Abstract

Climate-driven changes in the quality and availability of sea ice habitat (e.g., spatial extent, thickness, and duration of open water) are expected to affect Arctic species primarily through altered foraging opportunities. However, trophic interactions in Arctic marine systems are often poorly understood, especially in remote high-latitude regions. We used quantitative fatty acid signature analysis to examine the diets of 198 polar bears (Ursus maritimus) harvested between 2010 and 2012 in the subpopulations of Baffin Bay, Gulf of Boothia, and Lancaster Sound. The objective was to characterize diet composition and identify ecological factors supporting the high density of polar bears in these regions. Polar bears across the study area fed primarily on ringed seals (Pusa hispida, 41–56 %), although bearded seals (Erignathus barbatus, 11–24 %) and beluga whales (Delphinapterus leucas, 15–19 %) were also important prey. Harp seals (Pagophilus groenlandicus) were a major food source in Baffin Bay. Dietary diversity was greatest in Baffin Bay, perhaps because marine mammals were attracted to the nutrient-rich waters in and downstream from the North Water Polynya. Foraging patterns differed across age and sex classes of polar bear. In Baffin Bay, adult females had high levels of bearded seal in their diet, whereas adult males and subadults consumed high levels of harp seal. Seasonal variation in polar bear foraging was related to known migration patterns of marine mammals. Our results add to existing evidence that polar bears in these three separate subpopulations have a shared conservation status.
ORIGINAL PAPER
Characterization of polar bear (Ursus maritimus) diets
in the Canadian High Arctic
Melissa P. Galicia
1
Gregory W. Thiemann
2
Markus G. Dyck
3
Steven H. Ferguson
4
Received: 28 December 2014 / Revised: 6 July 2015 / Accepted: 14 July 2015
ÓSpringer-Verlag Berlin Heidelberg 2015
Abstract Climate-driven changes in the quality and
availability of sea ice habitat (e.g., spatial extent, thickness,
and duration of open water) are expected to affect Arctic
species primarily through altered foraging opportunities.
However, trophic interactions in Arctic marine systems are
often poorly understood, especially in remote high-latitude
regions. We used quantitative fatty acid signature analysis
to examine the diets of 198 polar bears (Ursus maritimus)
harvested between 2010 and 2012 in the subpopulations of
Baffin Bay, Gulf of Boothia, and Lancaster Sound. The
objective was to characterize diet composition and identify
ecological factors supporting the high density of polar
bears in these regions. Polar bears across the study area fed
primarily on ringed seals (Pusa hispida, 41–56 %),
although bearded seals (Erignathus barbatus, 11–24 %)
and beluga whales (Delphinapterus leucas, 15–19 %) were
also important prey. Harp seals (Pagophilus groenlandi-
cus) were a major food source in Baffin Bay. Dietary
diversity was greatest in Baffin Bay, perhaps because
marine mammals were attracted to the nutrient-rich waters
in and downstream from the North Water Polynya. For-
aging patterns differed across age and sex classes of polar
bear. In Baffin Bay, adult females had high levels of
bearded seal in their diet, whereas adult males and sub-
adults consumed high levels of harp seal. Seasonal varia-
tion in polar bear foraging was related to known migration
patterns of marine mammals. Our results add to existing
evidence that polar bears in these three separate subpopu-
lations have a shared conservation status.
Keywords Canadian Arctic Feeding ecology Marine
food web Polar bear (Ursus maritimus)Quantitative
fatty acid signature analysis (QFASA)
Introduction
Sea ice is a fundamental characteristic of Arctic marine
systems, serving as habitat and substrate for a wide range
of species and biological processes. However, the Arctic
region is experiencing rapid warming resulting in an
overall reduction in sea ice extent and thickness (Screen
and Simmonds 2010; Maslanik et al. 2011; Stroeve et al.
2011). The ecological consequences of ongoing and future
sea ice declines are not well understood, and low species
diversity in Arctic regions makes these ecosystems vul-
nerable to habitat-mediated changes in species assemblage
(Chapin et al. 1997).
Apex predators can reveal broad-scale changes in the
structure and functioning of ecosystems (Bowen 1997). As
highly specialized apex predators, polar bears (Ursus mar-
itimus) may be sensitive indicators of environmental change
(Laidre et al. 2008; Peacock et al. 2011). Sea ice is the primary
habitat for polar bears, which use it as a platform for hunting,
Electronic supplementary material The online version of this
article (doi:10.1007/s00300-015-1757-1) contains supplementary
material, which is available to authorized users.
