North Atlantic right whales are one of the most endangered whale species on the planet. Their population has plummeted to around 400 individuals, and efforts to protect the whales have not led to a steady increase in their numbers. Last year, not a single new right whale calf was born, as far as scientists can tell. But this year, there is cause for measured optimism. As CNN’s Theresa Waldrop reports, experts with the Massachusetts-based Center for Coastal Studies recently spotted two right whale caves in Cape Cod Bay, bringing the total seen in New England waters up to three.

The calves were already known to researchers; earlier this year, seven baby right whales were observed off the coasts of Florida and Georgia, where right whales go to give birth. In the spring, the animals travel north up the east coast and spend the warmer months feeding and nursing calves in the waters off New England in the the Bay of Fundy. The fact that at least three of the new babies made it to Cape Cod Bay is a “good sign” and suggests that the calves have formed solid relationships with their mother, Charles Mayo, director of the Right Whale Ecology Program at the Center for Coastal Studies, tells Waldrop.

“These three are doing well,” Mayo adds.

North Atlantic right whales were once hunted to the brink of extinction; the animals get their name because they were considered the “right” whales to target. In 1935, the League of Nations banned hunting of right whales in all oceans, but the species has not rebounded in the way conservationists hoped. Last year, the North Atlantic Right Whale Consortium revealed that the population had fallen from 451 to 411 individuals in a single year—“a big drop for a small population,” Philip Hamilton, a research scientist at the New England Aquarium and co-author of the report, told the CBC’s Emma Davie at the time.

In place of hunting, North Atlantic right whales now face other threats. A major one is entanglement in commercial fishing nets, which can prevent whales from feeding and even cause them to drown. Ships can strike whales and kill them, and shipping traffic cuts right whales off from calving areas. The noise these vessels emit is thought to interfere with the animals’ communication, which in turn impacts their ability to find food, mate and care for their young. Warming ocean temperatures and changes in currents due to climate change may also be disrupting right whales’ food supplies; scientists have recently observed a migration away from the Bay of Fundy, once a popular feeding ground.

So while experts are encouraged by the birth of seven new right whale calves this year, the fate of the species is still far from certain. Hamilton, the New England Aquarium researcher, tells the Scientist’s Ashley Yeager that an average of 17 calves per year are needed to start building up the population. But the frequency at which female right whales are giving birth has declined dramatically; a healthy female should be having a calf every three to four years, but scientists have instead been observing nine and ten-year gaps between births.

“The signs are better than they were last year or the year before,” Hamilton says, “but we’re not out of the woods yet.”