Despite the fact that it’s in graph type solely, we lastly have an replace on sea ice freeze-up dates for Western Hudson Bay for 2016-2020 (however not breakup dates).
This graphed knowledge revealed by Miller et al. 2022 extends by 5 years that revealed in 2017 by Castro de la Guardia and colleagues, which contained graphed knowledge for breakup and freeze-up dates from 1979-2015 (with precise dates for 2005-2008 solely).
It confirms an announcement I made final month, that between 2016 and 2021 “there was just one ‘late’ freeze-up 12 months (2016)–however 5 very early ones.” After all, 2021 was not included on this new dataset, so that might be “4 very early ones” as much as 2020.
Right here it’s, as a part of Determine 2. The freeze-up knowledge is higher left (a):
Right here is that tiny panel (a) by itself, enlarged (a screencap from the pdf), exhibiting the pattern line from1991-2020:
Extracting numbers off graphs is time-consuming and sometimes inaccurate, however apparently polar bear specialists don’t care: that’s all the general public and their colleagues are being given.
Within the lists under, the primary quantity is the 12 months, the second quantity is the Julian day of the 12 months (e.g. 313), and the third is the calendar date of the corresponding Julian day from the Miller paper vs. the de al Guardia paper. For the final 5 years, I’ve added my very own evaluation made on the time, and since it is a screencap, listed here are the hyperlinks for my estimates: for 2020 (when bears had been killing seals on offshore sea ice by 31 Oct), 2019, 2018, 2017, 2016. I didn’t transcribe all the pre-2005 dates, solely a choose few.
Most of entries within the interval of overlap between the 2 datasets are both an identical or differ by solely 1-3 days. Nevertheless, these in daring differ by nearly per week or extra (e.g. 2008, 2011), despite the fact that there isn’t a clarification within the Miller paper concerning why that might be so:
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As you’ll be able to see, the earliest freeze-up 12 months was 1993 (though 1991, 1986, and 1978 had been nearly that early) and the most recent apparently in 2016 (though 2009, 1998, and 1981 had been nearly as late relying on which dataset you have a look at).
Given the potential error price of 2-3 days both means, freeze-up was as early in 2020 because it had been in 1978, 1979, 1986, 1991, and 1993 (the earliest on report); freeze-up dates in 2017, 2018, and 2019 had been the identical as the common within the Eighties (de la Guardia et al. 2017).
General, Miller and colleagues discovered no temporal pattern in sea ice or departure dates of polar bears from shore between 1991 and 2020, and maybe counter-intuitively, that bears departed for the ice earlier in years when freeze-up was earlier.
This implies WH sea ice protection within the fall has not been ‘steadily declining’ during the last 30 years and polar bear haven’t been departing for the ice later and later within the season over that interval, as many suggest.
Nevertheless, though the authors collected long-overdue knowledge on physique situation of females with cubs and impartial juveniles, these values are reported solely as a ‘vulnerability index’ which is unattainable to match with uncooked knowledge collected within the Seventies and Eighties.
Whereas these indices point out that the physique situation of females with cubs-of-the-year (however not these with yearling cubs) “declined during the last 30 years“, it’s unattainable to say by how a lot in comparison with detailed research finished previous to the Nineteen Nineties (eg. Derocher and Stirling 1992, 1995; Ramsay and Stirling 1988) or to these used to justify classifying polar bears as ‘threatened’ on the US Endangered Species Listing (Regehr et al. 2007).
In different phrases, physique weight knowledge–so crucial to the argument that the well being of WH polar bears is declining resulting from sea ice loss–is nonetheless being withheld.
References
Castro de la Guardia, L., Myers, P.G., Derocher, A.E., Lunn, N.J., Terwisscha van Scheltinga, A.D. 2017. Sea ice cycle in western Hudson Bay, Canada, from a polar bear perspective. Marine Ecology Progress Sequence 564: 225–233. http://www.int-res.com/abstracts/meps/v564/p225-233/
Derocher, A.E. and Stirling, I. 1992. The inhabitants dynamics of polar bears in western Hudson Bay. pg. 1150-1159 in D. R. McCullough and R. H. Barrett, eds. Wildlife 2001: Populations. Elsevier Sci. Publ., London, U.Ok.
Derocher, A.E. and Stirling, I. 1995. Temporal variation in replica and physique mass of polar bears in western Hudson Bay. Canadian Journal of Zoology 73:1657-1665. http://www.nrcresearchpress.com/doi/abs/10.1139/z95-197
Miller, E.N., Lunn, N.J., McGeachy, D., and Derocher, A.E. 2022. Autumn migration phenology of polar bears (Ursus maritimus) in Hudson Bay, Canada. Polar Biology 45:1023-1034.
Ramsay, M.A. and Stirling, I. 1988. Reproductive biology and ecology of feminine polar bears (Ursus maritimus). Journal of Zoology London 214:601-624. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1988.tb03762.x/summary
Regehr, E.V., Lunn, N.J., Amstrup, S.C. & Stirling, I. 2007. Results of earlier sea ice breakup on survival and inhabitants measurement of polar bears in Western Hudson Bay. Journal of Wildlife Administration 71: 2673-2683. Paywalled, subscription required. http://onlinelibrary.wiley.com/doi/10.2193/2006-180/summary
