Hong Kong’s endangered river otters are inhabiting broader tracts of the city than previously thought, scientists have said after discovering signs the mammals have ventured into local streams previously considered to be too polluted for them. Researchers from Kadoorie Farm and Botanic Garden found fresh secretions from an Eurasian otter while conducting a study of the Ng Tung River near the urban centre of Sheung Shui in February, the first indicator the mammals might also inhabit water channels close to urban areas. Yang Jianhuan, manager of the NGO’s Kadoorie conservation China department, said the location was the easternmost recorded trace of the mammals found in recent years and overturned past conclusions that the otters only stayed in protected wetlands, mangrove thickets and fish ponds in Mai Po, Lok Ma Chau and San Tin.
“There had not been any records of otters in the city’s rivers,” he said. “This is particularly meaningful because the biggest problem facing otters in Hong Kong is the shrinking of their already few habitats.” Eurasian otters are believed to be the rarest and most threatened terrestrial mammal species in Hong Kong, with a 2019 study by the University of Hong Kong suggesting that only seven remained in the city.
The mammals are considered critically endangered in the region and are a near-threatened species worldwide. Eurasian otters were once widely distributed across the city’s western waters, including the New Territories, some outlying islands and even Hong Kong Island, with the first recorded sighting in Victoria Harbour in the 1890s. But the species began to vanish from most parts of Hong Kong in the 1930s due to poachers targeting them for their fur and culls after being labelled pests, as well as water pollution and habitat degradation.
Kadoorie Farm began a study in 2020 to find the city’s last remaining otters, using camera traps, field trips and eyewitness accounts to chart the mammals’ potential habitats. As part of the study, researchers uncovered traces of an otter in Pak Nai, the city’s westernmost record for the mammals. The team also brought together 12 citizen scientists to conduct field surveys in the northwest New Territories earlier this year, which found evidence of otters on a piece of rock in Ng Tung River.
“These discoveries have expanded the otters’ range in Hong Kong to the city’s northwest. They are still utilising the entire Deep Bay area and the Shenzhen River catchment area,” Yang said. “The findings also show these mammals can live close to human settlements, despite being so elusive and rare.
” The biologist suggested that the otters’ return to the local river courses was the result of revitalisation work by authorities in recent years. The Drainage Services Department has tried to introduce ecological conservation elements to large-scale improvement projects in open channels and riverways for more than 10 years, including along the Ho Chung River in Sai Kung in 2007 and Tai Po’s Lam Tsuen River in 2012. “Our engineers also enhanced biodiversity by introducing eco-conservatory elements to the natural stream habits for fish and other aquatic wildlife,” a department spokesman said.
Four-year ecological monitoring in the Upper Lam Tsuen River showed that the numbers of bird, fish and dragonfly species had returned to pre-construction levels by 2017, he added. “In particular, the population of one rare [salamander] species in Lam Tsuen River ― the Hong Kong newt ― exceeds the previous level from just over 200 recorded by pre-construction baseline monitoring to more than 600,” the spokesman said. The Hong Kong newt is only found in the city and select parts of Shenzhen.
The department earlier carried out beautification works along the Ng Tung River, which draws on the “blue-green infrastructure” concept, a strategically planned network of natural and semi-natural areas with environmental features. Authorities also conducted routine maintenance work at the site, including removing debris and silt, cutting weeds and planting flowers along the embankment. The presence of otters is considered a gauge for the health of an ecosystem, since the mammals and their prey are susceptible to poor water quality, pollution and habitat loss.
In 2011, England celebrated the return of local species from the brink of extinction across each county, with environmental authorities hailing the turnaround as a sign that rivers were at their healthiest in more than two decades. Over in Singapore, the smooth-coated otter population has more than doubled since 2019 and consists of about 170 mammals divided into about 17 families. But Yang said most of the coastal and wetland areas inhabited by Hong Kong’s otters lacked protection and were vulnerable to urbanisation and the prospect of development.
“There are fewer otters than Chinese white dolphins and pangolins in Hong Kong,” he said. “If we can do more to improve our rivers, our otters can venture into more places.”.
