; a few writers refer to it as the Japan Current. A branch of the Kuroshio Current, known as the Tsushima Current, passes through the Tsushima Straits between Japan and Korea, into the Sea of Japan.

The warm waters of the Kuroshio Current are largely responsible for the abundance of coral reefs off the east coast of Japan, bringing coral reef larvae from other coral reefs in the South China Sea and off the coast of the Philippines. As a result, the coral reefs off Japan are the northernmost coral reefs in the world; the waters off the coast of Japan are as warm as 68 degrees F (20 degrees C) off the Ryukyu Islands, and even reach 60 degrees F (16 degrees C) in winter off the southern coast of Honshu Island. It has been the center of the Japanese fishing industry since prehistoric times. Since the 1940s, there has been a significant decline in the fish in the Kuroshio Current; this can be attributed to overfishing, or to global warming and climate change since the 1960s. In 1988, studies of the coral reefs showed heavy coral bleaching, which resulted in the deaths of many of the reefs. The pressure of population, with some waste dumped in the sea, has been a major contributory factor, as well as the rise in temperature of the Kuroshio Current.

This rise in temperature is the major actor in coral bleaching off the Osasawara Islands, which have 460 hectares of coral reefs, especially around Muko, Chichi, and Haha islands. These losses cannot be simply attributed to overpopulation. The local fishing industry has been unable to sustain itself by fishing in Japan’s territorial waters, leading to increasing numbers of Japanese fishing and whaling ships operating throughout the Pacific. Between 1993 and 1998, the fishing catch off Okinawa dropped by 21 percent. Off the Ryukyu Islands, although the number of fish has increased, the species diversity has dramatically fallen. The worst losses in coral reefs have occurred near Okinawa, where overpopulation has led to pollution. An aerial survey by the Environment Agency of Japan from 1990 to 1992 revealed that some 90.8 percent of the coral communities near Okinawa had less than 5 percent cover. In the summer of 1998, some 97 municipalities reported bleaching of coral reefs in their communities, especially of the Acropora species, which appears the worst affected.