Reposted from Dr. Susan Crockford’s Polar Bear Science
Posted on June four, 2020 |
Listed below are ice circumstances on the finish of Could, which indicators the near-end of the important spring feeding interval for polar bears. It’s because young-of-the-year seals take to the water to feed themselves, leaving solely predator-savvy adults and subadults on the ice from a while in June onward (relying on the area).
Spring is the important feeding interval for polar bears (Crockford 2019, 2020; Lippold et al. 2020; Obbard et al. 2016):
“Unexpectedly, physique situation of feminine polar bears from the Barents Sea has elevated after 2005, though sea ice has retreated by ∼50% because the late 1990s within the space, and the size of the ice-free season has elevated by over 20 weeks between 1979 and 2013. These adjustments are additionally accompanied by winter sea ice retreat that’s particularly pronounced within the Barents Sea in comparison with different Arctic areas. Regardless of the declining sea ice within the Barents Sea, polar bears are possible not missing meals so long as sea ice is current throughout their peak feeding interval. Polar bears feed extensively from April to June when ringed seals have pups and are notably susceptible to predation, whereas the predation charge throughout the remainder of the yr is probably going low.“ [Lippold et al. 2019:988]
NISDC comparative graphs reveals 2020 ice extent at 31 Could 2020 was greater than 2016 on the identical date (and about the identical as 2015).
Beneath is the map for Arctic Canada at 31 Could 2020, which has a noteable lack of open water within the Beaufort Sea:
Examine to 31 Could 2016:
Final yr (31 Could 2019), nonetheless, was fairly totally different once more, particularly in Hudson Bay and Hudson Strait:
Stirling et al. (1981:54) mentioned why polynyas may be so necessary within the Southern Beaufort and Hudson Bay (my daring):
“One helpful strategy is to ask what would occur if the polynya was not there? Clearly that is inconceivable to judge on an experimental foundation, however by analyzing the results or pure seasonal variation, some helpful insights may be gained. For instance, the affect of quickly altering ice circumstances on the provision of open water, and consequently on populations of seals and polar bears, has been noticed within the western Arctic. Apparently in response to extreme ice circumstances within the Beaufort Sea throughout winter 1973-74, and to a lesser diploma in winter 1974-75, numbers of ringed and bearded seals dropped by about 50% and productiveness by about 90%. Concomitantly, numbers and productiveness of polar bears declined markedly due to the discount within the abundance of their prey species. …If the shoreleads of the western Arctic or Hudson Bay ceased opening throughout winter and spring, the impact on marine mammals could be devastating.”
Ice cowl over Hudson Bay for the final week of Could:
Ice cowl over the western Canadian Arctic (Jap Beaufort Sea) for the final week of Could:
The Alaskan portion of the Beaufort was nonetheless predominantly multiyear ice on the finish of Could and thick first yr ice within the Chukchi Sea (observe this map doesn’t present areas of open water):
Areas of open water within the western Beaufort/Chukchi/Bering Seas at finish Could 2020:
Ice thickness right now (much less related for bears and seal, preferring first yr ice):
See earlier posts on spring feeding right here and right here, with references, and on the Beaufort Sea polynya (recurrent open water) right here and right here.
Crockford, S.J. 2019. The Polar Bear Disaster That By no means Occurred. International Warming Coverage Basis, London. Accessible in paperback and e-book codecs.
Crockford, S.J. 2020. State of the Polar Bear Report 2019. International Warming Coverage Basis Report 39, London. PDF right here.
Lippold, A., Bourgeon, S., Aars, J., Andersen, M., Polder, A., Lyche, J.L., Bytingsvik, J., Jenssen, B.M., Derocher, A.E., Welker, J.M. and Routti, H. 2019. Temporal traits of persistent natural pollution in Barents Sea polar bears (Ursus maritimus) in relation to adjustments in feeding habits and physique situation. Environmental Science and Know-how 53(2):984-995.
Obbard, M.E., Cattet, M.R.I., Howe, E.J., Middel, Okay.R., Newton, E.J., Kolenosky, G.B., Abraham, Okay.F. and Greenwood, C.J. 2016. Developments in physique situation in polar bears (Ursus maritimus) from the Southern Hudson Bay subpopulation in relation to adjustments in sea ice. Arctic Science 2:15-32 Doi 10.1139/AS-2015-0027 http://www.nrcresearchpress.com/doi/abs/10.1139/AS-2015-0027#.VvFtlXpUq50
Stirling, I, Cleator, H. and Smith, T.G. 1981. Marine mammals. In: Polynyas within the Canadian Arctic, Stirling, I. and Cleator, H. (eds), pg. 45-58. Canadian Wildlife Service, Occasional Paper No. 45. Ottawa. Pdf of excerpts of above paper right here.