Tag Archives: feeding

Breakup of sea ice on track in Canada as critical feeding period for polar bears ends

Relative to recent years and potential impacts on polar bear health and survival in Canada, there is nothing alarming in the pattern or speed of sea ice breakup for 2017, either over Hudson Bay, the southern Beaufort, or the eastern high Arctic.

Sea ice Canada 2017 June 8

Last year at this time (see map below), there was more open water in Hudson Bay and in the Southern Beaufort yet the polar bears came ashore in fine shape that summer and there was no hue-and-cry of dying bears anywhere. Breakup this year is on track to be about 3 weeks earlier than it was in the 1980s, as it has been since at least 2001, a conclusion reached by polar bear specialists (Castro de la Guardia et al. 2017; Lunn et al. 2016), who examined sea ice breakup to 2015.

Sea ice extent Canada 2016 June 8 CIS

Here are critical words to remember (more details here) from biologist Martin Obbard and colleagues (2016:29) on the relationship between body condition and sea ice for Southern Hudson Bay (SH) polar bears, which apply equally well to bears in other regions:

Date of freeze-up had a stronger influence on subsequent body condition than date of break-up in our study. Though models with date of freeze-up were supported over models with other ice covariates, we acknowledge that lower variability in freeze-up dates than in ice duration or break-up dates could have influenced the model selection process. Nevertheless, we suggest that a stronger effect of date of freeze-up may be because even though break-up has advanced by up to 3-4 weeks in portions of Hudson Bay it still occurs no earlier than late June or early July so does not yet interfere with opportunities to feed on neonate ringed seal pups that are born in March-April in eastern Hudson Bay (Chambellant 2010). Therefore, losing days or weeks of hunting opportunities during June and July deprives polar bears of the opportunity to feed on adult seals, but does not deprive them of the critical spring period (Watts and Hansen 1987) when they are truly hyperphagic. No doubt, the loss of hunting opportunities to kill adult seals has a negative effect on body condition, but it appears that for bears in SH a forced extension of the fast in late fall has a greater negative effect on subsequent body condition.” [my bold]

In other words, by mid-June at least (maybe earlier), polar bears have largely finished their intensive feeding that’s so critical to their survival over the rest of the year.

That’s why the latest count of SH polar bears (Obbard et al. 2015) showed a stable population (and see this recent post on WHB polar population estimates). But freeze-up was late last year and that’s what will make the difference to polar bears over the coming year.

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Svalbard polar bears thrive in part due to ringed seal pups in the spring pack ice

Few people know that Arctic ringed seals (Phoca hispida, aka Pusa hispida) give birth and breed in the offshore pack ice in the spring, as it is seldom mentioned by either seal or polar bear specialists.

While it is true that some ringed seals give birth in stable shorefast ice close to shore, many others give birth well offshore in thick pack ice – where polar bears also live and hunt in the spring but where few Arctic scientists ever venture – and the existence of pack ice breeding ringed seals is one of the reasons that polar bears are such a resilient species.

ringed-seal-in-snow-cave_b-kelly-wikipedia

Ringed seal pup in a snow cave, B. Kelly photo (Wikipedia).

As a consequence, despite fears expressed by Ian Stirling, low shorefast ice and associated snow around Svalbard this winter (and any time in the past) is not necessarily a hindrance to polar bear survival because there are ringed seal pups available out in the surrounding pack ice – where bearded seals also give birth.

Of course, ringed seals pups are also available to Svalbard polar bears in the shorefast ice in the Franz Josef Land archipelago to the east (see map below) but it is the pups born in the offshore pack ice that are of interest here. The existence of pack ice breeding ringed seals may be why Norwegian biologists do not currently monitor ringed seals in the Barents Sea, despite many years of poor ice conditions around Svalbard in spring – this simply is not a species of concern.

barents-sea-ice-2017-feb-6_nis

The fact that distinct ringed seal ecotypes (or habitat-specific morphotypes) exist in the Arctic – one that gives birth and breeds in shorefast ice and another that gives birth and breeds in offshore pack ice, perhaps driven by competition for limited shorefast ice habitat – is a phenomenon a colleague and I discussed in a peer-reviewed book chapter published several years ago. Have a look at the excerpt below and see what you think.

