The tape was rolling. Woods Hole researchers used hundreds of acoustic devices placed on the ocean floor to develop new evidence of shifts in the distribution of endangered North Atlantic right whales.
Analyzing the sea creatures’ alien-sounding calls, the researchers found that the time the whales spend in the Bay of Fundy and greater Gulf of Maine appears to be decreasing, while it’s increasing in the mid-Atlantic region.
More of the whales also seem to be gathering in Cape Cod Bay in recent years, said Genevieve Davis, an acoustician at the NOAA’s Northeast Fisheries Science Center’s Woods Hole Laboratory and lead author of the study.
Davis said the cause of the shifts, previously noted in visual surveys, remains unclear. One possibility could be that rising temperatures are driving the whales’ prey elsewhere, so they are following their food supply. Another factor could be human impacts, such as ship noise, fishing gear entanglements, and seismic surveying that sends loud shock waves through the deep, Davis said.
It’s not clear if the shifts are temporary or part of a long-term change, she said.
The study, which was published last week in Nature Scientific Reports, warned that if the movements of the endangered species are changing, new measures to protect them might need to be put in place.
“With recent studies finding the Gulf of Maine is the fastest-warming body of water in the world, it is not surprising to see distributional changes across marine species. We suspect further changes in distributions will occur as water temperatures continue to rise, forcing movements towards both favorable oceanographic conditions and food sources elsewhere,” the study said.
“Regardless of the factors influencing these changes in distribution, it is critical for management strategies to reflect new threats that may arise for this species as they move into regions outside of existing management areas,” the study said.
The government can protect right whales by barring ships, or setting speed limits for them, in specified areas.
The study said that “in an ocean where conditions are changing rapidly, adaptive management is needed to identify and protect areas that are crucial for species on the brink of extinction.”
It suggested real-time monitoring of whale calls or a new approach beyond classifying the whales’ habitat as “static, confined areas.”
The whales “really don’t fit in a box so we have to think about broader ranges for management,” said Davis.
Davis said the study also filled gaps in knowledge of whales’ whereabouts. Scientists knew that some whales were migrating to southern calving grounds during the winter and back to northern waters to feed in the summer. Davis said that left the question: Where were the rest of the whales?
The research found that the whales were spread more widely than previously known, Davis said. In the winter, they were detected from Nova Scotia to Florida, while in the summer they were spread north of Cape Hatteras, N.C.
“It’s a much larger range all year round than we originally thought,” she said. “The areas they occupy are much bigger.”
The study used 324 listening devices placed by 19 organizations through the western North Atlantic. It analyzed data from 35,600 days, collected between 2004 and 2014, finding the changes in whale distribution beginning in 2010.
Davis said it showed that the devices were a powerful, cost-effective, long-term montioring tool. One reason is that they work even during bad weather and darkness when the traditional method of visual surveying doesn’t work.
The whales were threatened with extinction by centuries of whaling when protection was introduced in 1935. Their population rose from 350 in 1990 to 476 in 2010, but since then there’s been evidence of decline, the study said. The cause is not known, but human impacts, from fishing and shipping, and climate change are seen as likely causes.