ARCTIC VOL. 57, NO. 1 (MARCH 2004) P. 59–67 Implications of Warm Temperatures and an Unusual Rain Event for the Survival of Ringed Seals on the Coast of Southeastern Baffin Island IAN STIRLING1 and THOMAS G. SMITH2 (Received 31 January 2003; accepted in revised form 16 July 2003) ABSTRACT. We recorded an unusually warm period in early April 1979 along the coastline at the end of the Hall Peninsula on southeastern Baffin Island, Nunavut. Maximum temperatures remained at or above freezing for almost a week, and rain fell on our field camp on three consecutive days. In contrast, meteorological data collected from three nearby coastal stations (Brevoort Island, Cape Dyer, and Resolution Island) between 1950 and 1992 indicated that the mean minimum and maximum air temperatures for the month of April are normally10–20˚C cooler than the averages we recorded at our camp. Periodic warming to near freezing, probably due to the maritime influence of nearby open water in Davis Strait, occurs in this area in late March and early April, but not usually to the degree we observed. Between 1950 and 1992, additional similar rain events were recorded only twice at the coastal weather stations. In late March, we found slumped roofs over some ringed seal (Phoca hispida) birth lairs and others that had collapsed, probably because of four days of weather only slightly below freezing and heat generated by seals within the lairs. After the rain in April, we found subnivean lairs with melted roofs, and several snowdrifts that had previously contained lairs were completely washed away. Newborn pups were left lying on the bare ice, subject to thermoregulatory stress and vulnerable to significantly increased predation by polar bears (Ursus maritimus) and arctic foxes (Alopex lagopus). If the climate continues to warm in the Arctic, as is predicted, it is likely that rain will be more widespread during early spring. If that occurs, the premature removal of protection offered by subnivean birth lairs may expose young ringed seal pups to high levels of predation, which may negatively affect populations of ringed seals and the polar bears that depend on them for food. Key words: ringed seal, Phoca hispida, predation, birth lairs, climate change, polar bear, Ursus maritimus RÉSUMÉ. Au début d’avril 1979, on a enregistré une période anormalement tempérée le long du littoral aux confins de la péninsule Hall dans le sud-est de l’île Baffin, au Nunavut. Les températures maximales sont restées au niveau du point de congélation ou au- dessus pendant presque une semaine, et il a plu sur notre campement trois jours de suite. À titre de comparaison, les données météorologiques recueillies entre 1950 et 1992 à trois stations côtières situées à proximité immédiate (Brevoort Island, Cape Dyer et Resolution Island) indiquent que la moyenne des températures minimales et maximales de l’air pour le mois d’avril est normalement de 10 à 20 ˚C plus froide que celle enregistrée à notre campement. Fin mars et début avril, il se produit dans la région un réchauffement périodique se rapprochant du point de congélation, dû probablement à l’influence maritime des eaux libres toutes proches du détroit de Davis, mais pas en général au niveau que nous avons observé. Entre 1950 et 1992, on n’a remarqué que deux fois d’autres épisodes pluvieux similaires aux stations météorologiques côtières. À la fin mars, on a trouvé des toits de tanières de mise bas de phoques annelés (Phoca hispida) affaissés et d’autres effondrés, probablement en raison de la température qui était restée juste au-dessous du point de congélation pendant quatre jours et de la chaleur dégagée par les phoques à l’intérieur des tanières. Après la pluie en avril, on a trouvé des tanières subnivales dont le toit avait fondu, et plusieurs amoncellements de neige qui abritaient auparavant des tanières avaient été complètement emportés. Les phoques nouveau-nés gisaient sur la glace vive, sujets au stress lié à la thermorégulation et exposés à une prédation beaucoup plus grande de la part des ours polaires (Ursus maritimus) et des renards arctiques (Alopex lagopus). Si, comme on le prédit, le climat continue de se réchauffer dans l’Arctique, la pluie sera vraisemblablement plus généralisée au début du printemps. Si c’est le cas, le retrait prématuré de la protection fournie par les abris subnivaux pourrait exposer les petits phoques à de hauts niveaux de prédation, affectant ainsi de façon négative les populations de phoques annelés, et donc celles des ours polaires qui en dépendent pour se nourrir. Mots clés: phoque annelé, Phoca hispida, prédation, tanières de mise bas, changement climatique, ours polaire, Ursus maritimus Traduit pour la revue Arctic par Nésida Loyer. INTRODUCTION polar bear (Ursus maritimus). A primary adaptation of the ringed seal for survival in the landfast ice, where seals are The