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Locals in for long haul in battle against non-native fish

07/06/2007

BY RINTARO SAKURAI AND NAOKI SHOJI

THE ASAHI SHIMBUN

A two-year battle to rid the nation's waterways of harmful non-native animal and plant species is increasingly taking on the appearance of trench warfare.

No matter what experts do, lakes and swamps are still plagued with black bass, bluegill and other fish that are not indigenous to Japan.

Officials have even resorted to passing electrical currents in water systems inhabited by such species--with limited effect.

Other methods are more traditional, for example, using nets, artificial breeding beds and promoting fishing events.

In mid-June, members of the volunteer group Bass Busters and others waded into the muddy waters of the Izunuma-Uchinuma marshland in northern Miyagi Prefecture.

Their mission was to catch young black bass in the 387-hectare swamp, a migratory bird conservation area designated as internationally important under the Ramsar Convention, an intergovernment treaty on wetlands.

The members, in water up to their chests, pulled out a net full of young black bass.

The operation is done twice a week during the black bass breeding season between May and June.

Operations to reduce the number of black bass at Izunuma-Uchinuma have been designated as a pilot project of the Environment Ministry.

In addition to the nets, artificial breeding beds are also being used at the marshland.

About 400 square plastic trays, measuring 60 centimeters down each side, are laid on the bottom of the swamp.

Black bass prefer laying their eggs in gravel rather than in mud or sand. So, by covering the trays with a black sheet and filling it with gravel, the fish can be tricked into spawning on them.

Using this method, about 10,000 eggs can be collected per tray each time.

The artificial breeding bed was developed by Kiyotaka Takahashi, vice president of Shinaimotsugo Sato no Kai, a nonprofit organization devoted to conserving the natural environment.

The beds, which cost about 5,000 yen each, are being introduced in other areas, too.

"It is important to fight fish with a cheap and fun method," Takahashi said.

"But if the beds are abandoned, they will only help the fish to multiply."

This season, black bass eggs were laid on 120 trays in the Izunuma-Uchinuma marshes.

The Invasive Alien Species Act, which took effect in June 2005, bans importing, raising and transporting 83 foreign species regarded as harmful to humans, crops or local ecosystems.

Large mouth and small mouth bass, both varieties of black bass, as well as bluegill are among the 13 fish species banned by the law.

This May, Hokkaido declared that black bass had been eradicated from the region.

Black bass were first detected in Hokkaido in 2001. Since then, it has used a variety of methods, including the use of electric shocks, to get rid of them.

Hokkaido may well have benefitted from the fact that temperatures of its lakes and rivers are lower than in other parts of Japan, making it hard for the fish to breed, observers said.

In other prefectures, it will probably be impossible to remove all non-native fish without draining water from their lakes or ponds.

Lake Biwako in Shiga Prefecture is also swarming with black bass and bluegill. The two species have been breeding there since the 1980s.

The lake's extermination operations have also been designated as a government pilot project.

At the end of May, the prefectural government organized a fishing event at the lake as part of its efforts to remove non-native species.

One of the participants, Katsuhiko Terada, 65, was surprised when he caught about 20 bluegill in the first 30 minutes.

Terada came from Otsu with his wife, to fish at the lake for the first time in 50 years.

Other anglers caught fish every time they cast their rods.

"I can't imagine how many there could be in the entire lake," Terada said.

Shiga Prefecture estimates that the black bass and bluegill in the lake total some 1,700 tons.

"It is no easy matter to destroy the species from Japan's largest lake," said Masahiko Takada, a representative of a local nonprofit organization that is trying to rid the lake of alien fish.

"There is no way other than to make sure as many people as possible know about the extraordinary situation here," he said.

Kazumi Hosoya, a zoology expert specializing in fish and also professor at Kinki University, says these and other efforts must continue for the next 20 to 50 years to be effective.

"It is a step-by-step process," he said. "It is also important to protect the native fish."(IHT/Asahi: July 6,2007)

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