A little-known population of orcas living off the coast of Chile has been seen hunting and eating dusky dolphins for the first time. The behavior may offer insights into the lives and diets of all orcas in the southern hemisphere, which could help future conservation efforts.

Off the coast of Chile is the Humboldt Current system, also known as the Peru Current, which flows north along the western coast of South America. The waters are rich in krill and anchovies, which makes it a prime location for various predators, including an elusive population of orcas. These animals have been seen hunting sea lions, but little else is known about them and their hunting behavior or diet.

Adults know the best hunting techniques and may show the youngest individuals how to hunt.

Dr Ana García Cegarra

In the Humboldt Current there is a lack of studies regarding orca sightings and foraging ecology”, Dr Ana García Cegarra of the Universidad de Antofagasta told IFLScience. 

“In the Chilean Patagonia there were studies indicating that orcas hunted sea lions, and in the Antarctic Peninsula that orcas predate on toothfish during the fishing activity. However, in northern Chile we did not know if orcas were marine mammal specialists or fish specialists.”

With the help of citizen science and years of careful surveillance, Cegarra and colleagues have now confirmed that the Humboldt orcas have more ambitious diets too.

“[I]n this new study we confirm orcas are dolphin specialists as we have sightings of orcas foraging on dusky dolphins in consecutive days in the same area of Mejillones Peninsula.”

Studying orcas is not easy as they are a marine top predator that travel long distances while living offshore. This makes observing their behavior difficult, but understanding how they live in their marine environment is crucial for their conservation.

Food matters

Orcas have an impressively varied diet, but not all orcas eat the same things. Populations of the animal can therefore be separated into different ecotypes based on their food preferences, alongside other factors, like their acoustics or genetics. When it comes to their diet, there are five different ecotypes in the southern hemisphere.

These include Type A and Type B1 orcas, which specialize in hunting marine mammals, and Type B2, Type C, and Type D that prefer to fish. So, understanding where the Humboldt Current populations fit in with these other hunters would help us understand how these animals relate to one another.

Cegarra and her colleagues carried out surveys and combined the results with citizen science data collected by whale-watching trips and fishing vessels that monitored and tracked the animal’s behavior.

“Citizen sciences has become a powerful tool for the study of cetaceans in remote places where research efforts are scarce,” Cegarra added. This is especially true across along the northern Chilean coast where fishermen and divers have shared their “sightings” of orcas and taken “pictures to identify them.”

With these contributions, Cegarra and her team were able to build up a map of the orcas’ presence in the area and tracked the pod’s behavior and prey choices. It was this that allowed them to capture evidence of the Menacho pod hunting and eating dusky dolphins for the first time. To date, no other orcas in the area have been reported hunting these mammals. There is even dramatic footage of the pod’s matriarch, called Dakota, tossing a dusky dolphin from the water.

This data suggests the orcas belong to the Type A mammal-hunting ecotype. This hypothesis is supported by the pod’s small size as well as their prey, though their white eye patches appear to be smaller than other Type A orcas. These animals have also never been recorded in Patagonia with other Type As.

Interestingly, the researchers saw the Menacho pod sharing their kills with one another. This behavior has been observed in other Type A populations.

“In terms of survival and energy intake of young individuals the sharing food is crucial for their welfare and survival. Adults know the best hunting techniques and may show the youngest individuals how to hunt. But in the meantime, the sharing ritual is also important to strengthen ties among individuals of the same group and probably family, and acquire the energy needed for the youngest to survive,” Cegarra explained.

In this study, the scientists show how the mother orcas are the ones to eat first, then they share the food with the adult males.

“This is similar to humans in family bonds when we offer food first to our kids and later to the adults.”

Conservation for hunters

The researchers now need to obtain more information and conduct systematic studies of these elusive orcas to help understand and protect them.

“Numerous human activities such as fishing, pollution from mining industry or ship strikes with vessels put […] the survival and welfare of orcas [at risk] in northern Chile.”

“Currently there are no conservation efforts for this species as […] distribution information is scarce in the area. However, after the results of our studies we aim to corroborate that orcas forage and breed in the area as we have observed new calves” in the groups around the Mejillones Peninsula, Cegarra said, along with them “hunting dolphins and sea lions.”

With this information, the scientists can encourage the authorities to create special conservation habitats for this species and hopefully reduce the speed of vessels in the area. 

The team would also like to obtain skin biopsy samples for genetic analysis to further help identify whether the orcas are ecotype A or ecotype B. They also want to check on a calf they observed in 2019 along with the population’s overall pregnancy rate. 

“We aim to perform photogrammetry studies with the help of a drone to understand the body condition of pod members but especially the mother and calf pairs,” Cegarra said.

Hopefully, in time, more citizen science and the careful work of these scientists can add more to our understand of these skilled predators.

The study is published in Frontiers in Marine Science.