The significant content of a new paper being heavily-hyped from the media1 is what wasn’t said rather than what the writers discovered about metabolic rates and weight maintenance of a little sample of eight Southern Beaufort Sea occupies in 2014 to 2016 (Pagano et al. 2018; Whiteman 2018).

This paper does not document starving or dying bears but only found some (5/9) that lost weight when they should have been gaining, provided that early April will be the start of the ringed seal pupping season (Smith 1987) and also the intensive spring feeding period to get polar bears (Stirling et al. 1981).

The question is, why were Southern Beaufort Sea polar bears off Prudhoe Bay (see map of the study region below), still hunting and capturing just adult and subadult ringed seals from sea ice contributes if newborn ringed seal pups and their mothers should have been abundant and comparatively easily available within theirabout the sea ice (see below)?

“Using video collar info, we recorded bears’ hunting behavior and foraging success. Bears used sit-and-wait tactics to hunt seals 90% of the time, and also stalking comprised the remaining 10% of hunts (movies S1 to S4) (19). Bears that successfully killed and ate adult or subadult ringed seals gained or maintained body mass, whereas conveys that just scavenged or showed no signs of ingesting lost mass”

There isn’t any discussion in the paper of ringed seal birth lairs, or sea ice conditions at the time of the analysis, but many mentions about what could occur in the near future to sea ice and possible implications for polar bears. The did exactly the same.

However, because you’ll see from the sea ice depth maps below, there may be good reason for the absence of ringed seal lairs, and an overall lack of seals except at the nearshore lead to forms due to tidal actions: the ice just a little further offshore ice appears too thick for a great crop of ringed seals in all three years of the analysis. That is reminiscent of circumstances that occurred from the (Burns et al. 1975; Cherry et al. 2009; Harwood et al. 2012, 2015; Pilfold et al. 2012; Stirling 2002, Stirling et al. 1987). Those events changed mostly occupies in the eastern half of the Southern Beaufort and so are almost certainly responsible to the recorded decrease in SB keep numbers from the 2001-2010 survey (Bromaghin et al. 2015; Crockford 2017; Crockford and Geist 2018).

It appears very strange to me that Pagano and colleagues implied no explanations for the unexpectedly weak showing of polar bear hunting success during their analysis except a bit of hand-waving about higher-than-we-thought metabolic rates from the bears. For years, I have stressed that the inevitable next episodes of heavy Southern Beaufort spring ice would lead to difficulties for polar bears and seals however, we would not understand it because whatever impacts were recorded would bee : I suspect that time could come.

Pagano et al. 2018 polar bear fat and energy fig 1

Figure 1 from Pagano et al. 2018 found to show just the study region off Alaska.

Here are some sea ice depth maps from the US Navy to its three years of the analysis, together with 2015 shown.

Beaufort sea ice thickness_2015 April 8 NRL

Ice depth map in the Naval Research Laboratory to get 8 April 2015. Take a look at the thick ring of 5 m thick ice along the specific stretch of Alaska coastline where the Pagano et al. 2018 study happened. Ringed seals can’t survive, let alone provide birth, at that sort of thick ice storm and have to move to regions of thinner ice using open leads (accessible to the west and east in 2015).

Beneath, ice depth map for April 2016, demonstrating slightly better conditions, especially to the east:

Beaufort sea ice thickness_2016 April 6 NRL

The group of thick multiyear ice (~5m thick) was more extensive in April 2016 but nevertheless present within the Pagano et al. 2018 study region. Thinner ice to the west and east would have been more appealing to mature ringed seals.

Beneath, ice depth map for April 2014, showing ice depth of 2 m or more across the Area, which is likely too thick in most areas for ringed seals:

Beaufort Sea ice thickness_arcticictnowcast_2014 April 18

Sea ice over the Pagano et al. 2018 analysis region at April 2014 wasn’t quite as thick as 2015 and 2016 (just 3 — 4.5m thick) but that was likely enough to drive breeding ringed seals off.   Note the absence of openings or regions of thinner ice that would attract seals except very close to shore.

