Poisonous sea slugs: The deadly threat on our beaches

Auckland Council is asking residents to watch out for the sea slugs. Photo / Supplied

After weeks of social media speculation, the Auckland Council has sounded a note of caution over the presence of poisonous sea slugs on the city's beaches - and confirmed it has received a sighting in the past week.

The threat comes from the toxic grey side-gilled sea slugs (Pleurobranchaea maculata), a native species that carries a poison strong enough to kill a human and that has been previously been responsible for the deaths of dogs on Auckland beaches.

The slugs contain tetrodotoxin, a neurotoxin also found in puffer fish that can paralyse a person in seconds and kill within an hour.

Despite the deadly toxin they carry, Auckland Council considers the sea slugs a low risk for people, who are unlikely to consume them, but is warning dog owners to remain alert.

Social media has been abuzz recently with tales of Auckland dogs being poisoned, but the council told the Herald it had received no reports of dogs falling ill from coming into contact with the slugs.

The Herald contacted the owners of two dogs at the centre of these rumours.

The owner of the animal said to have died told the Herald the sea slugs were not confirmed as the cause of death. The owner believed it was more likely that seizures killed the much-loved pet.

The Herald also understands the incident took place at least three years ago.

The owner of a dog that reportedly became unwell after coming into contact with a sea slug on Ōrewa beach posted on social media that his dog had survived the scare but refused to comment further.

In response to the rumours, Auckland Council alcohol and environmental health manager Mervyn Chetty said: "There has been some social media activity around dogs becoming unwell after visits to Ōrewa and Takapuna beaches."

"While it hasn't been confirmed that this is due to the dogs being poisoned by eating toxic sea slugs, it is a timely reminder for people to be vigilant and remain cautious at all times," Chetty said.

He advised people not to touch sea slugs and said they should report sightings to the Auckland Council.

"It's a normal occurrence for sea slugs to be washed ashore, but if there's unusually high numbers council will investigate."

Caution signs on Narrowneck Beach in 2010, warning of health issues caused by toxic sea slugs. Photo / Richard Robinson

In response to Herald inquiries, Chetty acknowledged that the sea slugs do contain enough poison to kill - and revealed one sighting has recently been reported.

Chetty cited research from the Cawthron Institute in 2009, which analysed Pleurobranchaea maculata in 2009 and found that they contain levels of tetrodotoxin (TTX) of between 600-5600 mg/kg with a median of 2500 mg/kg.

"The lethal dose in mice is 0.334mg/kg," said Chetty.

"So yes, if consumed they could be lethal."

Chetty reiterated that the risk of someone consuming a slug is extremely low.

"We would only consider taking action if the incidences of sightings increased or there were confirmed poisoning of dogs happening," he said.

"If council start getting confirmed cases of dogs being poisoned by TTX or multiple sightings of the slugs we would look at other options to reduce the risk of poisoning."

Chetty said the Auckland Council has received no recent reports of dogs becoming sick but a sighting of one of the toxic slugs on Narrowneck Beach on Monday had been reported.

Chetty advised anyone who spots a toxic sea slug to phone the Auckland Council on 09 301 0101 to report the sighting or email Healthenforcement@aucklandcouncil.govt.nz.

"People can also take a photo and send it to us so our staff can help with identification."

'Dead within the hour'

At the height of the panic that followed the deaths of two dogs in 2009, the Cawthron Institute's Paul McNabb spelled out the risk posed by the creatures.

Touching a dead animal on the beach could be enough to endanger human life, McNabb told the Herald at the time.

He said warnings for people to keep away from beaches were not extreme, because of the effects the toxins had on humans.

"People can die from this," McNabb said.

"If you put a slug in your mouth, you'd be vomiting and your entire body would be tingling.

"Within minutes you'd be paralysed. Your heart and lungs would shut down and you'd be dead within the hour.

"Or if you touched it and it was all over your hands and you went and ate a sandwich ..."

McNabb said anyone who came down with symptoms including vomiting and drowsiness after being at a beach should see a doctor.

But the only way a person would die was if they consumed the poison.

Auckland Council advises the following:

•Sea slugs may be present on any beach and if found should be avoided

•Only the grey side-gilled sea slugs (Pleurobranchaea maculata) are known to contain tetrodotoxin (TTX) and can be highly poisonous

•Do not touch any sea life (dead or alive) found on the beach as it may contain harmful levels of bacteria or be poisonous

•Do not eat anything washed ashore

•Children and pets should be kept under supervision at all times and kept away from any sea life as it may contain harmful levels of bacteria or be poisonous.

•If you believe someone has come into contact with a sea slug and they start to feel unwell call 111 for emergency assistance immediately.

•If you believe a dog has licked or ingested a sea slug contact your vet immediately.

- Additional reporting, Julia Gabel