Abstract
Harp seals (Pagophilus groenlandicus) have evolved life history strategies to exploit seasonal sea ice as a breeding platform. As such, individuals are prepared to deal with fluctuations in the quantity and quality of ice in their breeding areas. It remains unclear, however, how shifts in climate may affect seal populations. The present study assesses the effects of climate change on harp seals through three linked analyses. First, we tested the effects of short-term climate variability on young-of-the year harp seal mortality using a linear regression of sea ice cover in the Gulf of St. Lawrence against stranding rates of dead harp seals in the region during 1992 to 2010. A similar regression of stranding rates and North Atlantic Oscillation (NAO) index values was also conducted. These analyses revealed negative correlations between both ice cover and NAO conditions and seal mortality, indicating that lighter ice cover and lower NAO values result in higher mortality. A retrospective cross-correlation analysis of NAO conditions and sea ice cover from 1978 to 2011 revealed that NAO-related changes in sea ice may have contributed to the depletion of seals on the east coast of Canada during 1950 to 1972, and to their recovery during 1973 to 2000. This historical retrospective also reveals opposite links between neonatal mortality in harp seals in the Northeast Atlantic and NAO phase. Finally, an assessment of the long-term trends in sea ice cover in the breeding regions of harp seals across the entire North Atlantic during 1979 through 2011 using multiple linear regression models and mixed effects linear regression models revealed that sea ice cover in all harp seal breeding regions has been declining by as much as 6 percent per decade over the time series of available satellite data.
Highlights
We are currently witnessing significant changes in high latitude ecosystems, manifested most noticeably by rapid declines in the extent of summer ice, significant reductions in perennial ice cover, and declines in sea ice thickness in Arctic and Antarctic regions [1]
Study Region and Time Frame To illustrate the recent links between sea ice cover and seal mortality, we used stranding data for dead harp seal pups extracted from the US Northeastern Region stranding dataset covering marine mammal strandings in the Northeastern US from 1993 to 2010 [12,13]
Using the upper range of lengths (115 cm) and avoiding animals listed as sub-adults regardless of standard length, we identified a total of 693 YOY seals in the stranding database and extracted these records for linear regression modeling
Summary
We are currently witnessing significant changes in high latitude ecosystems, manifested most noticeably by rapid declines in the extent of summer ice, significant reductions in perennial ice cover, and declines in sea ice thickness in Arctic and Antarctic regions [1]. Rapid changes in temperature and ice conditions in Arctic ecosystems pose significant challenges for marine mammals that use sea ice as a platform for breeding and social activity (for reviews, see [4], [5] and [6]). Less attention has been paid to how changes in seasonal sea ice in adjacent sub-Arctic regions are changing over time. Few studies assess the extent to which ice conditions are changing at the spatial and temporal scales relevant to sub-Arctic pinnipeds that rely on seasonal ice during the critical breeding period
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