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RESEARCH ARTICLE
Evidence of molting and the function of “rock-
nosing” behavior in bowhead whales in the
eastern Canadian Arctic
Sarah M. E. Fortune
1,2
*, William R. Koski
3
, Jeff W. Higdon
4
, Andrew W. Trites
1
, Mark
F. Baumgartner
2
, Steven H. Ferguson
5
1Department of Zoology and Marine Mammal Research Unit, Institute for the Oceans and Fisheries,
University of British Columbia, Vancouver, British Columbia, Canada, 2Biology Department, Woods Hole
Oceanographic Institution, Woods Hole, Massachusetts, United States of America, 3LGL Limited, King City,
Ontario, Canada, 4Higdon Wildlife Consulting, Winnipeg, Manitoba, Canada, 5Fisheries and Oceans
Canada, Freshwater Institute, Winnipeg, Manitoba, Canada
*s.fortune@oceans.ubc.ca
Abstract
Bowhead whales (Balaena mysticetus) have a nearly circumpolar distribution, and occa-
sionally occupy warmer shallow coastal areas during summertime that may facilitate molt-
ing. However, relatively little is known about the occurrence of molting and associated
behaviors in bowhead whales. We opportunistically observed whales in Cumberland
Sound, Nunavut, Canada with skin irregularities consistent with molting during August 2014,
and collected a skin sample from a biopsied whale that revealed loose epidermis and
sloughing. During August 2016, we flew a small unmanned aerial system (sUAS) over
whales to take video and still images to: 1) determine unique individuals; 2) estimate the
proportion of the body of unique individuals that exhibited sloughing skin; 3) determine the
presence or absence of superficial lines representative of rock-rubbing behavior; and 4)
measure body lengths to infer age-class. The still images revealed that all individuals (n =
81 whales) were sloughing skin, and that nearly 40% of them had mottled skin over more
than two-thirds of their bodies. The video images captured bowhead whales rubbing on
large rocks in shallow, coastal areas—likely to facilitate molting. Molting and rock rubbing
appears to be pervasive during late summer for whales in the eastern Canadian Arctic.
Introduction
The skin (epidermis) and hair (keratinized epidermal cells) of marine mammals are specially
adapted for life in an aquatic environment. The periodic shedding of part or all of their outer
layer of epidermal covering, which is then replaced by new growth [1] has been well studied
for seals and sea lions—which molt annually to repair and renew their skin and pelt [2–8]. In
contrast, whales, dolphins and porpoises are generally thought to continuously shed and
replace their epidermis [9,10]. However, this may not be the case for Arctic species that experi-
ence pronounced changes in environmental conditions by seasonally occupying uncharacter-
istically warmer areas such as estuaries and fiords [11].
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OPEN ACCESS
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://doi.org/10.1371/journal.pone.0186156
Editor: Songhai Li, Institute of Deep-sea Science
and Engineering, Chinese Academy of Sciences,
CHINA
Received: July 6, 2017
Accepted: September 26, 2017
Published: November 22, 2017
Copyright: ©2017 Fortune et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
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)
Beluga whales (Delphinapterus leucas) and most likely narwhal (Monodon monoceros) (e.g.,
Inuit hunter observation [12]) undergo a seasonal epidermal molt during summer. The beluga
whale molt appears to be facilitated in part by the warm and low salinity environmental condi-
tions found in seasonally occupied estuaries [11,13]. The elevated water temperatures are pos-
tulated to influence the growth and turnover of epidermis by increasing metabolic activities
[11] or provide an evolved physiological cue (e.g., daylight [14]). Furthermore, physical fea-
tures of estuaries such as gravel bottoms provide an abrasive surface to rub against and expe-
dite exfoliation [15].
In contrast to what is known about molting for beluga whales, little is known about this
phenomenon in bowhead whales (Balaena mysticetus). It is known, for example, that the struc-
ture of epidermal, dermal and hypodermal layers of balaenid whales (bowhead and right
whale, Eubalaena sp.), closely resembles that of odontocete species that are known to slough
skin (e.g., beluga whales) and differs from the more closely related balaenopterids (e.g., fin,
blue, and sei whale) [1]. Furthermore, southern right whale (Eubalaena australis) calves are
known to shed multiple layers of their epidermis [16], which is similar to beluga calves that
conduct a multilayered molt to remove fetal epidermis [17]. Histological analysis has revealed
that bowhead whales belonging to the Okhotsk Sea population molt during summer months
while occupying a warm, shallow bay in the Shantar Achipelago [18]. However, it is not
known whether other populations of bowhead whales, such as the Eastern Canada-West
Greenland (EC-WG) population, undergo a seasonal molt or whether they molt continuously
and whether the molting process is similar for all age classes of whales.
