Stanford tracker gives a whale-back view of feeding time

Attached to a whale with suction cups, this device tracks their movement in three dimensions, and records video both forwards and backwards simultaneously(Credit: Jeremy Goldbogen)

A wide array of technology has been deployed to track and study whales unobtrusively, from drones that watch from overhead to acoustic buoys that listen for their cries. Now a team from Stanford has used a new suite of sensors to study the feeding habits of baleen whales in greater detail, and released a video from the vantage point of riding of a whale's back.

The whales in question belong to the rorqual family, which feed by taking in huge gulps of water as they lunge towards a school of krill or small fish, then use brush-like plates called baleen to filter out the food. While the technique itself is well understood, the mechanics of just how the whales do it is still uncertain.

"This feeding process is facilitated by a complex suite of biomechanical and anatomical adaptations that together allow the whales to engulf a volume of water and prey that is larger than their own body," says co-author Jeremy Goldbogen. "For a large blue whale, this represents a volume of water and prey that is approximately the size of a large swimming pool or a school bus, and this is engulfed in a matter of seconds."

The team, from Stanford's Hopkins Marine Station, specifically wanted to determine just when a whale opened its mouth during that process: at the peak speed of its lunge, or a few seconds before that point. The significance of that question is a matter of efficiency, as taking in that much water produces huge amounts of drag and takes a serious amount of energy from the animal.

"When these animals dive down to 300 meters (984 ft), holding their breath for 12 minutes or more, they had better be sure it's worth the cost," says David Cade, lead author. "To regain the energy lost, the prediction is that they are foraging on a pretty dense, rich resource."

To answer these questions, the team attached a new suite of sensors to whales in South Africa, Patagonia, and in the waters off the east and west coasts of the US. Harmlessly stuck to the specimens with suction cups, the devices housed sensors that tracked the movement of the whales in three dimensions, while two cameras simultaneously shot video facing forwards and backwards.

"Combining these two modalities is really eye-opening," says Cade. "Every time we do a deployment, we get something back that's new and interesting."

The results of the research showed that the timing of the whales' lunges depended on their lunch. Species that dined on krill consistently opened their mouths when they hit their top speed, and closed it again when they slowed back down. Fish-eating whales, however, tended to vary their timing much more, behavior that the researchers attribute to the animals countering the ability of the fish to dodge out of the way.

Along with producing some impressive footage from a new perspective, the purpose of the research is to improve our understanding of the behavior and feeding habits of whales, and their role in the ocean ecosystem, in order to help with conservation efforts.

The research was published in the journal Current Biology.

The video taken from the whales' backs can be seen below.

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