A microplastic collection device that does not involve small fish.

Abstract

To provide a microplastic collection device that does not involve small fish and can protect aquatic life such as small fish. [Solution] The system features a tank 1 in which small fish can swim, a net 3 inside the tank 1 that can catch microplastics 2, a pump 5 that draws seawater into the tank 1 and discharges the seawater that has passed through the net 3, the pump 5 is installed downstream of the net 3, a speaker 7 is installed on the underside of the lid 6 of the tank 1 and the speaker 7 is positioned higher than the water level H inside the tank 1, the pump 5 is periodically stopped at predetermined intervals and a deterrent sound is emitted from the speaker 7 at the time the pump 5 is stopped, thereby causing small fish that have entered the tank 1 to escape into the sea through the passage 8 into which seawater is drawn.

Description

Technical Field

[0001] The present invention relates to a microplastic recovery device that does not entangle small fish.

Background Art

[0002] "Microplastics" floating in the ocean have a serious impact on marine life and human health. Microplastics are very small plastic pieces, generally referring to those with a size of 5 mm or less. In recent years, the environmental impact of microplastics flowing into the sea has become more serious, and research on them has also advanced. Microplastics are roughly classified into two types: "primary microplastics" and "secondary microplastics". Primary microplastics are small plastics such as scrubbing agents contained in facial cleansers and toothpastes, and flow into the sea through sewage treatment from household wastewater. Once they enter the sea, recovery is almost impossible, and countermeasures after productization are considered very difficult. Secondary microplastics are plastic products such as plastic bags, PET bottles, and cigarette nets that flow into the sea via roadside ditches and rivers, and are degraded and fragmented by ultraviolet rays and waves to become micro-sized. In the modern ocean, such microplastics exist in large quantities, and due to their small size, it is extremely difficult to recover them, which has become a major problem. In particular, in the sea, aquatic organisms such as small fish eat microplastics thinking they are food, causing a food chain disruption, which is very serious. Therefore, I became interested in how microplastics are recovered in the world and searched on the Internet. As a result, I found that the information is scarce and that no such recovery method has been established even in the world. Further research revealed that in Japan, Kanazawa Hakkeijima Sea Paradise has a microplastic collection device called "Seabin" and a marine debris cleaning device called "Jellyfish Bot," the only one of its kind in Japan, so I immediately went to see them. This was on December 23, 2022. Seeing them in person, I was impressed by how large and elaborate the devices were. According to the staff, one Seabin costs about 700,000 yen, and one Jellyfish Bot costs several million yen, making them quite expensive. Since the device is fixed to the pier and its installation location is limited, I wondered if it might be susceptible to the effects of waves and currents depending on the location and shape of the pier, which could result in a decrease in the efficiency of microplastic collection. I also wondered whether typical microplastic collection devices are adequately designed to prevent small fish from getting caught in them. Around this time, I started thinking about creating a device that could collect microplastics more easily and efficiently, while also protecting aquatic life such as small fish. Patent documents 1 to 3 describe large-scale devices and systems for collecting microplastics. Regarding the protection of aquatic life such as small fish, I focused on the fact that there are sounds that fish dislike. Since I was in elementary school, I used to enjoy playing sound tests where people who could hear a mosquito tone at XX Hz were young, and those who couldn't hear XX Hz weren't young! Also, when I visit cemeteries, there are places where mosquito sounds are played to keep cats away, and I always found that sound unpleasant, which was one of the reasons I became interested in sound. I wondered if small fish might also find certain sounds unpleasant, just as humans do. After doing some research online, I found information that fish dislike certain high-frequency and low-frequency sounds, and I initially speculated that sounds around 5000Hz might be the sound they dislike the most. Furthermore, Patent Documents 4 through 7 also describe the use of sound for fish. When I spoke to a professor who teaches at Hosei University about my idea, he agreed to cooperate and we conducted an experiment on September 15, 2024, in the sea off Nojima in Yokohama City, Kanagawa Prefecture. The experiment involved the teacher first catching small fish and shrimp with a special net, and then immediately placing the creatures and seawater into a boat-shaped bucket (a plastic container similar to a baby bath). When I played a 5000Hz sound from a speaker using Bluetooth® from my smartphone, it had no effect on any of the creatures, and no change was observed. This proved my initial prediction to be incorrect. Later, my teacher told me there was no evidence that small fish dislike 5000Hz, and advised me to read relevant papers and literature. Through reading numerous documents, I learned that the sound small fish dislike most is 100Hz and 110dB-160dB. I also learned that small fish dislike the sound of birds plunging their heads into the water the most. However, 110dB is an alarm-level noise, so I couldn't test it at home for the sake of disturbing the neighbors. Therefore, I decided not to pursue volume levels further and to continue the experiment at the maximum volume that wouldn't disturb the neighbors. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-66030 [Patent Document 2] Japanese Patent Publication No. 2022-108255 [Patent Document 3] Japanese Patent Publication No. 2024-42846 [Patent Document 4] Japanese Patent Publication No. 2014-171411 [Patent Document 5] Japanese Patent Publication No. 2016-111943 [Patent Document 6] Japanese Patent Publication No. 2024-20706 [Patent Document 7] Japanese Patent Publication No. 62-239935 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] I wanted to design a device that could easily, efficiently, and energy-savingly collect microplastics floating in the ocean, thereby improving the marine environment and protecting aquatic life such as small fish. Recent studies have shown that microplastics have been detected in fish, and it is becoming clear that they can affect humans who eat those fish. We believe that by mitigating the microplastic food chain in aquatic life, we can also solve the problem for humans.

