陸上では全てのモノがインターネットにつながる Internet of Things により、多種多様なビッグデータが生み出され、利活用されるようになりつつあります。Internet of Thingsとは、インターネットに接続されたセンサーを様々なものに搭載することで、大量の情報を収集し、世の中を良くしていこうという考え方です。ただし、現状では海洋に多くの情報収集端末を設置することは出来ていません。
これまでの研究によって、海洋動物を使って海面下の水温や塩分に関する情報を得たり、海表面流や波浪、さらに海上風の測定が出来るといった、思いがけない成果が次々と得られています。この海洋動物由来の情報をリアルタイムでインターネットに配信できるようにすれば、情報空白地帯であった海洋からも大量の情報を収集することが可能になります。動物は日々餌を求めて自律的に動き回るので、少数の端末からでも生物生産性の高い海域に関する有用な情報を効率的に集めることが可能です。このようなことが実現すればまさに Internet of Things ならぬ Internet of Animals と言えるでしょう。従来の人工衛星や自動昇降ブイを使った観測手段と相補的なやり方で情報を集めることで、より正確に海洋環境を把握して、精度良い予想ができるようになり、台風や干ばつなど海を起点とした自然災害による被害を低減させることが出来ると考えています。
Internet of Animalsが実現した世界では
Yay, Rays! This Year’s Autumn Pitted Stingray Field Research
Starting last autumn, I began participating in the research of pitted stingrays (Bathytoshia brevicaudata) in the Seto Inland Sea. Specifically, we are using biologging to study the swimming and migratory behavior of the species. In September 2023, we returned to Kaminoseki, Yamaguchi Prefecture, Japan. There was a feeling of uncertainty as we approached the field site, as we had heard that apparent damages from rays had decreased recently. The observation of what appeared to be decreased damages was positive news; we also hoped to deploy a sufficient number of miniPAT tags (which record depth, water temperature, 3-axis acceleration, and light level for geolocation) in order to further address the challenges encountered with sharing the Seto Inland Sea with this species.
As I looked outside the window of the Shinkansen, on my way back to the Seto Inland Sea, I was reminded of my first time seeing it approximately a year ago, also from a train, in September 2022, when I first went to Kaminoseki to collaborate with local fishermen in deploying miniPATs. That first trip, as I nervously looked out the train window, I had been struck with a sense of excitement; a feeling of the unknown – something new to be encountered. Now that I was in my second year, I had expected this feeling of unknown to be replaced by a feeling of familiarity. Although I now shared a connection with the sea, albeit a very small one compared to that of the people actually living and working there, there was still a sense of the unknown remaining. In fact, that feeling of unknown and mystery, as well as excitement, was even larger now. I had glimpsed the tip of the iceberg, sensed more tantalizing discoveries yet to be uncovered, from the data resulting from the miniPATs deployed the year previous.
I was happy to return to the small port town where we based our research out of. In addition to fond memories of research and delicious fish, I enjoyed running along the road in front of the water during the rest time in our research (some little kids had randomly started running with me on one occasion). However, before indulging in sashimi or jogging with the energetic locals, there were preparations to do.
However, the preparations themselves were also interesting. To prepare for longlining, we cut the tails off of frozen horse mackerel, in order to make them easier to be swallowed by rays. As I cut off the tails on the wooden cutting board, I noticed that some of the stray cats enviously watching me were the kittens I had seen in my last visit, reminding me that some time had passed since I had last come. It was nice to smell fresh fish as I cut, and I remembered that the fresh smell had actually helped me, a very inexperienced sea person, from getting too seasick when I had first participated in longlining the previous year. We also sharpened the hooks for longlining, and made sure the lines were not tangled in preparation.
Finally, the long-awaited time for longlining arrived. I fondly remembered the leader fisherman grading my line-throwing abilities earlier (if throwing longlines were a class, I can confidently say that it was a course I failed multiple times, but thoroughly enjoyed). Considering my level had been rock-bottom, I thought that that meant there was only room for improvement, and thus was happy to be able to gain more experience again (inland in Kashiwa, I think I would cause confusion if I randomly started throwing longlines in the park).
Despite our mental preparations for potentially not catching any rays, on our first longline, we successfully caught and tagged two rays, and over the course of the next two days, successfully caught and tagged another three. The first ray was the largest pitted stingray I had yet seen, and in fact, was the largest fish I had ever seen in my life in the wild. It was approximately two meters in disc width, and had a beautiful black spot, almost perfectly round, at the base of its tail. It was my first time seeing this kind of marking, too. Although difficult to maneuver due to its large size, the area of musculature at the tail base was ample, and I was able to securely attach the tag to the ray. In this way, we were able to successfully deploy the same number of miniPATs as the year previous. This reminded me that each time I am blessed with the opportunity to experience field research, I experience new things.
