Anthropogenic and natural changes in Arctic environments, as well as recognition of the shortcomings of our knowledge of Polar Bear ecology, are increasing the challenges for Polar Bear conservation and management. Higher ambient temperatures and erratic weather fluctuations, symptoms of anthropogenic climate change, are increasing across the range of polar bears. Polar Bears are dependent upon Arctic sea ice for access to their prey. Their dependence on an ephemeral habitat that exists as a function of sea surface and atmospheric temperatures means that climate warming poses the single most important threat to the long-term persistence of Polar Bears (Obbard
et al. 2010). Arctic sea ice loss has thus far progressed faster than most climate models have predicted (Stroeve
et al. 2007) with September sea extent declining at a linear rate of 14% per decade from 1979 through 2011 (Stroeve
et al. 2012, Stroeve
et al. 2014). Because changes in sea-ice are known to alter Polar Bear abundance, productivity, body condition, and distribution (Stirling
et al. 1999, Fischbach
et al. 2007, Schleibe
et al. 2008, Durner
et al. 2009, Regehr
et al. 2010, Rode
et al. 2010a, 2012, 2014b, Bromaghin
et al. 2015), continued climate warming will increase future uncertainty and pose severe risks to the welfare of Polar Bear subpopulations (Stirling and Derocher 2012, Derocher
et al. 2013). Arctic sea ice extent is linearly related to global mean temperature, which in turn, is directly related to atmospheric greenhouse gas concentrations (Amstrup
et al. 2010). Population and habitat models predict substantial declines in the distribution and abundance of Polar Bears in the future (Durner
et al. 2009, Amstrup
et al. 2008, Hunter
et al. 2010, Castro de la Guardia
et al. 2013, Hamilton et al. 2014). Although Polar Bears living in historically colder regions of the Arctic might derive transient benefit from a climate-driven transition away from multi-year ice (Derocher
et al. 2004), the annual sea ice must persist long enough for Polar Bears to derive benefit from associated changes in seal availability and biological productivity. Recent sea ice simulations suggest large regions of the Canadian Arctic Archipelago will be ice free for >5 months by the late 21
st century (Hamilton
et al. 2014). In other parts of the Arctic, the 5-month ice-free threshold may be reached by the middle of the 21
st century (Atwood
et al. 2015). These studies are based on sea-ice data obtained from the World Climate Research Programme's Coupled Model Intercomparison Project phase 5 (CMIP5) (
http://cmip-pcmdi.llnl.gov/cmip5/). An annual ice-free period of ≥5 months is likely to lead to extended fasting, which is predicted to lead to increased reproductive failure and starvation (Molnár
et al. 2011, 2014a, Robbins
et al. 2012b). Nevertheless, uncertainty and regional variability in the near-term effects of climate change must be included in Polar Bear management and conservation plans.
Although there have been local and regional studies on polar bear denning habitat (Kolenosky and Prevett 1983, Messier
et al. 1994, Lunn
et al. 2004, Richardson
et al. 2005, Durner
et al. 2003, 2006, 2013, Andersen
et al. 2012), large scale mapping of Polar Bear denning habitat across the Arctic has not occurred. It is also unknown how climate change will change denning locations and habitats, though predicted increases in forest fires may have adverse effects on maternity denning habitat in sub-Arctic regions (Richardson
et al. 2007). Declining sea ice availability can impair the ability of pregnant females to reach traditional denning areas (Derocher
et al. 2011, Cherry
et al. 2013) and increases of rain events will be detrimental for denning Polar Bears (Stirling and Derocher 1993, Derocher
et al. 2004).
The occurrence of diseases and parasites in Polar Bears is rare compared with occurrences in other ursids. However, with warming Arctic temperatures, altered climate could influence infectious disease epidemiology through mechanisms such as novel pathogen introduction due to range expansion of carrier animals and arthropod vectors; modification of host susceptibility; changes in pathogen evolution, transmission, and number of generations per year; host immunosuppression; shifts in main food sources; altered behaviour; and co-infections with multiple agents (Harvell
et al. 2002, Parmesan 2006, Burek
et al. 2008, Hueffer
et al. 2011). As a result, the potential for exposure to pathogens and resulting disease outbreaks may become more significant threats as Polar Bears experience the cumulative effects of multiple stressors (Patyk
et al. 2015).