[0005] Therefore, the present invention aims to propose a microplastic collection device that can protect aquatic organisms such as small fish. [Means for solving the problem]

[0006] The microplastic recovery device that does not involve small fish, as described in claim 1 of the present invention, comprises a tank 1 in which small fish can swim, a net 3 in the tank 1 that can catch microplastics 2, a pump 5 that sucks seawater into the tank 1 and discharges the seawater that has passed through the net 3, the pump 5 is installed downstream of the net 3, a speaker 7 is installed on the underside of the lid 6 of the tank 1, the speaker 7 is positioned higher than the water level H inside the tank 1, the pump 5 is periodically stopped at predetermined timings, and when the pump 5 is stopped, an repellent sound is emitted from the speaker 7, thereby causing the small fish that have entered the tank 1 to escape into the sea through the passage 8 that sucks in the seawater. The present invention as described in claim 2 is a microplastic collection device as described in claim 1 that does not entangle small fish, wherein the deterrent sound is the sound of splashing water generated by striking the water surface H about 3 to 8 times per second, and the splashing sound has a frequency between 773 Hz and 13544 Hz, and includes irregular frequencies between 1000 Hz and 11000 Hz. The present invention according to claim 3 is a microplastic recovery device that does not entangle small fish according to claim 1, and is characterized in that an LED light 10 is installed in the tank 1 together with the speaker 7 thereof, and the LED light 10 is blinked at the timing when the pump 5 is stopped. The present invention according to claim 4 is a microplastic recovery device that does not entangle small fish according to claim 1, and is characterized in that aeration is performed at the timing when the pump 5 is stopped.

Effect of the Invention

[0007] According to the microplastic recovery device that does not entangle small fish of the present invention, when the pump is stopped, there is no flow toward the tank in the passage for sucking seawater, and by emitting a repellent sound from the speaker, small fish take repellent actions and try to escape from the tank, so they can escape to the sea from the passage for sucking seawater.

Brief Explanation of the Drawings

[0008] [Figure 1] Figure showing the microplastic recovery device that does not entangle small fish of the present invention [Figure 2] Figure showing the operation of this microplastic recovery device [Figure 3] Figure showing the experimental results conducted with 2 masked angelfish and 4 dusky dottybacks, which are marine fish [Figure 4] Photograph showing the movements of masked angelfish and dusky dottybacks when testing the sound of water splashing (the pichipicha sound of water) [Figure 5(a)] Photograph when generating the sound of water splashing [Figure 5(b)] Photograph when generating the sound of water splashing [Figure 5(c)] Photograph when generating the sound of water splashing [Figure 6(a)] Photograph examining the frequency change of the sound recorded for 10 seconds [Figure 6(b)] Photograph examining the frequency change of the sound recorded for 10 seconds [Figure 6(c)]A photograph showing the frequency changes of a 10-second recording. [Figure 7] This diagram shows the experimental results conducted on rockfish (10-12 cm), which swim in the lower layers of the water. [Figure 8] A photograph showing the movement of a rockfish when we tried making splashing water sounds. [Figure 9] This diagram shows the experimental results from a study using horse mackerel (21 cm) swimming in the mid-air. [Figure 10] Diagram showing experimental results from a study using Japanese dace (Tribolodon hakonensis). [Figure 11] Similar to Figure 4, this photograph shows the movements of clownfish and damselfish when the sound of splashing water (water sloshing sound) was tested. [Figure 12] A photo taken when we confirmed the sound-repellent effect of the collection device we designed. [Figure 13] A photograph showing the additional experiment. [Figure 14] This diagram shows the experimental results of a study on the effects of light on horse mackerel (21 cm). [Modes for carrying out the invention]

[0009] The first embodiment of the present invention is a microplastic collection device that does not involve small fish, which has a tank in which small fish can swim, a net inside the tank that can catch microplastics, a pump that sucks seawater into the tank and discharges the seawater that has passed through the net, the pump is installed downstream of the net, a speaker is installed on the underside of the tank lid and the speaker is positioned higher than the water level inside the tank, the pump is stopped periodically at predetermined intervals and a deterrent sound is emitted from the speaker at the time the pump is stopped, thereby releasing small fish that have entered the tank into the sea through the passage into which seawater is sucked. In this way, having a tank in which small fish can swim allows small fish that have mistaken microplastics for food and entered the tank, or small fish that have been accidentally sucked in by the suction force of the pump through the intake, to swim in the tank for a while. The pump is installed downstream of the net, so small fish will not be sucked in and harmed. The pump is stopped periodically at predetermined intervals. When the pump is stopped, there is no flow of seawater towards the tank through the intake passage, and by emitting repellent sounds from the speaker, small fish will exhibit repellent behavior and try to escape from the tank, allowing them to escape into the sea through the intake passage. In the experiment, the effect was better when the sound was emitted from above the water surface rather than underwater, so the speaker was positioned above the water surface in the tank. By not mounting the speaker underwater, we believe it will withstand long-term use. Also, we think that emitting sound downwards from the tank lid will enhance the acoustic effect.

