Most whales, dolphins and porpoises are thought to shed and replace their skin continuously. However, this may not be true of Arctic species — including beluga whales, narwhal and bowhead whales — that seasonally occupy warmer waters such as estuaries and fiords. Beluga whales and likely narwhal molt in estuaries during the summer. However, little is known about molting in bowhead whales.
Sarah Fortune from University of British Columbia, Canada, and colleagues
studied molting and behavior of bowhead whales summering in Cumberland Sound, Nunavut, Canada. Data included still photographs of 81 bowhead whales and videos of four bowhead whales. The video below shows one bowhead whale rubbing on a large rock in Brown Harbor, which was observed with three other bowheads that proceeded to rub on rocks, as well.
The still images showed that all of the bowhead whales studied were molting, and that nearly 40 percent of them had mottled skin over much of their bodies. Both molting and rock rubbing appeared to be pervasive among bowhead whales during late summer in the study area.
This work supports the hypothesis that warmer water may facilitate molting, perhaps by boosting the whales’ metabolism or by providing an evolved physiological cue such as daylight.
The new findings suggest that rock-rubbing facilitates exfoliation. Moreover, the researchers speculate that bowhead whales may molt to shed parasites, such as whale lice, or to shed skin that has been damaged by the sun. The latter could reduce the risk of ultraviolet radiation during the summer at high latitudes, which could be important for long-lived species such as bowhead whales because skin damage accumulates with age.
Reference: Fortune SME, Koski WR, Higdon JW, Trites AW, Baumgartner MF, Ferguson SH (2017) Evidence of molting and the function of “rock-nosing” behavior in bowhead whales in the eastern Canadian Arctic. PLoS ONE 12(11): e0186156. https://doi.org/10.1371/journal.pone.0186156
Image and Video Credit: Fortune et al (2017)