A mother orca was seen supporting and pushing her dead calf to the surface of the water for more than two days.
The killer whale, named J35, was seen propping the newborn on her forehead and trying to keep it near the surface of the water off the coast of Victoria, British Columbia, said Ken Balcomb, senior scientist with the Center for Whale Research on San Juan Island, which closely tracks individual whales.
"The baby was so newborn it didn't have blubber. It kept sinking, and the mother would raise it to the surface," he said Wednesday.
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The baby was spotted alive and swimming with its mother Tuesday morning, but just a half hour later, when a team of researchers arrived, the orca was dead, according to the Center for Whale Research.
The mother continued pushing her calf to the surface until at least sunset Thursday. There have been no sightings of the whales as of Friday morning, Balcomb told NBC News.
The death represents another reproductive failure for the salmon-eating southern resident killer whales that typically show up in Puget Sound waters from spring to fall and a major setback for a struggling species with under 100 remaining.
The distinctive black-and-white orcas have struggled since they were listed as an endangered species in the U.S. and Canada over a decade ago. They're not getting enough of the large, fatty Chinook salmon that make up their main diet. They also face overlapping threats from toxic pollution and noise and disturbances from boats.
"This baby whale failed to be viable because the mothers do not have sufficient food," Balcomb told NBC News.
About half of the 11 calves born during a celebrated baby boom several years ago have died.
The orcas are distinct from other killer whales because they eat salmon rather than marine mammals. Individual whales are also identified by unique markings or variations in their fin shapes, and each whale is given a number and name. Their movements are closely tracked and photographed by researchers, whale watchers and fans.