Alien species, the largest issue in the rejuvenation of wetlands.
In a different method from Mr. Kudo, there is a facility, Tsuruoka City Community Nature Study Center, also called, “Hotoria". They manage a 7.7ha tract, Miyakozawa Wetland, which is one of their matters of business. It used to be a muddy rice field and is situated next to Oyama Shimo-ike pond, which was built as a flood control measure and a reservoir. Because it was deeper than the surrounding areas, it had had a lack of agricultural machinery to access it, and with an acreage-reduction policy in effect, it became uncultivated farmland. The city of Tsuruoka and its citizens have taken over the property, and the restoration of the wetland has begun.
With local preservation of the natural environment, which is intended to rejuvenate the wetland, it has brought an abundance of wild birds, insects, and hydrophytes. But there are many hurdles in its preservation. “After all, alien species are a problem. We have a large number of Procambarus clarkii, a freshwater crayfish (a native to Southeastern United Sates) and bullfrogs. With the shortage of protein sources before the war, bullfrogs were used as food for humans, and imported crayfish were used as bait for them. Both escaped into the wild, said Mr. Sato, who is a local resident and works for Hotoria as a facility management staff member. After the war, once Japan could maintain sufficient amounts of protein from other foods, bullfrogs were no longer needed as a source of protein, as were crayfish. Ironically, wetlands, with their abundance of preserved nature, became ideal habitats for these alien species.
We heard, “Through water canals, crayfish infest paddy fields, dig holes, and furrow. It causes great damage to farmers.” In Japan, there is practically no natural enemy for Procambarus clarkii and bullfrogs in our waters. In a food chain where bullfrogs prey on small crayfish, and humans eating bullfrogs continued, it might be balanced. But it is already irreparable. “We must exterminate the bullfrogs and crayfish fast in order to protect the native life in the wetlands. It has a long way to go,” Mr. Sato sighs.
According to the Community Nature Study Center, or Hotoria, in the city of Tsuruoka, the purpose of introducing bullfrogs was not only for human consumption, but also developing farmers’ side incomes by breeding and exporting them. But in 1969, in Seattle, USA, BHC that exceeded the accepted limit was detected in the frozen bullfrogs exported from Japan. Because of this, this undertaking collapsed. With a decline in the domestic cultivation, abandoned bullfrogs increased, and they affected the ecosystem negatively.