When Charles “Stormy” Mayo helped found the Provincetown-based Center for Coastal Studies in 1976, he said there were very few, if any, North Atlantic right whales for him to study in Cape Cod Bay in the spring.
Right whales, a type of large baleen whale, have long been considered endangered, historically hunted for their oil-rich blubber and baleen before it was outlawed in 1935. Today, only an estimated 340 remain worldwide.
But despite the dramatic decline in population, in recent years Mayo has found dozens if not hundreds of right whales out on the waters of Cape Cod Bay, where he ventures out in a small boat with a team of researchers from December until mid-May.
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The rare animals have been spotted frequently this spring already, with the Cape Cod Canal shutting down to vessel traffic on two occasions when right whales and their calves made their way into the canal.
“One always feels overwhelmed to be in the presence of such an extraordinary creature‚” said Mayo, director of research for the Center for Coastal Studies’ right whale ecology program. “It’s almost like being in the presence of a dinosaur.”
Mayo’s team spotted at least 79 North Atlantic right whales in Cape Cod Bay on March 31, constituting about a quarter of the world’s population. More and more are gathering to feed here, and they’re sticking around for longer than they have in the past.
One possible reason for the shift is climate change. In past decades, right whales have typically moved on from Cape Cod Bay to deeper Gulf of Maine waters in early May. But rapidly rising temperatures in the gulf, among the fastest warming bodies of water in the world, could be depleting the whales’ food supply, marine scientists say, and keeping them in the zooplankton-rich Cape Cod Bay for several weeks longer.
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“Warm water entering the Gulf of Maine has reduced the supply and growth of their primary food source,” said Dan Pendleton, a research scientist at the New England Aquarium. “The Gulf of Maine and the other traditional habitats are not used as heavily as they as they were for decades.”
Right whales feed on a zooplankton called Calanus finmarchicus, which aggregates in Cape Cod Bay and the Gulf of Maine seasonally and has predictably drawn right whales for decades.
The bay offers “extraordinarily dense patches” of zooplankton, which are extremely rich in caloric value, according to Mayo.
Between late winter and early spring each year, this large right whale population routinely congregates in the bay, migrating north after birthing and nursing calves in the warm southeastern waters of Florida and Georgia to eat an estimated 125-140 wet pounds of food per hour in the bay’s 600-square-mile ecosystem.
Typically, the right whales arrive in January and leave in early May, heading farther north into the Gulf of Maine and Bay of Fundy in Canada.
But as feeding conditions in the Gulf of Maine decline, not only are the whales leaving Cape Cod Bay weeks later, in mid-May, they’ve also begun arriving almost a month earlier than in past decades.
“It could be a bad thing that’s telling us that they are coming here because they’re not finding the food where they used to anymore,” said Christy Hudak, a research associate in the Right Whale Ecology Program at the Center for Coastal Studies.
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Right whales have a dramatically reduced presence in other places they used to heavily occupy when feeding, such as the Bay of Fundy in the provinces of New Brunswick and Nova Scotia in Canada and the Great South Channel between Nantucket and Georges Bank. That could indicate that their food supply isn’t thriving in the same places anymore, researchers said.
“The plankton is a delicate working creature and it lives in an ecosystem that is changing,” Mayo said. “Many of the other places where right whales were only 20 years ago are no longer seeing right whales, and I think it is likely the case that that’s because of changes in the distribution of their food.”
A recent study of the gulf, which recorded its second-hottest year on record in 2022, found that phytoplankton there are about 65 percent less productive than two decades ago, which could jeopardize the marine food chain and imperil the supply of Calanus finmarchicus.
“It’s all part of a mysterious science,” Mayo said. “A somewhat miraculous system all working together, and it can be easily upset, which is what we’re worried about with climate change.”
While Cape Cod Bay is a portion of the much larger Gulf of Maine, the bay is relatively shallow, helping maintain unique zooplankton resources for right whales.
“Warming water temperatures are affecting the zooplankton diversity, life stages, and distribution,” Hudak wrote in an e-mail. “In turn, the changes in the right whales’ food resource will affect the right whales’ health, migration patterns, and distribution.”
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Eventually, right whales could drastically reduce their use of the Gulf of Maine and even adopt new habitats, though it’s unlikely they will fully abandon the gulf, according to Pendleton. But scientists say it’s hard to predict whale behavior and prove causation between warming waters and shifting migratory patterns.
“The system is clearly changing and it’s clear, also, that climate change is having its effects,” Mayo said. “The problem with all these things is trying to show that’s why a whale does something. To do that, you have to be in the mind of the animal. And that’s a place I haven’t been.”
Sonel Cutler can be reached at sonel.cutler@globe.com. Follow her @cutler_sonel.