Why do otters in S’pore prey on koi fish but not eat them?

An overlap between domestic environment and natural behaviour.

Gawain Pek | December 20, 2022, 11:53 AM

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Of late, the otters' cutesy image has been tainted by their notoriety for entering homes, killing fishes in ponds and leaving carcasses for owners to discover.

This happened again on Dec. 6 in a home along Surin Avenue near Kovan.

20 koi fish dead

Residents of the Surin Avenue home woke up to the sight of death on Dec. 6 when they discovered that as many as 20 of the koi fish they reared had been dismembered.

The resident, Dai, 63, told Chinese media Shin Min Daily News (Shin Min) that his helper woke up at around 7am in the morning to discover that "all of the koi fish" in the pond were dead.

Dai shared that he had been rearing the exotic fish for 30 years, starting when he first moved into his current Surin Avenue home.

"It feels like I didn't just lose money, but also old friends. I am very upset and this has affected me greatly", Dai told Shin Min.

Image via Shin Min Daily News/Facebook.

According to 8 World News, the CCTV at Dai's residence was not working at the time of the incident, so no footage of the otters were caught.

However, Dai suspected that there was more than one otter based on the footprints that were found, Shin Min wrote.

The resident shared that he had fortified his home after hearing chatter about otter sightings in the area around two months ago.

Dai's home is around 100 metres from a nearby canal, Shin Min reported.

Dai's wife told 8 World News that she was shocked by the incident as this was the first time something like that has happened in the 30 years she has been staying in the estate.

Responding to Mothership's queries, NParks' Group Director for Wildlife Management, Adrian Loo, said that they are aware of the incident and are working with the Otter Working Group to advise residents on exclusionary measures to prevent otters from entering home premises.

"NParks has received about 450 pieces of feedback on otters in 2022 (as of Nov. 30, 2022), majority of which are of sightings. Of these, nine pieces of feedback were on otters in the Kovan area", Loo added.

But, why?

Sounds like senseless behaviour? Not quite.

While N. Sivasothi, Senior Lecturer at the National of the University of Singapore, also known as the "Otterman" among nature lovers, did not follow the Dec. 6 incident closely, he offered several factors that may explain the otters' behaviour, based on what was learnt from past incidents.

Interconnected waterways

The researcher pointed out that Singapore's waterways are more interconnected than they appear.

Map showing Singapore's natural waterways. Image via PUB.

These facilitate otter movement into residential areas.

What's more, otters are "semi-aquatic" creatures and can move great distances across land with relative ease.

All things considered, we should expect to be able to find the otters "anywhere in Singapore", Sivasothi mentioned.

Territoriality and exploration

For the otters, large waterways are the "optimal habitat" where they can get enough food.

However, otters can be forced to "eke out a living in the remaining space that's available" when they are pushed out of the main waterways by competing groups, Sivasothi pointed out.

In these cases, otters enter an "exploratory mode".

The now-relocated Seletar otters observed in the holt that they had established. Photo courtesy of Otter Working Group.

"So the primary purpose of why they are there, they are evaluating resources. So resources mean 'Is there a place to hide, rest? Is the place to feed, a potential feeding ground right?' Now, they will have several of these within a home range, right?" Sivasothi explained.

When exploring otters encounter a pond full of fish, they do what otters do - prey on the fish.

Being focused on "exploration", otters under such circumstances react to the sight of prey, and then "move on" with their exploration.

"They often don't stay in one spot for a very long time", Sivasothi said.

This may result in a situation where the kill rate is high, but the consumption rate is low.

Domesticated fishes

The confounding factors in such a situation are the home ponds and fishes themselves.

The design of home ponds, meant for viewing, may mean easy access for the otters and fewer hiding spots for the fishes.

Fishes in home ponds may also be habituated to swim towards you, having gotten used to being fed by their owners above the pond.

"A pet fish in a pet pond is not a wild fish in a wild habitat. So, a pond by design is meant to expose the fish and the fish are pets, so they are not hiding", he said.

In such circumstances, "the fish don't stand a chance".

The result is that when the otters pass through a home pond, the number of fish they kill can be "very dramatic" and "distressing".

Overlapping domestic and natural environment

"So, what we're having is an overlap of a domestic situation (home ponds) with a wild situation (otters in exploratory mode)", Sivasothi remarked.

The caveat is that, in reality, it is not always the case where otters kill fish but not eat them.

Sivasothi revealed that in his work researching otter behaviour in Singapore, he and his students have observed incidents where otters kill fish and fully consume their catch.

The Seletar otters that were eventually relocated. Photo courtesy of Otter Working Group.

The researcher also highlighted that in our urban landscape, the phenomena of the overkilling of prey is not observed among otters living in larger waterways.

When a family of otters in the waterways forage for food, they are focused on just that -- "feeding".

Adapting to the otters

Earlier this year, NParks shared more about its otter management practices.

When otters have access to natural food sources but have entered residential areas to prey on easy targets in residential ponds, their presence are likely to only be transient, NParks explained.

In such cases, NParks will work together with the Otter Working Group (OWG), to help residents and estate managers set-up exclusionary measures to prevent otters from gaining access to their compound.

These measures include simple infrastructure alterations such as meshing up gaps in gates to prevent the otters from entering, NParks said.

Photo courtesy of Otter Working Group.

Image via NParks.

In certain situations, otters will be relocated.

Relocation will only be carried out if the otters are found to have established a holt in residential areas and are cut off from natural food sources, NParks explained.

Otters cut off from natural food sources are more likely to turn to other food sources, like home ponds.

This was the case for the Seletar otters.

Ground realities

Speaking on his experiences interacting with residents and observing otters, Sivasothi said that "the majority (of residents) are quite understanding".

"When we lay out all the factors, then they are actually quite open to realising 'okay, what are the measures we need to take and realising it can't be immediate", he shared.

Most notable are the responses from residents who had lost fish to otters.

"Maybe because they have some kind of relationship with animals, they are actually quite understanding", the researcher opined.

That being said, Sivasothi recognised there is a minority who are "angry" and "upset" and who may require more patience when engaging with to find a middle ground.

Learning to live with wildlife

Under the Singapore Green Plan 2030, becoming a "city in nature" is its first pillar.

The plan recognises that as re-wilding and conservation efforts continue, there will be more wildlife amongst us and the chances of human-wildlife conflict will arise.

"We will work with communities and non-governmental organisations (NGOs) to develop programmes to allow humans and wildlife to live in harmony", the Ministry of Sustainability and the Environment wrote on the website.

As Singapore works towards realising its "city in nature" vision and aspire towards living in harmony with wildlife, we (the humans of Singapore) are now in a moment of adaptation, Sivasothi pointed out.

While animals will act as predicted, humans are more adaptable.

"Eventually, we realise that we are the ones who you know, are technically smarter, so we can make adjustments. The animals will tend to do things as predicted by an understanding of their behaviour", Sivasothi remarked.

If chicken wires and fish nets do not work, sturdier materials can be deployed.

Where exclusionary measures are hard to erect, such as on large compounds like condominium grounds, alternatives like removing the attractant can be considered.

With effective exclusionary measures, otters that are not able to get adequate nutrition will naturally die out as their ability to raise healthy litters are impeded.

This provides a natural control on otter numbers over time.

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