Materials and methods
We opportunistically made boat-based sightings of EC-WG bowhead whales in Cumberland
Sound, Nunavut, Canada—specifically in Kingnait Fiord (located on the northeast side of
Cumberland Sound Fig 1)—on five days from 13–21 August, 2014. As a result of these prelimi-
nary observations, a directed study to test the hypothesis that bowhead whales use Cumberland
Sound in part for molting during summer months was carried out in August 2016.
Zooplankton samples were opportunistically collected during August 2014 from surface
waters (0.5 m) near bowhead whales, and also following an unusual observation of bowhead
whales in shallow, coastal waters in Kingnait Fiord. All samples were collected using 333-
micrometer (μm) conical mesh net (30 cm in diameter) fitted with a General Oceanics helical
flow meter. The zooplankton net was sprayed down with a hose using seawater to collect the
sampled organisms in an attached cod-end bucket once it was brought onboard the boat.
Once organisms were no longer visible in the zooplankton net, the cod-end bucket samples
were filtered through a 333 μm mesh sieve and transferred to a 250 mL sample jar and pre-
served in 5% buffered formalin solution for identification.
Boat-based and aerial sightings of bowhead whales were made in Pangnirtung Fiord,
Brown Harbour (located between Pangnirtung Fiord and Kingnait Fiord, Fig 1) and Kingnait
Fiord from 7–31 August 2016. High-resolution aerial images (n = 1143) and video were
obtained of encountered whales using a small unmanned aerial system (sUAS), the DJI Phan-
tom 3 Professional. The sUAS was equipped with a global positioning system (GPS) and altim-
eter that allowed for the whale’s position and the sUAS altitude to be automatically recorded
when each image was captured. The sUAS was flown at an average altitude of 12.9 m (±5.4 SD)
with a maximum distance of 1000 m from the survey vessel, and was hand-deployed and
hand-retrieved from the ~8 m aluminum vessel. Flight times lasted ~8–12 min. The sUAS data
were collected under Special Flight Operation Certificate File Number 5812-11-682, ATS 16-
17-00014027, RDIMS 12044419 and approved by the University of British Columbia Animal
Bowhead whale molting and rock-nosing
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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.
Care Committee (Animal Care Amendment A14-0064-A002). Bowhead whale behavioral data
were collected under permit Department of Fisheries and Oceans License to Fish for Scientific
Purposes S-16/17 1005-NU and Animal Use Protocol FWI-ACC-2016-09.
Still sUAS images of bowhead whales were used to determine unique animals during
August 2016 as well as their body lengths and skin conditions. Individual animals were identi-
fied using well-established permanent black and white dorsal patterns [19]. The markings used
to identify unique individuals included: 1) white scars on their body attributed to breaking sea
ice, encounters with fishing gear or from interactions with killer whales (Orcinus orca) (i.e.,
killer whale rake marks [20]; and 2) white pigmentation found on the dorsal flukes, caudal
peduncle and lower jaw. Body length measurements (distance between snout and fluke notch)
were made for animals that were photographed with the vessel (an object of known size used
for calibration) in the same frame or another animal of known size (i.e., previously photo-
graphed with the vessel). The measuring tool in Adobe Photoshop CS6 extended was used to
measure body length. Skin condition was also assessed from still images to determine: 1) pro-
portion of the body that contained sloughing skin (0 = none, 1 = <33%, 2 = 33–66%, 3 =
>66% and <100% and 4 = 100%; Fig 2); and 2) the type of sloughing (0 = none, 1 = light gray
lines across the body likely caused by rock rubbing, 2 = irregular patches of gray sloughed
skin, 3 = smooth gray body attributed to complete or near complete sloughing; Fig 3). The
Fig 1. Locations of fieldwork conducted in the eastern Canadian Arctic showing Baffin Island, Canada (left panel), and Iqaluit, the capitol of
Nunavut (designated with a black ) and Pangnirtung, a community located in Cumberland sound (red ◆). The inset map of Cumberland Sound
shows where bowhead whale (Balaena mysticetus) observations were made in a small bay in Kingnait Fiord (blue ●) in 2014 from a vessel and from sUAS
in Brown Harbour (blue ■), Pangnirtung Fiord and Kingnait Fiord in 2016. The polygon shapefiles and polyline shapefile used to generate this map were
accessed through Esri Canada and were licensed through Natural Resources Canada for free distribution.
