Otter watch keeps eye on urban rivers

Challenges faced

Once they decided to take the matter seriously, answering a series of practical questions took precedence.

"If otters are returning to the city, we want to know whether otters are currently residing in Chengdu's urban waterways. How do they utilize the habitat resources of Chengdu's rivers? What challenges might urban river and channel management pose to the survival and population expansion or reproduction of otters? How do Chengdu residents perceive and feel about otters?" Hu said.

They soon found that answering these questions was challenging.

At first, the otter's elusive, solitary and nocturnal habits posed significant challenges for investigation.

The complex urban context they faced proved even more difficult. Chengdu is not just a city; it is a river system. Thousands of years of interaction between nature and humans have shaped the unique water system and urban layout of the Chengdu Plain. "This is the context we face — a complex system and a species difficult to observe. We must design our strategies very cleverly, observe carefully and interpret our data prudently," Hu said.

Their project officially launched on July 1, 2025. During the conceptual phase, they made a clear decision — to make citizen science their core strategy.

They combined public reporting with scientific monitoring as their primary approach. Their initial leads came from public reports. They also noticed that there were scattered observation records on social media platforms.

"One of our most important tasks is to gather this information and encourage more citizens to become 'otter observers'," Hu said. In collaboration with the Tencent Foundation, the project established a public reporting platform. When citizens spot otters, they can submit their information through this online system, including location, time, photos, videos, behavioral descriptions and other observations.

They compiled nearly 40 public otter sighting records, all with video evidence, from 2021 to December 2025. The results surprised them. Chengdu administers 20 districts, counties and county-level cities, including Dujiangyan, and half of them had public sightings of otters during that period.

The two key monitoring river segments they selected were determined based on the preliminary public report data.

Once a sighting was identified, they conducted on-site investigations, including habitat surveys, feces and trace searches, feces collection, infrared monitoring and social surveys.

Meanwhile, volunteers recruited by the team could also participate in field investigations after training. They also established close scientific collaboration with a team from a research institution in Chengdu.

Otter feces samples collected in the field were sent to their laboratory for DNA sequencing, which would be used for subsequent analyses of the number of individual otters, population structure, kinship, genetic diversity and effective population assessment in the Chengdu area, Hu said.

Conservation questions

The project also sought to answer the question of how urban rivers could be made more otter-friendly. To address the challenge of steep, hardened riverbanks, especially during dry seasons, the team tested three low-cost otter-friendly climbing facilities. Two of these were successfully used by otters within three months, showing that small changes to urban river design could significantly benefit otters.

As the project progressed, Hu, Yu and their colleagues began to ask larger questions, such as what kind of river ecosystems and urban governance mechanisms could support healthy otter populations and their coexistence with humans.

"We realized that addressing these questions required collaboration across scales and disciplines," Hu said.

The project is becoming a model for multi-stakeholder collaboration, involving citizens, researchers, universities, government agencies, media and businesses, she said. "It demonstrates how public participation could bridge science and action, fostering a shared understanding of urban ecosystems."

Professor Zhang Lingqing, deputy dean of Sichuan Agricultural University's College of Architecture and Urban-Rural Planning, is a consultant for the otter watch project. He was impressed by his encounter with an otter at an artificial drainage channel in Dujiangyan.

"Cities, often perceived as concrete jungles, are ecosystems in their own right," he told local media.

"What might appear as 'negative spaces', like small islands and artificial channels, are in fact 'active spaces' that play a crucial role in safeguarding urban biodiversity. These areas can serve as ecological corridors for wildlife."

The return of the otters to Chengdu is more than just a conservation success story, Zhang said.

It highlights the potential for cities to support biodiversity and for citizens to play a role in environmental stewardship. "When we talk about living in harmony with nature, it shouldn't just be a grand vision. It should be a process we can observe, analyze and act upon," Hu said.

For Hu and Yu, their project is far from over. They will continue to monitor the otters, knowing that long-term data will be crucial for understanding their population size, breeding status and survival in the city.

In the long term, Hu said, they will explore greater potential for the project and make an effort to turn it into a model conservation project with public participation.

"In Chengdu, we have snow leopards in the mountains, giant pandas in the forests, and now, otters in our rivers," said Yu, who also leads a citizen science project to monitor the migration of raptors in Chengdu. "We expect that our project can not only advance scientific knowledge but also foster a deeper connection between people and their urban environment, proving that even in a metropolis of over 20 million people, there is room for wildness to thrive."

chenliang@chinadaily.com.cn