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The sea, sky, mountains, and rivers are all connected. Yoshihiro Suenaga, Creative Engineering, Kagawa University

We interviewed Yoshihiro Suenaga about marine ecosystem conservation who is professor and Dean of the Faculty of Creative Engineering at Kagawa University, an expert in fisheries and marine engineering.

Professor and Dean, Faculty of Creative Engineering, Kagawa University

Yoshihiro Suenaga

Born in Nagato City, Yamaguchi Prefecture in December 1964. Degree: Doctor of Engineering from the Graduate School of Science and Engineering, Nihon University, and the Oceanographic Research Institute, University of Tokyo. He joined Kagawa University in April 1996, and became a professor in April 2009. Appointed as Dean of the Faculty of Creative Engineering, Kagawa University from October 2019, and concurrently serving as Dean of the Graduate School of Emergent Sciences, Kagawa University from April 2022.
Specialized in aquatic environmental engineering, fisheries engineering, and marine engineering; recipient of the Commendation for Science and Technology. Received the Commendation by the Minister of Education, Culture, Sports, Science and Technology in the fields of science and technology in 2007, 2017, and 2019.

Decline of seaweed beds. The changing marine environment.
What is the future of the fishing industry?

Professor Suenaga, who has been conducting research mainly in the Seto Inland Sea, a region of Japan surrounded by bodies of water, has an illustrious career that has included multiple awards for science and technology from the Ministry of Education, Culture, Sports, Science and Technology. Please tell us about the “problems of marine ecosystems” as you have been working on sustainable fisheries and water quality improvement.

The supply of nutrients from the land has changed over the years.
The ocean used to be moderately rich in nutrients. When those nutrients become excessive, red tides, one of the ocean’s environmental problems*1, occur frequently in the Seto Inland Sea, causing serious damage to fishery resources.

Kagawa Prefecture is positioned as a prefecture that has fought against red tide, so to speak, and has a history of fighting against red tide.

*1 harmful algal blooms that grow out of control and release toxic or harmful effects on humans, fish, shellfish, marine mammals, and birds

I have heard that red tides have decreased considerably compared to the period when they were most prevalent.

We are told that laws and regulations such as the Law Concerning Special Measures for the Protection of the Seto Inland Sea Environment have changed and, conversely, the sea has become cleaner. However, the fishermen told us that they asked us to make the sea cleaner, but they did not ask us to make it impossible to catch fish.
It is difficult to decide whether to seek a clean sea or a rich sea, although it would be ideal if both were possible at the same time.

It is often said that we should return to the peak of what we used to be, but things have deteriorated to such an extent that we have not reached that peak. Fishery resources are also decreasing accordingly.

Above all, the “seaweed beds” where seaweed grows, the foundation of the marine ecosystem, are disappearing. As a result, there are no more spawning grounds, no more hiding places, and fewer and fewer places for fish and shellfish to grow.
There are many reasons for this, including the extraction of sea sand for infrastructure development.
However, since this is also necessary for human life, I don’t think it can be said that the developers are unilaterally to blame.

Therefore, our most important mission for the ocean is to show the optimum value, the point of compromise between the side that develops and the side that preserves the ecosystem! I believe this is our primary mission.
I believe that the decline of seaweed beds, among many other things, is the major cause of the most serious ecological disturbance.

How many people do you think are aware of those issues?

I think the voice of the fishermen is strong. However, the number of these fishermen is decreasing every year.
Not only in Kagawa Prefecture, but primary industries such as agriculture and fishing are now in need of a truly significant revolution. I call this the sixth industrialization.
The conventional methods of biological production and environmental protection cannot keep up with this trend. I believe that a new way of agriculture and fisheries using AI and informatics technology, including drones, will be required.

It means that people in industries that have not been directly involved in the primary industry up to now have the potential to exert great power.

I believe that a new way of aquaculture is already being questioned.
The natural environment has been changing considerably in terms of both biomass and diversity, as exemplified by the rise in water temperature. It seems that both are going in the wrong direction.
In the future, I think the question will be how to complete the cycle of marine biological production on land.

