Scientists who track a rare species of whale said more pairs of mother whales with babies have been spotted this year than the previous few.

The scientists follow North American right whales, which number only about 400. The New England Aquarium said Friday that scientists with the institution have identified a right whale mother and calf off Nova Scotia, bringing this year’s total of mother-calf pairs to 18.

That’s the highest number since 2013. Researchers have observed poor reproduction and high mortality among the whales in the years since then.

The aquarium said in a statement that “calving in this decade has been well below the annual average of 23 from the previous decade.” However, they added that “every calf brings hope.”

The whales are vulnerable to ship collisions and entanglement in fishing gear.

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