Thankfully, although I nervously checked the ARGOS satellite website for any notification of a detached tag, no signals arrived, indicating that all tags were still securely attached to their host rays (miniPAT data loggers send out signals to a satellite, which are then sent to a website, when they have detached from their host rays and floated to the sea surface). Like the year previous, this trip was successful, and I also was able to explore Kaminoseki during the rest time. Thus, I was able to head back to Kashiwa with many scenic photos of the Kaminoseki area (and delicious fish in my stomach). Furthermore, compared to last year’s survey, where one tag was unfortunately detached from the fish, this year no signals have been detected as of the writing of this report, indicating that all tags are still successfully attached to their rays. I hope for more interesting data from the five rays newly tagged after eight months.
I would like to express a deep thank you to all of the members of this pitted stingray team.
ARGOS 衛星 Web サイトでタグの切り離しに関する通知がないか神経質にチェックしましたが、嬉しいことに信号は発信されていませんでした。これは、すべてのタグがまだ魚にしっかりとついていることを示しています (miniPAT データ ロガーが魚から切り離されて海面に浮かぶと、信号を衛星に送信し、その信号が衛星に送信されるのです)。昨年同様、今回の旅も無事に終わり、休憩時間には上関を散策することもできました。 こうして私は、上関地域のたくさんの美しい写真（そしておいしい魚をお腹に）を抱えて柏に戻ることができました。昨年の調査では、残念ながら1つの装置がすぐに外れてしまいましたが、今年はこのレポート執筆時点で信号は検出されておらず、すべてのタグがまだ正常に魚に付いていることが確認できています。8ヶ月後に装置が魚から切り離されて興味深いデータが送られてくることを期待しています。 調査チームの全員に深く感謝しています。
Additionally, in this biologging fund, I would to thank you for your generous donations which aid in enabling the continuation of research such as this.
マグロが針にかかった瞬間、船上に漂うなんとものどかな雰囲気は一瞬にして吹き飛びます。「ジーィィィィィッ!!」とけたたましい音を立てつつ、リールから飛ぶように引き出されていく極太の釣り糸。釣り竿に取り付き、巨大なリールを抱え込んで糸を巻き取ろうとする釣り人。バタバタと持ち場に走り、必要な道具の準備を始めるチーム各員。そして毎回必ず、自信に満ちた表情で「This is a big fish!!!（これは大きい魚だ！）」と叫ぶバーバラ（意図はよく分かりませんが、チーム全員を鼓舞したかったのかも？）。そこからは、圧倒的なパワーではるか水平線まで泳ぎ去ろうかというマグロの強烈な引きに対し、船をマグロと同じ方向に走らせながら徐々に糸を巻き取っては、糸を再び引き出されて、の繰り返し。マグロの体力をジリジリと削り、船の間近に寄せるまでには短くても30分、長いときには1時間半もかかります。一進一退の激闘の末、ようやく抵抗しなくなったマグロを船に引き上げる段階になると、そこからは打って変わって全ての作業が迅速に進みます。まず船尾のドア付近にマグロを寄せ、口にロープ付きの手鉤（てかぎ）を引っかけたら、綱引きの要領で5-6人がかりでマグロをデッキに引き上げます。マグロを濡らしたマットの上に横たえ、口にホースを差し込んでえらに海水を通すと同時に、両眼を濡れタオルで覆います（こうするとマグロが暴れない）。技術員のテッドがすかさずマグロの体長を測り、DNA解析用にひれの端を切り取ってチューブに保存。その傍ら、タグ取り付け用の銛を手にしたバーバラは、ロビーの手を借りながらマグロの背中に次々と機材を取り付けていきます。タグ装着が終わるや否や、マグロの乗ったマットをこれまた5-6人がかりで持ち上げて向きを180度入れ替え、船尾のドアからマグロを海中にすべり込ませるように放流して作業完了となります。マグロを引き上げてから放すまではわずか2分間という驚異的な作業スピードで、世界トップクラスの研究者（チーム）の洗練された手技手法をこうして目近で見られたことは実によい勉強になりました。
今日は調査に協力してくれている付近の定置網漁業者の方々に挨拶に行ってきました。今年の5月5日の朝日新聞の折々の言葉という欄で、「お酒もうれしいけど、俺たちが持ってきたカメで何がわかったのか知りたいなあ by 岩手県の一漁師」という言葉が紹介されました。これは、当研究室の卒業生である木下千尋さんが発信した情報が取り上げられたものです。木下さんはイラスト入りの本で動物たちの生態を紹介しています。今日は漁師さんにその本を手渡してきました。もちろん一升瓶も一緒に。
It was a long trip from Kashiwa to Taiji. I woke up at 4 AM to catch the first train heading to the airport. The view changed suddenly from downtown to seaside at the moment I stepped out the airport. There were no tall buildings but the azure sky and distant sea level. On the way driving to our destination- Taiji whale museum- we passed through a local attraction called Hashigui-iwa Rock, a landscape formed by magma (Figure 1). The rocks were like a barrier, standing between me and the waves. The tide retreated. I bended down, staring at the rocky shore and a small tidal pool. The last time I saw such view was probably 3 years ago. I missed all of these, the salty breeze, the splashed waves, and the tiny world in the intertidal zone.
