Tag Archives: winter ice maximum

Chukchi/Bering Sea ringed seals doing better despite declines in ice and snow: new study

Ringed seal pup in snow cave

Previously, I highlighted new research results that showed, contrary to expectations, polar bears in the Chukchi Sea subpopulation are doing better – despite declines in extent of September sea ice – since the 1970s. So it might not come as much of a surprise to find that the same is true for the primary prey of polar bears in the Chukchi and Bering Seas, Arctic ringed seals (Phoca hispida hispida).

Surprisingly, less than 6 months after Arctic ringed seals were placed on the American list of “threatened” species (under the ESA, see previous post here), actual research in Alaska has shown that declines in sea ice have proven better for ringed seals, not worse.

At a presentation given at the Lowell Wakefield Fisheries Symposium in March (Anchorage, Alaska) [program and links to pdfs here] Justin Crawford, a biologist with the Alaska Department of Fish and Game (ADF&G) presented the results of ringed seal research conducted by himself and fellow ADF&G biologist Lori Quakenbush in the Chukchi and Bering Seas (posted online by the event organizers, see references below).

As for polar bears, the Crawford and Quakenbush presentation provides some very interesting details on the status of Chukchi and Bering Sea ringed seals over the last 40 years, and contains some mighty “inconvenient” conclusions that should raise some eyebrows.

I’ve summarized these details and conclusions below in point form, with a map.
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Not much has changed in polar bear country since the sea ice maximum

I’ve been busy with work-related activities lately and will be for several more weeks. Until then…

Sea ice changes since March 15 [Update added May 10, see below]

Lots of ice everywhere – even in Hudson Bay. A bit less ice in the Barents Sea (north of Norway) than there was two months ago at the sea ice maximum March 15 (see Fig. 1 below compared to the extent at May 5 in Fig. 2: both from NSIDC). But there is still quite a bit around Svalbard – that group of islands between NE Greenland and NW Norway (see Fig. 3 below a MASIE image, where this situation is more apparent).

Polar bears are eating and mating at this time of year (early May being the tail-end of the season in most areas) – and right now, they have a huge, circumpolar ice platform for those activities.

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Polar bear-sea ice relationships: what biologists knew in ’72

1972 – a bit over 40 years ago. Seven years before we had reliable sea ice extent data from satellites and the year before the international agreement was signed by Arctic nations to protect polar bears from overhunting.

In 1972, a bear biologist by the name of Jack Lentfer was working for the Alaska Department of Fish and Game, stationed at the Naval Arctic Research Lab in Barrow. Lentfer was one of the founding delegates of the Polar Bear Specialist Group, where he represented US interests until 1981.

In the proceedings of the 1972 PBSG meeting (Lentfer 1972a), Lentfer stated the following in his report to the group:

“Long term warming and cooling trends occur in the Arctic and probably affect polar bear distribution and numbers. Climatic trends should be considered when assessing bear distributions and population data on a long term basis.” [my bold]

Warming and cooling, not just warming.

He also had a paper published that year (Lentfer 1972b), entitled “Polar bear: Sea ice relationships.” Forty years on, I thought it was worth having a look at what Lentfer told his fellow polar bear biologist colleagues back then. Continue reading

Sea ice maximum reached March 15: what it means for polar bears

On Monday, March 25, the National Snow and Ice Data Center (NSIDC) announced that March 15 2013 was likely the maximum extent reached this winter. Note that just a few days ago, I discussed the relationship between maximum extent of sea ice and the global distribution of polar bears around the Arctic (see March 20th post here).

NSIDC says: “Arctic sea ice extent on March 15 was 15.13 million square kilometers (5.84 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole.”

NSIDC says: “Arctic sea ice extent on March 15 was 15.13 million square kilometers (5.84 million square miles). The orange line shows the 1979 to 2000 median extent for that day. The black cross indicates the geographic North Pole.” Click to enlarge.

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Polar bear distribution shows they are limited by winter ice extent

I’ve said it before but it’s worth saying again now that the sea ice in the Arctic is approaching its seasonal maximum extent and thickness: polar bears are limited by winter sea ice extent (Fig.1), not by the minimum extent of ice in the summer. Otherwise, their distribution would resemble the summer sea ice minimum (Fig. 2), not the winter maximum.

Despite the hue and cry about “declining sea ice,” polar bears are still as well distributed throughout their available winter habitat as they were in 1979, when detailed sea ice records began – see the map below. See further details on polar bear distribution here.

Figure 1. Polar bear distribution map (adapted from the one provided by the PBSG) compared to sea ice concentration at Feb 28 (at or near the seasonal maximum extent) 1979 and 2013. I can’t see a difference – can you see a difference? The only place there is consistently sea ice in winter but not polar bears is the Sea of Okhotsk, but there is no evidence that polar bears have ever lived there despite the presence of seals. Click to enlarge

Figure 1. Polar bear distribution map (adapted from the one provided by the PBSG) compared to sea ice concentration at Feb 28 (at or near the seasonal maximum extent) 1979 and 2013. I can’t see a difference – can you see a difference? The only place there is consistently sea ice in winter but not polar bears is the Sea of Okhotsk, but there is no evidence that polar bears have ever lived there despite the presence of seals. Click to enlarge

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Polar bears are distributed throughout their available habitat

All Arctic sea ice habitats that are currently suitable for polar bears have polar bears living in them 1 – even the southern-most regions of Hudson Bay that are well below the Arctic Circle (see previous post on polar bear numbers here).

Have a look at the maps below and see how well the current maximum extent of sea ice correlates with the present range of polar bears around the Arctic.

Fig. 1. Sea ice extent at April 25, 2012, from NSIDC (the winter maximum). Note that although there is sea ice in the Sea of Okhotsk (top right of the map), polar bears do not currently live there nor is there any evidence they ever did1.
Compare to the polar bear’s official range below.

Fig. 2. The global range of the polar bear, showing the 19 regional subpopulations. Map from Polar Bear Specialist Group (PBSG), with a few extra labels added.

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