Dolphins Seen Herding Whales Away From Their Habitat in Fascinating Footage

A new video has been posted showing a group of Risso's dolphins aggressively herding pilot whales away from their habitat off the coast of Portugal.

The footage was taken by the Nova Atlantis Foundation while researchers conducted daily fieldwork, observing the species.

The video begins by showing a pod of long-finned pilot whales swimming into the bay of Ribeiras in Azores, Portugal. Soon after the whales were spotted, a group of Risso's dolphins arrived "traveling at high speed," according to captions on the video.

The Risso's dolphins approach the pilot whales, and four dolphins can be seen forming a wall of defense. The dolphins then begin charging at the pilot whales, and making sounds that the Noval Atlantis Foundation called an "acoustic show of strength,"

While the pilot whales remain calm at first, the harassment from the Risso's dolphins continues. The whales occasionally display signs of panic.

PIlot whales and Risso's dolphins
A picture shows the Risso's dolphins herding the pilot whales into a ball, to move the whales away from their habitat. Nova Atlantis Foundation

Researchers from the Nova Atlantis Foundation noticed a baby among the pilot whales—they suspected this may be the reason for the group forming a tight formation, in order to protect it from harm.

Shots taken from above, show many Risso's dolphins circling the pilot whales, forcing them into a ball.

As the Risso's dolphins succeeded in isolating individual pilot whales from the group, they begin charging toward the group more frequently.

This continued for half an hour, the Nova Atlantis Foundation said, until eventually, the Risso's dolphins succeeded in driving them away.

The pilot whales eventually left the area, moving further south.

Long-finned pilot whales usually prefer cooler waters and are not often seen in Azores, the foundation said, in a caption to the video. Whereas Risso's dolphins are a resident species in the waters.

The half-hour encounter was an example of the dolphins defending their habitat, the foundation said.

"In short, pilot whales and Risso's dolphins are competitors for food: they both hunt squid at great depths. Risso's are thought to forage to depths of up to [1,968 feet], whereas pilot whales make dives up to [3,280 feet] depth," Karin Hartman of the Nova Atlantis Foundation told Newsweek. "In the Azores, both species are frequently sighted. Risso's dolphins are resident and are often found close to shore, whereas pilot whales used to be regular visitors, especially during the summer months, but over the past few years, both their numbers and the frequency of their sightings have strongly increased, and they are getting closer to the shore every year, where they enter the Risso's dolphins' favorite 'hunting grounds'."

Hartman said there is a correlation "with the rise of the sea surface temperature observed over the past years," which may be attracting the pilot whales to the area.

"We have observed many habitat-defense events, in which mostly male Risso's dolphins work together to harass the bigger pilot whales in order to chase them away. The event that we filmed this year was, therefore, no exception, except that this time the intruders were long-finned pilot whales, who are usually seen in cooler waters," Hartman said.

According to Hartman, the water temperature in the Azores this year has been a few degrees below last year's levels.

"What struck us, is that the long-finned pilot whales clustered together in a tight pack under the assault by the Risso's dolphins. This reaction may explain why in places like the Faroe Islands and Iceland, humans are able to slaughter so many (long-finned) pilot whales during their traditional 'drives'. But that is another story," Hartman said.

In a Facebook post explaining the incident, the foundation said a preliminary study shows the number of pilot whales increasing over the last three years, while the number of Risso's dolphins is decreasing.

The researchers will continue to study the clash between these two species, in collaboration with researchers from the Madeira island- MARE research group, to assess it in more detail.