circumpolar ringed seal (Phoca hispida) is the small- highly vulnerable to predation by terrestrial carnivores, is est of the Arctic seals and the main prey species of the its small body size. This allows the seals to dig subnivean 1 Canadian Wildlife Service, 5320 122 St., Edmonton, Alberta T6H 3S5, Canada; [email protected] 2 E.M.C. Eco Marine Corporation and Drakeheath Kennels, 5694 Camp Comfort Road, Beaulac-Garthby, Québec G0Y 1B0, Canada © The Arctic Institute of North America 60 • I. STIRLING and T.G. SMITH lairs in snowdrifts over their breathing holes and remain (1960–75; 1989–92), Resolution Island (1950–61), Iqaluit hidden when they haul out to rest in cold weather and to (1950–99), and Cape Dyer (1960–90) (Environment give birth to altricial pups in spring (McLaren, 1958; Canada, unpubl. data). Resolution Island and Cape Dyer Smith and Stirling, 1975; Stirling, 1977; Smith et al., are approximately 200 km SW and 350 km NE, respec- 1991). The lanugo with which the pups are born, once dry, tively, of Brevoort Island (Fig. 1). From this database, we would probably provide adequate insulation for the pup to extracted mean minimum and maximum temperatures for survive birth on exposed sea ice if there were no predators the months of March and April, as well as days on which (Smith et al., 1991). However, because of the constant there were both trace (defined by Environment Canada as threat of predators, female ringed seals maintain access to less than 2 mm) and measurable amounts of rain, to a complex of subnivean haul-out lairs and forcibly take compare with our observations from Winton Bay. their pups underwater to escape predators until the young We were particularly interested in the frequency of can move independently to an alternative lair. When the occurrence of periods of several days with unseasonably lanugo of the pup is wet, the insulation of the subnivean warm weather, as well as of rain, because of their possible birth lair is critical to its survival during cold weather negative effects on the stability of ringed seal birth lairs (Taugbøl, 1984). In this paper, we describe how periods of when pups are young and not yet entering the water warm weather, aggravated by a heavy rain event, caused voluntarily. We thought that single days of above-freezing slumping and collapse of subnivean lairs, washed away weather, or rain, were less likely to have a significant snowdrifts containing subnivean birth lairs, and increased effect than several continuous days of such conditions. the exposure of young ringed seal pups on the sea ice, Thus, we defined a “warming event” as a period of three or where they were vulnerable to high levels of predation. We more consecutive days on which the maximum tempera- also discuss the potential significance of these observa- ture reached 0˚C or greater, with no rain recorded. A “rain tions in the context of climatic warming. event” was defined as a period of three or more consecu- tive days during which rain was recorded, with measurable precipitation that exceeded trace amounts on at least one METHODS day. Field Methods RESULTS In late March and most of April 1979, we were conduct- ing ecological research on ringed seals and polar bears in Weather Conditions during the Study the large bays along the end of the Hall Peninsula on southeastern Baffin Island, Nunavut (Fig. 1), using previ- We measured maximum and minimum temperatures ously described methods (Smith et al., 1979; Smith and and kept records of precipitation at the Winton Bay field Hammill, 1980, 1981; Stirling et al., 1980). To document camp from 17 March to 24 April 1979 (Table 1). For most the distribution and density of ringed seals’ subnivean of the time before 8 April, temperatures remained below haul-out and birth lairs, we traveled by snow machine and freezing, although there was a period of about four days, used a trained dog to locate lairs beneath snowdrifts by beginning on 21 March, when the maximum temperatures smell (Smith and Stirling, 1975). Predation on seals by were near freezing and reached +3˚C on one day (22 polar bears and other carnivores was documented both March). Beginning on 9 April and continuing for almost a during our travel on the ice in search of subnivean lairs and week, the maximum temperature reached or exceeded from a helicopter while searching for polar bears (Smith, freezing during the day (Table 1). Rain fell at the field 1976, 1980; Stirling and Archibald, 1977; Hammill and camp all day on 9 April, and continued until midday on 10 Smith, 1991). April and in light sporadic periods through 11 April. From 12 April through 24 April, when we ended the surveys in Weather Data the study area, we experienced clear days free of precipi- tation, with maximum temperatures above or only slightly From 17 March to 24 April, we used a standard maxi- below freezing (Table 1).