Harnessing natural energy to restore marine ecosystems.

Is there anything you are focusing on in your solutions for restoring the marine ecosystem?

I have been doing research for a long time, not just to develop something and just put things in the ocean, but to make good use of the tidal currents and natural energy that develop there, and bring it to the point where it leads to the recovery of the biological ecosystem.

In fact, the Seto Inland Sea is like a big river because it is an area where the current is predominant.
The high and low tides are repeated twice a day, forming a dominant east-west current that is the representative direction. This current, influenced by the topography of the islands and coastline, can become complex and flow into the bay, or conversely, there can be areas where there is almost no current at all.

In such areas, we hope to control the natural energy of the tidal currents in order to suppress the rise in water temperature and promote the growth of seaweed spores, which are essential for the biological ecosystem.

I believe that utilizing tidal currents, which are a valuable source of energy, is one possible solution to these basic problems.

I am surprised that you can even approach the water temperature issue.

I think it is possible to control water temperature to some extent by mixing water. However, if you spend a lot of money and use hard mechanical devices, it will cost a lot of money and not be cost-effective. What we have focused on is natural energy, which is the “tidal current.

We thought that by making it possible to control it without using mechanical devices, we could lead to the restoration of the ecosystem in the sea. In fact, there are several places where this has been effective.

If global warming progresses to the point where we cannot keep up with that control, we will have to come up with another method…but that is the only way to finally complete the project on land.

Forests, rivers, and oceans are connected.
Ocean acidification causes a collapse of the ocean’s ecological balance.

Your solution is going to be connected to the problem of ocean acidification.

Including carbon neutrality, I still think we cannot talk about it without algal beds. It’s about how to increase algae beds. It has decreased so drastically in the last 50 years that anyone can see it.

Recently, we have been talking about acidification of the oceans, and we often see shocking news for children, such as the dissolution of the shells of crustaceans and the decrease in the number of fish due to the disappearance of creatures that would have fed there.

There is a type of iron called fulvic acid, but it is not being supplied from the river to the extent that we can say that it has completely disappeared compared to the past. One of the reasons for this is that productivity is declining from the level of phytoplankton.
Of the series of systems that lead from the forest to the river and then to the ocean it will take 50 to 100 years, it is imperative to return the supply from the river to the old days.

If it is the Seto Inland Sea, from where does the influence of rivers come into play?

There are actually no major rivers on the Kagawa Prefecture side.
There are large rivers such as the Yoshino River in Tokushima Prefecture and the Yoshii River and Takahashi River on the Okayama side, but whether or not to open a sluice gate has a big impact on seaweed cultivation, which has a serious problem of color fading even in the Seto Inland Sea.
I think it will be important to control the supply of nutrients from the land area by opening weirs and sluice gates at the optimum time for marine organisms.

Lack of nutrient supply from land…
Nori (laver) cultivation has a serious problem with color fading.

I heard that the amount of Nori is decreasing very much.

Nori has a serious problem with fading.
Normally you would think of it as black wrapped around rice, but it has become a yellowish color. This makes it a poor grade and makes the seaweed unsaleable for the producers.

Why does the color fade?

It is because there is no supply of nutrients from the land.
If there is no supply from the land, the bottom of the ocean is rich in nutrients, so it is important to find a way to raise the nutrient-rich water underneath to the sea surface and allow it to reach the seaweed nets.
This also requires facilities that can control the flow, and methods that can control the flow without the use of hard mechanical devices.

In addition, Kagawa University is currently working independently with the local Shodoshima fishery cooperative and nori companies to set up a Kagawa University-style nori skirt on the nori nets.
The act of “fertilization” is the same as spreading fertilizer on a field as a source of nutrients.
In essence, the source of nutrients is artificially sprinkled on the nori nets. However, in the Seto Inland Sea, where the currents are fast, even if fertilizer is spread, it spreads quickly and is not easily absorbed by the laver.
To solve this problem, we are developing a technology that allows the artificial fertilizer to stay in the seaweed net for as long as possible after it is spread.

