Sick dogs a sign toxic slugs are spreading

The mottled grey and sand-coloured slugs are 2cm long. Photo / Supplied

Toxic sea slugs may have spread to Auckland's west coast.

A new case of poisoning has been reported at the region's most popular surf beach.

A dog began vomiting within an hour of visiting Piha Beach - a symptom of tetrodotoxin (TTX) poisoning. Another dog poisoning has been reported at Laingholm Bay, near Titirangi.

TTX, a potent neurotoxin, has been found in high concentrations in sea slugs on Auckland's North Shore and eastern beaches, and also on Coromandel beaches.

In the past two years, six dogs have died as a result of TTX poisoning.

A survey last June found 94 sea slugs - scientific name Pleurobranchaea maculata and usually about 2cm long - in subtidal water around seven beaches, but none on the west coast.

The Auckland Council says the toxin's spread must be carefully monitored . Testing has been done only in the Hauraki Gulf.

Waikato University biological scientist Craig Cary, who is studying TTX, said the spread of the toxin was predictable, because the mottled grey and sand-coloured sea slugs were found around the country.

But researchers had also found that not all sea slugs carried the poison - a group of slugs collected on Nelson beaches carried no trace of TTX.

This led scientists to believe sea slugs took up tetrodotoxin in their food chainbut this preliminary theory did not explain why the poison was fatal to some organisms and not others.

A 2009 study showed sea slugs may have carried TTX for many years.

It is not yet known why it has come into contact with dogs only in the past year.

The poison has baffled Japanese academics for 40 years.

They have investigated it in puffer fish and octopus.

Professor Cary said the university - which is working in conjunction with the Cawthron Institute - had a better chance than the Japanese of solving its mysteries, because sea slugs were easily grown and analysed in the laboratory.