Killer Whales Use Stealth Approach When Hunting Prey
December 4, 2013

Killer Whales May Use Acoustic Cues To Hunt Down Prey

[ Watch the Video: Stealthy Tactics Used By Orca To Catch Their Prey ]

redOrbit Staff & Wire Reports - Your Universe Online

Newly discovered evidence that killer whales can hunt marine mammals during the nighttime has led scientists to suggest that the creatures can use their hearing to help locate prey, according to research presented at the 166th Meeting of the Acoustical Society of America (ASA).

For example, the study authors said that the whales eavesdrop on male harbor seals when they use mating roars in order to attract a female. Previous research had shown that killer whales remain largely silent just before making a kill, refraining from vocalizing or using echolocation in order to avoid detection by the animals they stalk.

“If the mammal hunters just swam around clicking all the time, then all the prey would be warned,” Volker Deecke, a senior lecturer in conservation biology at the University of Cumbria’s Centre for Wildlife Conservation, explained in a statement Tuesday. “It looks like the whales are using a stealth approach instead.”

Seals and porpoises have excellent hearing, the researchers said, and while experts had known that whales did not use echolocation while hunting, they were unsure exactly how the creatures were able to locate their prey.

Deecke and his colleagues traveled to Alaska, placing acoustic recording tags approximately the same size as a cell phone on 13 killer whales. Those tags were attached to the whales with four suction cups and were able to remain on the creatures for up to 16 hours. The units were outfitted with an accelerometer, compass, depth sensor and hydrophone, which recorded data on the whale’s movements, the sounds it made and the sounds it received.

The investigators were able to identify predatory encounters based on the characteristic sound made by the whale while it does away with its victim with a hit from its tail fluke. After analyzing several hours of data, they found that the killer whales were able to successfully find potential prey, even in almost total darkness.

This discovery means that orcas do not rely on visual cues as the sole method of detecting prey, Deecke said. “We now suspect that mammal-eating killer whales are primarily eavesdropping on sounds generated by their prey to find food," he noted, recalling one whale which successfully hunted a seal shortly after being outfitted with a tag.

The device immediately “started to record seal roars,” and over the next 30 minutes, “the roars got louder and louder, then there are a sequence of three quite loud roars that suggest the seal is within a few hundred meters of the killer whale. Twenty-seven seconds later there are the sounds of a predation event, and then no more roars.”

While Deecke said that the story was compelling, he said that it does not provide concrete evidence that killer whales are using the sounds of their prey in order to locate them. He and his colleagues now hope to conduct playback experiments in order to determine whether or not the predators will respond to pre-recorded seal roars and porpoise echolocation clicks.

Determining the degree to which killer whales rely on acoustic cues could help provide new insight into the ecological impact of activities that produce underwater sound, such as shipping. Deecke explained that scientists “need to understand how the foraging process works so that we, as humans, can know how our behavior might impact the animals negatively and what we can do to minimize our impact.”