Marium was the name given to an 8-month-old dugong, a species of marine mammal found in the Indian and Pacific Oceans. The World Wildlife Foundation reports that dugongs are cousins of manatees, but don't swim in freshwater areas. Instead the "sea cows" graze in shallow coastal waters.
She earned widespread popularity after pictures were shared of her appearing to hug biologists who were helping feeding her.
Marium was being cared for by scientists after being found lost near a beach in southern Thailand, according the the Associated Press.
They were the ones who found her bruised last week, the AP reported. The bruises were attributed to aggressive male dugongs who were overly physical during mating season, but another possible factor in her subsequent death was less natural.
"We assume she wandered off too far from her natural habitat and was chased and eventually attacked by another male dugong, or dugongs, as they feel attracted to her," Jatuporn Buruspat, director-general of the Department of Marine and Coastal Resources, said on Saturday, according to the AP.
However, an autopsy also showed significant amounts of plastic waste in her intestine which Jatuporn said led to a blood infection and gastritis.
"She must have thought these plastics were edible," he said, according to the AP.
"Her death will remind Thais and people all over the world not to dispose trash into the oceans," Jatuporn said.