9/9/2014 6:02:18 PM
Impressions of Polar Bears in Svalbard in Early Summer, 2006-2014
For the last nine summers, I have been working for about a month early in the season as an ecotourism guide in Svalbard (the Norwegian Arctic). I go at that time of year because of the opportunity to observe the behavior of undisturbed polar bears on the sea ice and adjacent land areas. Late spring and early summer, before the annual ice disappears completely, is the most important time of the year for polar bear hunting. That is because the large annual crop of fat, newly weaned ringed seal pups—which are probably less wary of predators—along with the ever-present adult and subadult seals, are all available.
Compared to most other species of seals, ringed seals are small, but especially the newly weaned pups (20-25 kg), so they can be successfully captured by subadult polar bears just learning how to survive, as well as by young, less experienced females with their first litters of cubs. Most bears probably accumulate up to about two thirds of the fat they will need to survive the entire year during this vital feeding period prior to breakup of the annual ice in early summer.
However, polar bears need sea ice to be able to hunt seals because catching them in open water is a rare event. Thus, when breakup becomes progressively earlier, it shortens the amount of potential hunting time available to the bears at the most important time of year, resulting in some individuals being in abnormally poor body condition.
Breakup of the annual ice in the spring in Svalbard has been occurring progressively earlier in recent years, and freeze-up in the fall significantly later, than was the case only a couple of decades earlier. This trend has been most apparent on the western and southern coasts of the main island of Spitsbergen because of the incoming flow of warmer water from the Gulf Stream—a combination that can create problems for polar bears with home ranges centered on those areas. Even over the brief period I have been going to Svalbard, I have been surprised by some of my opportunistic observations of polar bears in relation to the ongoing effects of climate warming on the sea ice.
For example, last year we found a 16-year-old bear, with a history of living at the southern end of Spitsbergen, dead on a small islet at the north end of the island, far from where he had ever been known to range before (see related blog post). He was in good condition when he was captured three months earlier that year and should still have been in his prime at that age.
However, in the months that followed, most of the annual sea ice that would normally be present in the fiords where he usually lived was gone. When we found him on the north end of the island, he was but an emaciated shadow of his former self. It appeared most likely he starved to death while searching for better ice from which to hunt seals, though we were unable to collect specimens for a laboratory analysis to confirm the cause of death. In recent years, several other dead bears have been reported from different locations around the archipelago but, similarly, the causes of death have not been confirmed from an analysis of specimens.
Even by the standards of the rapid changes in amounts of sea ice around Svalbard in recent years, the timing of freeze-up and breakup through the winter of 2013-2014 was eye-popping. Freeze-up did not occur throughout much of the archipelago until early December or later. The map below shows how little ice was present around the coast of the entire archipelago as late as December 2. Note there is still a substantial amount of open water around the circumference of the entire archipelago! Very little annual ice formed at all in some of the fiords along the west coast of Spitsbergen through most of the following winter.
Further to the east, the ice did not get close enough to some formerly important denning areas, such as Hopen Island and Kong Karl's Land, in time for the pregnant females to dig their maternity dens in the snow drifts there. In a recent paper (see reference below) Andrew Derocher and colleagues showed that if the sea ice didn't reach Hopen Island by the middle of November at the latest, very few females were able to get to the island in time to den have their cubs there. In recent years, there has been little or no sea ice near Hopen Island by this time in the fall. In southern and western Spitsbergen, much of the ice was already gone from the fiords by the middle of May. The late freeze-up and low amounts of snow cover meant that ringed seal reproductive success was reduced and many of those pups that were born, were delivered onto open ice instead of into protective birth lairs beneath the snowdrifts, making them more vulnerable to predation. Superficially, it might appear to be beneficial for the bears to be able to capture lots of newborn ringed seal pups shortly after being born directly onto open ice. However, newborn seals weigh only 5-7 kg, of which about a third is fat. However, by late May, a pup may be weaned and weigh 20-25 kg, of which over 70% may be fat. This simple comparison illustrates why the energy value to a bear of killing very young ringed seal pups is so limited.
