Western Hudson Bay polar bears in great shape after five good sea ice seasons


By: - Climate DepotSeptember 6, 2019 9:47 AM

https://polarbearscience.com/2019/09/05/western-hudson-bay-polar-bears-in-great-shape-after-five-good-sea-ice-seasons/

Western Hudson Bay polar bears in great shape after five good sea ice seasons

Polar bear researcher Andrew Derocher says it takes four years of good sea ice conditions to recruit a polar bear from birth but implies that 2019 is the first year in decades that conditions for bears have been ‘good’ in Western Hudson Bay. He thinks he can get away with saying this because he hasn’t published any of the data on body weight and body condition he’s collected on these bears over the last 25 years (apparently, whatever funding agency pays for his research does not require him to publish the data he collects).

But independent observations such as dates of ice freeze-up in fall, ice breakup in summer, dates and condition of bears recorded onshore, suggest he’s blowing smoke: at least five out of five of the last sea ice seasons for WH bears have been good. That means we should be seeing more bears in the next official population count.

Derocher claims it takes four good sea ice years to recruit a polar bear and lays it out this way: year 1 spring, good hunting for pregnant female to get really fat to support the pregnancy; year 2 spring, good hunting so that nursing cub-of-the-year survives; year 3, good hunting so that yearling cub can nurse all year and get strong [although he leaves out the fact that cubs of all ages also feed on the seals their mothers catch]; year 4 spring, good hunting for 2 year old bear on its own for the first time [although he’s leaving out the fact that a 2 year old can catch plenty of seals and still have trouble surviving if there are lots of adult males around to steal his catch].

Fat pregnant polar bear intent on finding a secure place to dig a den in the permafrost where she can stay cool over the summer and give birth this winter, photographed by the RCMP during a manhunt for suspected murderers, probably near the western edge of Wapusk National Park.

That’s fair and accurate enough for twitter (which is his primary mode of communication). However, he implies that 2019 has been the first ‘good’ year that Hudson Bay polar bears have had in many years – and on that I call nonsense.

The tweet below is from late June (after his field season was over), and he reiterated the point in late August. In other words, he’s suggesting that ‘good’ cub recruitment in Hudson Bay will only be possible if ice conditions are as good as 2019 for the next three consecutive years (2020-2022).

We don’t have data from his field work, but we do have critical secondary information: breakup and freeze-up dates and reports on body condition since the fall of 2014.

Breakup, freeze-up, and condition of bears by year

2019: This year, WH polar bear started coming off the ice near Churchill the first week of July but at least half of Derocher’s tagged bears were still out on the ice at the end of July. I am assuming that the bulk of the population did not come off until the fourth week of the month (22-28) into the first week of August. This followed an early freeze-up last fall at about 10-12 November(which was slightly earlier than the 1980s average of 16 November and one of the earliest freeze-up dates since 1979). Derocher (see below) has declared this a good year for Hudson Bay bears:

Regarding dates of bears coming ashore and leaving for the ice, I’ve pointed out before,

“According to a recalculation of data that goes up to 2015 and back to 1979 (Castro de la Guardia 2017), in the 1980s bears left for the ice at freeze-up (10% sea ice coverage in WHB) about 16 November ± 5 days while in recent years (2004-2008) they left about 24 November ± 8 days, a difference of 8 days.

The relative change in the dates that bears left the shore between the 1980s and recent years is only about 1 week, on average (with lots of variation).

Freeze-up dates of 10-12 November or so (Day 314-316) for 2017 and 2018 are therefore two of the earliest freeze-up dates since 1979 (the earliest being 6 November, Day 310, in 1991 and 1993), see Fig 3 from Castro de la Guardia 2017 below.”

Derocher has stated outright that ice conditions this summer were “similar to the 1980s” (copied below) but conditions in the past four years were not appreciably different, as you’ll see.

2018: Most bears in 2018 were off the ice near Churchill by the third week in July (16-22) – only a week or so earlier than 2019 – with a few bears similarly reported off the ice the week before (9-15). Freeze-up the previous fall (2017) was as early as 2018 and therefore earlier than the average in the 1980s (about 10-12 November). How is this not ‘good’?