In a roughly Beaufort Sea polynyas, I discussed what marine mammal biologists Ian Stirling and coworkers had to say about polar bears and also the effect of the Cape Bathurst polynya about the origin of polar bears in spring (Stirling et al. 1981:49):

“Polar bears prey mainly on ringed seals and, to a lesser degree, on bearded seals. Polar bears appear to be richer in polynya areas and together shoreleads, likely because the densities of seals are far greater and they are more assessable. As an instance, between March and June from the Beaufort Sea by 1971 through 1975, 87 percent of the sightings of polar bears were created adjacent to floe edges or in distant regions of 9/10 or 10/10 ice cover using intermittent patches of young ice hockey. [my bold]

Later, the Very Same authors discussed why those Regions of open water could be so important from the Southern Beaufort region (Stirling et al. 1981:54):

“One useful strategy is to ask what will occur if the polynya wasn’t there? Clearly this is impossible to evaluate in an experimental basis, but by examining the effects or natural seasonal variation, some useful insights could be gained. As an instance, the influence of quickly changing ice conditions to the availability of open water, and consequently on populations of seals and polar bears, has been found at the western Arctic. Apparently in reaction to severe ice conditions in the Beaufort Sea during winter 1973-74, also to a lesser level at winter 1974-75, amounts of ringed and bearded seals fell by roughly 50% and productivity by roughly 90%. Concomitantly, productivity and numbers of polar bears dropped markedly due to the decrease in the abundance of their prey species. in the event the shoreleads of the western Arctic or Hudson Bay ceased opening during spring and winter, the effect on marine mammals would be catastrophic.” [my bold]

Footnotes:

1. The media frenzy has been no doubt helped by the fact that the writers made accessible four movies  that were part of their supplementary material.

Images, Video, and Other Media (watch them ):

Movie S1
Video from a camera collar on a polar bear (keep #1) whereas to the sea ice of the Beaufort Sea at April 2014. This video shows an adult female polar bear in April 9, 2014 digging a hole in the sea ice to entice a seal to develop to breath because she proceeds to still-hunt at the place and then pounces throughout the ice into the water. The video reveals her April 10, 2014 walking to the sea ice and about April 11, 2014 moving a recently captured ringed seal. The video shows her April 12, 2014 interacting with the adult male polar bear.

Movie S2
Video from a camera collar on a polar bear (keep #4) while to the sea ice of the Beaufort Sea at April 2015. This video shows an adult female polar bear in April 16, 2014 swimming below the sea ice hockey. The video shows her April 18, 2014 still-hunting and pouncing through the ice into the water. On April 19, 2014, the video shows her still hunting and pouncing through the ice into the water at another place.

Movie S3
Video from a camera collar on a polar bear (keep #5) while to the sea ice of the Beaufort Sea at April 2015. This video shows that an adult female polar bear in April 12, 2015 ingesting the muscle from the remains of the old seal carcass. Later on the same day, she is shown walking to the sea ice hockey.

Movie S4
Video from a camera collar on a polar bear (keep #8) whereas to the sea ice of the Beaufort Sea at April 2016. This video shows that an adult female polar bear in April 10, 2016 grabbing and eating a ringed seal. The video shows her April 12, 2016 stalking, operating, and trying to grab a bearded seal.

A few of todays headlines, in no Specific order (note that the hyperbole):

Polar Bears Really Are Starving Because of Global Warming, Study Shows (National Geographic, February 2018).

Polar Bears Burn Calories Faster than Scientists Realized. That’s a Problem (InsideClimateNews, 1 February 2018)

Polar bears ‘running from food’ (BBC, 1 February 2018)

What Scientists Learned From Strapping a Camera to a Polar Bear (The Atlantic, February 2018)

High-tech bear-cams suggest polar bears with tougher time hunting (National Post, Canadian Press, 1 February 2018) g

Polar bears may become extinct quicker than was worried, study says(The Guardian, 1 February 2018)

As Arctic sea ice thins, therefore do polar bears(Chicago Tribune, 1 February 2018)

The North’s ‘apex predator’ jeopardized by receding sea ice in the Beaufort Sea, study says(CBC, 1 February 2018)

Pagano said it would be tough to say how widely these results could apply across the Beaufort Sea.

“How activity patterns and forging success rates may vary between regions and times of year is tough to speculate.”

Other researchers have shown declining polar bear populations across the Beaufort Sea area, but this study wasn’t meant to handle concerns of entire polar bear decrease from the North.

“For this study we are not looking at trends,” Pagano said.

“There’s no information here documentation of our results may relate to historical patterns simply because there is no advice, as far as we are aware, of what the activity levels were of those bears historically.”

Metabolism study signals more trouble ahead for polar bears (Reuters, 1 February 2018)

What Cameras about Polar Bears Show Us: It’s Tough Out There (New York Times, 1 February 2018)

Polar bears are wasting away at a changing climate (NATURE, 1 February 2018)

References