The present and future of the ecosystem reflected in marine life

An animal ecologist researching large marine animals such as whales and dolphins, Assistant Professor IWATA Takashi of the Graduate School of Maritime Sciences has performed surveys in oceans across the world. By using a method known as “biologging,” which involves attaching various recording instruments to animals in order to collect data, Iwata is working to elucidate the activity and surrounding environment of mysterious marine life. In recent years, he has also focused on surveying endangered finless porpoises native to nearby Osaka Bay. We sat down with Iwata to learn more about the current state of the oceans revealed through his research, as well as problems facing ecosystem conservation.

Endangered finless porpoises widely inhabit Osaka Bay

You’ve continued to research finless porpoises in Osaka Bay. What led you to this topic?

Iwata: Up until I started at Kobe University in 2021, my research was mostly performed overseas. I carried out surveys primarily on marine mammals in places like Iceland, Norway, Canada, Thailand, the subantarctic island of South Georgia as well as Antarctica.

Upon moving my base of operations to Kobe, I decided to perform surveys in Japan, which gave me the idea to study finless porpoises in Osaka Bay. It was known to a certain extent that finless porpoises live in the area around Kansai International Airport, but we didn’t really know much about their ecology or the state of their habitat.

At about 1.5 meters long and weighing about 50~60 kg, they’re quite small when compared to other dolphins. There also aren’t many of them in Osaka Bay, so they’re tough to directly interact with. For the biologging used in my previous surveys, we attached recording instruments to whales that came up to the ocean’s surface, but this proved difficult to do with finless porpoises.

So, we sampled water from 100 different locations around Osaka Bay and surveyed the state of the finless porpoises’ habitat by analyzing the DNA found in the sampled water by season in an “environmental DNA survey.” We also installed underwater microphones to capture and analyze the sounds of finless porpoises. In addition, we took the stomachs of finless porpoises that had died due to being stranded and analyzed what they had been eating.

We performed these surveys over the course of three years from fiscal year 2022, securing funding from the many generous supporters of our crowdfunding campaign.

What did you learn from these surveys?

Iwata: It was revealed that finless porpoises may actually live in a very wide area between the Akashi and Kitan straits. We weren’t able to ascertain how many actually live there, but we did discover that they inhabit almost all of Osaka Bay. We were also able to infer based on measurements of finless porpoise sounds that there are more of them living on the east side of the bay near Kansai International Airport than on the west side near Awaji Island.

It is thought that there are more finless porpoises living on the shallow east side of the bay than the deeper west side because finless porpoises tend to prefer shallow places. As for why they have this preference, it may come from the fact that their prey lives on the sea floor. This conjecture was supported by investigations of the stomach contents of finless porpoises, which revealed that they do indeed often eat bottom-dwelling fish. While they do eat all sorts of different things, it appears that finless porpoises prey on animals that are slow and relatively easy to catch.

Populations of finless porpoises can be found in five ocean areas in Japan, namely from Sendai Bay to Tokyo Bay, Ise Bay and Mikawa Bay in the Tokai region, Seto Inland Sea (including Osaka Bay), Ariake Sea and Tachibana Bay in Kyushu, and Omura Bay, also in Kyushu. By getting a better picture of the state of their habitat in Osaka Bay, which was not previously well known, we’re now able to compare each of the ocean areas and use that knowledge to preserve the ecosystem.

Policy that protects the environment, not just food sources

What was a survey you performed overseas that left a particular impact on you?

Iwata: One paper that got quite the reaction was our survey on the Bryde’s whale in the Gulf of Thailand. The whales feed while treading water, which is fascinating.

Generally, rorquals, which include the Bryde’s whale, are known to charge into schools of small fish and other prey with their mouths wide open in what is called “lunge feeding.” However, the Bryde’s whales of the Gulf of Thailand were treading water with their heads stuck out of the surface simply waiting for prey to jump inside.

It’s thought that nutrient over-enrichment of the Gulf of Thailand due to human sewage has led to hypoxic conditions (low levels of oxygen) in the water, pushing all the fish to the surface; therefore tread-water feeding is an efficient strategy for capturing surface prey.

