Humpback bottom-feeding techniques

We just came across some news about a study of bottom feeding by humpback whales. It’s fascinating!

People have theorized about this type of feeding behavior for many years. Circumstantial evidence (such as scraping and scarring on the whales’ rostrums) suggests they do swim very close to the bottom. This study provides some of the most thorough evidence and descriptions of the behavior seen to date.

To study the behavior, the researchers attached data loggers to humpbacks in the Stellwagen Bank National Marine Sanctuary. The results allowed the scientists to map the whales’ paths as they dived, fed, and surfaced. They also recorded the orientations of the whales’ bodies. The results suggest that the whales feed by swimming fairly slowly just above the bottom, rotating and in some cases even rolling completely over as they skim the substrate.

This isn’t the classic “lunge feeding” technique that many of us are familiar with, where whales accelerate into a school of fish with mouths open, and their ventral pleats billow out from the water and fish rushing in. This bottom feeding process is slower and steadier—in fact, the data loggers captured spikes of acceleration for each strong fluke beat, and there were few of those as the whales skimmed and rolled on the bottom.

The behavior does have one more familiar dimension: cooperation. Many of the whales in the study appeared to be foraging together and may have been coordinating their behaviors.

The researchers also put a National Geographic “Crittercam” on the whales, resulting in some nifty footage, including good evidence that the whales are targeting sand lance.

The study was published in July by Ware et al in Marine Mammal Science. Here’s a link to the journal article. The visualizations of the whales’ feeding paths are wonderful. 

And here’s a link to the National Geographic write-up. Make sure you watch the end, to see the very cool Crittercam footage of a breach—from the whale’s perspective. Watch how it accelerates as it approaches the surface!

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