What is the principle behind it?

It is like a frame on the surface of the sea, with nets of laver stretched over it. The seaweed grows on these ropes, but if you just sow fertilizer on the ropes, the fertilizer will spread out from inside the frame due to the tide.
However, we put a skirt like a plastic sheet under the frame on all sides. When the fertilizer sow here, the skirt creates a trap.
The fertilizer can stay in the nets longer, and during that time the seaweed absorbs the fertilizer, making this a simple but effective facility.

It’s a very physical story.

Measurements have shown that this skirt reduces the velocity of the flow in the seaweed net. It creates a retention area, which means that more material can stay in that net.

Cooperation is possible.
Toward sustainable fisheries.

Don’t you think there will be a split between those who are willing to try new things like this and those who are not?

That’s right. However, it is a matter of life and death now, so everyone is wondering if there is any way to do it.
I am grateful that there are fishermen who are willing to take on this challenge with us because Kagawa University is locally located, but there is another challenge to this as well.
In a sense, the value of the university’s existence would be questioned if they were to say, “We did exactly what the professor at Kagawa University told us to do, but the seaweed didn’t grow at all”. We are determined not to let that happen.

Perhaps the presence of Kagawa University has made many of the vendors around Kagawa Prefecture more forward-looking.
However, nationwide, many are conservative and we often hear that it is not easy to get them to work on new things. How do you think we can create a system that is willing to change to a sustainable fishing industry?

I believe that if we can come up with some blockbuster technology, it will spread quickly.
It may be rough to say, but there is no one special technique in this world.
It is important to appeal not only to people in the coastal fishing industry but also to people involved in other industries by saying, “This could work,” even if it is on a small scale. If we do this, I think we can build a cooperative system.

The summer we saw a glimmer of hope in the fight against red tide

Can you tell us about a memorable episode you had with fishermen?

About 20 years ago, shortly after I was appointed to Kagawa University, we conducted an experiment to place a fish tank in an area where red tide was occurring.
At that time, I did not know the site where the fish tank was placed, and only heard about its placement and conducted the experiment in the hydraulic laboratory of Kagawa University. When I brought the results of the experiment to the fishermen, they said, “You don’t know anything about the local area, but the movement and distribution of the red tide in this experiment reproduced the site very well,” which led to the conclusion that this experiment might be useful.
After that, the fishermen all came to the university, lined up on both sides of the channel, and experimented with various placement patterns, and next time with this…and so on. That’s a matter of life and death.

Then, despite the fact that fish had been dying in large numbers due to red tide in the past, fortunately there was little damage that season. Therefore, they thought that if we put into practice the placement pattern described by the Kagawa University professor, the amount of fish dying could be reduced.

It is a heartbreaking memory that I recall now.

So you are here today because you have a system in place where you and the fishermen have worked together to accumulate successful experiences together.

Of course. I believe that in the future, new hydraulic experiments that were not possible before, new sustainable fishing methods using AI and IOT technologies, and the development of biological production technologies will be required.
And the many years of experience of fishermen is also becoming very valuable. I think it would be ideal to have a system that combines experience and technology to lead to a new 6th industrialization.

Vanishing Phantom Fish.
Research and Technological Development to Restore the Population

Professor Suenaga, you have been involved in various fish aquaculture projects. Could you tell us about your achievements in restoring the ecosystem of fish whose populations have been depleted by factors other than red tide?

There is a valuable fish called kijihata (Redspotted Grouper, also known as akou in the Setouchi area).
About 10 years ago, it was considered a phantom fish because it was no longer harvested at all.
It is a representative species of reef fish that huddles up to something and stays still.

Due to its status as a phantom fish, the price was very expensive for its daily consumers, and even more so during special holidays such as Bon Festival and New Year’s. However, the natural Kijihata have disappeared.

Fisheries research institutes and local governments in the Seto Inland Sea region have begun artificial seedling production of Kijihata fry.

This is a method of artificially hatching and releasing them into the sea to increase the number of fish.

