North Atlantic right whales are critically endangered, with just over 400 individuals left, and their numbers declining. The leading causes of death are well-known: right whales are susceptible to being struck by ships, and over 83 percent have shown evidence of being entangled in fishing gear at one point or another.
But the population has also seen low reproductive rates and declining health status in recent years that can't necessarily be explained by those impacts. Now, new research points to another possible culprit: climate change.
“This adds a piece that we didn't have before,” said Dan Pendleton, a research scientist at the New England Aquarium’s Anderson Cabot Center for Ocean Life and co-author on the study. “We haven't been able to say that climate changes are affecting right whales in a very specific way until recently.”
That changed when scientists looked at water temperatures in the Gulf of Maine, which is warming more rapidly than nearly any other ocean ecosystem on the planet. Scientists think the reasons include changes in the path of the Gulf Stream and the way its warm waters are interacting with other currents in the North Atlantic.
“Water depth is warming and we think that is having an impact on the life cycle, and the phenology, and the distribution of the critters that right whales eat,” Pendleton said.
Those critters - flea-like animals known as copepods, specificaly the species Calanus finmarchicus - are a critical food supply for the endangered whales.
Now, researchers think that supply is being diminished by warm water entering the Gulf of Maine.
“Until now,” Pendleton said, “we haven't really understood the mechanism for what would be causing a reduction in food.”
As the food supply declines, Pendleton’s team have found right whales shifting where they spend their time. For example, making greater use of an area south of Martha's Vineyard and Nantucket.
Although that migration is a good thing – it reflects their ability to adapt to changes in water temperatures – the whales’ new locations come with an increased risk of interactions with ships and fishing gear.
“The whales are going to be able to adapt,” Pendleton said. “It's just that the humans need to get out of the way.”
Pendleton says management strategies will need to be more nimble in order to protect North Atlantic right whales wherever they show up.