Male orca drowns a baby killer whale to mate with its devastated mother

"Horrified" scientists have witnessed the moment a male orca drowned a baby killer whale so it could mate with its mother.

A heartbreaking video shows the young orca - probably not yet even a day old - being hunted down by a 32-year-old male.

The attacking male was swimming with his 46-year-old mother who was instrumental in this never-seen-before attack, scientists say.

Scientists say this is the first recorded account of infanticide reported in killer whales, although the practice is common among mammals, reports Daily Mail.

Spotted off the coast of Vancouver Island on Canda's west coast, the 28-year-old mother was swimming with her new born calf and two other daughters, aged five and eight.

A group of scientists were watching the event after their research lab - OrcaLab - picked up strange calls with an underwater microphone, writes National Geographic.

"We saw some splashing and thought they were eating something," said Jared Towers, a cetacean researcher from Fisheries and Oceans Canada.

The male had grabbed the newborn infant and was dragging it away from its mother while the male's mother blocked the calf's mother from reaching her newborn.

"That all kind of came to a grinding halt when the mother of the infant hit the male so hard that … his blubber was shaking on his body and you could see blood flying through the air", Dr Towers told CBC.

"That was kind of the final impact, but he never let go of the infant."

"We were really quite horrified and fascinated", Dr Towers said.

Males of certain species are known to kill the offspring of others, particularly when it comes to their rivals.

Infanticide is more common in mammals when a few males must compete to reproduce with several females.

It has has been observed in mammal species ranging from dolphins to lions but this is the first time it has been seen in marine mammals.

Ecologist Ari Fiedlaender from Oregon State University told National Georgraphic this case could have been exception because the male orca had support from his own mother.

"The female, that male's mother, would effectively be helping to pass on her lineage if that male was then successful in breeding with the animal that lost her calf," said Dr Friendlaender.

"This is the first account of infanticide reported in killer whales and the only case committed jointly by an adult male and his mother outside of humans", researchers wrote in the paper, published in Scientific Reports.

"Consistent with findings in other social mammals, we suggest that infanticide is a sexually selected behaviour in killer whales that could provide subsequent mating opportunities for the infanticidal male and thereby provide inclusive fitness benefits for his mother."

Female chimpanzees have also been seen killing infant of other females, especially when food is scarce.

However, in this case researcher do not believe the murderous pair ate the youngster after killing it.

Scientists were unable to return and try and find the body as it was dark by that point.