2017: Most bears were off the ice near Churchill by the fourth week of July (24-30)and were reported to be in “great shape”. However, freeze-up had been late the fall before (2016 was an El Niño year, as was 1998) and the bears were not able to leave the shore in 2016 until early December. However, since they had come off the ice late and in such good shape, the extra few weeks ashore did not appear to cause them any harm. Number of conflicts with people in Churchill was up because of increased vigilance after the 2013 attack as well as increased time ashore. Derocher told the media (here and here) that WH bears were doomed. Seal researcher Steve Ferguson bizarrely predicted no ice in Hudson Bay in winter within 5-10 years. Despite the late freeze-up, this was still a pretty good year.

2016: Bears came off the ice at Churchill well-fed and in great shape by mid-July (11-17) The previous fall (2015), there had been enough ice along the west coast of Hudson Bay for bears to leave the shore by about 5-6 November, which would have tied 1991 and 1993 (see quote above) for the earliest dates bears had left since 1979 (Castro de la Guardia et al. 2017). How is this not ‘good’?

2015: There were a few bears around Churchill by the third week of July (20-26)but like 2019, there was lingering ice on the bay until mid-August. Also like 2019, most of Derocher’s tagged bears were still on the ice at 15 July. I presume based on this information that most bears were not off the ice until the end of July (i.e. like they were in the 1980s and in 2019). The previous fall (2014), bears left about the middle of November (13) – a bit earlier than the average in the 1980s (Castro de la Guardia et al. 2017). How is this not ‘good’?

Derocher often insists there is a downward trend in Western Hudson Bay sea ice conditions but the published data refute that.It’s not me claiming he’s wrong but rather me repeating what Derocher’s students and colleagues have published (Cherry et al. 2013; Castro de la Guardia et al. 2017; Crockford 2017; 2019a, b; Lunn et al. 2016; Obbard et al. 2015, 2016)

Derocher’s criteria for conditions that are ‘good’ for polar bears appears to be ‘like the 1980s’. He is hoping the public don’t realize that for the last 5 years at least, conditions have been almost identical to the 1980s (there was even a late freeze-up in the 1980s, in 1983).

However, Derocher, along with senior colleague Ian Stirling, is also willfully ignoring the great years of starvation, lower reproductive rates, and high cub mortality that Western Hudson Bay bears went through between 1983 and the early 1990s (Crockford 2019b). Both now pretend the 1980s were nothing but good times. Not so – there was avery late freeze-up in 1983 that is rarely mentioned but it hit the bears very hard because (unlike 2016), they had not come off the ice in very good shape.

This is what I wrote earlier this year:

And as I discuss in my new book, The Polar Bear Catastrophe That Never Happened, poor body condition, lowered reproductive rates and much reduced cub survival was a hallmark of Western Hudson Bay polar bears in the 1980s and early 1990s – before declining sea ice was any kind of issue but when polar bear numbers were higher than they’d been in perhaps a century or more (Derocher 1991; Derocher and Stirling 1992, 1995; Ramsay and Stirling 1988).

Too many bears relative to the food supply seemed a logical explanation at the time. But before Stirling had time to investigate fully, he jumped on the climate change bandwagon and banged the climate drum so loudly that concerns about WH bears in the 1980s were forgottern. From that point forward, everything bad that has happened to polar bears in general – and Western Hudson Bay bears in particular – has been blamed on global warming (Stirling and Derocher 1993; Stirling et al. 1999, 2012).

Derocher admitted to Mail on Sundayjournalist David Rose that Western Hudson Bay bears have not been suffering in recent years but that’s a back-handed compliment. It’s hard to imagine that life has not been ‘good’ for polar bears over the last five years given the 1980s-like breakup and freeze-up dates and reports of bears coming ashore in great condition every year. If Derocher wants to argue otherwise, he is going to have to present strong data from his field research to support his claim instead of twitter bluster. And if Western Hudson Bay population numbers aren’t up at the next count, there is good reason to ask why not.

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

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. http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12050/abstract

Crockford, S.J. 2017. Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus). PeerJ Preprints 19 January 2017. Doi: 10.7287/peerj.preprints.2737v1 Open access. https://peerj.com/preprints/2737/
Crockford, S.J. 2019a. State of the Polar Bear Report 2018. Global Warming Policy Foundation Report 32, London. pdf here.

Crockford, S.J. 2019b. The Polar Bear Catastrophe That Never Happened. Global Warming Policy Foundation, London. Available in paperback and ebook formats.

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., 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., 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