Dolphins’ ‘rough’ repeated attacks on manatee babies puzzle scientists: ‘Hard to understand’
Dolphins have been observed harassing and attacking baby manatees in an aggressive act that has puzzled scientists trying to understand why they would harm the most helpless members of their cousin species.
The behavior has been recorded ten times between 1999 and 2020 in the Caribbean Sea along the coast of Belize, with most of the interactions between adult bottlenose dolphins and manatee calves occurring in the last decade, according to a study published earlier this month in the peer-reviewed science journal PLOS One.
Although many of the interactions left the manatees injured, and in at least one instance, killed, it was unclear from scientists if the highly social and intelligent dolphins, who “play rough,” meant them any harm.
In one case captured on video, a group of four dolphins was observed harassing a baby manatee and its mother, and separated the two by “lifting the calf while swimming away.”
A lone dolphin then followed the baby for several minutes before “ramming the calf out of the water into the mangroves and repeatedly biting it,” forcing researchers to pull it out of the water and send it to be rehabilitated.
In three of the cases, baby manatees with “clusters of tooth rakes” and bite marks consistent with those from bottlenose dolphins were discovered, leading to the death of one of the manatee calves.
In another incident, “large splashes and vigorous subsurface movements suggested” that a dolphin who had been stalking a baby manatee had become aggressive.
Drone footage of a separate incident recorded a single dolphin swimming in a counterclockwise circular path around a mother and baby manatee 11 times in four minutes as the pair tried to escape. The device lost battery power before it could record how the interaction ended.
Several of the instances saw dolphins trying to push calves to the surface, which could be interpreted as a playful or caring gesture.
“We don’t know if they are really trying to hurt them or not. Dolphins play rough. They don’t have hands, so when they socialize or mate or play, they tend to bite each other and hit each other with their tails,” Eric Angel Ramos, study author and researcher at the Fundación Internacional para la Naturaleza y la Sustentabilidad, told Newsweek.
“They may be treating manatees roughly but not actually trying to hurt them. However, bottlenose dolphins are also known to kill baby dolphins of their species, and probably others. So the drive to attack and kill young could help explain how they treat babies of other species.”
Many of the manatees targeted were orphans, researchers noted.
The dolphins’ unknown motives were highlighted by an instance where a pod of orcas was reported to have adopted a pilot whale calf, a gesture that could have also been an abduction.
However, bottlenose dolphins can also turn on other marine mammals, including other species of dolphins, as they battle for resources, Ramos cautioned.
“But it’s really hard to understand these interactions because you don’t see them a lot and it’s difficult to determine who is involved and what the context of the interaction is,” Ramos told the outlet.
Researchers noted in their paper that the “dynamics and drivers of inter-species interactions in the wild are poorly understood, particularly those involving social animal species.”
“The take home message is that dolphins show complex behaviors and sometimes they interact with other species in ways similar to the way they interact with each other, and that can be aggressive and sometimes lead to injuries,” Ramos said.