[0010] A second embodiment of the present invention is a microplastic collection device that does not entangle small fish according to the first embodiment, wherein the repellent sound is the sound of water splashing, generated by striking the water surface about 3 to 8 times per second, and the sound of water splashing has a frequency between 773 Hz and 13544 Hz, including irregular frequencies between 1000 Hz and 11000 Hz. The sound of splashing water is similar to the sound of a bird plunging its head into the water to catch a fish swimming near the surface, or the sound of a caught fish thrashing about desperately. I think it's the kind of sound that small fish would hear when they sense their life is in danger.

[0011] A third embodiment of the present invention is a microplastic collection device that does not involve small fish, according to the first embodiment, in which an LED light is installed in the tank along with the speaker, and the LED light is made to flash when the pump is stopped. By using flashing lights in conjunction with repellent sounds, the small fish will swim more actively, which I believe will increase the effectiveness of releasing them back into the sea.

[0012] A fourth embodiment of the present invention is a microplastic collection device according to the first embodiment that does not involve small fish, wherein aeration is performed at the time the pump is stopped. By performing aeration along with deterrent sounds, the effectiveness of releasing small fish back into the sea is enhanced. [Examples]

[0013] Figure 1 shows the microplastic collection device of the present invention that does not involve small fish. This microplastic collection device has a cylindrical tank 1 in which small fish can be kept swimming. In this way, because there is a tank 1 in which small fish can be kept swimming, small fish that mistake microplastics 2 for food and enter the tank 1 can swim in the tank 1 for a while.

[0014] Tank 1 contains a net 3 that can catch microplastics 2. A cylindrical inner tank 4 is placed inside Tank 1, and the net 3 is attached to this inner tank 4. By attaching the net 3 to the inner tank 4 in this way, the surface area of ​​the net 3 can be increased, preventing clogging by microplastics 2 and allowing for long-term use. Pump 5 draws seawater into tank 1 and discharges the seawater that has passed through net 3. By installing multiple pumps 5, more microplastics 2 can be collected. Pump 5 is installed downstream of net 3. By installing pump 5 downstream of net 3 in this way, small fish will not be sucked into pump 5 and injured.

[0015] A speaker 7 is attached to the underside of the lid 6 of tank 1. The speaker 7 is positioned higher than the water level H inside tank 1. In the experiment, it was found that emitting sound from above the water surface H was more effective than emitting sound underwater, so speaker 7 will be positioned above the water surface H in tank 1. By not installing speaker 7 underwater, it can withstand long-term use. In addition, emitting sound downwards from the lid 6 of tank 1 will enhance the acoustic effect. Tank 1 is connected to the outside (underwater) by a passage 8 for drawing in seawater and a passage 9 for discharging seawater. The passage 8 for drawing in seawater should be close to the water surface H in order to collect microplastics 2. The passage 9 for discharging seawater should be placed at a lower position than the passage 8 for drawing in seawater. Pump 5 is attached to the passage 9 for discharging seawater. Inside tank 1, the LED light 10 is installed along with the speaker 7. The LED light 10 is also installed on the underside of the lid 6 of tank 1, together with the speaker 7.

[0016] Although not shown in the diagram, the microplastic collection device includes batteries to supply power to the pump 5, speaker 7, and LED light 10, as well as control devices to turn the pump 5, speaker 7, and LED light 10 on and off. The speaker 7 and LED light 10 do not need to be separate; a speaker 7 with an integrated LED light 10 that synchronizes sound and lighting can also be used. The small fish targeted in this study are defined as fish small enough to enter tank 1 and that can enter through the seawater intake passage 8.

[0017] Figure 2 shows the operation of this microplastic collection device. Figure 2(a) shows the pump in operation, and Figure 2(b) shows the pump stopped. As shown in Figure 2(a), the microplastics 2 are collected while the pump 5 is operating. As shown in Figure 2(b), small fish that have entered the tank 1 while the pump 5 is stopped are released back into the sea through the passage 8 that draws in seawater. Pump 5 is periodically stopped at predetermined intervals. At the moment pump 5 is stopped, speaker 7 emits an repellent sound. Also, at the moment pump 5 is stopped, LED light 10 is made to flash. With pump 5 stopped, there is no flow of seawater into the passage 8 toward tank 1. By emitting repellent sounds from speaker 7, small fish will take repellent action and try to escape from tank 1, allowing them to escape into the sea through the seawater intake passage 8. Furthermore, the flashing lights from the LED light 10, combined with the repellent sound, cause small fish to swim more actively, thus increasing the effectiveness of releasing them back into the sea.

[0018] The following describes an experiment on the effects of sound on small fish. Figure 3 shows the results of an experiment conducted with two clownfish and four damselfish, both of which are marine fish. Six small fish were placed in a tank (W40cm x H30cm x D12cm) filled with deep-sea water. Twenty different loud sounds were played from speaker 7 using Bluetooth®, and the fish's reactions were observed. Each experiment was repeated three times to confirm reproducibility.

