Tag Archives: Arctic Circle

Southern Hudson Bay subpopulation status, farthest south of all polar bears

“The Arctic” is a bit hard to define. While the Arctic Circle works as a good boundary for some purposes and the 100C isotherm for July for others, neither work for polar bears because several subpopulations live well south of these limits (Fig. 1).

In the east, Western Hudson Bay, Southern Hudson Bay and Davis Strait are all located well south of the Arctic Circle and the first two (and half of Davis Strait) are beyond the 100C July isotherm as well. In the western Arctic, the Chukchi Sea subpopulation is within the 100C July isotherm but at least half of its bears reside south of the Arctic Circle (Fig. 1) in the Bering Sea (see previous post here).

Unique amongst all of these is Southern Hudson Bay – all of its polar bears make maternity dens and/or spend the summer south of 600N.

Southern Hudson Bay (SH) bears live in the Canadian provinces of Ontario, while Western Hudson Bay (WH) bears reside in Manitoba and Nunavut. The two groups mix over the winter but appear to spend the summer/fall in their respective regions (Stirling et al. 2004). [See previous posts on Western Hudson Bay bears here, here, and here]

“Further south” in the Arctic usually means warmer, with open water present more weeks every summer, sea ice for fewer weeks over the winter. So, shouldn’t the bears of Southern Hudson Bay be already suffering more harm from global warming than virtually all other subpopulations, including those in Western Hudson Bay?

After all, Western Hudson Bay bears appear to have experienced a statistically significant decline in numbers, among other effects (Regehr et al. 2007; Stirling and Derocher 2012) — surely Southern Hudson Bay bears are doing worse?

You’d think so, but they aren’t.

Figure 1. Boundary limits for “the Arctic” (top map) such as the Arctic Circle (dashed line) or the 100C isotherm for July (solid red line) would not include several polar bear subpopulations that live south of these.

Figure 1. Boundary limits for “the Arctic” (top map) such as the Arctic Circle (dashed line) or the 100C isotherm for July (solid red line) would not include several polar bear subpopulations that live south of these.

UPDATED October 28, 2014: Reference added, Obbard et al. 2013 (aerial survey results).
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Polar bears in winter: insights from modern research and Inuit hunters

In a previous post (“Polar bears in winter: insights from Behouden Huys, 1596-1597”) I discussed the chronicle of Gerrit De Veer, who documented polar bear activity during the winter that William Barents’ crew spent on northern Novaya Zemlya more than 400 years ago. De Veer noted that the crew did not see or hear polar bears during the time that the sun was below the horizon, a period that did not correlate with the period of most intense storms and cold (De Veer 1609). However, the bears were active (and often causing trouble!) before and after that time.

De Veer’s account suggests the possibility that polar bears spend the darkest part of the winter curled up in a sheltered spot regardless of whether this is the coldest or stormiest period or not.

However, the experience of Barents and his men occurred over a single season and may not be representative of polar bear winter activity in general. As promised, in this post I’ll discuss the evidence collected by polar bear biologists and Inuit hunters relevant to the question of what polar bears do during the cold and dark of an Arctic winter.

 Figure 1. Effective advertising and amusing though it may be, one thing about this image is actually true – during the winter, while the sun does not rise above the horizon, the moon is visible on its usual cycle. Moonlight and northern lights (aurora borealis) are the only sources of natural light except for a few hours of dusk at mid-day. See other images here, here and here.


Figure 1. Effective advertising and amusing though it may be, this image also depicts a true Arctic phenomenon – during the winter above the Arctic Circle, when the sun does not rise above the horizon, the moon is visible on its usual cycle. Moonlight and northern lights (aurora borealis) – plus a few hours of dusk at mid-day – provide relief from total darkness. See other images of an Arctic moon and northern lights here, here and here.

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