Over the past 30 years,
polar bears have increasingly exchanged
ringed seal with harp seal and hooded seal
in their diet. This change exposes the polar
bear to more contaminants, according to
a recent international study.
2013.09.19 | JENS C.
PEDERSEN - Harp seal with cub. Polar bears
increasingly exchange ringed seal with harp
seal and hooded seal in their diet and therefore
become exposed to higher concentrations
of contaminants. Photo: Rune Dietz, Aarhus
University.
Polar bear with adult hooded seal, which
make up an increasing share of their food.
The hooded seal can weigh up to 300-400
kg, so it is a large prey for the approx.
500 kg heavy polar bear. Photo: Rune Dietz,
Aarhus University
Researchers expect the
climate to become warmer in the future and
predict that climate change will have a
significant impact on the Arctic. How will
a warming Arctic affect the polar bears?
The East Greenlandic
population of polar bears resides in an
area where the Arctic sea ice is expected
to disappear very late. However, the decline
in the ice sheet here occurs at a rate of
almost 1% per year, one of the highest rates
measured in the entire Arctic region.
How does this affect
the prey of the polar bears – and, in turn,
the polar bears’ intake of contaminants?
An international team of researchers set
out to explore this question. The team counted
researchers from the Greenland Institute
of Natural Resources, Aarhus University
(Denmark) and a number of Canadian institutions
including: Dalhousie University, Great Lakes
Institute for Environmental Research, University
of Windsor, Carleton University and the
National Water Research Institute.
The researchers studied
the fatty acid profiles in the adipose tissue
from a unique material of 310 polar bears
hunted by East Greenland Inuits from the
Scoresbysund area in the years from 1984
to 2011. The composition of fatty acids
in the fat tissue of the polar bears namely
reflects the profile of fatty acids in their
diet.
The results show that
the polar bears primarily feed on three
species of seals: the high Arctic ringed
seal and the two sub-Arctic species harp
seal and hooded seal. Moreover, the results
showed that the diet of the polar bears
had changed over the almost 30 years during
which the samples were collected. In this
period, the average relative decline in
the ringed seal’s significance for the polar
bears’ diet was 42%. Similarly, the intake
of the sub-Arctic seals increased during
the same period. Also, the researchers found
that polar bears are generally in better
condition now, so at a first glance the
polar bears should be happy with this development.
Climate change undermines
improvements
There are, however, a couple of problems
that might mar the happiness, explains Professor
Rune Dietz, Aarhus University:
“The problem is that
the sub-Arctic seals the polar bear has
switched to have a higher content of contaminants
because they live closer to the industrialised
world and are higher up in the food chain.
Therefore, climate change undermines the
improvements that you would otherwise have
obtained owing to international regulations
in the use of environmental use of persistent
organic pollutants (POPs). We can see that
the content of the POPs after year 2000
decreases slower in the polar bear than
in the ringed seal.”
In the long term, the
polar bear may very well lose access to
the sub-Arctic seals as these depend on
packed ice, where they give birth to their
cubs and are exposed to sunlight allowing
them to form vital vitamin D.