[0019] First, I tried the "expected 100Hz" that I read about in the reference materials. The results were that there was no particular change in the first and third attempts, but in the second attempt, it seemed to react slightly more than before the sound was played. Next, I tried 500Hz. The first time, the fish came closer to speaker 7. The second time, there was no particular change. The third time, the fish disliked it and moved away from speaker 7. Next, I tried 1000Hz. The first time, the fish disliked it and moved away from speaker 7. There was no particular change the second and third times. I tried the 5000Hz setting again, which I had used in the ocean experiment. However, just like last time, there was no change in any of the three attempts. Next, I tried 7500Hz. The first time, the fish disliked it and moved away from speaker 7. The second time, the fish came closer to speaker 7. There was no particular change the third time. Next, I tried 10kHz. On both the first and second attempts, the sound shifted towards speaker 7. On the third attempt, there was no particular change.

[0020] Next, I tried using the sound of splashing water (the sound of water sloshing). The reason was that I had read in some literature that fish dislike the sound of fish sticking their heads into the water to eat other fish (their companions), so I thought that the sound of splashing water might also be disliked by fish. I recorded the sound of splashing water by filling a washbasin with water at home and tapping it with my hand. I also made the sound of a fish plunging its head into the water, but this experiment had no effect on the fish, so I tried using the sound of splashing water, which worked well. The results showed that in all three instances, the small fish clearly moved away from speaker 7 and showed signs of dislike. I thought this sound was the most effective, so I decided to try it on other fish.

[0021] Next, I tried using seagull sounds. Surprisingly, there was no change in any of the three attempts. Then I tested the alarm sound. There was no particular change the first and third times. The second time, small fish gathered around speaker 7. Next, I tried it with a male voice. Again, no change was observed in any of the three attempts. I also tried a female (child) voice. Just like with the male voice, there was no change after all three attempts. I also tried a female (adult) voice. Just like with the male voice, there was no change in any of the three attempts. Next, we tried playing the sound of a humpback whale. The first time, the small fish clearly moved away from speaker 7 and showed signs of dislike. The second and third times, they reacted, though not as much as the first time. One damselfish in particular went into its octopus pot when the humpback whale sound was played and didn't come out for a while. The clownfish also backed away from speaker 7.

[0022] Next, I tried the machine sound. Again, there was no change in any of the three attempts. I tried the sound of the school bell. This also didn't make any difference after three attempts. Interestingly, each of the three times the man snored, fish were attracted to speaker 7. Next, I tried the sound of a motorcycle. The first time I played the motorcycle sound, small fish gathered around speaker 7. There was no particular change the second and third times. I also tried knocking on the door, making a tapping sound. In all three instances, small fish clearly gathered around speaker 7.

[0023] Next, we tried the sound of a mosquito flying. The first time, there was a clear change. The small fish disliked the sound and moved away from speaker 7. The second and third times, there was a reaction, though not as strong as the first time. Finally, I tried a high-pitched bird call. In all three attempts, the small fish reacted to the sound and moved away from speaker 7.

[0024] Before the experiment, I thought that a 5000Hz sound would be effective, but when I actually experimented with small fish, unexpectedly, the fish reacted best and disliked the splashing sound of water (the sound of water being sloshed in a washbasin) played from speaker 7, rather than any specific frequency sound. This sound was intended to resemble the sound of a bird plunging its head into the water to eat a fish swimming near the surface, and the sound of a caught fish struggling desperately. It's a sound source that makes fish perceive their lives as being in danger. Conversely, this experiment also revealed that some types of small fish are attracted to certain sounds, such as the sound of knocking on a door or a man snoring. I have also confirmed the reproducibility of this.

[0025] The experiments with 100Hz, 500Hz, etc., were conducted by playing the sound once, stopping it, and then trying the next frequency. In addition, we also automatically played sounds from 100Hz to 10KHz in one pass (gradually increasing the frequency) and observed at what frequency the fish reacted, but the results were almost the same in both cases. We were unable to obtain any definitive response from reproducible sounds of single Hz frequencies.

[0026] Figure 4 shows photographs of the movements of clownfish and damselfish when the sound of splashing water was used as a test. The photos were edited from a video. Speaker 7 is located at the position indicated by the arrow. L1 and L2 are reference lines from speaker 7. L1 is the reference line closest to speaker 7. When the sound of splashing water is played from speaker 7, one clownfish swims backward while facing speaker 7, then turns around and swims away from speaker 7. A damselfish also swims away from speaker 7.

[0027] Figures 5(a) to 5(c) are photographs taken when the sound of splashing water was produced. The photographs were edited from a video. Starting with photograph (1), photograph (2) is 0.05 seconds after photograph (1), and photograph (3) is 0.05 seconds after photograph (2). Photograph (21) is a photograph taken 1 second after photograph (1). As shown in the photo, I filled a washbasin with water and made a sound by tapping the water surface H with my palm. With my fingers spaced about 2 cm apart, I forcefully struck the water surface (H) vertically with my palm from a height of about 2-4 cm. To maximize the sound, I made the hand movements as quickly as possible and kept the height below 10 cm. (Anything higher would require a larger hand movement, making it difficult to produce small, rapid sounds.)

