Local Focus: Tauranga Harbour under threat from Asian crabs

Crab holiday homes or "condos" are being rolled out to entice Asian paddle crabs - but no pleasant stay is planned for them.

Three months ago, a Ministry for Primary Industries survey found the aggressive crabs in Tauranga Harbour. They could have devastating consequences for fisheries in the Bay of Plenty.

"They detected two Asian paddle crabs, Charybdis Japonica, a male and a female in a pot by the Matapihi Bridge," said biosecurity officer Hamish Lass.

Asian paddle crabs, Charybdis Japonica, have been found in Tauranga Harbour.

The Bay of Plenty Regional Council joined forces with the University of Waikato to survey the harbour for the pest.

"It's an aggressive species. It is also non-discriminant with its feeding - it will feed on both plant and animal species.

"We've got native paddle crabs - swimming crabs - in quite high numbers here in Tauranga. These would adversely affect them."

Marine ecologist Dr Kaeden Leonard said the Asian crabs had already caused havoc in other areas such as the Waitematā Harbour in Auckland.

Charybdis Japonica, the Asian paddle crab.

Leonard said the Asian crabs can be distinguished by six spines before the eye.

"The native paddle crab has five spines and is also a little more rounded."

The team was using a wide variety of trapping techniques throughout the area.

"We use crab condos, which are an array of PVC pipes that mimic burrows and provide artificial substrates for the crab.

"We use baited traps, do shoreline searches, and we also educate the public as to what the species looks like.

"We encourage them to contact us if they detect any of the species."

Leonard said more than 200 crab pots had been laid in the harbour but no more crabs had been found.

This was a good sign, but he said monitoring would need to continue in the months to come.

The Bay of Plenty Regional Council asked people to keep an eye out for Asian paddle crabs and said it was illegal to move living pest crabs.

Possible sightings should be reported to the Bay of Plenty Regional Council on 0800 STOP PESTS (0800 786 773).

The crab had six distinct spikes on each side of the carapace and five spines on each claw.

In New Zealand, they preferred to hide in estuaries where there was firm sand or muddy sand up to depths of 15m.

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