Mapping of the sea floor for fishing secrets

Sea birds fly around the Hauraki Gulf in search of food. Photo / Steven McNicholl

Mapping of the sea floor on Auckland's doorstep could reveal some of the area's best-kept fishing secrets.

Niwa is about to undertake research on the Hauraki Gulf including off the coast of the Coromandel Peninsula - among the most heavily used marine areas in the country - to help New Zealand better manage and preserve the area.

But it's likely to have an added benefit for recreational fishermen by letting them in on what commercial fishermen already know, said Niwa Marine fisheries ecologist Mark Morrison.

"We do habit mapping - it's excruciatingly detailed and the positive side of that is people can target things better. The negative side is the fish have less and less chance of hiding," he said.

The mapping would provide information about different habitats of the fish people may be trying to catch. It will be used for classification purposes, he said.

"That will help us to understand more about what fish do, where they go seasonally and therefore whether they are at risk from the effects of human activities, such as pollution and sediments."

It is the first time the Hauraki Gulf has been mapped this way.

The high-use area has been fished for 100 years and faces a number of pressures, including commercial and recreational fishing, marine transport, tourism, boating, aquaculture and sediment run-off from land, said project manager Neville Ching.

Special habitat areas: deep sponge gardens, tubeworm fields, horse mussel beds, bryozoan ('lace coral') patches, green-lipped mussel, dog cockle beds, and deeper water reefs will also be covered in the survey.

The gulf is vulnerable to the effects of tsunami, with evidence suggesting past tsunami deposits could have reached 14 metres above sea level on Motuihe Island and the inner Hauraki Gulf.

"The data collected will help to understand risks associated with tsunamis, said Mr Ching.

Research vessel Tangaroa will leave from Wellington later today and will spend 22 days within a 2100sqm area at depths of 40-200 metres.

The research is funded by Land Information New Zealand as part of the Government Ocean Survey 20/20.