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A Perishing Predator: Polar Bears Starve as Ice Recedes

Authors: Samantha Abarca, Vincent Chevreuil, Ray Hunter

Polar bears. Just seeing the name conjures images of an enormous apex predator with fearsome canines and deep, black eyes, able to propel itself through snow and water with equal ease. Weighing up to 600kg, these beasts spend days on end searching for food in a sub-freezing oasis of barren ice (1). If a polar bear gets lucky, it can snatch a ringed seal with its narrow jaws  and razor sharp claws and sustain itself for a few days until the next victim is found (2). 

Unfortunately, this doesn’t seem to be the case anymore. As global warming continues on a seemingly unstoppable course, a domino-like chain of environmental effects is having devastating impacts on polar bear populations, leaving them poisoned, emaciated, and on a desperate search for declining food sources. Reduction of sea ice and viable prey, both of which are essential for polar bear survival, have made surviving the harsh Arctic conditions nearly impossible for these animals. The root of all these threats plaguing polar bears lies close to home - our cars, our agriculture, our consumer lifestyles, and the exorbitant waste products of material society. Polar bears have become hostages to our waste, and if we don’t hurry they may become victims to it as well. 

Polar bears are dependent on large sheets of floating arctic ice, and spend much of their time using the ice to move, hunt, and find mates (3). With warming sea temperatures, the sea ice habitat they depend on for survival melts away into the ocean, literally fragmenting their homes and their lives. They are forced to travel and swim further and further to find fat-rich prey. These longer migrations increase energy demand, forcing hungry polar bears deeper into energy deficits (4). Unlucky polar bears may not find food for themselves or their cubs, and may even starve to death (3). The lack of food and longer migrations result in the starving, emaciated images we now frequently capture of the once-proud polar bear.

In the arctic regions of the world, the presence of ice is crucial for the wellbeing of seal populations as well. Where there is ice, there are seals, and a reduction of sea ice means a similar loss in the polar bear’s favorite food, the Ringed Seal. Ice serves as a habitat and breeding ground for these seals, so as it melts, these seals experience a similar reduction as the polar bear (3). In this way, climate change dramatically alters the predator prey dynamics between seals and polar bears. Fragmentation of ice sheets pushes seals hunting grounds further and further back along the stable ice which in return alters travel behavior and foraging in polar bears. The polar bear’s high metabolic rates (due to increased travel) and declining food intake means that they end up fasting for longer stretches of time (5). What’s worse is that these limitations can even affect the next generation - mother polar bears may lack the energy to produce milk and bring back food to the den, leading to high infant mortality (3). In return, a declining population puts more stress on individuals to find mates and reduces the genetic variation in a given area. It acts as a sort of positive feedback loop in which increased arctic sea ice melt indirectly drives down polar bear populations in many other ways.

In the search for new food, polar bears have turned to warm-water fish species that have migrated up north with increasing temperatures. These fish act as “biovectors” for manmade pollutants; in other words, they are convenient edible packages of pesticides, preservatives, and industrial runoff (4). These fish spend their time in more southern waters where they are exposed to much of the artificial chemicals and pollutants that humans introduce into marine environments. The fish grow up feeding on these compounds and collectively building up large concentrations of these pollutants in migratory populations (4). Due to polar bears’ high metabolic rates, they need to consume many of these little poisoned swimmers to meet growing energy demands. As polar bears start feeding on this new food source, these pollutants concentrate in the malnourished polar bear’s thin body, and may ultimately become toxic to them when enough is consumed (4). It is even possible that these pollutants are transferred from mother to cub via milk which introduces these poisons to young ones directly after birth. These pollutants have proven to disrupt physiological processes in the body and the brain, impacting regulation, metabolism, and even reproductive behavior (4). Alongside with climate change, these compounds are drastically reducing polar bear populations to alarming low levels.

The good news about all of this is that it is not too late to do something. We are still at a point in time where global emissions can be reduced to counteract climate change and not hit a threshold of unstoppable positive feedback loops. The Intergovernmental Panel on Climate Change (IPCC) claims that we need to remain under 1.5 °C post industrial revolution temperatures to prevent the worst possible outcomes (6). Even though it may seem like hope is lost at times and there is not much that can be done at this point, we still have a very strong fighting chance to save not just ourselves, but all of the wildlife around us. Reducing your carbon footprint can make a big difference in the long run and set an example to those around you. Consuming less meat and dairy as well as driving less are two big ways to help at an individual level. Voting for people in office who care about climate change and take active initiative to combat it is absolutely crucial in reforming policies concerning the climate and endangered animals. We have a voice in the government, so vote responsibly for representatives that share a concern for the wellbeing of our world. Lastly, contribute to environmental organizations who lobby and make a stand against large corporations that contribute to climate change. Individually, these actions can seem inconsequential. But collectively, they add up to enormous positive changes to our world - and just might save some polar bears.

Image Credits:

flickrfavorites. “Snow on Snout, Polar Bear.” flickr.com, 2009, www.flickr.com/photos/38485387@N02/3582475670.

Weith, Andreas. “Starving Polar Bear.” wikipedia.com, 2015, www.wikipedia.org/wiki/File:Endangered_arctic_-_starving_polar_bear.jpg.

All images shown are free to share under a Creative Commons license.


Citations

  1. I. Stirling, Polar Bear: Ursus maritimus. In Encyclopedia of Marine Mammals (pp. 888-890). Academic Press (2009).
  2. C. Freitas,  K. M. Kovacs, M. Andersen, J. Aars, S. Sandven,  M. Skern-Mauritzen, C. Lydersen, Importance of fast ice and glacier fronts for female polar bears and their cubs during spring in Svalbard, Norway. Marine Ecology Progress Series, 447, 289-304 (2012).
  3. P. K. Molnár, A. E. Derocher, G. W. Thiemann, M. A. Lewis, Predicting survival, reproduction and abundance of polar bears under climate change. Biological Conservation, 143(7), 1612–1622 (2010).
  4. B. M. Jenssen, G. D. Villanger, K. M. Gabrielsen, J. Bytingsvik, T. Bechshoft, T. M. Ciesielski,  R. Dietz. Anthropogenic flank attack on polar bears: interacting consequences ofclimate warming and pollutant exposure. Frontiers in Ecology and Evolution, 3 (2015).
  5.  A. M. Pagano, G. M. Durner,  K. D. Rode, T. C. Atwood, S. N. Atkinson, E. Peacock, T. M. Williamsc. High-energy, high-fat lifestyle challenges an Arctic apex predator, the polar bear. Science, 359(6375), 568–572 (2018).
  6. “Summary for Policymakers of IPCC Special Report on Global Warming of 1.5°C Approved by Governments.” IPCC Summary for Policymakers of IPCC Special Report on Global Warming of 15C Approved by Governments Comments, 2018.

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