[0028] In the experiment, the effect was confirmed by hitting the water approximately 3 to 8 times per second, with hitting it 8 times per second being the most effective. Speed ​​was tapped at extremely high speed to imitate the way a fish thrashes about. For the recording environment, I filled a basin with water in my bathroom at home and recorded in the open air. I chose the bathroom because the sound echoed in the shower. To prevent background noise during recording, I kept the room silent and left the bathroom door open to reduce sound reflection. The sound was recorded in the air using a smartphone microphone placed approximately 8 cm away from the water surface (H).

[0029] I then investigated the frequencies of the sound recorded in this way. Figures 6(a) to 6(c) show the frequency changes over a 10-second period. Each photograph was cropped at the point where the frequency changed. Specifically, photograph (1) shows the starting frequency of 10970Hz, and photograph (2) shows the point where the frequency changed from 10970Hz to 1401Hz. Note that subtle changes have been omitted.

[0030] As can be seen from Figure 6, the frequency of the splashing water sound ranged from a minimum of 773Hz to a maximum of 13544Hz, mainly consisting of repeated small ups and downs between approximately 1000Hz and 11000Hz (11KHz). Upon reviewing the experimental video, it was observed that in the sections where the fish were moving away from speaker 7, the sound consisted of repeated fluctuations in frequency from approximately 1000Hz to approximately 11000Hz (11KHz). This difference in pitch appears to be what stimulates the small fish.

[0031] When I consulted Professor Yamada of Tokai University about the results, he advised me to try experimenting with other types of small fish, not just clownfish (3-4 cm) and damselfish (2.0-2.5 cm). However, I was stuck because there were limited ways to obtain other saltwater fish. So, I decided to go to the Honmoku Sea Fishing Facility in Yokohama and conduct an experiment using fish I caught in the sea. The experiment was conducted immediately after the fish was caught, by filling a styrofoam container (W42cm x H30cm x D25cm) with seawater. In this experiment, we tested and compared rockfish that swim in the bottom layer (10-12 cm) and horse mackerel that swim in the mid-water layer (21 cm).

[0032] Figure 7 shows the experimental results using rockfish (10-12 cm), which are bottom-dwelling fish that swim in the lower layers of the water. One thing to be aware of in this experiment is that rockfish are bottom-dwelling fish, so when they are caught, they experience a significant change in water pressure, and even if you put them in a styrofoam container filled with seawater and let them swim, they will flip over. In deeper waters, the water pressure is high, but when the fish is seen near the surface, the water pressure drops sharply, which can cause the swim bladder inside the rockfish's body to expand. Normally, it's not a good idea to experiment with fish that are upside down like this, but I decided to record the results because the experiment yielded some very interesting findings.

[0033] Figure 8 shows a photograph of a rockfish's movement when the sound of splashing water was used as a bait. The photograph was edited from a video. When we played the sound of splashing water from speaker 7 to the overturned rockfish, it righted itself and began swimming forward with all its might. It ended up swimming in a range of 41cm to 144cm. After that, when the sound stopped, it flipped over again. I thought this might be evidence that the sound of splashing water is perceived by the rockfish as a threat to its life or some other form of fear, causing it to instinctively flee. I have also confirmed that this can be reproduced. Interestingly, when a 100Hz sound, which is generally disliked by many fish, was played from speaker 7, rockfish repeatedly approached speaker 7 on their own or even went completely under it. This suggests that 100Hz is a sound that rockfish like. After the 100Hz sound from speaker 7 stopped, the rockfish would swim away from speaker 7 for a moment, but then quickly return to it on their own.

[0034] Figure 9 shows the experimental results from a study using horse mackerel (21 cm) swimming in the mid-air layer. When we conducted the same experiment with horse mackerel (21cm), they reacted to both the sound of splashing water and the 100Hz sound. In the experiment, we observed that the horse mackerel were larger than the styrofoam, causing them to move faster in response to certain sounds. However, it was unclear whether they disliked or liked the sounds. It's true that when we made splashing water sounds or 100Hz sounds, the fish swam more actively than when we weren't making any noise. Also, when we stopped the sounds, their swimming slowed down, and they even took breaks.

[0035] Figure 10 shows the experimental results conducted with the Japanese dace (Tribolodon hakonensis). The Japanese dace, a type of carp, is said to migrate to the sea, and its habitat has been confirmed in brackish and saltwater areas. When the schooling dace were exposed to the sound of splashing water, just like other fish, they exhibited avoidance behavior.

