Mapping the bottom of the sea

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Barbara Dean-Simmons
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MUN team hopes to determine how topography helps cod in Smith’s Sound

It’s a good day for exploring. The waters of Smith’s Sound are calm, the air warm on this late-July morning, as researchers lower a bright yellow mini-submarine into the water from the wharf at Lower Lance Cove.

Graduate student Katy Mac-Pherson  from England and a team from Memorial University are on a mission.

They are hoping the Explorer, MUN’s autonomous underwater vehicle (AUV), will collect enough data about the topography and plant life beneath the water to help them determine why this area is a favourite gathering place for cod.

Smith’s Sound runs the length of the north side of Random Island; the fjord-like channel is fed by the waters of Trinity Bay.

For years, scientists from MUN and the Department of Fisheries and Oceans have been tagging and tracking cod here, proving this area is the over-wintering home for large congregations.

The research has shown that the cod swim to the sound in the fall and early winter, and swim out again in spring to the further reaches of Trinity, Bonavista and Notre Dame Bay.

John Bratty of DFO has tracked their migratory path by implanting battery-operated transmitters in cod and tracking them with underwater receivers set up along the coast all the way to Notre Dame Bay.

George Rose of the Marine Institute, and other fisheries scientists, have been collecting reams of data from here since the mid-1990s, building a picture of water temperatures and salinity.

MacPherson hopes to add to the data by determining what Smith’s Sound looks like underwater.

The submarine will help her do that, mapping not only the topography of the seabed, but using sonar to tell scientists exactly what type of sediment and plant life is at the bottom.

The technology they’re using is a little different than the typical remotely operated vehicle (ROV) explains Ron Lewis.

 

More efficient

“This is much more hydro-dynamically efficient than a ROV,” said Lewis. “On a full (battery) charge it can cover 60-70 kilometres a day. And it isn’t tethered, so you can cover a lot more area and it can go deeper and stay down longer than a ROV.”

Before they launch the mini-sub, researchers program its computer to follow a certain path for the dive.

They monitor the sub to check its progress through the dive, but other than that the vehicle carries on until its mission for the day is complete and then it comes to the surface.

Unlike a ROV, it does not carry a video camera. Instead, the submarine “sees” with sonar; using sound waves to create a data picture for scientists.

Because it can operate close to the seabed, Lewis said, the clarity of the sonar image is better than a sonar image from a vessel operating at the surface.

The team has been in the Smith’s Sound area for most of July, and will wrap up the mission within the next week or so.

MacPherson is not just collecting data for science on this project; she will also use the information for her thesis for her master’s in geography.

She says before she started the project, she didn’t know about Smith’s Sound, or Newfoundland for that matter.

When she was seeking out a good location for habitat mapping, she said Smith’s Sound stood out as an area that had a lot going on.

“There’s already a lot of detail on the fish regarding fish abundance, fish stomach contents, and so on, and I just thought it would be incredibly interesting to add that extra layer of data to the knowledge that’s already here.

“What we’re going to be adding in is that little bit of information about what the bottom is like, and if that has anything to do with the activities of the fish.”

MacPherson will be going out on the water with local fishermen to get “grab samples” of sediment from the ocean floor.

While she won’t have her thesis completed until next year, MacPherson said snippets of information from this research will be available to other scientists as it is compiled.

While the main aim of this project is to collect information about the seafloor in Smith’s Sound, they may collect historical information about the area as well.

With its side-scan sonar, explained Lewis, the sub may be able to detect any debris from long-ago shipwrecks and pass that information along to the archeology unit at MUN.

 

 

Organizations: Department of Fisheries and Oceans, Marine Institute

Geographic location: England, Random Island, Newfoundland

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