&Melissa P. Galicia
melissa.galicia@gmail.com
1
Department of Biology, York University, Toronto,
ON M3J 1P3, Canada
2
Faculty of Environmental Studies, York University, Toronto,
ON M3J 1P3, Canada
3
Wildlife Research Section, Department of Environment,
Government of Nunavut, P.O. Box 209, Igloolik,
NT X0A 0L0, Canada
4
Fisheries and Oceans Canada, 501 University Crescent,
Winnipeg, MB R3T 2N6, Canada
123
Polar Biol
DOI 10.1007/s00300-015-1757-1
traveling, and mating (Stirling and Derocher 1993; Amstrup
2003). Evidence to date suggests that polar bears across their
circumpolar range feed primarily on ringed seals (Pusa
hispida) and bearded seals (Erignathus barbatus; Stirling and
Archibald 1977; Smith 1980; Thiemann et al. 2008a). Where
available, polar bears will also feed on a variety of other
species, including harp seals (Pagophilus groenlandicus;
Derocher et al. 2002; Iverson et al. 2006; McKinney et al.
2013), beluga whales (Delphinapterus leucas; Lowry et al.
1987; Smith and Sjare 1990; Thiemann et al. 2008a), nar-
whals (Monodon monoceros; Smith and Sjare 1990), and
walrus (Odobenus rosmarus; Kiliaan and Stirling 1978;
Calvert and Stirling 1990; Thiemann et al. 2007).
Projected changes in sea ice conditions associated with
global warming will unavoidably alter the accessibility of
ice-associated prey and, in turn, the feeding ecology of polar
bears. Satellite imagery has shown that sea ice extent and
thickness has declined at a faster rate than initially modeled
(Stroeve et al. 2007). Furthermore, projections indicate a
continued accelerated decline until 2100 (Holland et al. 2006;
Stroeve et al. 2007). Increased seaice fragmentation has been
observed in the southern portion of the polar bear’s range and
has resulted in an overall decrease in optimal foraging habitat
(Sahanatien and Derocher 2012). Thus, understanding cur-
rent patterns of polar bear foraging and the link between prey
and sea ice conditions is essential to understanding and pre-
dicting how Arctic marine ecosystem may be affected.
Although several recent studies have examined the effects of
sea ice changes on the ecology and behavior of polar bears in
the southern and western parts of their North American range
(e.g., Regehr et al. 2007; Molna
´r et al. 2011; Rode et al. 2014;
Pilfold et al. 2015), the ecological consequences of ice cover
changes in the High Arctic are largely unknown (Stirling and
Derocher 2012). Initial increases in primary productivity
have been hypothesized as first-year ice replaces thicker
multi-year ice at high latitudes (specifically in the Canadian
Archipelago–Gulf of Boothia and Lancaster Sound), but
longer-term reductions in sea ice ultimately mean the loss of
polar bear foraging habitat (Derocher et al. 2004; Hamilton
et al. 2014). Baffin Bay is seasonally ice-free, and negative
effects on polar bear body condition have been recorded as a
result of declining summer sea ice and increasing periods of
open water (Rode et al. 2012).
Fatty acid (FA) analysis has emerged as an important
tool in understanding the feeding ecology of marine ani-
mals, including fish (Budge et al. 2002), sea birds (Iverson
et al. 2007), pinnipeds (Beck et al. 2007; Meynier et al.
2010), cetaceans (Pomerleau et al. 2014), and polar bears
(Iverson et al. 2006; Thiemann et al. 2008a; McKinney
et al. 2013). Quantitative FA signature analysis (QFASA,
Iverson et al. 2004) uses a statistical model to estimate the
diet composition of individual predators by determining the
combination of prey FA profiles (or ‘‘signatures’’) that
comes closest to matching the observed predator, after
accounting for FA-specific patterns of metabolism.
Because dietary fat is integrated into predator fat stores
over weeks to months, the resulting diet estimates reflect
patterns of feeding across ecologically relevant timescales
(Iverson et al. 2004; Nordstrom et al. 2008).
Few studies have attempted to quantify the trophic
relationships between polar bears and their prey in the
Canadian High Arctic. Previous work by Thiemann et al.
(2008a) found that polar bears in Baffin Bay, Gulf of
Boothia, and Lancaster Sound had similar FA profiles that
were distinct from bears elsewhere in the Canadian Arctic.
