Census Shows Exotic Species Habitat Spreading in Japanese Rivers

Japan's Ministry of Land, Infrastructure and Transport has released a summary of the results of the FY 2002 "National Census on River Environments." According to the census, many exotic species have become established in rivers nationwide, and ragweed beetles in particular have been expanding their habitat rapidly in recent years. Ecological surveys in rivers and at dams for this census were started in FY 1990.

Ragweed beetles were found at 55 percent of the surveyed rivers from 2001 to 2002, though they were completely absent during the period 1990 to 1995. This corresponds to the expanding distribution of the exotic plants, ragweed and giant ragweed, on which the ragweed beetle feeds.

The ragweed beetle is a yellow-brown coleopteran about four millimeters in length, originally from North America. Since 1996 when it was first identified in the vicinity of Tokyo Bay, distribution of this species has been rapidly expanding, mainly in roadsides, vacant lots and riversides, and it now seems to be established nationwide except in Hokkaido and the Southwest Island archipelago stretching southwards from Kyushu.

The survey has also confirmed that habitat for the controversial exotic fish species, bluegill and large-mouth bass, which prey on Japanese native fish species, continues to spread.



Posted: 2004/05/07 10:21:23 AM
Japanese version