The call of the North Atlantic right whale is one of Genevieve Davis’s favourite sounds.
“It’s a very cool sound — hearing whales communicate is always one of my favourite things about the job,” said Davis, an acoustician at the Northeast Fisheries Science Center in Woods Hole, Mass.
But researchers like Davis are hearing fewer of those calls and locating fewer whales visually in northern waters in recent years. In a wide-ranging study using data from 2004 to 2014, her team concluded that North Atlantic right whales are spending more time in the mid-Atlantic since 2010 and have decreased their presence in the northern Gulf of Maine.
The whales also aren’t showing up in the Bay of Fundy as frequently, choosing to feed along the East Coast year-round, where they previously were only seen for a few weeks passing through, Davis said.
There also appears to be a growing stable population in the Cape Cod Bay area, according to the study, which processed more than 35,600 days of data from 324 listening devices from Florida to Canada using an automated classification and detection system.
The data was contributed by 19 organizations in the United States and Canada, including the federal Department of Fisheries and Oceans.
The study didn’t get into the possible reasons why the whales appear to have changed addresses, although it could be a response to human causes and/or to the changing environment, Davis said in an interview from Woods Hole on Thursday.
It’s also not clear whether the spate of right whale deaths in the past year is linked to population shifts.
“It’s hard to say that from the data,” said Davis, who has worked in acoustical research in Woods Hole for seven years and is studying toward her doctorate at the University of Massachusetts. “They’ve always been overlapping with where we’re using the ocean,” which results in collisions with ships and entanglement in fishing gear.
Most of the data, besides visual- sighting records, was gathered by hydrophones, large bell-shaped microphones that work underwater. The equipment is weighted so it stays on the ocean bottom, Davis said.
These sensitive receivers can pick up the whales’ low-frequency modulated sound, known as an up-call. This call is produced by male and female North Atlantic right whales of all ages and is considered the most reliable way to determine their presence.
After between a month and a year, a remote release mechanism sends the hydrophone to the surface and researchers pore through the mostly blank recordings for instances of that distinctive up-call.
Experts like Davis can differentiate among the calls of the various whale species, although sometimes it can get tricky, she said.
“Humpback whales, which are often overlapping with right whales, are hard to tell apart. They . . . can mimic every sound that I’ve heard from the baleen whales in our ocean, so humpbacks often throw kind of a wrench into the system.” (You can hear samples of whale calls at https://www.nefsc.noaa.gov/psb/ acoustics/sounds.html).
The study results will be discussed at meetings of the North Atlantic Right Whale Consortium, which includes non-governmental and governmental organizations as well as individuals in the United States and Canada. The group is dedicated to studying and conserving the North Atlantic right whale, which is the one of the most endangered large whales.
“This information can be used to direct science and management to areas of interest,” Davis said. “In an ocean where conditions are changing rapidly, adaptive management is needed to identify and protect areas that are crucial for this species.”
BY JOHN MCPHEE/THE CHRONICLE HERALD