Towards a Better Understanding of the Effects of UV on Atlantic Walruses, Odobenus rosmarus rosmarus: A Study Combining Histological Data with Local Ecological Knowledge

Abstract

Walruses, Odobenus rosmarus, play a key role in the Arctic ecosystem, including northern Indigenous communities, which are reliant upon walruses for aspects of their diet and culture. However, walruses face varied environmental threats including rising sea-water temperatures and decreasing ice cover. An underappreciated threat may be the large amount of solar ultraviolet radiation (UV) that continues to reach the Arctic as a result of ozone loss. UV has been shown to negatively affect whales. Like whales, walrus skin is unprotected by fur, but in contrast, walruses spend long periods of time hauled-out on land. In this study, we combined the results of histological analyses of skin sections from five Atlantic walruses, Odobenus rosmarus rosmarus, collected in Nunavik (Northern Quebec, Canada) with qualitative data obtained through the interviews of 33 local walrus hunters and Inuit Elders. Histological analyses allowed us to explore UV-induced cellular lesions and interviews with experienced walrus hunters and Elders helped us to study the incidences and temporal changes of UV-induced gross lesions in walruses. At the microscopic scale, we detected a range of skin abnormalities consistent with UV damage. However, currently such UV effects do not seem to be widely observed at the whole-animal level (i.e., absence of skin blistering, erythema, eye cataract) by individuals interviewed. Although walruses may experience skin damage under normal everyday UV exposure, the long-term data from local walrus hunters and Inuit Elders did not report a relation between the increased sun radiation secondary to ozone loss and walrus health.

Fig 1. Map of Nunavik (Northern Quebec, Canada), showing the four communities involved in the project (Inukjuak, Ivujivik, Quaqtaq and Kangiqsualujjuaq).

The quadrat show the limits of the base maps used to gather spatial data of walruses during the interviews (e.g., where walruses have been observed). Base maps in both English and Inuktitut of the areas surrounding participating communities were created using the geographic information system software ArcMap 10.1 (Digital vector datasets: RNCan-National Topographic Database). The scale of the maps, varied between 1:100,000 and 1:450,000 depending on the extent of walrus hunting areas provided by the local Hunters Fishers and Trappers Association during our first visit. A large scale, regional map (scale: 1:2,000,000) was also created. The mapping process of the interviews followed guidelines previously described [38]. The red areas correspond to the areas where walruses were reported by participants. The five walruses sampled in the study were hunted in the red area around Quaqtaq (latitude between 60.3975°N and 61.0775°N, longitude between 69.6339°W and 68.1703°W).

Fig 2. Sections of the dorsal skin of three walruses stained with H&E (microscope magnification X40; b & d correspond to the same walrus).

a) The different layers of walrus’ skin. b) Examples of cells showing cytoplasmic vacuolation (indicated by arrows). c) An example of a sunburn cell (note the shrunken nucleus indicated by the arrow). d) An example of a microvesicle and intracellular edema (indicated by arrows). Walruses’ skin samples were collected during the Inuit subsistence walrus hunt near Quaqtaq in July 2013 and 2014.

Fig 3. Presence of cellular lesions observed in the samples obtained from the dorsal region of the walruses (dark grey bars; total number of dorsal samples = 5) and the samples obtained from the ventral region of the walruses (light grey bars; total number of ventral samples = 4).

The binary response data used for microvesicles were: zero = absence; one = presence, and for sunburn cells, cytoplasmic vacuolation and intracellular edema: zero = absent or low levels, and one = high levels and widely distributed. Raw data are available in S1 Table. Percentages are provided on the bars. Bars ± SE.

Fig 4. Walrus skin pigmentation.

a) Walrus’ dorsal skin sections showing the presence of melanin in the epidermis. Melanin is produced in the melanocytes, which become dendritic to distribute the melanin to the neighbor epidermis cells called keratinocytes. b) Prevalence of melanin and dendritic melanocytes observed in the samples obtained from the dorsal region of the walruses (dark grey bars; total number of dorsal samples = 5) and ventral samples (light grey bars; total number of ventral samples = 4). The binary response data used for melanin and dendritic melanocytes were: zero = absence; one = presence. Prevalence is provided on the bars. Bars +/- SE. Raw data are available in S1 Table. c) and d) Skin samples of around 1cm³ obtained from the dorsal (c) and ventral (d) regions of the walrus body. The photographs show the highly pigmented skin (dark color) of the dorsal sample compared with the less pigmented skin of the ventral sample (light color).