When I heard of loggerhead turtles, I imagined them swimming in the blue sea of a tropical country, but in October I heard that a loggerhead turtle was caught in a fishing net off the coast of Hokkaido.
And not just one.
It is said that more than 20 were caught in the net during about a month from mid-September.
What the hell is going on?
In order to confirm with my own eyes, in mid-October, I asked Kazuya Hashimoto, a fisherman in
Noboribetsu
City, Hokkaido, who had given me information, to accompany me on a fishing trip.
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Mr. Hashimoto has been a fisherman in Noboribetsu for 34 years.
From autumn to winter, we set gill nets on the seabed at a depth of about 70m, about 7km off the coast of Noboribetsu, and catch monkfish and kasube, a type of ray.
On the day I went with him, when I started pulling up the net, there were several kasube.
And about an hour later.
"It's a turtle."
Hashimoto pointed at the net.
When I looked into the sea from the boat, a male loggerhead turtle about 1 meter in length was entangled in a net and came up to the surface.
The body is white and motionless.
It is believed that he died because he could not catch his breath.
I tried to pull it up on the boat to untie the net, but the weight untied the net on its own and the loggerhead sank into the sea.
This is the first time Mr. Hashimoto has seen loggerhead turtles off the coast of Noboribetsu.
However, it is said that more than 20 were caught in the net during the month from mid-September.
Mr. Kazuya Hashimoto: “Every time I pull up the net, I catch two or three. At times, there were nine in one day. I had never seen one before, so I was surprised. I want to help her, but I can't do anything because she's already dead."
Damage to fisheries
After returning to the port, Mr. Hashimoto showed me a net that was no longer usable.
Nets that have become entangled with large loggerhead turtles have to be cut and cannot be used for fishing anymore.
In addition, it is said that the catch of kasube and monkfish in mid-October this year is less than half of what it usually is.
Mr. Hashimoto told us about his complicated feelings.
Mr. Kazuya Hashimoto: “If the turtles get caught in the net, the number of turtles will decrease, and it’s not good for the environment.
"Endangered species" Loggerhead turtle Why is it in the sea of Hokkaido?
What kind of creature is the loggerhead turtle?
▽It spawns on the coasts of areas south of Ibaraki Prefecture, such as Okinawa, Yakushima, and Wakayama.
▽ In addition to crabs and sea urchins that live on the seabed, they often eat jellyfish.
▽ It repeatedly dives to a depth of about 30m, but sometimes dives to a depth of 100m or more.
It is designated as an "endangered species" in the Red List 2020 of the Ministry of the Environment.
According to the Sea Turtle Association of Japan, annual surveys of the number of times loggerhead turtles land and lay eggs at spawning grounds all over Japan show that both numbers have continued to decline since 2013, raising concerns about a declining population.
Why was the endangered loggerhead turtle caught in a net in the sea of Hokkaido?
We asked Professor Katsufumi Sato of the University of Tokyo's Atmosphere and Ocean Research Institute, who has been studying the ecology of sea turtles for many years.
Professor Katsufumi Sato, Atmosphere and Ocean Research Institute, The University of Tokyo "I believe that the habitat of loggerhead turtles is most likely expanding little by little to the north. I imagine that when the water temperature gradually warmed up and it became possible to go to Hokkaido, loggerhead turtles would gather because there was plenty of food there.”
Loggerhead turtles are caught in nets outside of Noboribetsu...
Further investigation revealed that loggerhead turtles were caught in nets around the same time in places other than Noboribetsu.
The photo shows a loggerhead turtle caught in a net off the coast of Hakodate in mid-October.
This photo was taken by Assistant Professor Nobu Tomiyasu of Hokkaido University's Faculty of Fisheries Science, who is investigating sea turtles caught in fishing nets in the sea around Hakodate.
According to Assistant Professor Tomiyasu, loggerhead turtles are sometimes caught in fishing nets off the coast of Hakodate from summer to autumn.
But no one has ever seen so many loggerhead turtles caught in the net at once, he says.
Assistant Professor Nobu Tomiyasu, Faculty of Fisheries Sciences, Hokkaido University: "Sea turtles are not creatures that swim around in groups, so it's quite surprising that they are bycatch in the same place all at once."
Why did so many loggerhead turtles gather in Noboribetsu?
Assistant Professor Tomiyasu focused on the "sea surface temperature" around Noboribetsu.
From previous surveys, it has been confirmed that loggerhead turtles come to the coast around Hokkaido when the sea surface temperature reaches around 18 degrees Celsius in the summer.
On October 13th, when I went fishing, the sea surface temperature off the coast of Noboribetsu was about 18 degrees.
As winter approaches and the seawater temperature begins to drop due to cold currents, loggerhead turtles that have spent the summer off the coast of Hidaka and eastern Hokkaido begin to migrate, and some of them have gathered off the coast of Noboribetsu, where the temperature is still around 18 degrees. Assistant Professor Tomiyasu speculates.
Assistant Professor Nobu Tomiyasu, Graduate School of Fisheries Sciences, Hokkaido University “In the future, if the sea temperature rises, I think that an environment that makes it easier for sea turtles to migrate will be created widely around Hokkaido. We can't ask people to stop fishing to protect sea turtles, so we need to think about ways to protect sea turtles while continuing to fish."
Loggerhead turtles haven't been caught in nets since late October when the water temperature dropped.
However, when the sea warms up again next year, loggerhead turtles may be caught in nets and killed.
Mr. Hashimoto, a fisherman, says that if loggerhead turtles are frequently caught in nets from next year onwards, he would like to consider measures such as delaying the timing of putting in nets until the sea temperature drops and reducing the number of nets.
A new incident that occurred off the coast of Hokkaido, may be a warning that climate change is happening all around us.