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presence of gray tissue is indicative of new skin growth—based on our observations and those
of bowheads molting in the Okhotsk Sea [18]. Three people independently scored each animal,
and agreement between at least two people was required to obtain a final score.
We opportunistically collected oceanographic data during August 2016 to evaluate the
physical properties of Kingnait Fiord. Vertical profiles of the water column were made using a
seabird SBE19Plus conductivity, temperature, and depth (CTD) profiler. CTD data were cor-
rected using Seabird software and temperature and salinity plots were generated using the
downcast data for each cast (n = 86).
Results and discussion
2014 Observations
Unusual behaviors of bowhead whales in shallow coastal-waters were first noted on 21 August
2014 in Kingnait Fiord when 8–10 bowhead whales were observed frequently rolling onto
Fig 2. 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).
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their sides and backs and lifting their pectoral flippers out of the water (Fig 4). The small, shal-
low bay was marked with large boulders (65˚ 55’15.2”N and 65˚ 17’50.8” W, Figs 4&5) and
the whales were in ~8 m of water. The animals did not appear to be associated with one
another as they were widely distributed throughout the bay and exhibited individually specific
behaviors. Several audible vocalizations were heard without a hydrophone from the vessel
over the course of the sighting. Net sampling revealed very low zooplankton biomass, particu-
larly for species that are known bowhead whale prey (e.g., calanoid copepods, euphausiids,
Fig 3. Example of (A) a bowhead whale with thin and sharp light gray lines and (B) of a whale with shorter and
wider gray lines, that both likely reflect prior rock-rubbing behavior.
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amphipods), indicating that the whales were not feeding in the bay. There was little likelihood
that the whales were feeding because subsequent zooplankton sampling failed to capture bow-
head whale prey.
Irregularities in bowhead whale skin condition were observed from animals visiting the
bay. Photographs taken of two whales before they reached the bay revealed large pieces of
loose epidermis. The sloughing epidermis was predominately located posterior to the whale’s
blowholes (Fig 6). Animals also presented mottled skin consisting of light gray irregular
patches on their heads near the blowholes and on their backs (Fig 6). Furthermore, histological
analysis of a sample of loose epidermis from one whale obtained using a crossbow and biopsy
dart was consistent with molting. These documented skin irregularities were similar to the his-
tology of biopsy and opportunistic skin collected from bowhead whales in the Okhotsk Sea
[18], and provide support that molting occurs during summer based on the timing of collec-
tion and histological properties of our bowhead samples [21].
2016 Observations
Rock rubbing. Following our initial observations in 2014, we used the sUAS to document
four bowhead whales rubbing on large boulders in shallow coastal waters on 7 August 2016
in Brown Harbour (65˚ 58’31.0” N and 65˚ 57’19.0” W, Fig 1). While simultaneously filming
this rubbing behavior, we made boat-based observations of whales rolling onto their sides
with pectoral flippers extended out of the water similar to our prior observations (during
summer 2014). The aerial video and high-resolution still images of the animals displaying
surface behaviors confirmed that they were rubbing their bodies against rocks (Fig 7 &S1
Movie). The whales were seen rubbing their chins, head, back and sides on a cluster of boul-
ders and had mottled skin with what appeared to be long superficial scratches that ran length-
wise and widthwise along their bodies (e.g., Fig 7 animal C). This rubbing behavior was
consistent with previous observations and supported our hypothesis that bowhead whales
Fig 4. Example of observed behavior and relative distribution of three individual bowhead whales (A-C)
inside the bay in Kingnait Fiord (2014). Whale (A) is resting close to shore with its head out of the water, (B) is
on its back with pectoral flippers extended, and (C) is breaking the surface of the water in the distance.
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engage in exfoliation activities during the summer in Cumberland Sound. 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 (S1 Movie).
