Bottlenose Dolphins Mysteriously Attacking Manatee Calves; Study Says It's Intentional

(Photo : Getty Images/ROSLAN RAHMAN)

A study said that bottlenose dolphins are mysteriously attack manatee calves, with experts finding out that the hostile action is intentional.

Experts said that the dynamics and drivers of inter-species interactions in the wild are poorly understood, particularly those involving social animal species.

They pointed out that inter-species interactions between cetaceans and sirenians have rarely been documented and investigated.

Adult Dolphins' Interactions

In the study, scientists reported ten cases of interaction initiated by adult bottlenose dolphins (Tursiops truncatus) towards Antillean manatee (Trichechus manatus manatus).

Furthermore, interactions were documented through behavioral observations in the wild and from the examination of orphaned calves that entered a rehabilitation facility.

They said that they observed interacting with dolphins and found stranded ones with bite marks.

Bottlenose dolphins were observed interacting with orphan manatee calves and with mother-calf pairs, exhibiting agonistic behavior and affiliative or neutral behaviors; however the behavioral contexts of these interactions remain unclear in most cases.

The study noted that information on stranded individuals was collected from four calves recovered in poor condition with bottlenose dolphin tooth rakes and bite wounds on their bodies, one of which died.

Injury from bite wounds varied in extent and severity, ranging from superficial scratches leaving rake marks to deep lacerations.

''Our findings suggest the regular occurrence of agonistic behaviors initiated by adult bottlenose dolphins and directed toward manatee calves. However, the drivers of these interactions remain unknown and need to be further investigated,'' the study, titled Agonistic interactions initiated by adult bottlenose dolphins on Antillean manatee calves in the Caribbean Sea, said.

Agonistic behaviors among small cetaceans, particularly initiated by common bottlenose dolphins, often involves the delivery of blows by the flukes and peduncle, ramming with its rostrum causing blunt force trauma.

It also includes bites on animal bodies that leave behind external tooth rake marks.

The detection of tooth rake marks on stranded animals and the measurement of inter-tooth distances has been essential for confirming interactions between bottlenose dolphins and several species of cetaceans, involving harbor porpoises, common dolphins (Delphinus delphis), Atlantic spotted dolphins (Stenella frontalis), long-finned pilot whales (Globicephala melas), Risso's dolphins (Grampus griseus), and striped dolphins (Stenella coeruleoalba) in the Mediterranean Sea, the Atlantic and Indian Oceans.

The findings revealed the occurrence of previously unreported interspecies interactions between adult bottlenose dolphins and Antillean manatee calves.

The behaviors that were documented in bottlenose dolphins displayed towards manatee calves are similar to behaviors this species exhibits with calves of their own species and of other species.

Scientists said that understanding the drivers of these interactions is important, but often challenging, particularly for elusive marine mammals occurring in regions where research efforts remain limited.

However, further investigating the context and potential drivers of these interactions will be critical to advance our understanding their effects on manatee calf survival in this region.

Highly Intelligent Species

The National Oceanic and Atmospheric Administration said common bottlenose dolphins (referred to hereafter simply as bottlenose dolphins) are found throughout the world in both offshore and coastal waters, including harbors, bays, gulfs, and estuaries of temperate and tropical waters (estuaries are the areas where rivers meet the sea).

They are one of the most well-studied marine mammals in the wild.

In addition, they are easy to view in the wild because they live close to shore and are distributed throughout coastal and estuarine waters.

They are a highly intelligent species and use sound both for communication and to hunt for food.