Scientists say critically endangered North Atlantic right whales gave birth over the winter in the greatest numbers seen since 2015.

That’s an encouraging sign for researchers who became alarmed three years ago when right whales produced no known offspring at all.

Survey teams from the Carolinas to Florida spotted 17 newborn right whale calves swimming with their mothers between December and March.

One of those calves was later struck by a boat and killed. The death was a reminder of how fragile the species has become.

Scientists estimate only about 360 North Atlantic right whales remain.

As many as 49 are believed to have died since 2017, compared with 39 recorded births.