In Singapore, otters live within a heavily urbanised environment. Singapore historically had populations of at least Asian small-clawed otters and smooth-coated otters but all otter species became locally extinct in the 20th century. A repopulation of the island state by smooth-coated otters began in 1998, and accelerated in 2013. The growing otter population was seen as a success story for the greening of the city. Otters have become popular with the public, and have been adopted as national symbols.
This disappearance of otters in the 20th century was due to a combination of habitat destruction and pollution. The vast majority of Singapore's natural forest had been cleared, and many waterways were too polluted to support wildlife. Government efforts to improve the city's environment began in the late 1960s, and eventually saw many rivers cleaned and returned to a more natural state. Otters crossed the Straits of Johor from the Malay Peninsula to Singapore sporadically, but in 1998 a couple established itself permanently in the northwest. Others followed, settling in various locations on the northern coast. In 2013, otters were recorded migrating south, and they soon spread throughout most of the major waterways of the island.
Singapore's otters have become adapted to the urban landscape of the city. Unlike smooth-coated otter populations elsewhere, they are often tolerant of human presence. Otter families often nest in artificial environments, use stairs and ladders to enter and exit waterways, and use human infrastructure to travel both on land and in water. They are opportunistic feeders, eating food that is most common in their territories, and face few natural predators. Otter families are sometimes larger than those recorded elsewhere, and pups are recorded staying with their family longer than they do elsewhere. Multiple families have been observed with more than one simultaneously lactating female. The smooth-coated otters have been found to be hybrids with Asian small-clawed otters, although the origin of this is unknown. Some Asian small-clawed otters may also have returned, although they are restricted to mangroves and smaller islands.
Both otter species are protected by Singaporean law. Volunteer groups observe the otters, and the extensive popularity and recording of the otters has enabled the use of citizen science to conduct research. Human–otter conflict is rare, and otters are generally viewed positively by the public. An Otter Working Group (OWG) brings together the government, academics, and civil society organisations to conduct research and promote better human–otter relations. The success of Singapore's otters is viewed as a potential model for the success of urban otters elsewhere.
Geographic background
Singapore consists of one main island and 62 surrounding islands of various sizes. The Straits of Johor separate these islands from the mainland Malay Peninsula, and ranges in width from around to . The strait is effectively divided into two by the Johor–Singapore Causeway. Only about 5% of Singapore's original natural environment remains, although about 56% of the country is covered in some form of greenery, including parks. Many of these managed green spaces occur alongside waterways.
The island has three main drainage basins: western, central (including the Downtown Core), and eastern (encompassing the northern and eastern coasts). Singapore has no natural lakes or large rivers, although artificial reservoirs have been created. Most large rivers are sealed at their mouths.
History Historic presence and disappearance Historically, the Asian small-clawed otter was likely the most common species on Singapore. The smooth-coated otter was found in the region, but records from Singapore are limited. It may have mostly been a visitor to the island. Records of the hairy-nosed otter are difficult to confirm due to potential confusion with the smooth-coated otter. While there are Eurasian otters in other parts of Eurasia and to the south in Sumatra, there are no confirmed historical records for its presence in Singapore or the wider Malay Peninsula.
Otters are highly vulnerable to habitat destruction stemming from urbanisation. Pollution affects both otters and their prey. Furthermore, the modification of rivers can often create riverbanks unsuitable for otters, as they need to spend time on land. Large-scale deforestation of the island likely began only after the founding of modern Singapore in the early 19th century. An increase in agricultural production saw lowland and mangrove forests cleared for cash crops and aquaculture. By 1900, around 90% of the original forests were lost. Increasing pollution further damaged river ecosystems, and by the 1850s, some rivers were too polluted to support aquatic life. The island's otter population disappeared sometime before the 1960s. At this time, the island's mangroves were estimated to have been reduced to 1% of their former range. By 1990, all otter species were considered locally extinct. Some small-clawed otters were kept in Singapore Zoo.
Following the independence of Singapore in 1965, rapid urbanisation saw natural forests and agricultural plantations cleared for buildings, while coastal development included land reclamation. Rivers and streams were canalised, and river mouths were dammed. However, significant government efforts to improve Singapore's environment began as early as 1967 with the introduction of the garden city vision, which included protecting some natural areas and creating urban parks. A large river cleanup effort took place from 1977 to 1987, which successfully rehabilitated the rivers into a state healthy enough to support wildlife. Later efforts to achieve a more eco-friendly city included remodifying some rivers to have a more natural flow, including in Bishan–Ang Mo Kio Park. Clean waterways were seen as a security necessity, in addition to having environmental benefits.