That was a fresh start for this field trip, you may say, but it was certainly not compared to what has about to come next. A dozen of dolphin swim around the bay connected to the museum. They were the reason of this field research – we were going to measure their resting metabolic rate using a flow cup and a heart rate logger. After settling down the equipment and tomorrow’s schedule, I had a wonderful dinner and fell into a peaceful slumber quickly.
The light-hearted mood lasted until the experiment. As an assistant of my mentor, my job was to observe and record details of the experiment setting, including but not limited to date, temperature, and start time, using whether pen or camera. Our research objects were two spotted dolphins called Rio and Lana. Everything seemed to be smooth at first. Dolphins were resting on the stretcher and the logger was attached properly. But when it came to the flow cup, Rio became reluctant and started to struggle. Although we managed to finish the experiment, Rio’s data was not that promising. Luckily, Lana was more cooperative and we had some valuable data.
Figure 2. The spotted dolphin called Rio／図2 マダライルカのリオ
In the next day, we tried to remove the stretcher and let the trainers hold the dolphin as still as possible in the water. It did work well. It was a pity that I had to leave before the end of this research due to school affairs. Nevertheless, it was a valuable experience to me. It showed me the difficulties I might encounter in my future research, and most importantly the way to resolve them. No matter how well you prepare in advance, there would be always unforeseen circumstances and the research should be adjusted accordingly.
On the way back to the housing, I noticed the painted tiles on the road with numerous cetacean species on them. Some were aged and weathered by the salty wind. Yet, the grass stretching out from the junction of tiles brought some liveness after all. It has always been good to go out.
2022年は計9本の原著論文を公表する事ができました。その中でも2018年3月に学位を取得し、現在名古屋大学で特任助教として活躍中の後藤佑介さんとの共同研究成果が5月にPNAS Nexusに公表されました。論文タイトルは“How did extinct giant birds and pterosaurs fly? A comprehensive modeling approach to evaluate soaring performance(絶滅した巨大鳥類と翼竜類はいかにして飛んでいたか？滑空能力を評価する包括的モデルによるアプローチ)”はYahooニュースをはじめとした国内外のマスメディアで大きな反響がありました。
Maya Stock (Master’s Student, Department of Natural Environmental Studies, Graduate School of Frontier Sciences, University of Tokyo)
In the last week of September 2022, I headed to Kaminoseki to study pitted stingray (Bathytoshia brevicaudata) in the Seto Inland Sea. The goal for this trip was to attach MiniPAT tags to five rays, so that we can gain insights into their behavior and ecology in the region by collecting data such as location, temperature, depth, and 3-axis acceleration. We are specifically interested in how these rays might be moving seasonally, and where they go after longline capture and release. These are important questions, not only from an academic perspective, but also from a societal perspective, as these rays are known to take the fish caught by fishermen, and also damage nets. By conducting biologging research for this species, we hope to find ways to reduce the damage they are causing, while also learning more about the species’ swimming behavior and ecology. At the same time, we can also gain helpful experience on how to conduct biologging on these fish, since biologging on more coastal rays is currently still rather rare.
Considering the relative rarity of literature on coastal stingray biologging techniques, I was uncertain about how well this field excursion would go. Furthermore, the only fishing experience I had prior to heading to Kaminoseki was one time many years ago at a summer camp in the U.S.A., where as a young girl I reeled in an unimpressively small trout—a very different experience from longline fishing for rays in the Seto Inland Sea. Thus, I was very nervous, and the excitement of my first visit to Kaminoseki did not sink in at first. However, once I started the final leg of the journey to Kaminoseki, I was able to get a good view of the Seto Inland Sea from the train window. Before coming to Japan as a research student this summer in preparation for beginning my master’s studies later in the fall, I had mostly grown up periodically visiting the West Coast of the U.S.A. with my family, where you can see the Pacific Ocean stretching out as far as the eye can see. The Seto Inland Sea, in comparison, felt much more sheltered and closed, with many small islands scattered throughout. “Do pitted stingrays stay mostly in the Seto Inland Sea, or do they move out to other areas—even the Pacific Ocean—depending on the season or if they are disturbed?” That was one of the many questions we had heading into the field study. From my train seat, as I clutched my hiking backpack and suitcase containing the five precious tags we hoped to deploy, I thought “We’re really, actually going to do ray research in the Seto Inland Sea”. As the reality finally began to hit me, my excitement and anticipation grew.