However, previous dietary estimates based on QFASA
were ambiguous likely because low sample sizes (e.g., zero
prey from Gulf of Boothia) limited the ability of the
QFASA model to reliably distinguish harp seals from other
potential prey in these regions (Thiemann et al. 2008a).
The objective of this study was to characterize polar
bear diet composition in these same three High Arctic
subpopulations using an expanded and improved prey data
set. Given that Baffin Bay, Gulf of Boothia, and Lancaster
Sound contain some of the highest densities of polar bears
in their circumpolar range (Obbard et al. 2010), we also
sought to identify possible ecological and environmental
correlates of polar bear foraging habits. Polar bears in the
High Arctic have not yet experienced major declines in sea
ice conditions comparable to those in more southerly
regions. Moreover, predictable polynyas (areas of open
water) in northern Baffin Bay and the shallow continental
shelf of the Arctic Archipelago may serve as important
habitat for migratory and resident marine mammals. We
hypothesized that polar bears in the High Arctic would
exhibit diverse and seasonally variable diets related to
marine mammal migration routes and sea ice conditions.
We also hypothesized that polar bear diets will be affected
by sex and age as larger male polar bears have a greater
ability to successfully capture larger prey (Derocher et al.
2005,2010). The ability to exploit diverse marine mammal
prey has been identified as a possible factor delaying the
effects of sea ice loss (Rode et al. 2014). Thus, a better
understanding of polar bear foraging ecology within these
regions is essential to better assess current and future
effects of climate change in the Arctic.
Materials and methods
Sample collection
Polar bears
We analyzed adipose tissue samples from 198 individual
polar bears in three subpopulations: Baffin Bay, Gulf of
Polar Biol
123
Boothia, and Lancaster Sound (Fig. 1). The samples were
collected by local Inuit subsistence hunters between July 1,
2010, and June 30, 2012 (i.e., the 2010–2011 and
2011–2012 harvest seasons). Hunters assessed the age of
bears, and samples included male and female adults (5?
years), subadults (3–4 years), and independent 2-year-olds
(Table 1). Harvest management is based on a 2:1
male:female ratio, and it is illegal to hunt females with
dependent cubs. Adipose tissue samples (ca. 6 cm 93 cm)
were taken through the full depth of the subcutaneous
adipose layer over the rump. Samples were individually
wrapped in aluminum foil, sealed in a Whirl–Pak, and
stored at -20 °C until analysis.
Polar bear prey
A total of 390 blubber samples were collected from
potential polar bear prey, including ringed seals (n=206),
bearded seals (n=43), harp seals (n=9), harbor seals (P.
vitulina,n=17), beluga whales (n=57), narwhals
(n=37), and walrus (n=21). Full-depth blubber samples
were collected during Inuit subsistence hunts from nine
polar bear subpopulations (Baffin Bay, Davis Strait, Foxe
Basin, Gulf of Boothia, Lancaster Sound, Northern Beau-
fort Sea, Southern Beaufort Sea, Southern Hudson Bay,
and Western Hudson Bay) in Nunavut, Canada, from 2004
to 2012. The collection of seal and whale samples included
all sex and age classes. Samples were wrapped in
aluminum foil, sealed in labeled Whirl–Pak bags, and
stored at -20 °C until analysis. Data from Thiemann et al.
(2008b) for 247 marine mammals [bearded seals (n=31),
beluga whales (n=105), harp seals (n=101), and nar-
whals (n=10)] were also included, for a total prey library
of 637 samples.
Laboratory analysis
Sample analysis
A subsample of approximately 0.5 g was taken from the
center of larger polar bear adipose tissue pieces, and lipid
quantitatively extracted according to Iverson et al. (2001).
Prey samples were subsampled through the full depth of
blubber, since studies have found significant vertical
stratification in blubber of cetaceans and pinnipeds
(Koopman et al. 1996; Best et al. 2003). Fatty acid methyl
esters (FAME) were derived from isolated lipid extracts
using sulfuric acid as a catalyst (Budge et al. 2006). FAME
were analyzed in duplicate using temperature-programmed
gas chromatography on a PerkinElmer Autosystem II
capillary gas chromatograph (GC) with a flame ionization
detector (FID), using a polar column (Agilent Technolo-
gies, DB-23; 30 m 90.25 mm ID (Budge et al. 2006). FA
data were reported as the mass% of total FA ±1 SEM and
expressed by the shorthand nomenclature of A:Bn-X, where
Arepresents the length of the carbon chain, Brepresents
Fig. 1 Location of polar bears
(n=198) harvested by local
Inuit hunters 2010–2012 in
three Canadian subpopulations:
Baffin Bay (BB,n=56), Gulf
of Boothia (GB,n=62), and
Lancaster Sound (LS,n=80)
Polar Biol
123
the number of double bonds, and Xindicates the position of
the first double bond relative to the terminal methyl group.