While mangrove areas had been mostly destroyed outside of a few northern pockets, the establishment of protected areas such as the Sungei Buloh Wetland Reserve meant habitats that might support otters were conserved. Development along the northern coast was common from the 1950s until the early 1990s, but slowed after that point, likely leading to more stable environments.
There were sporadic otter sightings along the northern coast, although it is likely these were visitors rather than residents. In 1989, two adults and at least three cubs were spotted on Pulau Tekong, probably Asian small-clawed otters. All Asian small-clawed otter sightings were in mangrove areas.
Repopulation
In 1998, smooth-coated otters were seen in Singapore's northwest, likely having crossed the Straits of Johor. This was likely a breeding pair that established themselves in the Sungei Buloh Wetland Reserve and raised pups. Juveniles were seen every year from 1999 to 2003, and again from 2009 to at least 2014. (The years 2004 to 2007 had very few sightings, although this was likely a result of sample bias rather than due to a disappearance of the otters.)
In 2007, smooth-coated otters were seen on the northeastern island of Pulau Ubin, likely originating from a separate crossing of the Straits of Johor. These crossings were possibly prompted by urbanisation in Johor driving the otters from their previous habitats. The otters were likely able to successfully adjust to their new environment as Singapore's northern coast retains some protected natural coastline. Juveniles were seen in Pulau Ubin most years following. Sightings in the east quickly went from sporadic to outnumbering sightings in the west, even as the absolute number of sightings in the west also grew. A 2010 sighting on the country's southern islands was the first recorded smooth-coated otter sighting from that area since 1938.
Sightings were most frequently made at Sungei Buloh and at the Chek Jawa wetlands on Pulau Ubin. Initially, sightings were mostly restricted to areas near the coastline. However, in 2008 otter sightings began to occur in Sungei Punggol and Sungei Serangoon. These two rivers were in the process of being dammed, with Sungei Serangoon fully dammed in December 2009 and Sungei Punggol fully dammed in October 2010. Juveniles were first observed in what had become the Punggol Reservoir in 2011, and in Serangoon Reservoir in 2012. By 2012, a group of 13 lived in the Punggol Reservoir, the largest group known at that time.
Populations remained restricted to areas near the northern coast until 2013, after which smooth-coated otters spread into other waterways throughout the island. In 2014, recorded sightings in the south made up 48% of all sightings. That year also saw five pups spotted in the southern Marina Bay. The central watershed went from having few sightings in 2015, to having two resident groups in 2017, to five resident groups in 2021. A count in 2017 identified 79 individuals divided between 11 groups.
In 2019, pups were seen in the Singapore Botanic Gardens, in artificial ponds far from natural waterways. The otter population expanded significantly as they colonised new waterways, although by 2021 most of the waterways of the central drainage basin and parts of the eastern one were occupied. A survey around March 2021 found 170 individuals (including 35 pups) divided between 17 groups, plus further individuals and groups which were not confirmed. The group sizes ranged from 2 to 24. From 2019 to 2022, it is thought that the population doubled.
Ecology
Singapore is highly urbanised and has a highly modified environment. Mangrove forests cover 0.11% of the country, old-growth forests 0.16%, swamp forests 0.39%, and secondary forest 21.01%. Many rivers are canalised and barraged. While smooth-coated otters naturally inhabit wetlands and rivers whose banks have a lot of vegetation, populations have adapted to more human-modified landscapes in many locations. Otters in Singapore have been sighted in mangroves, brackish water, reservoirs, sandy beaches, and urban areas. Some northern populations may have ranges that extend across the Straits of Johor. Increased focus by the government on improving the urban environment, including better pollution management and expanding green spaces, has created more areas otters can inhabit.
While some otter groups still live mostly on the coast, others have established territories fully within modified waterways. Urban otters have learned to nest in artificial hollows, such as gaps underneath buildings. Otters use stairs to climb otherwise inaccessible riverbanks, and have even been seen using ladders. While smooth-coated otters are usually shy, many in Singapore are tolerant of human presence to the point of indifference. Where wild populations elsewhere tend to groom on sand, urban populations in Singapore are known to rest on grass and even concrete. Some of these adaptations, such as using artificial holts and traversing steep river banks using ladders, are the first known instances for smooth-coated otters, although they have been observed in other species. The Zouk family and the Singapore Botanic Gardens family are known to use roads to travel between isolated water bodies, possibly due to being outcompeted on the main waterways.