Ito salmon shows its vivid red breeding colours in a river in Hokkaido. (Photo: National Institute for Environmental Studies)
Japan's biggest salmon gets tech help to escape troubled waters
Wednesday, June 01, 2016, 03:20 (GMT + 9)
Scientists have to see in the dark and examine feces to ensure Japan's biggest freshwater fish is safe.
The endangered monster in question is commonly known as the ito in Japan. It's the Sakhalin taimen, or the Japanese huchen, or in plain English, a rare type of salmon. And these big beauties can reach almost 2 metres in length.
Sonar video cameras can capture images of the salmon when the waters are murky or even when it's pitch black.
The emerging environmental DNA technique is used to examine animal debris such as feces, allowing researchers to see if the rare salmon has been swimming nearby.
The cameras have been installed on the upstream side of a fish passage built into a dam located on the Sarufutsugawa river here in Japan's northernmost reaches. They were placed in 2013 and are operated during the spawning season every April through May to track the number of the endangered salmon swimming upstream to lay eggs.
About 30 people were on the riverside of the tributary in Sarufutsu on May 2, inspecting the location of the cameras.
They were participating in a symposium on the ito held the same day by the Sarufutsu Itou Conservation Council and the National Institute for Environmental Studies (NIES).
Like most Salmonidae, ito hatch from eggs laid in upstream rivers and then grow up in the ocean. They swim back up rivers for spawning. But unlike many other fish in the salmon family, these salmon repeatedly spawn during a lifespan believed to range between 20 and 25 years.
After the participants checked out the camera sites, a lecture and briefing session on the ito was held, in which Michio Fukushima, a senior researcher at NIES, reported the population statistics and fluctuation patterns based on the river trips of the fish between 2013 and 2015. The study was based on data recorded with sonar devices.
The ito salmon was once commonly found across Hokkaido and even parts of the Tohoku region, but today their population has significantly diminished, mainly due to the compromising of their habitats by development projects.
Today, only a handful of rivers in the northern island serve as their habitats.
According to Fukushima, taimen begin making their way upstream along the tributary where the cameras are installed toward the end of April every year. The migration peaks around noon every day and the fish stop moving up during the evening.
Research also revealed a tendency in which large individuals believed to be elderly make their trip earlier in the season than smaller, younger fish.
In the three years surveyed, 335 ito were recorded in 2013, 424 in 2014 and 528 in 2015. Although the figures show a steady increase in the fish population, Fukushima said that this year’s batch is not as numerous as 2015.
“As their migration upstream may follow a periodic pattern, we cannot yet simply conclude that the taimen in the Sarufutsu area has increased in number,” the scientist said.
Hitoshi Araki, a professor of biology at Hokkaido University’s Lab of Animal Ecology, and a group of other researchers are also studying the rare salmon in the area using an emerging technique known as environmental DNA.
The method checks the feces, mucus and other samples released by aquatic creatures that drift in water to determine what sort of organism lives there. The study is anticipated to unveil the distribution of rare fish species like the taimen in the entire Hokkaido area in detail.
“By understanding the population sizes and their fluctuation patterns, we are able to examine the effectiveness of our efforts to conserve the river environments of Hokkaido and come up with data to support the technological development of the environmental DNA method,” Fukushima said. “We hope to continue our efforts by using a method that allows the comparison of data taken in set intervals.”
Source: KENICHIRO SHIMADA/Asahi