QFASA modeling
We used quantitative FA signature analysis (QFASA;
Iverson et al. 2004) to estimate the diet composition of
individual polar bears. Briefly, the QFASA model esti-
mates diet by comparing the predator FA profile, or ‘‘sig-
nature,’’ to the average FA signatures of its potential prey.
To account for FA-specific patterns of metabolism in the
predator, we used calibration coefficients developed by
Thiemann et al. (2008a) from captive feeding studies on
mink (Mustela vison); a terrestrial carnivore fed a marine-
based diet. The combination of prey FA profiles that
minimizes the statistical distance between the prey and the
calibrated predator represents the relative contribution of
each prey type to the predator’s diet, on a lipid biomass
basis.
We used diet simulations based on the methods of
Iverson et al. (2004) to test the ability of the QFASA model
to distinguish between prey types (Appendix A). Polar bear
diets were estimated using 30 dietary FAs derived solely or
primarily from the diet (Iverson et al. 2004). The only
difference between our modeling FA set and that of
Thiemann et al. (2008a) was the exclusion of 20:1n-11,
which appeared to contribute to the overlap among prey
species as detected by principal component analysis (PCA).
Diet simulations (Appendix A) revealed better separation
of prey species when 20:1n-11 was excluded from the
analysis. When available, prey species from the specific
subpopulation were used to model predator diets of that
same region. However, when necessary, samples collected
from another region were used to increase the sample size
(Appendix B). Regional differences in prey FA signature
within a prey species were small compared to species-
specific differences, and thus, prey species were pooled
across geographic regions. As well, multiple diet simula-
tions were conducted to determine the most accurate
combination of prey species which would give the best
resolution in the simulation. All diet simulations and
QFASA estimates were performed in R (R version 2.1.0,
The R Foundation for Statistical Computing, 2005).
Statistical analyses
We used PCA and multivariate analysis of variance
(MANOVA) to test for geographic (three regions), sex,
age class (adults and subadults), and seasonal differ-
ences in polar bear FA profiles. The PCA used a set of
38 FA (32 dietary FA and 6 extended dietary FA; sensu
Iverson et al. 2004) transformed by calculating the log
of the ratio of each FA to 18:0 (Budge et al. 2002,
2006). We also restricted the sample:variable ratio to
5:1 as suggested by Budge et al. (2008) and used
MANOVA on PCA scores to compare FA across
subpopulations.
We used randomization–permutation analyses (Good
2000; Anderson 2001a,b; Thiemann et al. 2008a) to test
for geographic, sex, age class, and seasonal differences in
polar bear diet composition. We tested sex and age class
differences within each region; a two-way MANOVA was
performed. A two-way MANOVA was also used to test
spatial and seasonal variation while accounting for sex
effects on polar bear diet composition. Seasons were
defined as fall (September–November), winter (December–
February), and spring (March–May) based on the date the
bear was harvested. Summer (June–August) was excluded
from all the seasonal analyses, due to a small sample size.
A consequence of the integrative timeframe of QFASA
(i.e., indicative of diet over the preceding weeks to months)
is that point diet estimates may reflect feeding across two
seasons. However, predator FA profiles respond rapidly to
changes in diet (Nordstrom et al. 2008) and seasonal dif-
ferences in diet estimates are reliable indicators of temporal
change. All statistical comparisons were performed in R (R
version 2.15.3, The R Foundation for Statistical Comput-
ing, 2013).
