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Understanding sea ice break up and impacts on Arctic wildlife in Hudson Bay

2010-02-05

Understanding sea ice break up and impacts on Arctic wildlife in Hudson Bay

Arctic environments are experiencing climate change-induced warming at twice the global rate. Over the past 30 years, scientists have found that sea ice is breaking up as much as three weeks earlier in the year, resulting in primary productivity in the North starting much sooner in the year than before.

In response, some species are altering their breeding behaviour and feeding habits, in some cases with adverse consequences for populations and ecosystems. These changes will have an impact on traditional harvesting practices of northern peoples and communities, whose physical and cultural health is derived in part from marine resources.

Environment Canada wildlife researchers Dr. Tony Gaston, Dr. Birgit Braune and Dr. Robert Letcher study the impacts of earlier sea ice break up on wildlife in Hudson Bay to explain how climate change affects species, ecosystems, and the distribution of harmful chemicals in the North. Tracking these changes in wildlife will allow researchers, policy makers, and northern communities to better plan and adapt to a warming climate.

Sea ice break up and food availability for thick-billed murre chicks

Tony Gaston descends the cliffs at Coats Island to band thick-billed murres | Photo: Leah de ForestSeabirds are excellent indicators of ecosystem change, and for the past 30 years, Dr. Tony Gaston has been monitoring changes in seabird diet, breeding cycles, and population trends at colonies across Canada. An important colony of thick-billed murres nesting on Coats Island in northern Hudson Bay is the focus of a partnership project for the International Polar Year.

Gaston’s research has shown that while sea ice is breaking up as much as three weeks earlier than it did 20 years ago, the birds’ breeding schedules are lagging behind by 12 days. This ‘mismatch’ in avian breeding cycles leads to the birds feeding their young after the timing of peak availability of food.

Missing this feeding opportunity means that adult birds must work harder to provision their chicks, and the chicks leave the colony at a lighter weight, a factor that can reduce their chances of survival.

If these trends continue, says Gaston, it could lead to a reduction in recruitment of seabirds adapted for Arctic living, with more southern species taking their place – something that is already happening in Hudson Bay.

Gaston has also observed a change in nestling diet, with the ice-associated Arctic cod being replaced by lower trophic level Arctic fish, such as capelin, which have a lower fat content and are less nutritious for growing murre chicks.

Seabirds utilize food webs over a wide area of the marine environment during their travels between overwintering and breeding areas. Therefore, information gathered from one location can apply to vast marine areas. This is a relatively easy and economical means to gather information that would require intensive resources to acquire otherwise.


Continuing research sheds light on understanding connections between sea ice break up, species adaptations, and changing contaminant exposure

Thick-billed murre pair with offspring Prince Leopold Island | Photo: Timothy J.F. LashWork continues on understanding how earlier warming can change species behaviour and health. As part of the Northern Contaminants Program and in collaboration with International Polar Year studies, Dr. Birgit Braune and her research partners are conducting a study on thick-billed murres in Hudson Bay. They want to know if changes in levels of mercury and other persistent and bioaccumulative contaminants in the birds can be attributed to a change in feeding pattern linked to earlier sea ice break up, in conjunction with changing contaminant levels in the environment.

Her research team has proposed that birds’ exposure to contaminants may have changed over the past 20 years due, in part, to the observed change in the species of fish they eat, from Arctic cod and benthic fish species, to capelin and sandlance.

It is proposed that this diet shift may decrease birds’ exposure to toxic chemicals over time, but as these fish are smaller and less nutritious, the birds will have to travel farther and expend more energy to obtain the dietary requirements they need to survive. The relationship between contaminant exposure and bioenergetic demand is still currently under investigation and conclusions from Braune and her collaborators’ study will be forthcoming later in 2010.

Arctic climate change affects sea ice condition, diet and the rate of contaminant level changes in polar bears

Polar bear during summer in the Davis Strait | Photo: Elizabeth PeacockSimilar to seabirds, polar bear mating and feeding is also timed to correspond with sea ice break up. As part of International Polar Year, Dr. Robert Letcher, Ph.D. student Melissa McKinney, and other research partners have been studying the western Hudson Bay sub-population of polar bears because, at the southern point of the species’ range, it is more affected by warming than its northern counterparts.

Recent studies show that early sea ice break up is linked to lower body condition, and to lower birth and survival rates in this sub-population.

At the same time, Letcher and coworkers have reported that this sub-population of polar bears appears to have experienced a shift in diet over the last 20 years as a result of the change in sea ice condition. Over time this dietary shift has been linked to changes – positive or negative depending on the contaminant class – in the rate of contaminant loading of various classes of organohalogen contaminants (OHCs), including some persistent and bioaccumulative contaminants like polychlorinated biphenyls, organochlorine pesticides, and polybrominated diphenyl ethers and other brominated flame retardants.

The alteration in the rate of change of OHC levels over time, as indicated by dietary tracers – fatty acids, and stable isotopes – appears to be the result of the bears’ dietary shift from ringed and bearded seals to harbour and harp seals. These latter seal species accumulate more contaminants in their tissue because they eat at a higher trophic level with a diet rich in fish. Upon ingesting the seals, polar bears uptake the toxic chemicals, which become more concentrated yet again, and may pose health risks to subsistence hunters who eat a traditional diet.

This dietary shift may be altering the level and type of chemical stress, and is one more pressure on polar bear populations already contending with a loss of hunting grounds in a warming world.

Organohalogen contaminants are highly persistent and bioaccumulative chemicals that have been found to cause cancer and adversely affect reproductive success, immune health, neurodevelopment, cardiovascular function, and hormonal balance.


Living in a changing environment

Greater understanding of how climate change is altering the Arctic environment can help scientists and decision makers create science-based policy to help protect, conserve, and restore northern ecosystems and species. Environment Canada expert wildlife researchers like Gaston, Letcher and Braune are collectively leading the way to understanding how climate change affects species and ecosystems, what these changes mean, and how to develop science-based public policy that will better position northern communities to plan, adapt, and live in a changing environment.

For more information

Visit Environment Canada expert profiles to learn more about the scientific interests and projects of each researcher:

  • Dr. Tony Gaston is working in partnership with researchers from Memorial University of Newfoundland, the University of Manitoba, the University of Victoria, the British Antarctic Survey UK, consultants, and other Environment Canada scientists including those from the Canadian Wildlife Service.
  • Dr. Birgit Braune is working in partnership with other researchers at the National Wildlife Research Centre, the University of Victoria, Fisheries and Oceans Canada, and Environment Canada researchers including scientists from the Canadian Wildlife Service.
  • Dr. Robert Letcher is working in partnership with other Canadian and international circumpolar, polar bear and Arctic scientists, including those from Government of Nunavut, U.S. Fish and Wildlife Service, Norwegian Polar Institute and other Norwegian institutes, and the Danish Department of the Environment. 

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