An environmental group wants a two-year ban on the commercial fishing of crayfish in the Hauraki Gulf and Bay of Plenty.

The Minister of Fisheries is due to make a decision by April on a proposal to halve the amount of crayfish taken there.

But with stocks estimated to have dropped by as much as 95 per cent in some areas within the past 60 years, anything but a total ban risks the fishery disappearing altogether, says the Environmental Defence Society.

Its executive director, Gary Taylor, says the government did not have an accurate picture of fish stocks and that was a major problem.

"We need to have a pause while that data is assembled and, when we get proper data, we could look at reopening the fishery on the basis of enabling it to recover over time."

It was not good enough to use records of how much crayfish was being caught to judge how healthy stocks were and scientific surveys should be done, says Gary.

However, head of the Rock Lobster Industry Council, Mark Edwards, says a total ban was unnecessary.

Even halving the catch would have a big impact on a fishery made up of many small family-run operations, he says.

Such a ban would have "pretty severe" socio-economic impacts, he says.

-RNZ