Demographic, ecological and physiological responses of ringed seals to an abrupt decline in sea ice availability

Abstract

To assess whether demographic declines of Arctic species at the southern limit of their range will be gradual or punctuated, we compared large-scale environmental patterns including sea ice dynamics to ringed seal (Pusa hispida ) reproduction, body condition, recruitment, and stress in Hudson Bay from 2003-2013. Aerial surveys suggested a gradual decline in seal density from 1995-2013, with the lowest density occurring in 2013. Body condition decreased and stress (cortisol) increased over time in relation to longer open waterperiods. The 2010 open water period in Hudson Bay coincided with extremes in large-scale atmospheric patterns (NAO, AO, ENSO) resulting in the earliest spring breakup and the latest ice formation on record. The warming event was coincident with the highest stress levels and the lowest recorded ovulation rate and low pregnancy rate, few pups in the Inuit harvest, and observations of sick seals. We conclude that although negative demographic responses of Hudson Bay seals are occurring gradually with diminishing sea ice, a recent episodic environmental event played a significant role in a punctuated population decline.

Comparing temporal patterns in body condition of ringed seals living within their core geographic range with those living at the edge

“…In addition, we would hypothesize that the core population would display more density‐dependent responses to environmental change in contrast to more dramatic density fluctuations in the peripheral population representing density independent or extreme responses to environmental fluctuations. Data is not currently available for the core region but our hypothesis fits the description of density responses found in the peripheral Hudson Bay population (Ferguson et al ).…”

“…The proximate explanation for variability in body condition would be food availability. Although the assumption of highly seasonal food resources has been made for the Hudson Bay region (Parks et al , Mallory et al , Ferguson et al ) the casual linkages have not been thoroughly explored. For example, few forage fish abundance estimates exist for either region (Hoover ), largely because the fisheries have been deemed economically inviable.…”

“…Spring breakup and its associated measurements (duration of open water and timing of autumn freeze‐up) have been consistently reported as key environmental drivers for ringed seal demography (Stirling et al , Ferguson et al ). We used archived weekly sea‐ice data from the Canadian Ice Services (<http://iceweb1.cis.ec.gc.ca/archive>) to calculate sea‐ice breakup date as the day when total ice concentration for the regions (Canadian Eastern Arctic for core habitat and Hudson Bay for peripheral habitat) decreased and remained below 50%.…”

“…Spring breakup and its associated measurements (duration of open water and timing of autumn freeze-up) have been consistently reported as key environmental drivers for ringed seal demography (Stirling et al 2008, Ferguson et al 2017. We used archived weekly sea-ice data from the Canadian Ice Figure 1.…”

“…We compared ringed seals in two habitat regions, a core region from Pangnirtung to Grise Fiord, Nunavut in northern Canada where some of the largest ringed seals have been harvested, and a southern peripheral population located in the Hudson Bay region characterized by smaller seals (Ferguson et al 2018). Seals at the southern limit of their distribution in Hudson Bay have also shown dramatic fluctuations in numbers over 25 yr (Young et al 2015, Ferguson et al 2017. In contrast, less is known about the more northerly core ringed seal habitat region.…”