Example of an animal with nearly no sloughing skin (i.e., proportion of body with sloughing skin = <33%) (A) and another bowhead whale with a high degree of sloughing (>66% of body) and a blotchy skin type (B). Credit: Fortune et al (2017) CC BY
Bowhead whales molt and rub on large rocks -- likely facilitating exfoliation -- in coastal waters in the eastern Canadian Arctic during late summer, according to a study published November 22, 2017 in the open-access journal PLOS ONE by Sarah Fortune from University of British Columbia, Canada, and colleagues.
Most whales, dolphins and porpoises are thought to shed and replace their skin continuously. However, this may not be true of Arctic species -- such as 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, where warmer water is hypothesized to facilitate skin turnover by increasing metabolic activities or by providing a physiological cue such as daylight. However, little is known about molting in bowhead whales.
Fortune 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 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 (more than two-thirds). The videos captured bowhead whales rubbing on large rocks in shallow coastal areas. 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, and suggests 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.
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