In July 2023, we captured a group of smallmouth bass, a designated invasive species, at a reservoir in Gujo City, Gifu Prefecture.
Specified alien species that threaten the ecosystem have been found all over the country, and in 2021, Nagoya City conducted a pond drying event at Idaka Green Park in Meito Ward.
Additionally, in 2022, an activity was carried out at Higashiyama-Shinike in Chikusa Ward to remove the “water lily”, which is considered to “oppress native species” according to prefectural ordinances. As time passed, I followed the place to see what it was like.
■Large numbers of smallmouth bass are being caught, threatening the ecosystem of the famous sweetfish
On July 27, 2023, in Gujo City, Gifu Prefecture, an operation to exterminate the smallmouth bass, a specified invasive species native to North America, was carried out at a reservoir connected to the Nagara River.
Smallmouth bass are carnivorous and prey on sweetfish, Gifu’s specialty, which can threaten the ecosystem. On this day, 76 fish were caught.
The fish are believed to have been secretly released, and the head of the local fishing cooperative is furious, calling it “environmental terrorism.”
■They also appeared in the moat of Nagoya Castle…What are specific alien species?
There are many other types of specified alien species. Raccoons, alligator gar, snapping turtles, black bass (largemouth bass), redback spiders, and fire ants are all designated alien species, and all of these have been confirmed in Nagoya. Alligator gar was also found in the outer moat of Nagoya Castle and became a hot topic at the time.
According to the Nagoya Biodiversity Center in Tenpaku Ward, specified alien species are designated as species that are likely to “destroy the ecosystem,” “damage the agriculture, forestry and fisheries industry,” and “endanger human life.”
In principle, breeding, importing, selling, and releasing them into the open are prohibited.
Violators are subject to imprisonment of up to 3 years or a fine of up to 3 million yen in the case of individuals, and fines of up to 100 million yen in the case of corporations.
■There are over 3,000 bluegills in a Nagoya pond that has been drained of all water.
Eradication activities have also been carried out in Nagoya. In November 2021, approximately 100 people conducted a “drain all the water in the pond” operation at Idaka Ryokuchi in Meito Ward, draining the water from the pond and drying it to capture invasive species.
During the mission, they caught fish one after another while getting stuck in the mud, and found 3,386 bluegill, a designated invasive species. According to the chairman of the Meito Nature Club, who participated in the extermination effort, they are a threat to the snailfish and medaka because they eat young fish.
In addition, 292 tadpoles of the bullfrog, a designated invasive species, and 320 American crayfish, a conditionally designated invasive species, were found.
A carp was also caught. Carp are familiar, but there are many non-native species. The “native species” found, such as crucian carp and catfish, were returned after the pond was refilled with water.
At Higashiyama Shinike Pond in Chikusa Ward, in November 2022, a “strategy to remove all the water lilies in the pond” was carried out to remove the “water lilies” covering the pond.
The water lily has beautiful flowers, but it is actually an invasive species and is characterized by its rapid growth. If left untreated, the stems and leaves will cover the entire pond, making it impossible for other plants to photosynthesize, reducing oxygen in the water, and potentially killing native species.
Although water lilies are not specified as invasive species, they are designated as “existences that oppress native species” under Aichi Prefecture regulations.
On this day, only about 10% of the total was removed in one hour, but it was a significant amount.
■We were able to catch all the bluegill, but what happened after the pond was completely drained of water.
The “Operation to drain all the water from the pond” was carried out in 2021, but what is happening now? I visited the current pond.
According to the chairman of the Meito Nature Club, the current state of Suribachi Pond in Idaka Ryokuchi in Meito Ward, Nagoya City, where invasive species were exterminated through a “strategy to drain all the water in the pond”, has completely eliminated all bluegill and carp. He says, “Maybe it worked.”
However, although the invasive species that were present two years ago are almost no longer seen, “another” specific invasive species is said to be proliferating.
Chairman of Meito Nature Club:
“We were introduced to a specific alien species called Kadayashi, and it is currently thriving.”
Kadayashi derives its name from the word “to exterminate mosquitoes” and is said to have been brought from overseas to exterminate mosquitoes that transmit diseases, but it was not seen before the pond was dried.
Their appearance and lifestyle are very similar to medaka fish, so they are stealing their habitat. Eggs are laid inside the body, hatch, and then come out.
Kadayashi has a high reproductive capacity because it is grown inside its body until it becomes a fry, and it may even eat young killifish, putting the killifish in the pond at risk.
Regarding the release, the chairman of the Meito Nature Club said, “I want you to remember that releasing living things outside may destroy the entire ecosystem.”
Two other lacewing turtles, which had never been seen before, were also discovered at Idaka Ryokuchi. Turtles usually withdraw their faces when a finger is pointed at their faces, but the lacewing turtles that were discovered put their faces forward and open their mouths, as if to say, “Give me some food.”
This is believed to have been a “domesticated” turtle, and is believed to have been abandoned by someone.
■After a year, the pond where the water lilies were removed is completely destroyed…
In August 2023, we visited Higashiyama Shinike Pond in Chikusa Ward, where we carried out the “strategy to pull out all the water lilies in the pond” to find out what is “current”.
When I visited the pond, more than three quarters of the water surface was covered with water lily leaves.
We spoke to two members of the Nagoya Chikusa Lions Club, who led the effort to remove water lilies in 2022.
Mr. Nonoyama of Nagoya Chikusa Lions Club:
“The speed at which it grows back is actually faster. The roots underneath are quite intricate and form a network.”
Mr. Wakayama of Nagoya Chikusa Lions Club:
“I think if we had more people and more time to work, we would have been able to get through more.”
Pulling out water lilies is hard work and takes time, but it is said that it is difficult to completely remove them unless you grow at a faster pace.
Mr. Wakayama:
“Just like in 2022 (in 2023), we are looking for volunteers from the general public and would like to do this together.”
The event is scheduled to be held in the fall of 2023.
Broadcast on August 9, 2023
2023-09-30 12:30:00
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