Abstract Bowhead whales (Balaena mysticetus) have a nearly circumpolar distribution, and occasionally occupy warmer shallow coastal areas during summertime that may facilitate molting. 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.

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: 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) 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.

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 experience pronounced changes in environmental conditions by seasonally occupying uncharacteristically warmer areas such as estuaries and fiords [11]. 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 conditions found in seasonally occupied estuaries [11,13]. The elevated water temperatures are postulated 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 features of estuaries such as gravel bottoms provide an abrasive surface to rub against and expedite 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 structure 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 preliminary 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. PPT PowerPoint slide

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larger image TIFF original image Download: 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 ↆ) 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. https://doi.org/10.1371/journal.pone.0186156.g001 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 preserved 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 Phantom 3 Professional. The sUAS was equipped with a global positioning system (GPS) and altimeter 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 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 identified 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 photographed 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) proportion 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 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. PPT PowerPoint slide

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larger image TIFF original image Download: 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). https://doi.org/10.1371/journal.pone.0186156.g002 PPT PowerPoint slide

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larger image TIFF original image Download: 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. https://doi.org/10.1371/journal.pone.0186156.g003 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 corrected using Seabird software and temperature and salinity plots were generated using the downcast data for each cast (n = 86).

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 evidence 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 surface 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 observations 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 subsequently engaged in rubbing behavior (Fig 6). https://doi.org/10.1371/journal.pone.0186156.s001 (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 = covered) and whether the mouth was closed (e.g., 0), slightly open (1), wide open (2), or indeterminable (9). https://doi.org/10.1371/journal.pone.0186156.s002 (XLSX) S1 Image. Example of a bowhead whale with mouth slightly agape near Brown Harbour during August 2016. https://doi.org/10.1371/journal.pone.0186156.s003 (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 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.