For many decades, the North Atlantic right whale was a conservation success story. After being hunted to near extinction, a series of protective actions that began in the 1930s, and accelerated in the 1960s, helped the population begin to rebound.
But in 2010, something changed. Since then, the number of North Atlantic right whales has started to decrease again. Last year was particularly bad; 17 bloated carcasses washed up on beaches along the East Coast, many of which were marred by scars from boat strikes and fishing gear.
With approximately 450 of these whales left, every death is a big deal. In fact, experts predict if the current trend holds, the species, which plays an important role in the marine ecosystem, will be extinct by 2040.
Yet, while much attention has been paid to mortalities, far less attention has been paid to what some biologists say is the whale’s real long-term problem: plummeting birth rates.
At its most basic level, population comes down to arithmetic. It’s a matter of births minus deaths, says Charles “Stormy” Mayo, director of the right whale ecology program at the Center for Coastal Studies in Provincetown.
“If a species doesn’t reproduce, eventually it’s gone,” Mayo says. “So the business of low calving is, I think, as horrific an issue as the mortality.”
This year, of the 71 females who were theoretically able to calve, none did. That’s according to Heather Pettis, executive administrator of the North Atlantic Right Whale Consortium and associate scientist at the Anderson Cabot Center for Ocean Life at the New England Aquarium. She says the last few years haven’t been much better.
“Right whales are in a quite precarious situation right now,” Pettis says. “We’ve seen variable reproduction over the years, but nothing like what we’ve seen this year.”
There are likely many interconnected reasons for declining birth rates. But in the last year or two, as biologists have noticed that the whales aren’t going to their normal feeding grounds, a new theory has emerged, and at its center are two key factors: nutrition and stress.
Right whales eat oily, rice-sized zooplankton called copepods, which up close look a little like bulbous shrimp. To sustain their 70-ton bodies, the whales need to eat billions of copepods every day, and they rely on the ocean currents to concentrate their food in dense patches to make this possible. When a right whale comes across one of these patches, it will open its mouth and “skim” the surface of the water. Every so often, the whale will close its mouth and backflush the water through its baleen, trapping the little copepods inside.
“These animals are optimizers,” Mayo says. “They don’t lay around in the sun and yawn. They are spending a great deal of their life naturally searching for food.”
And as climate change warms the ocean waters along the Eastern Seaboard, particularly in the Gulf of Maine, Mayo and others have noticed something happening to the copepods.
“We think that changes in temperature and circulation have essentially shifted the areas where copepods are,” says Dan Pendleton, a research scientist at the Anderson Cabot Center who focuses on copepods and right whales.
And where the copepods go, so go the right whales — even if it means swimming greater distances and using more energy to find food.
“There’s also some question about the prey quality, and what the nutritive status of these copepods is,” Pettis says. “And that, in turn, means that whales are having to feed on even larger patches of these copepods to just sustain their baseline metabolic needs.”
From there, it’s simple biology. Like any animal, an undernourished right whale can’t reproduce successfully.
“The females need to have a certain level of energetic reserve to get pregnant and carry a pregnancy to term. And if they don’t, they’ll delay their reproduction,” Pettis says. “So if these females are energetically stressed because they’re having to travel farther to find food, and their food resource is not high quality, they’re not going to build that necessary energetic reserve to get pregnant and carry an offspring to term.”
The problem doesn’t end there. As the whales move into different areas to find food, experts say they’re getting hit by boats and entangled in fishing gear more often because these new areas usually don’t have regulations designed to safeguard right whales.
“We’re seeing whales with pretty significant gouges on their heads, on their lips, on their tail stocks. Skin ripped away,” Pettis says. According to one estimate, 83 percent of all North Atlantic right whales have entanglement scars.
Some entangled whales are able to free themselves, but many aren’t so lucky and can end up dragging fishing gear around for years. Pettis likens it to swimming laps with a parachute attached to your back.
“You can imagine the amount of energy it would take just to swim,” she says.
Entangled whales often have ropes wrapped around their heads, making it difficult to feed efficiently, exacerbating their depleted energy reserves.
Entanglements also make whales prone to injury, illness and infection. If you’ve ever seen a right whale, you’ve probably noticed rough, white patches of skin. These patches are called callosities, and on a healthy right whale, they’re white. Sick right whales, on other hand, tend to have orange callosities.
According to Pettis, a lot of the entangled right whales she and her team see these days have orange callosities, open wounds from chaffing ropes, and look thin or emaciated. None of these things bode well for reproduction.
Entanglements also likely contribute to whales’ stress. Like any mammal, a stressed female right whale will struggle to reproduce because elevated levels of stress hormones in her body can depress reproductive hormones, Pettis says.
Sound is another likely culprit.
Humans have made the oceans a very noisy place. We drive ships, test weapons and radar systems, install offshore wind farms, and do all sorts of things that create what scientist call “acoustic smog.” While instinctually it makes sense that loud, disruptive noises are stressful, a 2012 study conducted in the Bay of Fundy found a direct link between noise and the levels of stress hormones in right whales.
“That was a really important study,” Pettis says. “That was one of the first to show definitely that at least vessel ship noise underwater is really impacting negatively this population of whales.”
It’s unclear whether the the noise itself causes stress, or whether the sounds disrupt the whales’ ability to communicate and find food, which in turn causes stress. Either way, this is something marine biologists in the area are actively studying.
There are other hypotheses out there to explain why these whales aren’t calving. It could be chemical or hormonal pollutants in the ocean, agricultural runoff, microplastics or even inbreeding, though Mayo and Pettis think those things are likely compounding the other problems.
One clue to saving the North Atlantic right whale may lie in the right whales of the Southern Hemisphere. That population is much larger, healthier and reproducing at a much more sustainable rate. It’s also more isolated from human activity.
“Do we have the ship strike problem [in the Southern Hemisphere]? No,” Mayo says. “Do we have the same insonification issues [down there]? We don’t. Do we have the DNA bottleneck problems? We don’t. Do we have contaminant problems? Yes, but not as bad.”
The North Atlantic right whale is incredibly resilient, Pettis says. “This population’s been contending with humans for a really, really long time, and they’ve been able to bounce back before.”
But the question, she continues, is “whether they can do it now.”