Japan legislates to ban the sale of crayfish
On May 11, Japan's Alien Biological Law was amended in the Diet, and the key message is that from now on, crayfish and Mississippi red-eared turtles cannot be sold or released, or even kept as pets, but if they are already raised, they can continue to keep them. This is clearly aimed at mitigating and preventing the impacts of alien species on native ecosystems.
Why not treat it by making it a dish and controlling crayfish in the wild? Because of Japan's strong exclusivity from food, the food culture of the native island countries is very deeply rooted. Crayfish, which were only transported to Japan as fodder in 1927, were clearly not enough to shake the status of indigenous food, and after the crayfish entered Japan, they quickly multiplied explosively in the ponds of 47 prefectures in Japan, and soon became invasive species. Japanese fishermen caught crayfish by crushing them and feeding them to livestock.
They have extremely low requirements for the living environment, and they are quite picky eaters, what aquatic weeds, algae, all kinds of small aquatic animals and even animal carcasses are acceptable, in the case of food shortage, mutual encroachment may occur, so all kinds of harmful substances are easy to accumulate in their bodies.
Of course, the problem of crayfish invasion does not exist only in Japan, how exactly did they expand rapidly in the world?
What are invasive alien species and why are they a problem?
We live in an ever-changing world where we can travel long distances easier and faster than ever before, and humans often accidentally or deliberately take many species out of their natural homes or native ranges, and the frequency of such events has increased dramatically in recent decades. Many species are eventually released into new environments where they can survive, successfully reproduce and become invasive species.
Because they do not have a place in the history of the native ecology, their reproduction cannot be limited, which means that they begin to outperform native species in competition.
The harm of invasive alien species is enormous. For example, crayfish piled up in water intake pipes used to irrigate farmland can clog pipes, causing farmers to lose a lot of money. There are also carp that are flooded in the United States, and when they forage, they turn up sediment to increase the turbidity of the water, which will reduce the ability of aquatic plants to photosynthesize.
Given their severe impact, invasive alien species are considered one of the greatest threats to biodiversity, ecosystem services and human well-being.
The departure of the crayfish
Crayfish are native to the southern United States and northeastern Mexico, but can now be found in the inland waters of all continents except Australia and Antarctica. This freshwater crustacean easily reaches high densities, becomes an invasive species, and causes serious ecological and economic impacts, such as preying on native flora and fauna, spreading disease to other aquatic species, and destroying dike and canal activity in rice paddies due to burrowing.
They spread around the world mainly because of their commercial value, and according to statistics, crayfish generate tens of billions of dollars in revenue around the world every year. In the last century, the development of the economy around the world was the focus, delicious and well-bred crayfish is obviously a good choice, due to the lack of awareness of its impact, and hope to make some money, people deliberately introduced this species into the wild in many parts of the world, not only crayfish enthusiasts or commercial companies, but even scientists at that time had a high evaluation of them.
The invasion of crayfish is actually very complicated
In recent decades, crayfish have been introduced to more places, leading to their rapid spread across the globe. Based on the number of introduction events and the number of individuals introduced, the scientists found that populations of crayfish were differentiated, with invading populations with low or high genetic variability appearing simultaneously.
Scientists can analyze the mitochondrial DNA of crayfish in different regions and their genetic sequences to find out where the crayfish come from. In this way, scientists were able to reconstruct the invasion routes of crayfish around the world.
This is critical for discovery to understand how invasive species are expanding. This knowledge could help scientists find more effective strategies to prevent their spread and the negative impacts they can have when they take over ecosystems.