[0036] These experimental results showed that many fish reacted to splashing water sounds (sloshing sounds, sounds like other fish fleeing from predation) and the sounds of humpback whales (sounds of marine predators), exhibiting avoidance behavior. They showed similar reactions to sounds like mosquitoes buzzing. Conversely, it was also found that there are sounds that attract fish. Humpback whales are not predators that attack other animals; instead, they efficiently obtain energy by consuming small marine organisms, although they are still predators in the food chain. They eat krill, capelin, mackerel, salmon, and other fish, and it is said that they eat 3% to 5% of their body weight, or about 1 to 1.5 tons, per day. The small fish seemed frightened by the sounds of the humpback whales. The frequency range of humpback whale vocalizations was between 10Hz and 1426Hz. The vocalizations primarily consisted of small, repeated ups and downs within the ranges of 10Hz-300Hz and 100Hz-900Hz. It appears that these fluctuations in sound within the 300Hz to 800Hz range affected the small fish. While monotonous sounds of 100Hz and 1000Hz did not elicit a good response, experiments confirmed that sounds with small frequency fluctuations were effective.

[0037] Based on these experimental results, we hypothesized that playing specific sounds, such as those of living organisms, with varying rhythms from speaker 7, could deter small fish from the device. For example, we considered patterns such as suddenly switching from quiet, natural sounds to splashing water sounds, or randomly looping splashing water sounds and humpback whale calls. Since fish will get used to repeated sounds, it would be effective to play sounds with rhythms and patterns that prevent the fish from becoming accustomed to them.

[0038] The mackerel I mentioned earlier are fish that swim near the surface of the ocean and are preyed upon by birds from the sky, as well as by humpback whales. This is true not only for mackerel, but also for horse mackerel and sardines. Humpback whales appear near the surface of the water when they are feeding or breathing. Large whales like humpback whales need to come up to the surface regularly to breathe, and they are also active near the surface when catching small fish and krill through "bubble-net feeding." It is said that humpback whales can sometimes be observed swimming near the surface in search of food in the waters around Japan. Thus, aquatic creatures such as small fish like horse mackerel, mackerel, sardines, and saury are targeted by humpback whales at the surface and sometimes preyed upon by birds from the sky. Therefore, it is thought that the sound of splashing water and the calls of humpback whales act as deterrents for these aquatic creatures.

[0039] When we experimented with splashing water sounds plus light, or 100Hz sounds plus light, we found that horse mackerel moved significantly more actively compared to sounds without light. I think that horse mackerel, which swim in the mid-water to near the surface, are probably able to perceive different environmental sounds than bottom-dwelling fish, and are quite sensitive to the sounds of birds coming from above.

[0040] Honestly, at the time, I wasn't sure if the horse mackerel were reacting to the sound or to the white light and sound. However, after conducting experiments with the horse mackerel using three patterns—sound only, sound + white light, and light only—I found that while they reacted to sound only and light only, the combination of splashing water sound + white light elicited the most active response.

[0041] Figure 11, like Figure 4, is a photograph showing the movements of clownfish and damselfish when the sound of splashing water (water sloshing sound) was tested. However, in the experiment in Figure 4, speaker 7 was placed above the water surface H, whereas in the experiment in Figure 11, speaker 7 was submerged in water. In Figure 11, speaker 7 is located at the position indicated by the arrow. The reference line from speaker 7 is defined as L3. In the water, one clownfish did react, but overall the response was sluggish, although they did show signs of approaching speaker 7. Since they did react in the water, I think they are reacting to the sound itself, so I think they basically don't like splashing sounds, but compared to the experiment in air, the effect was clearly less.

[0042] Figure 12 shows a photograph taken when the deterrent effect of the collection device we designed was confirmed. A cylindrical plastic container was used to represent Tank 1. A passage 8 was attached to the side of this container. Additionally, a speaker 7 was attached to the lid of the container. One damselfish was placed in the container. The damselfish is located at the position marked with a red circle in Figure 12(a). Figure 12(b) shows the container with the lid closed, and in this state, the sound of splashing water was played from speaker 7 as a deterrent sound. In Figure 12(c), the damselfish is still inside the container. In Figure 12(d), the damselfish has swum to the exit of passage 8, and as shown in Figure 12(e), the damselfish has successfully escaped from the container. The animal successfully escaped 10 seconds after we started playing the repellent sound from speaker 7. After several attempts, we concluded that it takes about 20 seconds to escape. Therefore, we decided that it would be best to set the operating time of pump 5 for collecting microplastics 2 to 3 minutes, and then the stopping time of pump 5 to 20 seconds, and repeat this process.

[0043] Figure 13 is a photograph showing the experiment with additional aeration and guide lights. We added aeration to the container used in Figure 12. As shown in Figure 12(a), we placed an air stone inside the container and supplied air from an aeration pump. Also, as shown in Figure 12(b), we shone a light (guidance light) into the escape route, passage 8. When air was sent from the aeration pump to the air stone, speaker 7 blasted loudly, and the damselfish immediately escaped in the dark without any light guidance. One damselfish escaped in as little as 7 seconds. We tried to reproduce the result, and although it sometimes took 29 seconds to escape, they all managed to escape successfully. Furthermore, another discovery was that when air was supplied from the aeration pump, sound was played through speaker 7, the room was darkened, and a light was shone on the escape route, the animal was able to escape in as little as 3 seconds. As a result, escape in a well-lit area took 10 seconds, and even in the dark, by using an aeration pump to blast air through speaker 7, the fastest escape time was 7 seconds. Furthermore, by shining a light on the escape route, escape was possible in as little as 3 seconds even in the dark. Furthermore, when only aeration was performed without playing sound from speaker 7, the damselfish remained in the container without escaping. However, when sound and a guiding light were added to the aeration, they immediately swam away. From this, I believe that the increase in air (or bubbles) in the water due to aeration may have had some effect on how sound was transmitted to the fish, that the increased oxygen in the water may have made the fish more energetic and active, and that in this state, the synergistic effect of sound and the guiding light may have prompted them to escape. The red circle in Figure 13(b) shows a damselfish that successfully escaped.

