Missing a 15,000-pound (6,804-kilogram) baby seems difficult, but scientists tracking rare marine life did just that for months, and the oversight has brought unexpected relief.

In September, researchers in Canada photographed an unidentified baby North Atlantic right whale off Anticosti Island in Quebec .

Boston's New England Aquarium analyzed the images and data, determining the calf was likely born months ago but went undetected during winter surveys.

The discovery brings the count of newborn right whales from the latest birthing season to 24, marking the species' most productive year since 2009 and the fourth highest on record.

The global population totals only around 380, having declined steadily since 2010.

The calf was seen alongside its 38-year-old mother, known to researchers as Silt. Right whales typically give birth off the southeastern U.S. coast in winter before traveling north to New England and Canada to feed.

Extensive photographic cataloging makes unrecorded births a rarity.…