Previous observations of bowhead rock-rubbing behavior have been documented during
late summer and early fall in Isabella Bay (Baffin Bay), whereby bowhead whales engaged in
“grooming” activities by rubbing on the bottom [22,23]. Similarly, whaling records [24] pro-
vide historical support for bowhead rubbing behavior dating back to ~1845, whereby whales
found in the bays and inlets of Davis Strait (such as Cape Searl) were referred to as “rock-nose”
whales because they would place their head or “nose” close to the shore on a rock [25]. More
recently, similar “rock-nose” behavior was observed during an aerial survey of Isabella Bay on
13 September 1979 [26].
Recent Inuit observations of bowhead whales with molting skin during summer were made
near Clyde River (nearest community to Isabella Bay) [27]. Whales were also observed circling
around a large rock off the coast of Clyde River [27], and were hypothesized to use the rocks
for resting purposes [24]. However, the association between EC-WG bowhead whales with
molting skin and their physical environment suggests otherwise. The whaling data provide fur-
ther evidence that they have engaged in rock-rubbing behavior off the coast of Baffin Island
for at least hundreds of years.
Aerial image analysis. Our analysis of high-resolution images from the sUAS indicates
pervasive molting for individuals occupying Cumberland Sound during summer. Overall,
Fig 5. Large boulders located in the shallow bay where the bowhead whales (Balaena mysticetus) aggregated in
Kingnait Fiord, NU, during 2014 and where prey samples were subsequently collected.
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image quality was sufficient to assess molting extent and type for 97.6% (n = 81) of the
uniquely identified individuals (n = 83), and revealed that 100% of the individuals had skin
irregularities consistent with molting (Fig 8A &S1 Data). We found that molting was extensive
for 37.4% of the identified whales, whereby sloughing skin represented >66% of their body.
We also found that 37.04% of animals had sloughing skin over 33 to 66% of their body and
25.93% had molting skin on <33% of their body. Over half (58.02%) of the photographed ani-
mals had the mottled skin pattern without evidence of rubbing, while 40.74% showed signs of
rock-rubbing behavior (Fig 8B).
Our estimated occurrence of rock rubbing from our photographs is likely underestimated
due to: 1) limited image quality, particularly when whales were photographed below ~10 m
depth; and 2) limited perspective of individual’s body whereby evidence of rock rubbing (i.e.,
light gray lines) may be on the ventral side of the animal and thus excluded from our analysis.
As a consequence, our estimate of the proportion (40.74%) of unique individuals bearing
marks from probable rock-rubbing behavior is a minimum estimate.
Overall, we measured body lengths for 16 unique whales ranging from 6.3–14.2 m, with a
mean length of 10.60 m (±2.01 SD) (Fig 9). Age-class was broadly inferred based on previous
studies [23,28,29] that found calves (i.e., young-of-the year) are ~4–7.5 m in August and Sep-
tember, young juveniles (1 to 8–10 y) are 5.8–10 m [26], sexually immature sub-adults (8–10
to ~25 y) are 10–13 m, and sexually mature adult (25+ y) males exceed 12.5 m [30] and females
exceed 13 m [31]. We used the threshold of 13 m for assigning individuals adult status. Of the
Fig 6. Example of sloughing epidermis (A) located behind the blowholes of a bowhead whale (Balaena mysticetus) and
mottled skin (B) found near the blowholes.
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animals measured, none were calves based on the morphological differences between calves
and yearlings [26]. However, we did observe one small yearling measuring 6.26 m. Conse-
quently, we concluded that 38% (n = 6) of the measured animals were young juveniles (8.59 m,
±1.33 SD), 56% (n = 9) were sub-adults (11.54 m, ±0.91 SD), and only one animal was an
adult (6%) with a body length of 14.22 m. Overall, our measurements of total body length dem-
onstrated that both juvenile and adult animals occupied Cumberland Sound, and that all ani-
mals had sloughing skin.
Energetic implications of molting. Although we were unable to quantify the proportion
of time allocated to molting activities, whales were routinely observed, during daylight hours,
resting in addition to actively rubbing against the rocks suggesting that individuals allocate
considerable time to these two activities. On numerous occasions, our sUAS deployments doc-
umented molting individuals resting in nearshore waters where rock rubbing was previously
observed.
