A recent article in PLoS ONE reports that bottlenose dolphins pursue manatees, particularly their calves, whether they are swimming alone or alongside their mothers.
Dolphins do indeed behave aggressively — bottlenose dolphins actively chase manatee calves, pushing them hard and biting them in an attempt to separate the young from their mothers. This resembles a situation in school where stronger students bully weaker ones. Manatees, being slow herbivores, cannot fend off dolphins and can only try to seek refuge in shallow waters, where dolphins prefer not to swim.
Over two decades of observations of dolphins and manatees off the coast of Belize have recorded ten instances of harassment. Theoretically, injuries and bites can lead to the death of a calf, and one of the injured manatee calves was later found dead. However, even in this single case, it could not be definitively stated that its death was caused by injuries from bottlenose dolphins. It seems that dolphins have no reason to harass manatees, as they are not their food. Nevertheless, despite their intelligence and social skills, bottlenose dolphins are not known for their friendliness. They exhibit strong nervousness towards dolphins of other species, perceiving them as competitors for territory and resources.
It is likely that manatees are also considered competitors, and the calves are chosen as victims because they appear less imposing compared to adult individuals.
