Critical spring feeding for polar bears is over – sea ice levels are now irrelevant

Polar bears in virtually all regions will now have finished their intensive spring feeding, which means sea ice levels are no longer an issue. A few additional seals won’t make much difference to a bear’s condition at this point.

Relative importance of seasons polar bear graphic_PolarBearScience_June2016

The only seals available on the ice for polar bears to hunt in early July are predator-savvy adults and subadults but since the condition of the sea ice makes escape so much easier for the seals, most bears that continue to hunt are unsuccessful – and that’s been true since the 1970s. So much for the public hand-wringing over the loss of summer sea ice on behalf of polar bear survival!

The fact is, most ringed seals (the primary prey species of polar bears worldwide) move into open water to feed after they have completed their annual molt, which occurs by late June to mid-July for adults and subadults; newborn pups leave the ice soon after being weaned, usually by the end of May in southern regions (like Hudson Bay) and by late June in the Canadian Arctic Archipelago, aka “CAA” (Kelly et al. 2010; Smith 1975, 1987; Whiteman et al. 2015).

Thus, the most abundant prey of polar bears is essentially unavailable after mid-July (and earlier than that in Hudson Bay).

Adults and subadults of the similarly-distributed but much larger (and less abundant) bearded seal tend to remain with the ice over the summer (Cameron et al. 2010:11-12) and are most likely to be available to polar bears that remain on the sea ice over the summer throughout the Arctic. Some adult harp seals (an abundant, strictly North Atlantic species) may also be available to bears on the pack ice in Baffin Bay and Davis Strait, as well in the northern sections of the Barents and Kara Seas, and northern East Greenland (Sergeant 1991).

However, research on polar bear feeding has shown that from June to October, bears are rarely successful at catching seals because broken and melting ice affords so many escape routes for the seals. Bears may stalk the seals but they often get away (see video snapshot and video below)

Bearded seal hunted by polar bear BBC snapshot 2

[Full video clip below]

The facts on this feeding pattern were documented back in the 1970s and 1980s and are assumed by polar bear biologists to be true today (Derocher et al. 2002; Stirling 1974; Stirling and Øritsland 1995; Obbard et al. 2016; Pilfold et al. 2015).

But they don’t say so in public and Polar Bears International – led by former USGS biologist Steven Amstrup – seldom (if ever) mention this salient point.

Amstrup et al 2011 fig 1 ecoregions_sm

This intensive spring feeding phenomenon means that virtually all polar bears residing in so-called Seasonal and Divergent ecoregions (see above) – predicted to be extirpated by 2050, according to documents supporting the ESA listing of polar bears as ‘threatened’ with extinction (Amstrup et al. 2007; USFWS 2008) – effectively fast from late spring to early fall whether they spend this time on land or on the sea ice.

Which means we should indeed be worried if there is NO sea ice in May but that’s nowhere near happening. There might have been slightly less ice this year in May than in the early 1980s but a bit less is not the same as none.

To imply that less ice impacts polar bears and seals suggests they are incapable of moving laterally in response to changing conditions – which is clearly not true.

For example, many ringed seals and polar bears of the Southern Beaufort moved west to the Chukchi and Bering Seas in 1974 and 1975 when thick spring ice made staying in the Beaufort untenable (Burns et al. 1975; Stirling et al. 1975a,b; Stirling et al. 1982, Stirling et al. 1985:75).

If bears and seals moved massive distances to avoid excessive ice in the Beaufort in the 1970s, they can certainly move short distances in response to less ice now. It’s called adaptation.

So much for the Save our Sea Ice campaign run by Steven Amstrup and the drama queens at Polar Bears International, scheduled for 15 July 2016.

Here is what PBI claim:

This summer [2016], the sea ice retreat could well break records, impacting polar bears, other wildlife, and people too. Sea ice loss in the month of May covered an area three times larger than the state of California compared with the historical average.” [my bold]

However, by July 15, few bears will be eating seals even if they remain on the ice – and most bears will have effectively stopped feeding many weeks before that. There is no evidence that the “sea ice loss” in May had any effect on polar bears whatsoever.

Knowing the facts means you won’t be taken in by the hype.

