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Starting in 2007, with approval from the Tokyo Metropolitan Government, the group began capturing bluegill and black bass — freshwater species indigenous to North America — in the pond to protect its native species and ecosystem.
As of April 21, the group's 23 members had caught a total of 289,101 bluegill and 24,309 bass. Their efforts, though low-key, have been effective in preventing the foreign fish from expanding their numbers — and saving native breeds from extinction.
Nevertheless, the group hasn't been able to effect a major drop in the invaders' population or reverse the decline in indigenous species.
"There are limits to what we can do," Tanaka said. "The reproductive power of black bass and bluegills is high."
Today, Inokashira pond is almost dominated by bluegill and bass. The native species, including the stone "moroko" (a type of carp) and the "toyoshinobori" rhinogobius [a type of goby], are in decline.
In the meantime, Tanaka said that the park's "kaitsuburi" (dabchicks), which depend on the stone moroko as food, are nearly gone.
"A few years ago, there were three breeding pairs of dabchick (in the park). But now only one pair remains," he said of the ducks.
Last fall, the Tokyo Metropolitan Government blocked off a corner of the pond to build a protected space where native fish species can live and hopefully breed. Tanaka said he is eager to see indigenous species flourish again but hasn't been able to confirm an uptick in the population yet.
The metropolitan government also plans to drain the pond to clean the muddy water and to eliminate foreign species. A similar method was used a few times in the moat around the Imperial Palace and had been considered effective in eliminating the two interlopers.
However, Norio Iwami, a professor of environmental microbiology at Meisei University, said it's anyone's guess how long that measure will work.
"By draining the water, we can clearly see what kind of creatures are living in the pond and we can retrieve them. So it would be effective," Iwami said. "But if an Adam and Eve remain, they breed again. If they can't retrieve all the eggs, then I don't know what will happen. We'll have to wait for a year or two to know the result."
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Interesting read as to anglers' effort vs. success in removing invasive species (in this case bluegill and largemouth bass), and the strong reproductive capability of bluegills and largemouth bass given an ideal environment. If you are seriously concerned about the re-establishment and stability of largemouth bass population in Lake Wilson, check this out.
This is an example of what I've been trying to say all along. Given the ideal environment, bluegills and bass has an absolute high reproduction capability.
Illegitimus Non Carborundum
