A clearer picture of Thunder Bay
NOAA scientists continue to map lakebed with sonar tech
ALPENA — Scientists with the National Oceanic and Atmospheric Administration’s National Centers for Coastal Ocean Science are conducting research in Thunder Bay that will help scientists understand what kind of habitat exists for fish and other aquatic life.
Hydrographers Will Sautter and Brendan Guthrie have spent the last week and a half using multi-beam sonar and side-scan sonar to map the lakebed.
The sonar creates an image of the lake bottom by measuring the amount of time it takes for a sound wave to bounce back to the researcher’s instruments. Scientists also can determine the texture of the lake bottom from the intensity of the return.
The multi-beam sonar has the ability to send multiple sound waves at one time, which allows it to cover larger swaths of territory.
Sautter said the data they collect from the bottom of Thunder Bay will eventually be used to make a habitat map, which can help scientists understand the ecology of the lakebed. He said it can help scientists manage natural resources as well as the cultural resources within the Thunder Bay National Marine Sanctuary.
The sanctuary protects waters off of Alcona, Alpena, and Presque Isle counties and part of Cheboygan county, all the way to Canadian waters.
Sautter used mussels, such as zebra mussels or quagga mussels, as an example.
“We can use habitat maps to monitor their spread and kind of understand where they are colonizing,” he said. “That’s an important issue, because they’re an invasive species. Another big part is habitat maps can help researchers identify suitable areas for fisheries — so spawning areas or aggregation sites.”
Charlie Menza, project lead and marine biologist with National Centers for Coastal Ocean Science, said mussels are new to the Great Lakes and have been “pretty catastrophic to the ecosystem.”
“Knowing where they are, monitoring their populations over time, it’s really important for ecologists to understand how they’re impacting the environment and how those impacts will change over time,” he said. “The technologies we’re using are ways of looking at invasive mussels that is different than most of data that exists. Most people collect a sample from a point in space, whereas we can collect data from an area in space, so it gives you more information.”
The scientists have collected data about 25 to 30 miles from shore, according to Sautter, with a portion of the Alpena-Amberley Ridge one area of focus.
The Alpena-Amberley Ridge first became the subject of a paper written by researchers John O’Shea and Guy Meadows and published by the National Academy of Sciences in 2009. In that paper, the researchers reported evidence of human activity and structures associated with hunting for caribou some 7,000 to 11,500 years ago.
Now, scientists with NOAA believe the ridge could also be important to the ecology of the Great Lakes.
Menza said not a lot is known about the ridge, but scientists know fish in the Great Lakes are attracted to certain types of habitat, such as cobbles, a rock that is larger than a pebble but smaller than a boulder.
“So we are trying to determine if there are cobbles and other habitats important to fish on the ridge,” he said.
The scientists have also taken interest in a reef on the Alpena-Amberley Ridge a location Wayne Lusardi, maritime archaeologist for the state, dived on for years. Lusardi said U.S. Fish and Wildlife Service and the Michigan Department of Natural Resources also are interested in the reef, because its “prime fish habitat.”
Lusardi said that, though the government agencies have been studying the reef over the years, they’ve never seen it in great detail.
“Obviously, when you want to manage an area, you have to understand that area, and this is one of the best ways of really getting a three-dimensional feel of what is on the lake bottom,” he said.
While the marine sanctuary was originally mapped by scientists decades ago with a lead weight and hundreds of feet of rope, much of the lake bottom has yet to be mapped using modern technology.
Sauter said less than 50% of Thunder Bay and less than 20% of the sanctuary as a whole has been mapped using the latest technology. The marine sanctuary’s boundaries, which were expanded in 2014, encompass 4,000 square nautical miles of Lake Huron.
In addition to mapping the lake bottom, scientists have also mapped known shipwrecks like the Flint and the Monrovia. They are also keeping a lookout for new shipwrecks or manmade objects of cultural significance that have yet to be discovered.
Menza said there are plans to return for another mission in September, when Menza and his colleagues will collect ground-truthing and accuracy assessment data with their drop camera.
“That’s where we toss a camera off the side of the boat and we try to see what’s in the video and match that to the information that Will and Brendan are collecting right now,” he said.
Crystal Nelson can be reached at 989-358-5687 or firstname.lastname@example.org.