Rock Rubbing Whales Itch to Shed Old Skin

Before and After: At bottom a bowhead whale with significant exfoliated skin; at top, one who has not sloughed off skin.

THE SINGULAR BEHAVIOR OF “ROCK-NOSED WHALES” who return to shallow inlets along the coast of Canada’s Baffin Island each summer and rub their bodies against boulders, has finally been definitively explained – they’re using the rocks as giant pumice stones to help slough off molted skin.

The unusual behavior of the bowhead whales (Balaena mysticetus) was first noted by whalers in the mid-19th Century and since then has generally been attributed to their use of the boulders to “rest.”

EVIDENCE OF MOLTING   British Columbia biologist Sarah E. M. Fortune and her team first came upon the whales in 2014 and noted that skin irregularities on them that seemed consistent with molting. They returned in 2016 equipped with drones to photograph and video them. They published their findings in Evidence of molting and the function of ‘rock-nosing’ behavior in bowhead whales in the eastern Canadian Arctic in the online journal PLOS ONE.

Still photos revealed that all the 81 whales observed were sloughing skin and that nearly 40 percent had mottled skin over more than two-thirds of their bodies, the study said.

THAT’S THE RUB   The rubbing behavior “supported our hypothesis that bowhead whales engage in exfoliation activities during the summer in Cumberland Sound,” they wrote.  “We presume that rubbing activities caused the linear markings. One animal was observed rock rubbing for a minimum of 8 minutes based on aerial imagery.”

These are not the only whales known to molt (such as beluga whales, which also rub on rock surfaces), although it’s not known whether other bowhead whales engage in rock rubbing, the report notes.

SOURCE: “Evidence of molting and the function of ‘rock-nosing’ behavior in bowhead whales in the eastern Canadian Arctic”, PLOS ONE,  November 22, 2017, https://doi.org/10.1371/journal.pone.0186156.

 

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