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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Citation: 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:/
Funding: Fieldwork was funded by: Fisheries and Oceans Canada (Emerging Fisheries 41436-810-120-4D875), Nunavut Wildlife Research Trust Fund (project 3-13-29 Bowhead Whale Movement's and Ecology), Molson Foundation (318366), Ocean Tracking Network (NSERC NETGP 375118-08), and ArcticNet Centre of Excellence (317588) awarded to S.H. Ferguson and World Wildlife Fund Canada (Arctic Species Conservation Fund) awarded to W.R. Koski and S.M.E. Fortune. Additional field work support was provided by: U.S. Department of the Interior, Minerals Management Service (MMS; now Bureau of Ocean Energy Management), through Inter-agency Agreement No. M08PG20021 with the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, as part of the MMS Alaska Environmental Studies Program awarded to M.F. Baumgartner. Personnel support was provided by: Natural Sciences and Engineering Research Council Canadian Graduate Scholarship, the W. Garfield Weston Award for Northern Research, University of British Columbia Affiliated Fellowship and Northern Scientific Training Program (Canadian Polar Commission) awarded to S.M.E. Fortune.
Competing Interests: Two co-authors (WRK & JWH) have commercial affiliations (LGL Limited & Higdon Wildlife Consulting). The commercial affiliations of our co-authors has not altered our adherence to all PLOS ONE policies on data sharing and materials.