Critical evidence on W Hudson Bay polar bears still not published after 25 years

Posted on June 6, 2018 | Comments Off on Critical evidence on W Hudson Bay polar bears still not published after 25 years

Polar bear researchers have been doing capture/recapture studies in Western Hudson Bay for decades yet most of the data claimed to be critical for assessing effects of human-caused global warming on this species have not been published. I raised this point in one of my early blog posts (27 Sept 2012) but the situation has not changed in 6 years. Here’s an update.

Derocher in the field in WH_CBC story 2016

From CBC story 14 Sept 2016.

Years ago now, in an oft-cited paper, Stirling and Derocher (2012) claimed to summarize the evidence that climate warming was negatively impacting polar bear health and survival. Several life history parameters were considered crucial, particularly body condition.

Despite almost a dozen papers (and perhaps more) on various aspects of WH polar bear health and life history studies based on capture/recapture data published since 2004  (e.g. Castro de la Guardia 2017; Lunn et al. 2016; Pilfold et al. 2017), none have reported the body condition data that supposedly support the claim that sea ice loss is having a severe impact — and the same is true for litter size, proportion of independent yearlings, and cub survival.1

Body condition studies

There has been no more recent data published on body mass of lone females since 2004, or of adult males and females with cubs in WH since 1998 — 20 years ago — (Stirling et al. 1999:296; Stirling and Parkinson 2006:265), even though this is the data (declining weights of bears) that is said to show sea ice loss due to human-caused global warming has been negatively impacting WH polar bears since 1985.

For example, in their review of body condition evidence, Stirling and Derocher (2012) added data for 2005-2007 to those collected by Stirling and Parkinson (2006), in the figure they presented for the mass of lone female bears (see their Fig. 5 below) but cited “unpublished data.” This means Nick Lunn and Ian Stirling had the data for 2005-2007 but by 2012, hadn’t yet bothered to publish it in the peer-reviewed literature. They still haven’t.

Nor have they or anyone else published any of the body condition data collected since 2007, despite the public handwringing from Derocher and Stirling (e.g. here and here) about weight loss due to reduced sea ice since then.

A hint as to why the recent data hasn’t been published is right there in the Stirling and Derocher (2012) graph: of those three years of added unpublished data, only one year’s value (2006) fit the trend line of a decline: the other two had values as high as the 1980s.

Stirling and Derocher 2012 fig 5

Figure 5 from Stirling and Derocher 2012, pg. 2697. Note that “Stirling and Parkinson 2006” report data up to 2004 only. Without the 2005-2007 data, the decline was 22% (a 65 kg loss, from an average of 295 kg in 1980 to 230 kg in 2004). However, adding 2005-2007 data drops the decline to 20% (a 59 kg loss, from an average of 295 kg in 1980 to 236 kg in 2007).

The result: the overall decline from 1980 to 2007 was only 20%, compared to a 22% decline based on the 1980-2004 data.

Recording body mass is standard protocol

Since recording body mass is part of taking standard morphometric data for polar bears (Derocher and Stirling 1995; Obbard et al. 2016), this critical data must exist for all years after 2007 for Western Hudson Bay but has simply not be reported.2 If more recent data is similar to 2005-2007 or better, it’s no mystery why it has been kept secret: evidence that bears have been as heavy (or heavier) in recent years than in the late 1990s to early 2000s would not fit the climate change catastrophe narrative.

Previous research in WH (Derocher et al. 1992) on animals captured between 1982 and 1990 suggested that the critical mass for lone females (presumed pregnant) was about 189 kg: that is, below this weight females could not maintain a pregnancy. That means that the reduced mass of lone females in the mid-2000s (230-236 kg) was still a long way from the number that was a known cause for critical concern regarding the maintenance of population size.

One recent published paper Sciullo et al. (2016) assessed body condition of polar bears using subjective fatness indices, the lipid content of adipose tissue, energy density models, and something called “bioelectrical impedance analysis” (BIA), none of which were used between 1980 and 2007.

Note that without being able to compare such data to earlier values, such studies are useless for assessing impacts of global warming but are useful for generating graduate degree topics for university students.

However, even the new body condition proxy data generated by Sciullo et al. (2016:54) for 2012 and 2013 did not correlate well with earlier breakup or later freeze-up of sea ice in Western Hudson Bay:

“…we found sea ice to influence body condition metrics across age and sex classes. The differing response of various metrics to changing ice conditions, however, suggests that timing of breakup and freezeup may not be the sole factors involved in influencing polar bear body condition. For example, energy density, storage energy and skull width declined over time in solitary adult females (Fig. 7), but these metrics were not predicted by sea ice breakup or freeze-up dates.” [my bold]

In other words, researchers have been trying new metrics to assess body condition rather than measuring and reporting body mass, but the data haven’t provided any evidence for a continued decrease in body condition that correlates to earlier sea ice breakup and/or later freeze-up.

In fact, capture/recapture data collection continues to this day in WH (see 2018 tweets from Derocher below), but none of the data on mass of bears collected since 2004 has been published.

Conclusion

Eventually, some journalist or reviewer will ask to see the body mass data. Western Hudson Bay researcher Andrew Derocher’s enthusiasm for the value of location data of captured, tagged and collared bears every year is a smoke-screen for the data he isn’t showing.

In the tweet below (24 May 2018), Derocher states the length of time ashore is correlated to “survival and reproduction” but no paper describing such a long term relationship has been published in the last 20 years.

Bottom line: Derocher and his students keep collecting raw data on body mass but don’t publish the results. Derocher and colleague Nick Lunn keep insisting loss of body fat is an indicator of sea ice loss (see here, here and here) but they don’t publish the body weight (mass) data.

