Why do otters in Singapore prey on koi fish but not eat them?

Recently, otters in Singapore have gained a notorious reputation for entering homes, killing fish in ponds, and leaving behind uneaten carcasses, tarnishing their once-cute image. This situation occurred again on Dec. 6 in a home along Surin Avenue near Kovan.

20 Koi Fish Dead

On Dec. 6, residents of the Surin Avenue home woke up to a grisly scene—20 koi fish in their pond had been dismembered. The homeowner, Dai, 63, told Shin Min Daily News that his helper discovered the fish carcasses around 7 a.m. Dai, who has been rearing koi fish for 30 years, said, “It feels like I didn’t just lose money, but also old friends. I am very upset, and this has affected me greatly.”

According to 8 World News, the CCTV at Dai’s home wasn’t working during the incident, but footprints suggested more than one otter was involved. Despite fortifying his home after hearing about otter sightings in the area, the otters struck. Dai’s home is about 100 meters from a nearby canal, which could explain their presence.

NParks’ Group Director for Wildlife Management, Adrian Loo, stated that NParks and the Otter Working Group are working together to advise residents on measures to keep otters out of residential areas. NParks had received about 450 feedback reports about otters in 2022, with only nine from the Kovan area.

But why do otters exhibit such behavior?

The seemingly senseless killing of fish by otters can be explained by several factors. According to N. Sivasothi, Senior Lecturer at the National University of Singapore (NUS) and also known as the “Otterman,” Singapore’s interconnected waterways allow otters to travel long distances, bringing them into residential areas. Otters, being semi-aquatic creatures, can traverse large expanses of land with ease.

In cases where otters are pushed out of prime habitats by other groups, they enter an “exploratory mode” in search of food and territory. When they stumble upon home ponds filled with fish, their natural instincts take over—they prey on the fish. However, because they are focused on exploration, they often don’t consume their kills. This explains why the kill rate is high, but consumption is low.

Domesticated Fish and Pond Design

Home ponds are designed for easy viewing, often with fewer hiding places for fish, making them easy targets for otters. Moreover, domestic fish are used to being fed and may swim toward potential threats rather than away from them. Consequently, “the fish don’t stand a chance” when otters come across a pond, leading to dramatic and distressing outcomes for homeowners.

Overlapping Domestic and Natural Environments

This behavior results from the intersection of otters’ natural instincts with a domestic environment. Although it may seem like otters always kill but don’t eat the fish, Sivasothi and his team have observed instances where otters fully consume their catch. Such behavior is more commonly observed in otters that live in larger waterways, where they focus on feeding rather than exploring.

Adapting to Otters

To manage otter-human conflicts, NParks works with the Otter Working Group to help residents implement exclusionary measures, such as meshing gates to prevent otters from entering. In some cases, otters may even be relocated, especially if they establish a holt (den) in residential areas and are cut off from natural food sources, making them more likely to prey on home ponds.

Living in Harmony with Wildlife

As Singapore works toward its “city in nature” vision under the Singapore Green Plan 2030, interactions with wildlife will inevitably increase. Sivasothi points out that humans, being adaptable, are better equipped to adjust to the presence of wildlife. By implementing effective exclusionary measures, the number of otter-related incidents can be naturally reduced over time.

Top image via Shin Min Daily News Facebook, @sunshineyiling/Instagram