Last month of Arctic spring fails to bring sea ice to its knees, even in Southern Hudson Bay – Watts Up With That?

From Polar Bear Science

Susan Crockford

Polar bear habitat for June — the last month of spring in the Arctic — is still within 2 standard deviations of the long-term average despite sea ice experts’ predictions that catastrophic declines can be expected any year now.

The Arctic sea ice cover in June 2024 retreated at a below average pace, leading to a larger total sea ice extent for the month than in recent years. NSIDC, 3 July 2024

Oddly, the National Snow and Ice Data Center (NSIDC) employees who wrote up the sea ice summary for June felt it appropriate to bring up a recently-published prediction of impending doom for Southern Hudson Bay polar bears based on a sea ice prediction (Stroeve et al. 2024), which I covered here. The inclusion of this topic is a naked promotion of the Stroeve sea ice modelling paper which not only doesn’t fit the reality of this year’s sea ice conditions but their discussion doesn’t include a single piece of evidence that Southern Hudson Bay polar bears came off the ice earlier than usual.

Arctic Summary

Here is the NSIDC chart and graph for June sea ice:

Extent this year for June, at 10.9 mkm2, compared to previous years was just about exactly what it was in 2006 and slightly lower than it was last year, as the graph below shows:

Southern Hudson Bay

The NSIDC report states: “The average date for ice retreat of southern Hudson Bay ranges between mid-June to late-July, so there is typically enough ice available for polar bears to hunt ringed seal pups, a major food source for them. If the ice breaks up too early, as is the case this year, the bears are stranded on land for more of the summer and autumn season, which extends their annual fasting period.”

First of all, polar bears do not “hunt ringed seal pups” from mid-June to late July in Hudson Bay. Young seals have been weaned by that time and are out feeding in open water. The only potential prey are adult and subadult seals that may be resting on sea ice while they are moulting, but it is very rare for bears to successfully hunt these older seals since they are experienced enough to be ever-vigilant and predator-savvy. As I have pointed out countless times, polar bears may stay on the ice into July or even August if they can but it is not to hunt seals.

Moreover, there was still ice in James Bay at 18 June (see chart below), so breakup wasn’t unusually early and there was still abundant ice along the SW shore of Hudson Bay where many SH bears come off the ice.

In fact, there is still abundant ice along the SW shore of Hudson Bay and all the way up into Western Hudson Bay and it’s almost mid-July! The sea ice chart closeup of Hudson Bay shown below is for July 10 and there is still ice along the shore of the Southern Hudson Bay subpopulation region:

In other words, despite the fact that a large swath of open water developed in eastern Hudson Bay in May, all indicators point to this not being an early breakup year for Southern Hudson Bay sea ice as far as polar bears are concerned.

And I would be remise if I did not point out that the supposedly dire consequence of a modelled early breakup for Southern Hudson Bay bears contradicts an earlier study that showed only late freeze-ups negatively affected this subpopulation (Obbard et al. 2016).

Here’s what Obbard and colleagues had to say about the relationship between body condition and sea ice of Southern Hudson Bay bears(my bold):

“Date of freeze-up had a stronger influence on subsequent body condition than date of break-up in our study. …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. 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 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]

Western Hudson Bay

By the end of June in Western Hudson Bay this year, all but one of University of Alberta’s tagged bears were still on the ice:

Note that the “behavioural plasticity” that Derocher refers to above refers to a pattern noted since at least 2015, where polar bears have been staying out on melting sea ice well past the stage that “experts” previously insisted would cause bears to abandon the ice for shore. Their sea ice/polar bear survival models all depend on this failed assumption, including the Stroeve paper.

It’s getting harder and harder for Derocher and colleagues to ignore the fact that their assumptions about sea ice concentration and polar bear behaviour was flat-out wrong. This year, some WH bears could again remain on the ice until August, despite what has been, on paper, the earliest breakup year on record for Hudson Bay sea ice.

References

Obbard, M.E., Cattet, M.R.I., Howe, E.J., Middel, K.R., Newton, E.J., Kolenosky, G.B., Abraham, K.F. and Greenwood, C.J. 2016. Trends in body condition in polar bears (Ursus maritimus) from the Southern Hudson Bay subpopulation in relation to changes in sea ice. Arctic Science, in press. 10.1139/AS-2015-0027

Stroeve, J., Crawford, A., Ferguson, S., Stirling, I., Archer, L., York, G., Babb, D. and Mallet, R. 2024. Ice-free period too long for Southern and Western Hudson Bay polar bear populations if global warming exceeds 1.6 to 2.6⁰ C. Nature Communications Earth & Environment 5:296 [open access] https://doi.org/10.1038/s43247-024-01430-7