Sea ice maps (NSIDC Masie) below for mid-May, mid-June and 4 July, for reference.

masie_all_zoom_4km 2016 May 14

 

masie_all_zoom_4km 2016 June 16

And now…

masie_all_zoom_4km 2016 July 4

References

Amstrup, S.C., Marcot, B.G. and Douglas, D.C. 2007. Forecasting the rangewide status of polar bears at selected times in the 21st century. Administrative Report, US Geological Survey. Reston, Virginia.

Burns, J. J., Fay, F. H., and Shapiro, L.H. 1975. The relationships of marine mammal distributions, densities, and activities to sea ice conditions (Quarterly report for quarter ending September 30, 1975, projects #248 and 249), pp. 77-78 in Environmental Assessment of the Alaskan Continental Shelf, Principal Investiagors’ Reports. July-September 1975, Volume 1. NOAA, Environmental Research Laboratories, Boulder Colorado. [available online]

Cameron, M. F., Bengtson, J. L., Boveng, J. K., Jansen, J. K., Kelly, B. P., Dahle, S. P., Logerwell, E. A., Overland, J. E., Sabine, C. L., Waring, G. T. and Wilder, J. M. 2010. Status review of the bearded (Erignatha barbatus). NOAA Technical Memorandum NMFS-AFSC-211.

Derocher, A.E.,Wiig,Ø. and Andersen, M. 2002. Diet composition of polar bears in Svalbard and the western Barents Sea. Polar Biology 25 (6): 448–452.

Kelly, B. P., Bengtson, J. L., Boveng, P. L., Cameron, M. F., Dahle, S. P., Jansen, J. K., Logerwell, E. A., Overland, J. E., Sabine, C. L., Waring, G. T. and Wilder, J. M. 2010. Status review of the ringed seal (Phoca hispida). NOAA Technical Memorandum NMFS-AFSC-212.

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

Pilfold, N. W., Derocher, A. E., Stirling, I. and Richardson, E. 2015. Multi-temporal factors influence predation for polar bears in a changing climate. Oikos 124(8):1098-1107. http://onlinelibrary.wiley.com/doi/10.1111/oik.02000/abstract

Sergeant, D.E. 1991. Harp Seals, Man and Ice. Canadian Special Publication of Fisheries and Aquatic Sciences 114. Fisheries and Oceans Canada, Ottawa.

Smith, T. G. 1975. Ringed seals in James Bay and Hudson Bay: population estimates and catch statistics. Arctic 28:170-182.

Smith, T. G. 1987. The ringed seal, Phoca hispida,of the Canadian Western Arctic. Canadian Bulletin of Fisheries and Aquatic Sciences 216, Ottawa.

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 Aquatic Sciences 52:2594–2612.

Stirling, I., Andriashek, D., Latour, P.B. and Calvert, W. 1975a. Distribution and abundance of polar bears in the Eastern Beaufort Sea. Beaufort Sea Technical Report #2, Department of the Environment, Victoria, B.C.

Stirling, I., Archibald, R. and DeMaster, D. 1975b. Distribution and abundance of seals in the Eastern Beaufort Sea. Beaufort Sea Technical Report #1, Department of the Environment, Victoria, B.C.

Stirling, I, Kingsley, M. and Calvert, W. 1982. The distribution and abundance of seals in the eastern Beaufort Sea, 1974–79. Canadian Wildlife Service Occasional Paper 47. Edmonton.

Stirling, I., Schweinsburg, R.E., Kolenasky, G.B., Juniper, I., Robertson, R.J., Luttich, S. and Calvert, W. 1985. Research on polar bears in Canada 1978-80. In: Anonymous, 1985, Proceedings of the 8th meeting of the Polar Bear Specialists Group IUCN/SSC, 15-19 January 1981, Oslo, Norway. Gland, Switzerland and Cambridge UK, IUCN, pp. 71-98.

US Fish and Wildlife Service. 2008. Determination of threatened status for the polar bear (Ursus maritimus) throughout its range. Federal Register 73(95):28212-28303.

Whiteman, J.P., Harlow, H.J., Durner, G.M., Anderson-Sprecher, Albeke, S.E., Regehr, E.V., Amstrup, S.C., and Ben-David, M. 2015. Summer declines in activity and body temperature offer polar bears limited energy savings. Science 349 (6245):295-298.

 

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