After arriving in Kaminoseki in the evening of September 25th, we headed out in the morning of September 26th from Shirahama Port to put out the first longline. I was looking down a lot of the time while putting bait on the hooks, but still was able to take in the scenery of the coastline, emerald water, and islands in the distance. Once we returned to port, we waited for some hours, and then went out to sea again to check on the longline we had previously set. Unfortunately, the rays had evaded us this time, so we set out a fresh longline and then headed back to port.
After another period of waiting, we headed out to sea once again, where we found that we had finally caught a pitted stingray. A buoy was first attached to the line leading to the fish so that we could keep track of where it was prior to deploying the tag. I could see the buoy bobbing up and down furiously, and almost being pulled under water. Although I could not yet see the actual ray, I thought that it must be extremely strong and large to be able to pull the large buoy with such force. Once the ray was brought to the surface, this guess was confirmed. It was a female pitted stingray measuring 156 cm across, and with tiny white spots like many stars on its back, just like its Japanese name suggests. We successfully attached a tag to the muscular region near the tail, where we hoped to avoid the vital organs and minimize negative impacts on the fish. After releasing the ray, we once again set out a longline and then returned to port. When we checked in the evening, we found a smaller male ray, which we also put a tag on and released. We then set out another longline, which we planned to keep in the water overnight, and then check in the morning.
The morning of September 27th was stormy, so we waited indoors as the rain hammered down, hoping that after the storm passed, we would find more rays. We finally were able to head out around noon, and found three rays (two males and a female), all of which we attached tags to and released. Thus, we were able to successfully deploy all five of the tags we brought.
For the deployed tags, we are still eagerly waiting in anticipation for the arrival of information in hopefully about 8 months, when they are programmed to detach from the rays, float to the surface, and transmit collected data to us. If we are lucky, and can track down and actually retrieve the tags, we will be able to access more detailed data as well. Speaking of luck, we had both lucky and unlucky events happen shortly after deploying the five tags. The unlucky part was that we learned about a week after deployment that one of them had prematurely detached from its host ray and was drifting about in the Seto Inland Sea, and the lucky part was that we were able to retrieve it. After carefully watching the map tracking the path of the detached tag and considering the local fishermen collaborators’ expert advice regarding sea conditions, we hurriedly departed port from Kaminoseki several days later at around 2:00 when the sea conditions were supposed to be favorable, and used a Goniometer (a direction finder that detected signals from the tag and pointed us in that direction) to search the dark predawn waves for the tag. I mainly checked the Goniometer (my assigned role) and was nervous (not my assigned role), and thus was mostly staring at the direction finder screen’s arrow pointing us in the right direction. The actual spotting of the tag once the sun came up was done by the local fisherman collaborator who was part of the search party. He spotted the tag floating in the middle of some floating debris. Thanks to his and everyone else’s efforts, we fished the tag out of the water with a net and triumphantly headed back, arriving in port at about 6:00. Our approximately four-hour search was fruitful, as the data logger, when plugged into a laptop, was seen to contain recorded data, which we will be analyzing. Meanwhile, back out at sea, we hope that the other four data loggers are busily collecting information on the lives of their rays, so that we will be able to gather more long-term data.
Finally, although the majority of the data we hope to gather are yet to arrive, I have been able to make a couple of other preliminary conclusions from my first trips to Kaminoseki. First, fishing for rays in the Seto Inland Sea is indeed—unsurprisingly—very different from fishing for trout in a pond. The former is more challenging, but also much more intriguing, than the latter. Second, and more importantly, I am very fortunate to be able to conduct this interesting research, and as part of a team with many kind and knowledgeable people. I would like to extend a special thank you to all of the researchers and fishermen who are a part of this endeavor.
調査の話に入る前に、この調査が行われるに至った経緯を少し記述します。世界中のカジキ釣り師の間で、釣ったカジキをリリースする際、衛星発信器（カジキの行動を記録して衛星経由で送信する装置）を装着して放流する「IGFA Great Marlin Race」が行なわれています。このレースは日本でも行なわれています。このレースでカジキに装着された装置は一定期間経過後に自動的に切り離されて海面に浮上してきます。海面に浮上すると、得られたデータを衛星に発信し、衛星経由で私たちはデータを確認することができます。衛星経由で得られるのは、蓄積されたデータの一部のみです。もしこの装置を回収できれば、カジキ類の詳細な生態を知ることができるのです。