25 Jun 2015

Mapping Underwater Landscapes

From Our Changing World, 9:45 pm on 25 June 2015

By Veronika Meduna Veronika.Meduna@radionz.co.nz

NIWA marine geologist Geoffroy Lamarche on board the research vessel Ikatere.

NIWA marine geologist Geoffroy Lamarche on board the research vessel Ikatere. Photo: Dave Allen / NIWA

Marine geoscientists from the National Institute of Water and Atmospheric Research (NIWA) are mapping the submarine landscapes around Kapiti Island, north of Wellington, this month.

Kapiti Island is one of New Zealand’s earliest bird sanctuaries, and it is surrounded by one of our oldest marine reserves, straddling the Rauoterangi Channel that separates the island from the Waikanae Estuary Scientific Reserve. The waters around the 70-metre deep channel were once frequented by whales and are an important breeding area for fish and invertebrates, including paua and rock lobster.

But despite its significance as one the Department of Conservation’s network of coastal protected areas, the seafloor around Kapiti Island has never been mapped with the latest echo-sounding technology.

The project to collect state-of-the-art topographical information about the seafloor was prompted by diving surveys. Alix LaFerriere, who is studying paua populations within the marine reserve, says getting detailed underwater bathymetry will help DOC to plan future monitoring projects.

It will allow us to decide where to use drop cameras, remote vehicles or diving, and that allows us to look at how the marine reserve is working and if it’s providing protection for species that are economically and ecologically important.
Alix LaFerriere, Victoria University

You can listen to an earlier Our Changing World feature about marine reserves and how ocean creatures respond to protected areas.

NIWA’s multibeam echo-sounder maps the seafloor using a fan of acoustic beams providing complete coverage of the seabed. The resulting surveys show far greater detail than was possible with older equipment.

NIWA’s multibeam echo-sounder maps the seafloor using a fan of acoustic beams providing complete coverage of the seabed. The resulting surveys show far greater detail than was possible with older equipment. Photo: NIWA

The multibeam echo-sounder being lowered below the vessel to start data gathering.

The multibeam echo-sounder being lowered below the vessel to start data gathering. Photo: RNZ / Veronika Meduna

NIWA’s research vessel Ikatere is equipped with multibeam echo-sounding technology that produces highly accurate bathymetry and habitat maps of the seafloor to a depth of 50 metres over an area of 50 square kilometres. The information will also be used by Land Information New Zealand (LINZ) for the next update of the region’s navigational charts.

In addition, data recorded throughout the full water column can also be used to characterise water masses, identify gas seeps and sediment plumes, and detect schools of fish.

NIWA marine geologist Geoffroy Lamarche says the underwater map will be useful to many people, including geologists studying potential hazards such as landslides and ecologists wanting to understand seafloor habitats.

If you have a flat sandy seafloor, you have a high probability to find scallops or flounders, and if you have a very rugged steep seafloor, you are far more likely to find rock fish and paua. We see that the biology relates very directly to the geomorphology and geology. And that is what we call habitat mapping. We don’t map the animals, we map the substrate and the geomorphology on which they live.
Geoffroy Lamarche, NIWA

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