Molting is energetically costly for pinniped species that elevate their resting metabolism
while increasing blood flow to the epidermis and generating new hair [32–35]. Seals and sea
lions have behavioral adaptations to partially offset the metabolic costs associated with molt-
ing, such as increasing the time spent on land (i.e., reduced energy expenditure due to thermo-
regulation and activity costs associated with swimming). Similarly, bowhead whales may
adjust their daily activity costs by increasing the proportion of time spent resting. This may be
simultaneously beneficial as warmer water may expedite the molting process [4] and taking
refuge in shallow, protected bays may mitigate predation from killer whales.
Unlike seals and sea lions that reportedly experience thermoregulatory benefits by hauling
out while molting, bowhead whales may overheat while molting in warmer water because they
are too well-insulated (bowheads have the thickest blubber of any marine mammal, ranging
from 20–35 cm) [36–40] and have small surface area to volume ratios that favor retention of
Fig 7. Example of four bowhead whales (Balaena mysticetus) with mottled skin rubbing their bodies
against boulders in Brown Harbour on 7 August 2016. Animal (A) pictured rubbing the right side of its
head on a boulder (S1 Movie) and animal (D) is using the rocks to exfoliate its chin. Evidence of prior rock-
rubbing is apparent for animal (C) with long, thin lines running length and width-wise across the body.
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metabolic heat. Maximum daily surface water temperatures ranged from ~4 to 9.5˚ C in King-
nait Fiord based on the CTD data collected during August 2016, and appeared to be highest
near the rock-rubbing habitat with surface temperatures ranging from ~8 to 9.5˚ C. However,
maximum water temperatures encountered by bowhead whales may be even warmer in shal-
lower (~8 m) areas compared with our measurements, which were made in comparatively
deep (~100 m) areas of the bay just outside of where rock rubbing occurred. Consequently,
Fig 8. Percentage of photographically identified bowhead whales with sufficient image quality to quantify the
amount of the body containing sloughing skin (n = 81) (A). Overall, all animals showed signs of molting in late
August, and no animals had bodies with 100% new skin cover. Also shown is type of sloughing skin (B)
whereby ‘none’ represents animals with no skin irregularities, ‘rock rubbing’ is indicated by animals with both
sharp, thin light gray lines and/or wider, less pronounced light gray lines which are likely a result of prior rock
rubbing, ‘blotchy’ comprises animals with irregular patches of new epidermis and ‘covered’ includes animals
with extensive new skin growth.
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bowheads may have to use vascular adaptations to dissipate excess heat while rock rubbing in
the warmer, coastal waters.
One way for bowhead whales to dump excess heat may be to use their intraoral thermoreg-
ulatory organ located in the root of the tongue (i.e., counter current retial vessels) [41] and at
the center of the hard palate stretching to the tip of the rostral palate (i.e., palate rete or corpus
cavernosum maxillaris) [36]. They could effectively use this organ by slightly opening their
mouths to permit cooling seawater to enter their mouth and flow over the retial vessels in the
tongue and the palate rete. We observed several bowhead whales in the aerial images with their
mouths slightly agape (S1 Image) near rock rubbing areas (i.e., Brown Harbour). While it is
possible that they were feeding, prior prey sampling in similar shallow habitats in Kingnait
Fiord found very few zooplankton and their baleen was not visibly extended. It therefore
seems more plausible that the whales opened their mouths to cool themselves because they
were thermally stressed in the warmer, shallow rock-rubbing habitat while actively swimming
during exfoliation activities. They may have thus regulated their body temperature by exchang-
ing heat from enlarged blood vessels in their tongues and palates with the comparatively cooler
seawater [36–41].
Biological significance of molting. There are biological factors affecting skin condition
that may explain why bowhead whales molt. One is that they may slough their skin to shed
ectoparasites such as cyamids (i.e., whale lice) [42,43] and accumulated diatoms (i.e., phyto-
plankton) [44] that may damage their epidermis and potentially impede thermoregulation.
Another possibility is that bowhead whales are shedding solar damaged skin [45]. Annual
replacement of skin may reduce the risk of extended exposure to ultraviolet radiation during
summer in high-latitude habitats [46], and may be particularly important for long-lived species
such as bowhead whales because skin damage accumulates with age [47]. Regularly sloughing
Fig 9. The measured body lengths of 16 unique bowhead whales separated into 8 bins where ~6 m
was the minimum size and ~14 m was the maximum. The total body length represents the straight-line
distance calculated between the tip of the snout to the fluke notch.
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skin damaged by the accumulation of parasites, diatoms and solar radiation may thus allow
bowhead whales to maintain epidermal function and integrity over time.