[0044] Figure 14 shows the experimental results regarding the swimming speed of a horse mackerel (21 cm) when exposed to light. Figures 14(a-1) through 14(a-5) show the subject under light, while Figures 14(b-1) through 14(b-5) show the subject without light. Each photograph was edited from a video. Figure 14(a-2) is 1 second after Figure 14(a-1), Figure 14(a-3) is 1 second after Figure 14(a-2), and Figure 14(a-5) is 4 seconds after Figure 14(a-1). Similarly, Figures 14(b-1) through 14(b-5) are photographs taken at 1-second intervals. As shown in Figures 14(a-1) to 14(a-5), when illuminated, the horse mackerel swim more than one full rotation, but as shown in Figures 14(b-1) to 14(b-5), when not illuminated, the horse mackerel swim only about half a rotation.

[0045] Next, I will explain the comparative experiment we conducted on the swimming speed of horse mackerel using sound and light. the purpose The purpose of this experiment is to investigate how sound and light stimuli affect the swimming speed of fish. Specifically, we will compare how fast fish swim in the absence of sound and light and in the presence of sound and light to determine the extent to which sound and light stimuli influence fish movement.

[0046] method To numerically demonstrate the effects of sound and light on fish swimming, we calculated the time it took for the fish to complete one lap under each condition and analyzed the differences. Live horse mackerel were used for the experiment. In the dark of night, the horse mackerel were placed in a styrofoam container (30cm long x 42cm wide, 25cm deep), and their swimming speed was measured under the following three conditions. The experiment began around 6 PM on September 22, 2024, when it was getting dark.

[0047] conditions Condition 1 (No sound or light, before sound is introduced): Observe the fish swimming calmly in the dark, without sound or light, and quantify the speed at which they are swimming. Condition 2 (with sound and light): When specific sounds and lights are provided from speaker 7, the speed at which the swimmer is swimming is quantified. Condition 3 (No sound or light / After sound is introduced): Observe the fish swimming calmly in the dark, without sound or light, and quantify how fast they are swimming. Under each condition, we measured how many laps the fish completed around the tank within 31, 25, and 26 seconds. From these results, we calculated the average swimming speed of the fish (how many seconds per lap) and compared how much sound influenced the results. We thought that by deliberately conducting experiments comparing the state before and after applying auditory and light stimuli, we could more clearly demonstrate the experimental results.

[0048] result The following results were obtained. Under condition 1 (no sound or light, before sound is produced), it completes 4.2 laps in 31 seconds (time per lap = 31 seconds ÷ 4.2 laps = 7.38 seconds). Under condition 2 (with sound and light), it completes 5.5 laps in 25 seconds (time per lap = 25 seconds ÷ 5.5 laps = 4.55 seconds). Under condition 3 (no sound or light, after sound is produced), it completes 3.5 laps in 26 seconds (time per lap = 26 seconds ÷ 3.5 laps = 7.43 seconds). The shorter the time it takes to complete one lap, the faster the horse mackerel are swimming. The results show that, in the absence of sound and light, the horse mackerel complete one lap in an average of approximately 7.405 seconds (an average of approximately 7.38 seconds and 7.43 seconds). On the other hand, with sound and light, they complete one lap in 4.55 seconds, meaning they swim approximately 38.6% faster (7.405 - 4.55) ÷ 7.405 × 100. This difference suggests that sound and light act as a clear stimulus to the fish, increasing their swimming speed.

[0049] conclusion This experiment demonstrated that horse mackerel swim faster in response to auditory and light stimuli. Auditory and light stimuli can influence fish behavior and contribute to increased speed of movement in the water.

[0050] Around the same time, I came across a flyer from researchers at Kitasato University announcing that using green light-emitting diodes (LEDs) could increase the growth rate of flounder and sole by 1.6 times, and I thought, "This is it!" I then immediately found and read several articles on the color vision of fish, and although there are various theories, I learned that green, blue, and red are probably the colors that fish see best. Rockfish (bottom-dwelling fish) are sensitive to blue and green, but less sensitive to red and yellow. Also, small fish near the surface are sensitive to blue, green, and yellow, and also react to ultraviolet light. In my experiment with horse mackerel, they swam faster when exposed to white light, but their movements slowed down and they even stopped to rest when the light was turned off. This shows that color vision has evolved in accordance with each species' habitat. In other words, it was found that aquatic creatures swimming near the surface react actively and become more wary when illuminated with green, blue, or white LED lights. However, as mentioned earlier regarding sound, it is also possible that fish may become accustomed to the light and lose their wariness.

