¨The diet of polar bears (Ursus maritimus) from
Svalbard, Norway, inferred from scat analysis.BIO-3910 Master thesis in biology
Northern populations and ecosystems
Marianne Iversen
The University of Tromsø
The Norwegian Polar InstituteAbstract:The diet of polar bears in the Svalbard area was assessed based analyses of scats
(n=119) collected in the Archipelago between 2003 and 2010. Most of the
samples were collected in spring. Morphological analysis of the prey remains
together with genetic analyses of tissue fragments found in the scats showed that
ringed seals (
Pusa hispida) were the most important prey group present; this seal
species occurred in 58% (CI 48.6%-67.0%) of the scats. Ringed seal pups were
particularly abundant (45.4%, CI 36.2%-54.8%).
Bearded seal (Erignathus
barbatus) and birds seemed to be minor components in the diet, while Svalbard
reindeer (Rangifer tarandus platyrhynchus), considering its size and the frequency
with which it occurred in the scats (9.2 %), likely plays a more important role in
the diet than previously reported. Whether reindeer are hunted actively by the
polar bears or occur in the diet via scavenging is uncertain. Terrestrial plants and
marine algae occurred more frequently in the polar bear diet than would be
expected from accidental ingestion, with 32.8 % (CI 24.4%-42.0%) and 21.8 %
(CI 14.8%-30.4%) of scats containing these food items, respectively. It appears
that they are eaten deliberately; perhaps to meet nutritional requirements for
mineral nutrients or vitamins. This study has shown that scat analysis is a useful
method for assessing the diet of this large carnivore, despite the advanced state of
digestion of food items in most polar bear scats.
Keywords:
polar bears, diet, scatology, ringed seal, Svalbard, reindeer, terrestrial plantsText extract:Reindeer was not considered prey for polar bears in Svalbard by Lønø
(1970). However, Derocher et al. (2000) reported seven successful predation
events, and six observations of polar bears scavenging on reindeer carcasses.
Also, Hedberg et al. (2011) in their study of the composition of polar bear milk,
found fatty acids which could be linked to reindeer consumption in two out of 16
samples.
In the present study, 9.2% of all scats contained reindeer;
eight out of 11 samples were from spring. Whether the reindeers are derived from
predation or scavenging is unknown in the context of this study. However,
reindeer mortality in Svalbard is highest during late winter and spring
(Aanes et al. 2000; Kohler and Aanes 2004); the main reason for death is believed to
be starvation (Reimers 1983). Reindeer carcasses might thus be of some importance
for polar bears, especially for juvenile bears which have yet to develop good hunting skills.
Occurrence of reindeer in the diet was positively correlated with the category
Terrestrial plants (eight of 11 samples with reindeer also had plant material),
which suggests that plants might be incidentally consumed while eating reindeer.
However, it might also be simply that both reindeer and terrestrial plants occur in
the same areas and bears may target both.
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