Results
Polar bear FA composition
PCA revealed no clear separation among polar bear
subpopulations (Fig. 2). The FA with the highest loadings
on PC1 were 16:3n-4, 16:4n-3, 16:4n-1, 18:4n-3, 18:4n-1,
20:5n-3, on PC2 were 20:1n-9, 22:1n-11, 22:1n-9, 22:1n-
Table 1 Number of polar bear
harvest samples used in the
examination of diet composition
across three subpopulations in
the Canadian Arctic
Subpopulation Total (n) Adult Subadult Independent, 2 years old
Female Male Unknown Female Male Female Male
Baffin Bay 56 10 26 0 3 10 3 4
Gulf of Boothia 62 12 32 0 6 12 0 0
Lancaster Sound 80 9 44 1 5 15 3 3
Total 198 31 102 1 14 37 6 7
Polar Biol
123
7, 22:4n-3, and on PC3 was 18:3n-6. A MANOVA car-
ried out on PC scores showed a significant regional dif-
ference between the three polar bear subpopulations
(MANOVA, Wilks’ k=0.73, F
(6,384)
=10.81,
p\0.001). Only PC3 had a significant effect on the
regional variation. Another PCA was performed on each
subpopulation separately and MANOVA conducted on
PC scores for effects of sex, age class, and season. Sex
and age class had no significant effect on polar bear FA
in any region (MANOVA, p[0.06 in all cases). There
was no significant seasonal effect on polar bear FA sig-
natures in Gulf of Boothia (MANOVA, Wilks’ k=0.97,
F
(3,57)
=0.66, p=0.579). However, season did have a
significant effect on Baffin Bay (MANOVA, Wilks’
k=0.71, F
(3,48)
=1.16, p\0.001) and Lancaster
Sound polar bear FA signature (MANOVA, Wilks’
k=0.88, F
(3,73)
=3.34, p\0.05).
Polar bear diet composition
Geographic differences in polar bear diet
There was a significant regional difference in polar bear
diet composition between the three subpopulations (two-
way permutation MANOVA, p\0.001; Fig. 3). Ringed
seal had the highest dietary contribution across the study
area. However, polar bears in Gulf of Boothia consumed a
higher proportion of ringed seal compared to Baffin Bay
and Lancaster Sound (permutation ANOVA, p=0.020).
Ringed seal consumption was also the most frequent, being
present in nearly all bears across the three regions (Baffin
Bay 95 % of bears, Gulf of Boothia 100 % of bears, and
Lancaster Sound 93 % of bears). Bearded seal was found in
higher proportions and most frequent in the diets of bears in
Gulf of Boothia and Lancaster Sound (permutation ANOVA,
p\0.001; 89 and 90 % of bears, respectively) compared to
bears in Baffin Bay (63 % of bears). In contrast, harp seal
consumption was highest (21 ±2 %) and most frequent
(84 % of bears) in diets of polar bears in Baffin Bay, but
present as a minor component in Gulf of Boothia (6 ±1%
of diet, 69 % of bears) and Lancaster Sound (10 ±1%of
diet, 68 % of bears; permutation ANOVA, p\0.001).
Beluga whales had the third highest dietary contribution in
all three subpopulations; however, there was no significant
difference in consumption between the three regions (Baffin
Bay 19 ±4 %, Gulf of Boothia 15 ±3 %, Lancaster Sound
15 ±3 %; permutation ANOVA, p=0.235). Beluga whale
consumption was less frequent (Baffin Bay 55 % of bears,
Gulf of Boothia 48 % of bears, and Lancaster Sound 43 % of
bears), though present in high levels ([50 %) in some indi-
viduals (Baffin Bay 18 %, Gulf of Boothia 13 %, and Lan-
caster Sound 13 % of bears) with the majority of their diet
consisting of beluga whale consumption.
Sex and age class differences in diet
Sex and age class had no effect on polar bear diet composi-
tion in Gulf of Boothia (two-way permutation MANOVA,
p=0.833) or Lancaster Sound (two-way permutation
MANOVA, p=0.231). In Baffin Bay, there was a signifi-
cant interaction between sex and age class in overall diet
composition (two-way permutation MANOVA, p=0.006;
Fig. 4a). In Baffin Bay, bearded seal consumption was sig-
nificantly higher in adult females than in adult males and
younger age classes (permutation ANOVA, p\0.001) and
most adult females consumed bearded seal (90 % of bears).
The relatively high mean levels of bearded seal seem to be
influenced by 3 of 10 individuals consuming over 50 %
bearded seal. There was a significant interaction between sex
and age class for harp seal consumption, as adult females had
significantly less harp seal in their diets than did adult males
and subadults (permutation ANOVA, p=0.028). Harp seal
was most frequent in the diet of adult males (96 % of bears)
and subadult females (100 %). Sex and age class did not
significantly affect the consumption of ringed seal (permu-
tation ANOVA, p=0.217) or beluga (permutation
ANOVA, p=0.163) in Baffin Bay. However, beluga
whales were found more often in the diet of adult males
(77 % of bears) and subadult females (83 % of bears) than in
adult females (10 % of bears) or subadult males (33 % of
bears).
