Uncertainty over biosecurity rules covering crab

Charybdis japonica - Asian or Japanese paddle crabs - are a new pest to Northland, but they can't be collected for fear of spreading them further.

The availability of native paddle crabs entices thousands of Asian people to Northland every summer but ironically the find of Asian or Japanese paddle crabs in the region has authorities reminding people they are not allowed to collect them.

The Asian or Japanese paddle crabs - a popular food in Asian cultures - are not the same species as the native varieties that attract thousands of Auckland-based crab fishers to Bream Bay beaches over summer.

Biosecurity laws prohibit members of the public from moving the pest species from one location to another, so taking them for a feed is not on.

Northland Regional Council (NRC) and Ministry of Primary Industries (MPI) are working on a plan see any invasion of the unwanted crab species nipped in the bud after nine mature specimens were found in the Ngunguru estuary last month.

The find has turned up at the same time as the NRC is reviewing the Regional Pest Management Strategy regarding how it deals with pests in general, including redefining the term 'pest' and reclassifying which species meet the "dead or alive" rules regarding moving them out of the area they were found.

At present, the rules don't specify Asian (also called Japanese) paddle crabs or whether it is okay to kill them, then take them away from the site for eating, NRC aquatic biosecurity officer Irene Middleton said.

The Asian or Japanese paddle crab is larger and more aggressive than native species, preys on bivalve shellfish such as pipi and cockles, and can carry parasites and viruses that infect other sea life.

They have been found in the Whangarei Harbour and Hauraki Gulf since 2002, in numbers small enough to cast doubt on whether the species could breed to environmentally threatening numbers in New Zealand waters. But the discovery at Ngunguru has sparked concern because of the number and size involved.

"We're trying to get an idea whether there's a population outside the estuary or if they're contained to the one site in the estuary," Ms Middleton told the Advocate last week.

She said a wider infestation would probably have already been discovered by local fishers as the crabs are easily caught in flounder and other fishing nets after preying on their contents. They are good swimmers and they or their larvae are easily carried on boats' hulls, machinery and fishing gear.