Deadly sea slug ashore in Russell

It might look harmless, but the grey side-gilled sea slug can kill dogs - and people. Photo / supplied

A deadly sea slug, a native species that carries poison strong enough to kill both dogs and humans, has been seen on Russell's Long Beach over recent days, prompting a warning to locals and visitors who are holidaying with their dogs to keep their animals on a leash.

The grey side-gilled sea slug (Pleurobranchaea maculate) is a native species whose poison is powerful enough to kill a human, in the unlikely event of it being ingested, but even touching it then eating immediately can reportedly be fatal.

Natalie Struthers, from the Village Vet clinic in Paihia, said sea slugs contained the same neurotoxin (tetrodotoxin) as puffer fish.

"Even allowing a dog to nose a slug could kill the dog, and there is no antidote, only supportive intensive care," she said.

She recommended keeping dogs on leashes, using an inexpensive plastic cage-type muzzle, or avoiding beaches in the area altogether.

Signs that a dog might have been poisoned included difficulty trouble breathing and paralysis. Veterinary advice should be sought immediately.

Some grey side-gilled sea slugs were found to be toxic following the deaths of several dogs on Auckland beaches in 2009. It was not previously known that they contained tetrodotoxin, but they are now considered New Zealand's most toxic creature.

They are found on both North and South Island coastlines. Based on research conducted so far, it is believed that North Island slugs are toxic in varying degrees, while the South Island ones are not. One slug can contain enough toxin to kill at least four adults, a lethal dose being about half a teaspoon.