Conclusions
Overall, our observation of skin irregularities (e.g., mottled skin pattern, sharp light gray lines,
loose epidermis) of various age-classes (juveniles, sub-adults and adults) provides strong evi-
dence that molting is pervasive for bowhead whales during summer in Cumberland Sound. In
Cumberland Sound, molting occurred in shallow, warm coastal areas that had low-salinity sur-
face waters (characteristic of sub-Arctic fiords), and appeared to be facilitated by rubbing on
large rocks. The elevated water temperature in rock-rubbing habitat may stimulate epidermal
growth [11,48], whereby increased water temperature elevates skin temperature and enhances
the rate of cutaneous metabolic processes [11]. Furthermore, increased ambient temperatures
promotes cutaneous blood flow, bringing nutrients and hormones (e.g., thyroid hormone)
known to stimulate epidermal proliferation [11]. Such habitat is comparable to areas where
beluga whales rub on rocky substrate in estuaries [24,25], and where bowheads belonging to
the Okhotsk Sea population were observed molting [11,15,48].
Our findings lend support to previous hypotheses that molting is facilitated by pronounced
changes in oceanographic conditions such as water temperature [18], and suggest that rock-
rubbing behavior is used to facilitate the molting process through exfoliation. Additional
research needs to address questions regarding the seasonality of the molt (i.e., is molting more
pronounced during summer months or does it occur uniformly and continuously throughout
the year?) by collecting year-round aerial imagery (excluding winter months with 24 hour
darkness), and monitoring the skin condition of bowhead whales over time. Finally, our obser-
vations provide evidence that the function of “rock-nosing” observed by whalers, scientists,
and northern community members is related to exfoliation to facilitate molting.
Supporting information
S1 Movie. sUAS video of one bowhead whale rubbing on a large rock in Brown Harbour on
7 August 2016. This individual (A) was observed with three other individuals that subse-
quently engaged in rubbing behavior (Fig 6).
(MOV)
S1 Data. sUAS data for 83 unique bowhead whales used to determine body length (m),
sloughing amount (0 = none, 1 = <33%, 2 = 33–66%, 3 = >66% and <100% and 4 = 100%),
sloughing type (0 = none, 1 = light gray lines from probable rock-rubbing behavior, 3 = cov-
ered) and whether the mouth was closed (e.g., 0), slightly open (1), wide open (2), or inde-
terminable (9).
(XLSX)
S1 Image. Example of a bowhead whale with mouth slightly agape near Brown Harbour
during August 2016.
(TIFF)
Acknowledgments
We are appreciative of the aerial imagery and video collected and generously provided by
Thomas Seitz (VDOS Global LLC) and the boat-based images collected by Maha Ghazal. We
are grateful for the logistical support provided by our community partners, Ricky and Peter
Kilabuk, who were responsible for vessel operations. Histological analysis of sloughing
Bowhead whale molting and rock-nosing
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bowhead whale epidermis was graciously conducted by Stephen Raverty. This manuscript was
improved by the helpful comments and edits provided by Julie Mocklin and an anonymous
reviewer.
Author Contributions
Conceptualization: Sarah M. E. Fortune, Steven H. Ferguson.
Data curation: Sarah M. E. Fortune, William R. Koski.
Formal analysis: Sarah M. E. Fortune, William R. Koski, Jeff W. Higdon.
Funding acquisition: Sarah M. E. Fortune, William R. Koski, Mark F. Baumgartner, Steven H.
Ferguson.
Investigation: Sarah M. E. Fortune, William R. Koski, Steven H. Ferguson.
Methodology: Sarah M. E. Fortune, William R. Koski, Jeff W. Higdon.
Project administration: Sarah M. E. Fortune.
Resources: Andrew W. Trites, Mark F. Baumgartner, Steven H. Ferguson.
Software: Sarah M. E. Fortune.
Supervision: Sarah M. E. Fortune, Andrew W. Trites, Steven H. Ferguson.
Validation: Sarah M. E. Fortune, William R. Koski, Jeff W. Higdon.
Visualization: Sarah M. E. Fortune, Jeff W. Higdon.
Writing – original draft: Sarah M. E. Fortune, Steven H. Ferguson.
Writing – review & editing: Sarah M. E. Fortune, William R. Koski, Jeff W. Higdon, Andrew
W. Trites, Mark F. Baumgartner, Steven H. Ferguson.
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