Polar bear habitat in late autumn 2020 in comparison with some earlier years

0
16

Reposted by Polar Bear Science

Published on December 22nd, 2020 |

It is time to check out the sea ice habitat on December 15 (Julian Day 350) as virtually all bears except pregnant women in the entire Arctic are either out on the sea ice looking for seals or fighting the dark squat.

As usual at this time of year, the Canadian Archipelago, Beaufort, East Siberian and Laptev Seas are well covered in ice (see regions on the map below). Incidentally, despite the statements of a polar bear specialist, there is no evidence that a slower freezing of the falls in the other peripheral seas of the Arctic has a negative impact on the health or survival of the polar bears.

In fact, due to the attractiveness of the ice edge to seals in the fall, as I discussed last month, the longer the ice edge lasts in the fall, the more successful polar bears are at hunting seals – with the exception of those above the Arctic Circle where a lack of daylight from early November can lead polar bears to crouch and rest instead of trying to chase through the darkness. But we will never know for sure, as bears have never been studied at this time of year – experts simply make assumptions about what is happening (e.g., Stirling and Oritsland 1995).

The thickness of the sea ice also varies from year to year during the season, but it does not matter much for polar bears, who are most successful in their first year hunting ice less than 2m thick, which includes all regions currently in the ice thickness table below are purple.

HUDSON BAY

This year there was more ice than usual in the central and southern Hudson Bay (below) in mid-December and a little less than usual in the eastern part.

However, the ice is now forming so rapidly that by December 18, there was hardly any open water left over Hudson Bay and the ice in the north solidified (below). Recall that a similar freezing pattern stranded a pod from about a dozen killer whales in mid-January 2013 and killed four more in 2016. Such an ice inclusion suggests that despite a warming Arctic, freezing patterns would have to change very dramatically to make Hudson Bay an attractive location for killer whales. A recent DFO report concluded:

Killer whale ice inclusions are almost always fatal and can wipe out entire family groups, with long-lasting demographic effects. Ice inclusions could therefore slow the expansion of the Arctic killer whale range, especially in areas where killer whales unfamiliar with sea ice patterns cannot escape before winter ice formation.

Compare the weekly development charts for Hudson Bay (below) for this year through 2014 from the Canadian Ice Service archives. You will see that this year seems to have more ice in the first year (light green, about 30-70 cm) than any other year (although last year had almost as much) and that 2016 was a very late frost-on year :

The Western Hudson Bay polar bears with collars or markings deployed by Andrew Derocher and his University of Alberta crew (below) are scattered across the bay's ice (two on land are females), some on the thickest Ice in the north but others are on thinner ice in the south and east:

BAFFIN BAY, FOXE BASIN AND DAVIS STRAIT

According to CIS maps, the ice cover in the Canadian East Arctic in mid-December is average this year – only a little red and pink mean "below normal" in the east (off Greenland):

Pack ice has moved from the north through Baffin Bay into Davis Strait (below) and will soon be off the coast of Labrador, which has slightly less ice in mid-December than usual this year:

The ice off Labrador at this point is near-shore ice that develops and thickens on the spot (see below). As far as we know, polar bears are few and far between on the north coast of Labrador in the summer, so this late ice development is unlikely to affect local bears. However, pack ice will move down in January and February until it engulfs the area north of Newfoundland and brings in some polar bears.

GREENLAND AND BARENT SEA

Freezing in the Greenland Sea has been progressing slightly faster than usual over the past five years (see below), but not noteworthy:

The ice cover in the Barents Sea (below) has been slow so far, but has developed faster in recent weeks. There is now ice off the east coast of Novaya Zemlya, an offshore ice that should allow any summer bears there to search for seals, just as bears from western Hudson Bay do during the early freezing phases. Over the next few weeks, the Arctic pack ice will move south into the Kara Sea, allowing the bears to move more freely. As has been the case for years, the ice off Spitsbergen is well below normal (below), which is why practically all pregnant women in the Barents Sea are currently maternity wards in Franz Josef Land or on the sea ice in the north. These alternative areas for safe birth are the main reason that the greatly reduced sea ice around Svalbard has not adversely affected the health or survival of polar bears in the Barents Sea in recent years.

KARA SEA

Ice cover in the Kara Sea on December 15 (below) is lower compared to the last five years, but it is unclear how much this will affect local polar bears.

Animals who chose to spend the ice-free season on Novaya Zemlya or mainland Russia waited a long time for ice, but those who spent the summer in the Severnya Zemlya archipelago in the east had access to before the end Sea ice from November. Belushaya Guba did not say whether the polar bear problems they had due to poorly maintained garbage dumps in December 2018 and which lasted until February 2019 have recurred this year.

Despite claims by Andrew Derocher (below), there is no evidence that a little less sea ice in the fall affects polar bears' health or survival in the Kara Sea or anywhere else. It is possible that this is the case, but no one has investigated. Therefore, it is very misleading to claim that low sea ice cover is "trouble" for polar bears at this time of year.

High temperatures => low sea ice cover & problems for polar bears. Little is known about the Kara Sea polar bears, but we have many studies showing the negative effects of warming on polar bears in other areas. The problems all start with decreasing sea ice. pic.twitter.com/qlFilxrtHm

– Andrew Derocher (@AEDerocher) December 14, 2020

CHUKCHI / BERING SEA

The sea ice cover over the Chukchi Sea is slightly lower than in recent years, roughly as low as in 2017 (below).

The polar bears of the Chukchi Sea on December 14 (below) had plenty of habitat for sea ice.

In 2016, when the Chukchi polar bears were first counted, there was a similar amount of ice at that time of year (see below):

REFERENCES

Stirling, I. and Øritsland, N.A. 1995. Relationships between estimates of ringed seal (Phoca hispida) and polar bear (Ursus maritimus) populations in the Canadian Arctic. Canadian Journal of Fisheries and Water Sciences 52: 2594 – 2612. http://www.nrcresearchpress.com/doi/abs/10.1139/f95-849#.VNep0y5v_gU

Like this:

To like Loading…