The warming climate has been associated with an increase in pathogens in other Arctic marine and terrestrial organisms. Parasitic agents that have developmental stages outside the bodies of warm-blooded hosts (e.g., nematodes: Laaksonen
et al. 2010) will likely benefit from the warmer and wetter weather projected for the Arctic. Improved conditions for such parasites have already adversely affected the health of some Arctic mammals (Kutz
et al. 2013). Bacterial parasites also are likely to benefit from a warmer and wetter Arctic (e.g.,
Vibrio parahaemolyticus; Baker-Austin
et al. 2012). As the effects of climate change become more prevalent, there is concern about the emergence of new pathogens within polar bear range, new threats from existing pathogens that may be able to infect immuno-compromised/stressed bears, and the potential for new and existing pathogens to cross human–animal boundaries (e.g., giardia). Because of the previous limited exposure of Polar Bears to diseases and parasites (Fagre
et al. 2015), researchers have as yet been unable to determine whether they will be more susceptible to new pathogens. However, concern is exacerbated by the fact that Polar Bears appear to have a naïve immune system (Weber
et al. 2013), which may make them particularly vulnerable to infection. Many different pathogens have been found in seal species that are Polar Bear prey; the potential therefore exists for transmission of these diseases to Polar Bears (Kirk
et al. 2010). If Polar Bears become nutritionally stressed, altered foraging behaviours such as increased feeding on the internal organs of their primary prey and use of alternative foods (e.g., Prop et al. 2015) may increase the potential for exposure to pathogens. Ensuring the long-term persistence of Polar Bears will necessitate understanding how a rapidly changing physical environment modulates exposure to disease risk factors and, ultimately, population health.
Persistent organic pollutants, which reach Arctic regions via long range transport by air and ocean currents as well as river run off, also increase uncertainty for the welfare of polar bears (Obbard
et al. 2010,
www.pbsg.npolar.no). Although Polar Bears live in relatively pristine Arctic regions, a variety of industrial toxic substances are brought into Polar Bear management areas from human anthropogenic activities around the world. Polar Bears are apex predators and are therefore exposed to high levels of pollutants, which magnify with each step in the food web resulting in high concentrations in polar bear tissue (Letcher
et al. 2010). A key characteristic of these pollutants is that they persist in the environment due to low biotic and abiotic degradation. The contaminant burdens among Polar Bears are known to vary among regions (e.g., Letcher
et al. 2010, McKinney
et al. 2011). Even where contaminant burdens may be known, their effects on Polar Bear physiology and health are not well understood (Letcher
et al. 2010, Sonne
et al. 2012). However, Dietz
et al. (2015) showed that the risk for reproductive, immune suppressive and carcinogenic effects in polar bear subpopulations across the Arctic are high due to PCB and perflourinated compounds (PFCs) exposure.
Many of the contaminants are lipophilic and bond tightly to lipophilic tissues. Polar Bears are particularly vulnerable to organochlorines because they eat a fat rich diet. Ringed, bearded, and harp seals comprise the main food of Polar Bears and the blubber layer is preferentially eaten by the bears and subsequently, the intake of pollutants is high (Letcher
et al. 2010). Recent studies have documented new pollutants in polar bear tissues which expose the species to even more toxic and complex combination of industrial chemicals (Verreault
et al. 2005, 2006; Muir
et al. 2006; Smithwick
et al. 2006; McKinney
et al. 2009, 2011; Gebbink
et al. submitted). The potential for contaminants to impact Arctic systems is predicted to increase as climate warming alters global circulation and precipitation patterns (Macdonald
et al. 2005, Jenssen
et al. 2015) and predicting local and regional effects will become more complicated and uncertain.
A three decade study (1983-2010) of East Greenland Polar Bears revealed both declines of conventional POPs and increases in brominated flame retardants (BFRs) and PFCs (Dietz
et al. 2008, 2013a,b; Riget
et al. 2013). The last decade has showed climate related increases in PCBs as well as peaks of BFRs and PFCs due to recent industrial reductions (Dietz
et al. 2013b McKinney
et al. 2013).
Although the effects of pollutants on polar bears are only partially understood, levels of such pollutants in some subpopulations are already sufficiently high that they may interfere with hormone regulation, immune system function, and possibly reproduction (Wiig
et al. 1998; Bernhoft
et al. 2000; Skaare
et al. 2000, 2001; Gustavson
et al. 2015; Henriksen
et al. 2001; Derocher
et al. 2003; Derocher 2005; Dietz
et al. 2015; Sonne
et al. 2015). There are suggestions that species with delayed implantation are more vulnerable to the effects of pollution through endocrine (hormone) disruption (Knott
et al. 2011). Further, because female Polar Bears are food deprived during gestation, their pollution load increases in their blood, when energy and pollutants are mobilized from their adipose tissue. Because the cubs are nursed on fat rich milk they are exposed to very high pollution loads from their mother (Polishuk
et al. 2002, Bytingsvik
et al. 2012). This may pose the greatest threat to the species as the vulnerability of pre- and neonatal polar bears is the most sensible to life-long health effects from long-range transported pollution which decreases immunity, survival and reproductive success (Letcher
et al. 2010, Sonne 2010).