Perhaps not surprisingly, in view of these factors, in April 2014, Dr. Jon Aars of the Norwegian Polar Institute documented a marked reduction in reproductive success in Svalbard's polar bears. Only 10% of his sample of adult female polar bears with satellite radios (10 of 29) were accompanied by newborn cubs compared to a more normal rate in excess of 30% (see related news item).
In the last few years, I have observed several female polar bears with small cubs on land in several different areas of Svalbard, beginning their fast through the ice-free period, well away from the nearest sea ice, as early as late June or early July. More were in much poorer body condition than I would have expected that early in the summer. For example, the small cub with the thin mother I photographed on July 1, 2010 (see photo above) probably had over four months to go before the return of the sea ice. It is unlikely the cub survived. Although healthier females and cubs are also seen each year, especially in the more easterly and northern areas closer to where sea ice breaks up later in most years, even there I have seen more litters of thin cubs than I would normally expect early in the summer.
Other signs that polar bears are getting hungry early in the season include observations of bears trying to catch reindeer. Although the occasional bear has been observed feeding on a reindeer (which it may have killed or just be scavenging), successful predation of these faster running mammals is unusual. Even more surprising are increasing numbers of observations of polar bears expending inordinately large amounts of energy trying to feed on sea birds, their eggs, or their chicks in steep cliffs, such as the thin young bear observed on July 23, 2013 (see photo below). Bears have also been observed feeding on the eggs of skuas, arctic terns, eiders, and especially barnacle geese. However, despite the occasional irresponsible suggestion that somehow polar bears are going to adapt to the loss of ice by just feeding on land on things like goose eggs or chicks, the necessary energetic benefits are simply not there.
In the short-term at least, newly weaned pup and subadult bearded seals haul out for short periods onto small pieces of ice produced by the continuous calving of the glaciers (see photo below). Bears stalk them by alternately breathing with just their noses above the surface and then swimming underwater as much as possible until they are close enough to try to get on the floe quickly enough to try to capture one. However, even subadult bearded seals are much larger than ringed seals and are probably difficult for most subadult polar bears, and likely many females, to keep from escaping for long enough to be killed on a small piece of ice. However, the chance of success for large adult males is greater and some very fat individuals have been observed feeding on bearded seals in fiords free of annual ice, even near the southern end of Svalbard.
It is too early to be able to fully assess how soon the changes in the pattern of breakup and freeze-up of the annual ice might be serious for the overall polar bear population at Svalbard. Will female polar bears that can no longer reach traditional denning sites such as Hopen Island or Kong Karls Land be able to successfully den elsewhere? How long might bears continue to live and reproduce successfully enough in the eastern and northern regions of Svalbard to sustain the population if the climate continues to warm? What will be the consequences of reduced ice in the fiords on the reproductive success of the seals that the bears depend upon in those areas for survival?
Some of my casual observations over the last few years, as outlined above, along with the results of ongoing scientific studies by the Norwegian Polar Institute, indicate that if climate warming continues unabated, there will likely be significant negative implications for polar bears and ice-breeding seals at Svalbard. However, the fundamental concept is clear: polar bears need ice from which to hunt seals. Without it, few will survive in the long term. However, it is certainly too early to give up hope. Studies published by several scientists indicate there is still time to stop climate warming in time to protect arctic ecosystems. Only time will tell if humans are able to organize sufficiently on a global basis to meet this challenge.
Dr. Ian Stirling is a volunteer scientific advisor to Polar Bears International and author of "Polar Bears: The Natural History of a Threatened Species." He has studied polar bears for more than 40 years.
Derocher AE, Andersen M, Wiig Ì÷, Aars J, Hansen E, Biuw M (2012) Sea ice and polar bear den ecology at Hopen Island, Svalbard. Marine Ecology Progress Series, 441, 273-279. (Anyone wishing a pdf copy of this paper can request it from Derocher@ualberta.com.)