Image courtesy of YouTube
A large number of dead silver carp, a freshwater fish, have been found in the Sakuragawa River, which flows through Tsuchiura City and other areas in Ibaraki Prefecture. Why did they die in such large numbers?
On the 30th in Tsuchiura City, Ibaraki Prefecture, contractors were collecting the carcasses of silver carp, a freshwater fish native to China, from the river. The Sakuragawa River, which flows through Tsuchiura City and Tsukuba City, was floating with a large number of silver carp carcasses. According to the prefecture, silver carp carcasses have been confirmed along approximately 10 kilometers since the 24th of this month. Last month, silver carp were seen making large jumps in the river, characteristic of the spawning season, but on the 30th, there was no sign of this, and a large number of them were floating. In response to this situation, the prefecture installed fences along the river last week and began collection efforts, but the work has been difficult. They were picking up the fish one by one.
The largest silver carp are said to be about 1 meter long. Collection worker: “They’re heavy. They weigh more than 4 kilograms.” It’s not just the weight that’s difficult, but the sheer volume. A fish collection worker said, “There are thousands, tens of thousands, tens of thousands of them. We’ve been transporting them in 4-ton and 3-ton trucks multiple times.” The most difficult thing, however, is the strong, fishy smell. Residents were also bewildered by the foul odor wafting through the area. A nearby resident said, “The river smelled worse than usual, so I wondered what was going on, and then I was like, ‘What?!'” “I’ve lived in Tsuchiura for decades, and I’ve never seen anything like this before. There’s never been anything like this before.” ◇ So why did the silver carp die in such large numbers? The first to notice the change was the fishing cooperative that operates in this river.
Kiyoji Suzuki, head of the Sakuragawa Fisheries Cooperative, said, “The water has disappeared, so it’s no longer flowing. It’s hell.” On the 24th of this month, the flow of the river was stopped at a weir upstream to divert water to the rice paddies. According to the Niihari Land Improvement District, this is a necessary operation for maintaining the rice paddies, but it has caused the water level downstream to drop. Regarding the cause of death of the silver carp, the prefecture has determined that there were no problems with water quality and that the mass death was likely due to the drop in water level.
The aquarium that keeps the silver carp pointed out the following: Naoto Kobayashi, exhibit manager at Nakagawa Aquatic Park in Tochigi Prefecture: “When the water level drops, the total volume of water decreases, so if the number of fish in it remains the same, the amount of oxygen the water can hold decreases, and there is a high possibility that this is the cause of oxygen depletion.” According to the prefecture, the silver carp recovery operation is expected to be completed by the end of this week.
