Polar bears are apex predators in the Arctic, and are often one of the first animals we recognize from this region. They are a dominating symbol in our culture of the strength and endurance of the Arctic, traveling great distances to catch prey – primarily ringed and bearded seals. Polar bears reside in 19 subpopulations across the Arctic, including Alaska, Canada, Greenland, Russia and Norway. The World Conservation Union (IUCN) estimates that there are between 20,000-25,000 polar bears in the world. However, these powerful and majestic animals are facing increased threats due to human activities.
Sea ice loss is lengthening the summer fasting period for polar bears throughout the arctic according to multiple studies. In fact, sea ice is melting at a rate of 28 percent a year – faster than ever before (Atwood et al., 2016). This loss of habitat results in an increased risk for muscle atrophy and impaired performance in hunting and traveling.
There is a reduction in these abilities because atrophied muscles fatigue easier, produce less maximum force, and impair balance and coordination. Muscle atrophy is further exacerbated by the decreased abundance of prey. Furthermore, polar bears are no longer able to hunt in their preferred ice shelf habitats, leading them to become “trapped.” There is uncertainty as to whether polar bears – who have adapted to an existence on the sea ice – can change to better survive in these new conditions. Ultimately, because polar bears travel extensive distances for foraging and match force exertion to prey body size for maximum hunting efficiency, muscle atrophy due to sea ice loss could be a contributing factor in the decline of polar bear survival (Whiteman et al., 2017).
Losing more polar bears is cause for concern. Polar bears are at the top of the food web, meaning that they can signal problems in the Arctic marine ecosystem. Additionally, apex predators play a fundamental role in ecosystem functioning, disease regulation, and biodiversity maintenance (Stier et al., 2016).
The wide array of research on polar bears and sea ice loss highlights the growing concern within the scientific community regarding induced climate change, polar sea ice integrity, and the ability for species to survive in a changing climate.
So what can we all do about it? Due to the decline in sea ice and the expansion of human activities, proactive management of human-polar bear interactions will be needed to reduce conflicts and risks for both parties. These conflicts can adversely affect wildlife populations in the area, causing economic losses, and endangering both human and polar bear safety. Atwood et al. suggest that monitoring the timing and rate of seasonal ice loss may be an effective, reasonable way for managers to prepare for these interactions and assure long term polar bear survival in these changing conditions.
In the end, the challenges facing polar bears are the same that impact us. We can already see the impacts of drought on food production in Africa, the Middle East, and other highly populated areas around the world. We all can make a difference by spreading awareness about these issues and by reducing our carbon footprints. If we really want to save polar bears and play a part in reducing carbon emissions. This is as easy as turning the lights off or walking/biking instead of driving daily. Political leaders need to initiate the transition to sustainable energy sources to reduce emissions on a large scale. You can help this by contacting your representatives and by voting for officials who care about these issues. If we all do our part, and if we see political action on these issues, we can make a difference.
Atwood TC, Peacock E, McKinney MA, Lillie K, Wilson R, Douglas DC, Miller S, Terletzky P. (2016). Rapid environmental change drives increased land use by an Arctic marine predator. PLOS One. 11: e0155932.
Pilfold NW, Hedman D, Stirling I, Derocher AE, Lunn NJ, Richardson E. (2016) Mass loss rates of fasting polar bears. Physiol. Biocehem. Zool. 89(5): 377-388.
Stier AC, Samhouri JF, Novak M, Kristin MN, Ward EJ, Holt RD, Levin PS. (2016). Ecosystem context and historical contingency in apex predator recoveries. Science Advances. 2(5): e1501769.
Whiteman JP, Harlow HJ, Durner GM, Regehr EV, Rourke BC, Robles M, Amstrup SC, Ben-David, M. (2017). Polar bears experience skeletal muscle atrophy in response to food deprivation and reduced activity in winter and summer. Conserv. Physiol. 5(1): 1-15.
Time to evolve?
Pacific salmon are incredibly valued in society. They are the primary food source of many marine animals, a desired seafood that boosts economies, and they play an integral part in Native American culture. They require a wide array of structural, physiological, and behavioral adaptations throughout their lifespans as they travel from freshwater to seawater, and then back to freshwater to spawn. These changing environments lead to challenges salmon must cope with to survive. They respond by altering the timing at which the critical events in their lives occur, otherwise known as phenology.
A very pressing question is how the salmon can adapt to the unpredictability of climate change, and how these adaptations may occur. A recently published study, “Evolution of phenology in a salmonid population: a potential adaptive response to climate change,” examined the genetic mechanisms in which these responses to environmental change originated in a population of pink salmon in Auke Creek, Alaska. The researchers, Manhard, Joyce, and Gharret, also sought to determine whether the traits expressed were a response to climate change.
To answer these questions, they utilized a technique called genetic monitoring, in which a genetic marker associated with an observable trait is studied through a certain timeframe to identify adaptive changes of interest. In this study, the marker used was the late-migrating marker locus (LMML) which correlated closely to – however did not alter - the genes responsible for a trait in the salmon that resulted in later migration times when expressed. Migration time was selected opposed to other traits because of its high heritability and responsiveness to environmental change.
Manhard, Joyce, and Gharret found that the presence of LMMA (the allele for the late-migrating marker) increased in the population between the years 1984-1990, but fell significantly in adult salmon returning to spawning grounds the following year. Similar patterns were seen in younger generations. These patterns suggest that an event caused this decline in LMMA frequency.
Furthermore, there was a reduction in the survival rate of late-migrating salmon within freshwater conditions during this time. Possible reasons for this include that later ocean entry time inhibits growth, leading to more predation and less ability to compete for food. There was a significant temperature increase between 1986 and 1990, potentially leading to the rise of early-migrating salmon. These results support the authors’ hypothesis that there is an adaptive response to climate change.
What does this mean? The findings contribute a better understanding of the role that temperature plays in these migratory traits as well as the ability of salmon to reproduce. They also suggest that changes in climate significantly impact salmon populations, although genetic variation still enables a level of resilience in fish populations and maintains some reproductive success. Ultimately, the findings in this study demonstrate the importance of sustainable fishing practices that protect genetic variation and the fish populations in the midst of a changing climate.
You can read the full study here: www.nrcresearchpress.com/doi/pdf/10.1139/cjfas-2017-0028
Manhard, C. V., Joyce, J. E., & Gharrett, A. J. (2017). Evolution of phenology in a salmonid population: A potential adaptive response to climate change. Canadian Journal of Fisheries and Aquatic Sciences, 74(10), 1519-1527.
Zach Affolter is a filmmaker, writer, and environmental advocate. He is currently the Resident Sustainability Adviser at Humboldt State University, and has served as a youth representative for Dolphin Project, Peta2, Earthrace, and Global Wildlife Warriors.