Abstract
The harbour seal population in Svalbard occurs at the northernmost limit of the species' range. It experiences environmental extremes far beyond the norm for this species, including an extended period of polar night and extensive sea ice cover. In 2009 and 2010, 60 harbour seals (30 pups + 30 immature/mature seals) from this population were equipped with Satellite-Relay Data Loggers (SRDLs) to study their haul-out behaviour, with a special focus on the winter period. Using a combination of Generalized Additive Mixed Models and Cox Proportional Hazard models, the influences of sex, maturity, temporal, spatial and environmental factors on haul-out behaviour were explored. All of the seals continued to haul out even through the coldest periods during the polar night, though clear seasonality in the time spent hauled out daily was displayed by both immature and mature seals. Time spent hauled out daily decreased from ∼5.2 hrs in September to ∼1.2 hrs in February in these age groups, while pups displayed less seasonality (∼2.4 hrs/day throughout most of the year). The average at-sea period also exhibited seasonality, increasing to a maximum of ∼1.6 days in February (monthly maxima for individual animals ranged from 7 to 19 days). The seals showed a strong preference to haul out at low tide when hauling out on land but not when using sea ice as a haul-out platform. A diel rhythm in haul-out behaviour was present during the months with day–night cycling and midnight sun but not during the polar night. Haul-out behaviour was impacted to a greater extent by air pressure, through its effect on wind speed, than by absolute temperature values. The extreme environment in Svalbard likely causes some physiological challenges that might impact survival rates negatively, particularly among pups. Climate warming is likely to have positive effects on Svalbard's harbour seal population.
Highlights
IntroductionA strong dichotomy exists in the life history of all pinniped (true seals, fur seals, sea lions and walrus) species, with marine foraging dominating many aspects of their lives, though they remain tied to solid substrates (land or ice) for birthing and nursing their young [1,2]
A strong dichotomy exists in the life history of all pinniped species, with marine foraging dominating many aspects of their lives, though they remain tied to solid substrates for birthing and nursing their young [1,2]
The goals of this study were: 1) to quantify haul-out behaviour throughout the year; 2) to explore the potential use of ice as a haul-out platform; 3) to compare the winter haul-out behaviour of seals in Svalbard to temperate populations in order to explore whether arctic winter conditions might serve as a long-term stressor that currently limits longevity and survivorship in this population and; 4) to relate the behaviour of Svalbard’s harbour seals to the extreme environmental conditions experienced by this ‘‘temperate seal’’ in its northernmost population in order to explore the extent of their behavioural plasticity and likely responses to climate change
Summary
A strong dichotomy exists in the life history of all pinniped (true seals, fur seals, sea lions and walrus) species, with marine foraging dominating many aspects of their lives, though they remain tied to solid substrates (land or ice) for birthing and nursing their young [1,2]. Many pinnipeds mate on land and most prefer to be on a solid substrate when they undergo their annual moult (when seals replace their hair and several layers of skin) [2,3,4]. Outside the breeding and moulting periods, some pinnipeds, such as hooded seals (Cystophora cristata) and Ross seals (Ommatophoca rossii), undertake long migrations and remain pelagic for months at a time without hauling out to rest on ice or land [5,6]. Hauling out of the water has clear thermoregulatory advantages under the right (warm, calm weather) environmental conditions [2], and during the annual moulting period being in the air allows seals to circulate blood to their skin without undue heat loss to the water, which permits fast and energetically efficient hair re-growth [9,10]. Hauling out in groups that share predator vigilance provides advantages to pinnipeds in terms of the opportunity to rest more deeply while minimizing predation risk [2,12]
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