There had never been any reports of tread-water feeding in whales before we published our paper, but there have been reports since, even in other ocean areas.

Is there a reason why your research focuses on large marine life?

Iwata: By studying top predators in the ecosystem, we can get a better understanding of the marine ecosystem as a whole. In addition, many large marine animals are endangered species, so if we don’t study them now, it may be too late. Elucidating where they live and what they eat can also give us a benchmark for environmental change and allow us to think about ways to conserve our oceans and the animals that live in them.

In Japan, there are active movements to protect marine life as a food source, but policy for conserving the environment, which includes the living things within it, is lagging behind that of Europe and North America. I feel as though we need to think about these animals and their coexistence with humans and advance policies that establish protected areas for marine life. To that end, the data and analyses accumulated through research that will form the foundation for these policies are of utmost importance.

Data gathered through biologging has brought problems in the oceans to light

What merits are there to utilizing biologging to collect data?

Iwata: I mentioned this before, but biologging is when we attach cameras and sensors to animals to measure their activity and the surrounding environment. When targeting large whales, we approach the whales on a small boat and stick equipment, known as a “tag,” to their backs with a suction cup using a long pole. The tag detaches after several hours to about one day and drifts to the surface, where it is recovered by following the radio waves from the transmitters on the tags.

For surveys of marine animals, there is also a method in which information is received via satellites from transmitters attached to the animals (biotelemetry), but that only tells us relatively simple data such as their location. To understand behavior and foraging from the animal’s perspective, and to obtain three-dimensional information about the underwater environment, it is necessary to recover the biologging equipment. 

Fieldwork is really hard. It can be influenced by the weather and requires us to wait for just the right chance to attach equipment and go recover it in the open ocean. But the data we acquire is extremely valuable. It may even be useful in getting an understanding of ocean debris, pollutants and the state of climate change.

It’s only been 20 years or so since biologging was established as an academic field, but recent advancements in equipment miniaturization and research on minimizing burden on the animals could lead to even wider utilization of the technique.

What are some future prospects and challenges of your research?

Iwata: This year, I published a paper on dolphins that live in Osaka Bay. When we used underwater microphones to record and analyze the sounds of common dolphins, we confirmed that they mostly appeared in the winter and spring. This coincides with nori seaweed cultivation season, so it’s possible that these dolphins feed on prey such as fish around the seaweed nets that have become temporarily abundant during that period.

Moving forward, I plan to use biologging to perform surveys on marine mammals within Japan. Surveys on marine animals require funding and there will be plenty of challenges, but I’d like to collaborate and perform joint research with corporations. When thinking about activity related to corporate social responsibility, there are those who feel that environmental conservation of oceans is more difficult to tackle than that of terrestrial environments such as forests, but given the opportunity, I’d like to first consider what kind of collaborations are possible.

This research field is one in which results are hard to come by, and we’ve also got very few young researchers, so I’ll do my best to convey the appeal of ocean research to as many people as possible. I’d like to cooperate with young researchers in a variety of ways by providing them with my experiences, knowledge and data.

Resume

In 2006, graduated from the College of Bioresource Sciences, Nihon University. In 2012, completed the five-year doctoral program at the School of Multidisciplinary Sciences, The Graduate University for Advances Studies, SOKENDAI, and received his doctorate in science. In 2012, became research fellow at the Ocean Observation Center, Tokyo University of Marine Science and Technology. In 2013, became research fellow at the Atmosphere and Ocean Research Institute, The University of Tokyo and in 2016, became post graduate researcher for ocean science at the same institute. Also in 2016, became JSPS Postdoctoral Fellowships for Research Abroad visiting scholar at the Sea Mammal Research Unit, University of St Andrews. In 2018, became research fellow at the Atmosphere and Ocean Research Institute, University of Tokyo and in 2020, became post graduate researcher for ocean science at the same institute. Also in 2020, became researcher at the Ocean Policy Research Institute of the Sasakawa Peace Foundation. In 2021, became assistant professor at the Graduate School of Maritime Sciences, Kobe University.