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Polar bear habitat this fall shaping up fast – more like 2010 than 2007

Arctic sea ice tied 2007 for extent at the September minimum less than 3 weeks ago but with the refreeze proceeding much faster than 2007, seals will soon be returning to the ice edge and polar bears will be back to feeding like they did in 2010.

sea-ice-at-28-sept_2016_vs-2007_2012_5-point-0_nsidc-interactive

Sea ice extent less than 5.0 mkm2 lasted less than 6 weeks (23 August – 28 September), according to NSIDC.

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The polar bear problem no one will talk about – the downside to large populations

A large polar bear population with lots of adult males – due to bans on hunting – means more survival pressure on young bears, especially young males. To blame more problems with young male bears on lack of sea ice due to global warming ignores the downside to the reality Norway asked for when it banned hunting more than 40 years ago.

More hungry young males coming ashore looking for food is one of the potential consequences of living with a large, healthy population of polar bears. Biologist Ian Stirling warned of such problems back in 1974.

UPDATE: added below 6 Oct. 2016, statistics of defense of life shootings of polar bears in Svalbard since 1973.

svalbard-more-visitors-more-bears-shot_28-sept-2016-yahoo

Svalbard area polar bear numbers have increased 42% since 2004 and more hungry young polar bears almost certainly mean more polar bear problems, as folks in Svalbard (see map and quotes below) have experienced this year.
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Add human graves to the list of things that attract polar bears to communities

A report last week that a polar bear dug a human cadaver out of a coffin buried in the cemetery on the west coast of Hudson Bay did not get the media attention it perhaps deserved: it takes the term ‘grisly’ to a new level.

Early arrival of polar bears at Nunavut hamlet prompts early monitoring: One bear digs into burial plot at Arviat cemetery (NunatsiaqOnline, 29 August 2016).

mother-and-cub-on-beach_Stirling

Quotes from the story, a map, and comments on problem bears below.
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Tracking polar bears in the Beaufort Sea – all bears on the ice in June

The recent open water in the Southern Beaufort didn’t seem to change what polar bears were doing – bears tracked by USGS show them on the ice, likely trying to hunt. More ice edge means more hunting habitat at this time of year.

Beaufort tracking USGS bear-movements-June 2016 lg closeup

However, few hunts are likely successful at this time of year – because only older seals are on the ice and the broken ice makes escape so much easier for the seals (see previous post here). Fat bears on shore this summer (like the ones seen at Kaktovik in September) will tell us that they got enough to eat earlier in the season. Note that bears in good condition that appear at the whaling bone piles in September are there by choice (not stranding) and they got fat by feeding in the spring (March-May), not by picking at leftover whale scraps. Calories from terrestrial sources (for most bears) just reduce the amount of weight they lose over the summer.

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More polar bear habitat in Hudson Bay region at mid-May than in 2006 & 2011

What a difference a bit of historical perspective can make to one’s attitude on the annual Arctic sea ice breakup.

masie_all_r10_v01_2016137_4km

The usual recent pattern (since 1979) has been for breakup to begin on the east side. However, this year and last (below), it has begun in the NW (as it did in 1990 and a few other years).

Not all of the open water is due to melt, of course. As I discussed last week in relation to the Southern Beaufort Sea, winds and prevailing currents at this time of year start to fracture the ice and move it around well before much significant melt has begun.

Compare 2016 (above) to 2006 (below), when there was 0.1 mkm2 less overall – with much less ice in Hudson Strait and in the east of Hudson Bay than this year:
masie_all_r10_v01_2006136_4km

Compare to 2011, when there was also 0.1 mkm2 less overall than this year:
masie_all_r10_v01_2011136_4km

It’s important to keep in mind that the intensive feeding season for polar bears is drawing to a close – within another two weeks, most young-of-the-year seals will be in the water feeding and inaccessible to bears.

The only seals on the ice during June and July are predator-savvy adults and subadults that have hauled out to moult and for these seals the rapidly disintegrating ice creates many escape routes. That means that as long as the ice breakup sequence allows polar bears to get their fill of young seals before the end of May, even during early breakup years most bears should be fat enough to survive the coming summer and winter fasts (see more here). So we should expect to see some bears coming ashore within the next two weeks.

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