However, there are various obstacles in the production stage. First of all, suppose that a virus occurs in the artificial tank during the hatching stage. This would result in the death of 100% of the fry.

100% dead…that’s a pretty grim situation.

Let’s say the fish has gone through the virus and is about 5 cm (about 2 inch) in size until it can be released into the ocean.
Before being released into the ocean, the fish are put in a fish tank of actual seawater to acclimate them to the actual natural seawater, which is called stocking.

During this stage, instead of swimming around in the actual seawater fish tank, the fish huddle together in the four corners of the tank to stay still because they are reef fish.

When a big wave hits the reef and the fish tank is shaken, the sensitive fish get stressed by the shaking of the tank and die. You can tell right away that a stressed fry is about to die because its body turns completely white.

Although it is not possible to stop the fish tank, it is necessary to have a technique to control the shaking to the level that the fish will not die.
When the supplier who had repeatedly put the fish in the fish tank and died said to me, “Is it possible to make a fish tank that does not sway?”. It is easy to say “There is no way.” But when I looked out at the ocean, I realized that it might be possible.
Kagawa University has patented a technology to suppress the shaking of the waves.

The fact that it seems so is indeed impressive. How did you achieve this?

For example, suppose there is a pendulum with a weight attached to the end of a certain length of string.
When the pendulum swings, it creates a period of swinging, right? Since ocean waves also have various periods, the intrinsic period of the pendulum and the technology to suppress waves can be linked.

So, based on the formula for finding the natural period of a pendulum, we created a device to suppress the swaying of the pendulum.

In fact, when we installed the device, not all the fry survived, but the number of survivors was different.

In addition, there was also a difference in the obesity of the fry in the fish tanks with and without the device. The fish in the fish tank without the device were a little thin, but the fry in the fish tank with less shaking were more obese. When it becomes like this, we release them into the sea.

So you have achieved the first requested functionality?

Yes, we did. However, the release of the fish into the sea was not the end of the story.
For example, even if we released 200,000 fish into the sea, only 1% or less would survive.
Why are there so few fish left after releasing 200,000 fish?

As I mentioned earlier, Kijihata are reef fish that have a tendency to huddle together.
We have found that when placed in a large inshore tank with larger fish, such as larger Kijihata and Kasago (scorpionfish), they tend to gravitate to the larger fish themselves. Since these fry do not know what they are doing in the wild, they think that they are the target of their attachment.
The big fish will approach the best bait without any effort, and they will eat it in a single bite. Watching this, I realized that no matter how many fish we released, there would be none left.

So you see a new problem. How did you solve them?

We assumed that we needed a facility in the ocean that would grow to a size where the fish could be released and not be eaten.
So, we introduced an artificial fish reef that functions as a shelter, where the fry are released into a structure that can control the current, where they can feed and grow to a size where they cannot be eaten by larger fish.

This is a project that we have been working on for about 10 years in cooperation with the local fishery people of Ibukijima island.
In fact, stocks of kijihata have been increasing, and recently they are no longer a phantom fish (laughs).

The initial goal has been achieved.

But now the price has dropped because the catch has gone up, and a new problem has arisen: getting the price back to where it was.

I see. As a marine resource, it is not only the study of fish ecology, but there are other difficulties in terms of utilizing it for the economy.

We have been able to increase the number of Kijihata by working together with fishermen.

As a new challenge, I think the key to raising the price is to transport and haul the fish in a live state. Since this is a sensitive fish, it can die due to the stress of transportation, so we also need to develop technology to deliver the fish to the urban areas in a fresh, live state.

Energy from wave vibration into electric power.

I could see how one research could expand into another development. Are there any other technologies you are researching?

In the future, I would like to create a fish tank integrated with a device that absorbs wave energy.

Since we are still in the prototype stage, we are taking the method of retrofitting it to an existing fish tank. There are four large U-shaped tubes attached to it, and the waves come in and are synchronized inside the device to attenuate the energy of the waves.

