Look out for toxic sea slugs

00:12, Aug 25 2010
DO NOT TOUCH: Toxic sea slug pleurobranchaca maculate are washing up in the Hauraki Gulf this winter.

WAIHEKE Islanders are being asked to look out for toxic sea slugs washed up on beaches or in the island's intertidal zones after three were found on Kohimaramara beach last week and public warning signs were erected.

Island fishermen have been reporting finding sea slugs regularly attached to their bait when fishing off the rocks. One father says he and his son fished one up at the kids fishing competition at the Matiatia wharf in May. But there have been no reported sightings on our beaches yet.

The species to watch out for is the grey side-gilled sea slug pleurobranchaca maculate, which can contain the poison tetrodotoxin. They can measure up to 4cm, have feelers, they are mottled grey or brown, oval shaped, move like slugs and could be mistaken for a small flat jellyfish.

"If people find something on the beach which they think may be a sea slug, they should not touch them and contact the environmental health team at the council as soon as possible," Auckland City Council environmental health and licensing manager Chris Dee says.

Toxic sea slugs first became a public concern when the poison tetrodotoxin present in the slugs was blamed for the deaths of five dogs on North Shore beaches last winter.

A further dog was reported to have become ill after visiting Kohimaramara beach last year.


The Cawthron Institute which tested the sea slugs reported the slugs found on the North Shore contained ‘‘deadly amounts of TTX – enough that 0.25 grams of sea slug could kill a dog and 2 grams could kill a human’’.

‘‘It is evident that the sea slugs take up tetrodotoxin from their food chain, however it is unclear where they are getting it from,’’ Cawthron Institute chief Gillian Wratt says.

Further research is being undertaken by the institute.

A dive survey conducted by Auckland Regional Council in June 2010 indicated that Narrow Neck beach was again a hot spot for the slugs this winter, with 48 found – the highest number of all sites surveyed.

Sea slugs were also found underwater at Cheltenham 16, Illiomama Rock near Rangitoto Island 14, Long Bay 6, Mission Bay 5, the Bayswater mooring 4, and Browns Bay 1.

Omana and Eastern beaches were also surveyed, but no sea slugs were observed.

‘‘The sea slugs tend to be more present on our beaches in winter when there are strong north and north easterly swells. They are often present when large amounts of kelp or seaweed are also washed up,’’ Mr Dee says.

Waiheke Island has not yet been surveyed. But if conclusive proof is found that pleurobranchaca maculate is here, the regional and city councils will investigate.

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