[0051] Based on the above, I thought that by flashing a green LED light (which small fish dislike) in a sequence like 10 → white → blue → white → green..., stimulating them with white light after a color they dislike, such as blue, and then flashing it again with a color they dislike, such as green, in a loop of white → green → white → blue..., it might be possible to deter aquatic creatures by preventing them from becoming accustomed to the light. And my answer is to deter aquatic creatures by combining light technology with sound technology in the following style. The device works by randomly looping sounds of splashing water and humpback whales, and flashing green LED lights in a loop (10 → white → blue → white → green...), which small fish dislike. This double effect repels aquatic creatures. Furthermore, sound alone is fine, light alone is fine, or sound and light together are fine, and none of them are monotonous; variations are added to prevent aquatic creatures from becoming accustomed to them. The sound speaker 7 can also be played from a smartphone using Bluetooth®. Additionally, the LED light 10 can either light up simultaneously with the speaker 7, or it can be provided separately from the speaker 7.

[0052] This experiment demonstrated the potential of using sound and light to repel small fish, thereby efficiently collecting microplastics while protecting aquatic life. The sounds of splashing water, humpback whale calls, and green, blue, and white (yellow) LED lights proved particularly effective, and we plan to further test this effect on a wider variety of fish species. This device could be a promising tool for reducing marine plastic pollution in a sustainable way. [Industrial applicability]

[0053] In addition to microplastic collection devices, the following uses are also possible: (For use near sewage treatment plants) By preventing fish from approaching contaminated waters in areas where wastewater treatment plants discharge, we prevent them from ingesting contaminants, thereby protecting the health of fish and the food chain. (Measures to prevent the leakage of radioactive materials and protect the environment during disasters) When radioactive or hazardous materials flow into the sea or rivers, preventing fish from approaching the area helps prevent impacts on the food chain and reduces the risk of contaminants reaching humans through fish. It is also useful as an environmental protection measure during disasters such as tsunamis and earthquakes. (Applications in fishing) By incorporating this technology into fishing rods, you can repel smaller fish and selectively catch larger target fish. This is extremely effective for individual fishing activities. (Applications to aquaculture and fisheries) This technology can be used in aquaculture fields for seaweed, oysters, and sea urchins to prevent certain fish species from negatively impacting the industry, and it is also an effective means of protecting spawning grounds and preserving natural ecosystems. (Port and ship protection systems) Sound technology can be used to prevent excessive fish gatherings in harbors and around ships, and to protect ship navigation and equipment. It also contributes to the efficiency of harbor cleaning and ship hull cleaning operations. (Disease prevention in aquariums and aquaculture facilities) This technology, which reduces contact between fish using sound and light, can be applied to aquariums and aquaculture facilities to prevent the spread of infectious diseases. (Fish school control in diving and tourist areas) By temporarily moving fish to a different area during the tourist season, we can reduce stress on the fish caused by tourists and protect the fish ecosystem. (Efficiency improvements and selective fishing in the fishing industry) By incorporating sound and light into fishing nets and traps, "selective fishing techniques" can be enhanced to repel smaller fish and catch only larger ones. This is expected to improve the efficiency of fishing and prevent overfishing. (Protection of submarine cables and pipelines) By preventing fish from gathering around cables and pipelines installed on the seabed, damage and corrosion can be prevented, thus protecting the infrastructure. (Support technology for marine biology research) By using sound and light to guide schools of fish, researchers can more easily observe their behavior, making it an effective research method for controlling fish movements without capturing them. (Guiding fish in rivers and dams) By efficiently guiding fish in rivers and dams, it is possible to optimize dam operations while protecting ecosystems. (Integration with water quality monitoring equipment) By controlling fish behavior using sound and light technology and linking it with water quality monitoring devices, this technology can be applied to the development of a new environmental monitoring system that links pollution detection with fish behavior. [Explanation of Symbols]

[0054] 1 tank 2 Microplastics 3 Net 4. Inner tank 5 pumps 6 Lid 7 speakers 8. Inhalation pathway 9. Discharge passage 10 LED lights H water surface

Claims

1. There is a tank in which small fish can be kept swimming. The tank has a net that can catch microplastics. A pump draws seawater into the tank, and the seawater that passes through the net is discharged. Install the pump downstream of the net. A speaker was attached to the underside of the tank lid. The speaker was positioned higher than the water level in the tank. The pump is stopped periodically at predetermined intervals. The pump is stopped, and a repellent sound is emitted from the speaker, causing the small fish that have entered the tank to escape into the sea through the passage that draws in seawater. A microplastic collection device that does not involve small fish.

2. The repellent sound is the sound of water splashing, produced by striking the water's surface approximately 3 to 8 times per second. This splashing sound has a frequency between 773 Hz and 13544 Hz, including irregular frequencies between 1000 Hz and 11000 Hz. A microplastic collection device that does not involve small fish, as described in feature 1.

3. Along with the speaker, an LED light was installed inside the tank. The LED light will flash when the pump is stopped. A microplastic collection device that does not involve small fish, as described in feature 1.

4. Aeration is performed at the moment the pump is stopped. A microplastic collection device that does not involve small fish, as described in feature 1.

Images