A fish tank built on the principle of a pendulum. The blue part is a device that absorbs waves. The one with a person on it at the back of the photo is a conventional fish tank. 
 (Figure 1) Excerpt from Prof. Suenaga’s data ()

When water enters, a column of water is formed (Figure 1, light blue area).
The length of the column of water inside determines the period of this device. When a wave with the same period as the period of this device enters, the column of water in this device oscillates the most.

When the water vibrates in this hollow area (Fig. 1, white area), the energy of the water vibration is converted into the energy of the air.

Suppose you are looking through the white part with the human eye. Then, at a certain moment, there is a moment when you feel the wind. That is the moment when this water is most agitated.

I understood it from your explanation, but I had never thought about sensing wind from waves.

I would like to use this principle to generate electricity in the future by converting vibration energy into air energy.

For example, the current fish tank is on the sea, so there is no power source. However, fishermen need a facility to throw food to the fish they are farming.

We are getting to the point where we can use the energy from the vibration of the waves to power such feeding equipment, or to power lights for monitoring.

If we use electricity generated by the power of waves in offshore facilities, it is a wonderful technology that reduces transmission and distribution costs and emits no carbon dioxide or other harmful substances!

Improving the Environment through Effective Use of Fish Residues

I heard that you have a fish bone product that you led the research and development of.

As you know, Kagawa Prefecture is the birthplace of fish farming. It was the first prefecture to start a fishing industry to produce and raise fish, instead of catching them.
Fish that grow well in fish ponds are shipped to the market with both sides and bones removed.
However, the remaining bony parts of the fish are disposed of as industrial waste by the fishermen, who pay to have them removed.

As the birthplace of aquaculture, a large amount of residue is produced every day.

The university decided to take the residue that they had paid to dispose of and see if it could be used in some way.

With the cooperation of the people in the fishing cooperative, especially the women’s club, we first boil the fish and have them remove the meat and bones.

After that, we use an electric furnace. At 500 degrees Celsius (932 Fahrenheit), the bones turn black and charcoal-like, but at 700 to 900 degrees Celsius (1292F – 1652F), the bones turn pure white.

This is really a good material for improving the environment.

As you know, there are bones in the human body.

Mercury and cadmium, which are toxic heavy metals such as those used in Itai-itai disease and Minamata disease, have the property of attaching specifically to bones once they enter the body. This is what caused the pollution diseases.

Similar to this principle, hydroxyapatite is formed in the bone material, and calcium is removed and replaced by another metal.

In the Seto Inland Sea, there are many closed inner bays*1, so once something got into the inner bay, it was difficult to get out.
In other words, it is a land where bad things tend to accumulate in the mud once they enter.

In fact, there are places where there are no factories around, but when the mud is removed from the sea bottom, it contains a lot of metals.

Until now, we have not been able to treat this metal properly.
We have installed various porous substrates and tried using microorganisms, but it was difficult to treat the metals.

So, we focused on the effect of adsorbing harmful metals, mixed the ingredients of the white baked bones I mentioned earlier with concrete, and actually installed it in the ocean for verification and experimentation.

We are considering the possibility of using fish waste as a new method to improve mud and water quality.

When I hear about improving problems on the seafloor at fish farms, I imagine it would be a very large-scale project, but this would be a great way to reuse waste and reduce costs.

*11Bay shaped like a V or U in the alphabet

What we can do to protect marine life

What can we, as consumers, do to protect marine life?

From visible plastic to microplastics, we have a team working all the time. We are also setting up plankton nets in estuaries to see how much microplastics are coming in from the river.

Microplastics are ingested by organisms, so I think it is a very tricky problem.

Also, consumers should not take small fish, even for leisure. One person’s numbers may be small, but if everyone does it, the numbers will grow.

If we continue to do that, there will be no generations to come. I think we need to provide more environment in the ocean for such small fish to grow.

Impressions of CLASS EARTH

I think Nature Positive is a very agreeable concept.
I have the impression that it encompasses what each of us should keep in mind on a global scale.
I hope we can continue to build a cooperative and collaborative system for the recovery of the environment and global resources.

Faculty of Creative Engineering, Kagawa University


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