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Why do Japanese crayfish run rampant when they trample on crayfish as fertilizer?

Every summer, crawfish is the favorite of many eaters. But in Japan, crawfish is crushed to be fertilizer. What's the matter? Why is crawfish so popular?

Every summer and autumn, people come to catch crayfish near the ahan Lake in Hokkaido City, Japan. However, the purpose of catching crayfish is not to taste delicious food, but to control the expansion of this alien species and prevent damage to the lake ecosystem. Every time the next cage, soon can catch dozens of kilograms of crawfish.

Crayfish, scientific name of crayfish, originated from the United States. In 1930, it entered Japan with American merchant ships. In addition to being eaten in China and having to rely on artificial breeding, crawfish has grown at an amazing speed in other countries and regions, becoming a typical representative of the local alien species. The picture shows a warning sign that crayfish of alien species is forbidden to be put on the Bank of Ahan lake.

Local children sometimes help to catch shrimps. From May to November every year, it's the crawfish catching period. Due to the rapid growth of crawfish, the local government began to allow fishermen to catch crawfish in the 1980s, and there are about 4 tons of goods received each year.

But crayfish reproduce so fast that it can't be eradicated by fishing alone. So local universities, agricultural research institutes and so on track and observe the breeding habits and living habits of crawfish to determine a more scientific expulsion method. Not only the Ahan lake, but also many other large lakes in Japan have found traces of crayfish.

Some of the crayfish caught in Ahan lake are sent to Tokyo and other big cities for food. But this part of the population is very small, and the income from selling crawfish only accounts for 4% of the total income of fishermen. There is not much interest in selling crawfish.

The surplus crawfish fishermen trample it directly and use it as fertilizer. The expulsion of crawfish has been going on and has achieved some results. In 2010, 100000 crawfish were captured and eliminated, and by 2016, the number was reduced to 36000.