A Nelson-based Sealord trawler was setting off today on a trip to test technology that will show skippers what's happening on the ocean floor as it unfolds beneath them.

The company, which has invested $400,000 in this part of the project, says the result will be "smart trawling" with a reduction in impacts on the seabed and the ability to adjust catches. "That's down the track. First there's a lot of operational things that we're trialling," said Sealord resource manager Graham Patchell.

With the first and less advanced system trialled in 2009, the latest development uses an armoured fibre-optic cable to transmit video to the bridge from cameras in a pod attached to the trawl net. Powerful lights are used.

"It will be like driving at night with headlights and full visuals at depths of up to 1000 metres for the first time, versus navigating only on instruments."

The prototype installed on the Thomas Harrison is being used in conjunction with an already proven acoustic optical system to survey fish in an area of the Challenger Plateau that bridges the boundary of New Zealand's 200-mile exclusive economic zone.

Patchell said it would allow more accurate trawls and work towards a lighter footprint on the marine environment with less coral and sponges caught. "Rather than waiting to see what comes up, we will see it in real time and be able to take action."

The trawl-mounted system is deployed from a separate winch but computer-linked to the main trawl system.

Sealord has developed the technology over the past five years in partnership with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the trial of the new high-definition camera and equipment is a world first.

It has been installed on the Thomas Harrison over the past fortnight by CSIRO and Sealord staff and Nelson contractors.

Patchell said by being able to observe the fish in their natural habitats the company would get a far greater understanding of how they behave, and the equipment would provide the most efficient and accurate tool for stock assessment. Clear targeting of species improved efficiency and saved fuel.

It would also allow Sealord to show doubters that the impact of trawling on the sea floor was "not significant".

"We know that - but they won't believe us. This is verification."

The ship will be at sea for 19 days. It would be looking at orange roughy and other species around an undersea volcano, Patchell said. "We will be able to see them, and count them."

Sealord fishing general manager Doug Paulin said it was early days but the new system was part of the company's commitment to deliver the world's most sustainable fish.

"We are investing in an ecosystem approach to make sure we take as much care with the marine environment as we do with the fisheries."