Footnotes

1. There has also been no published data available for size of WH litters or proportion of independent yearlings since 1998 based on capture/recapture studies (Stirling et al. 1999) — 20 years ago — and no additional data on cub survival since 1992 — 26 years ago (Derocher and Stirling 1995).

There has been some data on litter size and proportion of independent yearlings based on aerial surveys, which may be broadly comparable to capture/recapture study data. However, cub survival metrics cannot be determined from aerial survey data and while some claim cub survival is declining, no data to support it has been published.

 2. Martin Obbard and colleagues determined that in the 2000s, females on average were about 31 kg lighter than they were in 1980s and males 45 kg lighter. However, the number of bears in the population did not decline over the same period (Obbard et al. 2015), which suggests that amount of weight loss is not biologically significant. A claim for a slight reduction in population size (17%) has since been made for the Southern Hudson Bay subpopulation (Obbard et al. 2018) but no coorelations with body condition and/or sea ice metrics were presented.

References

Derocher, A.E. and Stirling, I. 1995. Temporal variation in reproduction and body 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

Dyck, M., Campbell, M., Lee, D., Boulanger, J. and Hedman, D. 2017. 2016 Aerial survey of the Western Hudson Bay polar bear subpopulation. Final report, Nunavut Department of Environment, Wildlife Research Section, Iglolik, NU. http://www.gov.nu.ca/environnement/information/wildlife-research-reports#polarbear

Lunn, N.J., Servanty, S., Regehr, E.V., Converse, S.J., Richardson, E. and Stirling, I. 2016. Demography of an apex predator at the edge of its range – impacts of changing sea ice on polar bears in Hudson Bay. Ecological Applications, in press. DOI: 10.1890/15-1256

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

Obbard, M.E., Stapleton, S., Middel, K.R., Thibault, I., Brodeur, V. and Jutras, C. 2015. Estimating the abundance of the Southern Hudson Bay polar bear subpopulation with aerial surveys. Polar Biology 38:1713-1725.

Obbard, M.E., Stapleton, S., Szor, G., Middel, K.R., Jutras, C. and Dyck, M. 2018. Estimating the abundance of the Southern Hudson Bay polar bear subpopulation with aerial surveys. Arctic Science https://doi.org/10.1139/AS-2018-0004

Stapleton S., Atkinson, S., Hedman, D., and Garshelis, D. 2014. Revisiting Western Hudson Bay: using aerial surveys to update polar bear abundance in a sentinel population. Biological Conservation 170: 38-47. http://www.sciencedirect.com/science/article/pii/S0006320713004618#

Stirling, I. and Derocher, A.E. 2012. Effects of climate warming on polar bears: a review of the evidence. Global Change Biology 18:2694-2706. doi:10.1111/j.1365-2486.2012.02753.x

Stirling, I., Lunn, N.J. and Iacozza, J. 1999. Long-term trends in the population ecology of polar bears in Western Hudson Bay in relation to climate change. Arctic 52:294-306.
http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/935/960

Stirling, I. and Parkinson, C.L. 2006. Possible effects of climate warming on selected populations of polar bears (Ursus maritimus) in the Canadian Arctic. Arctic 59:261-275. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/issue/view/16.

Recent WH polar bear papers using capture data

Bechshoft, T., Derocher, A.E., Richardson, E., Lunn, N.J. and St. Louis, V.L. 2016. Hair mercury concentrations in Western Hudson Bay polar bear family groups. Environmental Science & Technology 50(10):5313-5319.

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 Series 564: 225–233. http://www.int-res.com/abstracts/meps/v564/p225-233/

Cherry, S.G., Derocher, A.E. and Lunn, N.J. 2016. Habitat-mediated timing of migration in polar bears: an individual perspective. Ecology and Evolution 6(14):5032-5042. https://doi.org/10.1002/ece3.2233 Open access.

Cherry, S.G., Derocher, A.E., Thiemann, G.W., Lunn, N.J. 2013. Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics. Journal of Animal Ecology 82:912-921. https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2656.12050

McCall, A.G., Derocher, A.E. and Lunn, N.J. 2015. Home range distribution of polar bears in western Hudson Bay. Polar Biology 38(3):343-355. https://doi.org/10.1007/s00300-014-1590-y

Lunn, N.J., Servanty, S., Regehr, E.V., Converse, S.J., Richardson, E. and Stirling, I. 2016. Demography of an apex predator at the edge of its range – impacts of changing sea ice on polar bears in Hudson Bay. Ecological Applications, in press. DOI: 10.1890/15-1256

Pilfold, N.W., McCall, A., Derocher, A.E., Lunn, N.J., and Richardson, E. 2017. Migratory response of polar bears to sea ice loss: to swim or not to swim. Ecography 40:189-199. https://doi.org/10.1111/ecog.02109

Sciullo, L, Thiemann, G.W., and Lunn, N.J. 2016. Comparative assessment of metrics for monitoring the body condition of polar bears in western Hudson Bay. Journal of Zoology 300: 45-58. doi:10.1111/jzo.12354

Towns, L., Derocher, A.E., Stirling, I., Lunn, N.J. and Hedman, D. 2009. Spatial and temporal patterns of problem polar bears in Churchill, Manitoba. Polar Biology 32(10):1529-1537. http://link.springer.com/article/10.1007%2Fs00300-009-0653-y [paywalled]

Viengkone, M., Derocher, A.E., Richardson, E.S., Malenfant, R.M., Miller, J.M., Obbard, M.E., Dyck, M.G., Lunn, N.J., Sahanatien, V. and Davis, C.S. 2016. Assessing polar bear (Ursus maritimus) population structure in the Hudson Bay region using SNPs. Ecology and Evolution 6: 8474-8484. DOI: 10.1002/ece3.2563

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