An additional emerging threat to Polar Bears is the increase in resource exploration and development in the Arctic along with increased ice-breaking and shipping. There are currently no data on the effects of ice-breaking on habitat use by Polar Bears. Although some studies suggest that Polar Bears are sensitive to localized disturbance at maternity den sites (Lunn
et al. 2004, Durner
et al. 2006), our knowledge about potential effects of large scale development is lacking.
Oil development in the Arctic poses a wide of range of threats to Polar Bears ranging from oil spills to increased human-bear interactions. It is probable that an oil spill in sea ice habitat would result in oil being concentrated in leads and between ice floes resulting in both Plar Bears and their main prey (Ringed Seal and Bearded Seal) being directly exposed to oil. Polar Bears are often attracted by the smells and sound associated with human activity. Polar Bears are known to ingest plastic, styrofoam, lead acid batteries, tin cans, oil, and other hazardous materials with lethal consequences in some cases (Lunn and Stirling 1985, Amstrup
et al. 1989, Derocher and Stirling 1991). Another concern is that seals covered in oil may be a major source of oil to polar bears. Although the biological threats and impacts of oil and gas activities on Polar Bears are reasonably well understood (Øritsland
et al. 1981; Hurst and Øritsland 1982; Stirling 1988, 1990; Isaksen
et al. 1998; Amstrup
et al. 2006), mitigation and response plans are currently lacking (but see Wilson
et al. 2014). Moreover, how Polar Bears will be affected by other types of human activity are less well known (Vongraven
et al. 2012).
Significant portions of the Polar Bear’s range already are being developed and exploration is proposed for many other areas. With warming induced sea ice decline, previously inaccessible areas will be exposed to development and other forms of anthropogenic activities (e.g., trans-Arctic shipping, tourism). The direct effects of human activities, the increased potential for negative human-bear encounters, and the potential for increased local pollution are all concerns that must be understood if we are to understand and manage impacts on the future for Polar Bears.
Our understanding of Polar Bear population dynamics has improved with ongoing development and refinement of analytical methods (e.g., Taylor
et al. 1987, 2002, 2005, 2006, 2008a,b, 2009; Amstrup
et al. 2001; McDonald and Amstrup 2001; Regehr
et al. 2007, 2010, 2015; Aars
et al. 2009; Stapleton
et al. 2014). These improved and new tools suggest that previous estimates of population parameters and numbers can be biased. Vital rates are subpopulation specific, and different from the generalized rates that were often used to generate previous status reports (Taylor
et al. 1987). For the two subpopulations (Southern Beaufort Sea, Western Hudson Bay) that are known to have been impacted by climate change and where a long time series of abundance exist, harvest represents an additive impact. Illegal take of polar bears in Russia, combined with legal subsistence harvest in the U.S., may exceed sustainable limits for the Chukchi subpopulation (
pbsg.npolar.no). In many cases harvest documentation and the population data necessary to assess the impact of harvest both are insufficient to allow managers to provide the desired balance between potential yield and take. Given the cultural and economic importance of Polar Bear hunting in many regions, understanding the potential for and the impact of hunting continues to be a critical part of management (Obbard
et al. 2010, Vongraven
et al. 2012,
pbsg.npolar.no).
It is important that subpopulation estimates and projections are based on substantiated scientific data. In some areas, studies to estimate abundance occur infrequently so if the harvest rate is either initially set above the sustainable level or it becomes so, the subpopulation may be reduced before the next inventory is made. In addition, harvest practices may have to be reconsidered given recent knowledge about long-term environmental trends and fluctuations that can affect sustainable removal rates. In some jurisdictions in Canada, the governance system includes aboriginal co-management boards and aboriginal hunting organizations. In some of these co-management systems, both local knowledge and science are to be considered equally in both management and research decisions. Although scientific studies have concluded that the long-term effects of capturing and collaring polar bears are minimal (Ramsay and Stirling 1986, Messier 2000, Thiemann
et al. 2013, Rode
et al. 2014a), some local groups nevertheless consider these techniques disrespectful or harmful to the animals. As a result, population inventory and ecological studies have been delayed or not permitted. On the other hand, alternative research techniques such as aerial surveys and genetic biopsy capture-recapture methods were designed and implemented. Reduced monitoring will constrain governments’ ability to assess sustainability of harvest especially if abundance is estimated from aerial surveys which cannot provide data on vital rates (Aars
et al. 2009, Stapleton
et al. 2014).
Human caused habitat change and increasing human-bear interactions also must be incorporated into polar bear population projections (e.g., Hunter
et al. 2010) and polar bear harvest management in the future. Due to increased access to previously isolated areas, Polar Bears will face increased risks from a variety of human–bear interactions. New settlements are possible with industrial development, and expansion of tourist visitations is assured. Although the fact of human–bear interactions can be reasonably measured, we have a long way to go to understand the effect of such interactions. The added stresses, resulting from a “more crowded” Arctic, may play an important role in the future welfare of Polar Bears.