Seasonal differences in polar bear diet
Season had no significant effect on overall diet composi-
tion in Baffin Bay (two-way permutation MANOVA,
-4
-3
-2
-1
0
1
2
3
-8 -6 -4 -2 0 2 4 6
PC2 (12.05%)
PC1 (60.55%)
Baffin Bay (n = 56)
Gulf of Boothia (n = 62)
Lancaster Sound (n = 80)
Fig. 2 PCA of the 38 dietary and extended dietary FA on polar bears
according to subpopulation. PCA score plot on PC1 and PC2 which
explained 72.6 % of total variance
Polar Biol
123
p=0.669) or Lancaster Sound (two-way permutation
MANOVA, p=0.056). In Gulf of Boothia, there were too
few samples to compare fall diets, but winter and spring
diets differed (two-way permutation MANOVA,
p=0.023; Fig. 4b). Ringed seals were consistently the
primary prey in all three High Arctic regions throughout
the year. In Gulf of Boothia, bearded seal consumption was
higher in the winter than in the spring (permutation ttest,
p=0.017). Beluga whale became the most abundant prey
next to ringed seal in the spring but declined in the winter
(permutation ttest, p=0.022). Beluga whale was also
more frequent in the diet of polar bears in the spring (61 %
of bears) compared to winter (25 % of bears). Walrus was a
minor component in Gulf of Boothia diets during the spring
(permutation ttest, p=0.006).
Discussion
This study quantified the diet composition of polar bears in
Baffin Bay, Gulf of Boothia, and Lancaster Sound, where
polar bears feed on diverse prey species, many of which
make seasonal shifts in habitat use among the three
regions. Our results help explain the relative similarities in
0
10
20
30
40
50
60
70
Bearded seal Harbour seal Harp seal Ringed seal Beluga whale Narwhal Walrus
Prey contribution to polar bear FA signature (%)
Baffin Bay
Gulf of Boothia
Lancaster Sound
Fig. 3 Diet composition of
polar bears (n=198) in each of
the three subpopulations (Baffin
Bay, Gulf of Boothia, and
Lancaster Sound). Prey
contribution is represented as
each species’ proportional
contribution to polar bear diet.
Data are shown as mean ±SE.
Diet composition of Gulf of
Boothia and Lancaster Sound
polar bears were not modeled
using harbor seals because the
species is not available in these
two regions
Prey contribution to polar bear FA signature (%)
0
10
20
30
40
50
60
Bearded seal Harbor seal Harp seal Ringed seal Beluga whale Narwhal Walrus
Female adults
Female subadults and 2 yrs
Male adults
Male subadults and 2 yrs
a
0
10
20
30
40
50
60
70
Bearded seal Harp seal Ringed seal Beluga whale Narwhal Walrus
Winter (n = 20)
Spring (n = 41)
b
Fig. 4 Diet estimates are
represented as mean ±SE.
aSex and age class variation in
polar bear diet composition
sampled in Baffin Bay during
2010–2012 and bseasonal diet
composition of polar bears
during 2010–2012 in Gulf of
Boothia
Polar Biol
123
FA profiles previously observed among bears in these three
regions (Thiemann et al. 2008a,c) and suggest that dis-
tinctive and diverse foraging opportunities may support the
apparently high density of polar bears in the Canadian High
Arctic. Although sea ice conditions may not yet be strongly
affected by climate change in Gulf of Boothia and Lan-
caster Sound, overall ice cover in Baffin Bay has declined
by approximately 9 % per decade since 1979 (Perovich and
Richter-Menge 2009). Seasonal variation in diet suggests a
link between sea ice conditions and the availability of
particular polar bear prey common throughout the three
regions.
Geographic variation in polar bear FAs and diet
The similarity of polar bear FA profiles across the three
subpopulations we studied (Fig. 2) is consistent with pre-
vious studies (Thiemann et al. 2008a) and is possibly a
consequence of bears using a shared resource pool. Shared
resource use may derive from similarities in available prey
(e.g., prey migrating throughout the area) or from polar
bear movement between adjacent areas (i.e., between Gulf
of Boothia and Lancaster Sound, as well as Lancaster
Sound and Baffin Bay) to common foraging areas. Genetic
similarities of polar bears in the Canadian Archipelago
(Peacock et al. 2015) are indicative of some degree of
genetic interchange among the subpopulations studied
here. Our results are also consistent with previous con-
clusions that polar bears in our study area have FA profiles
distinct from bears in other parts of the Canadian Arctic
(Thiemann et al. 2008a). The distinctiveness of these High
Arctic polar bears may be a consequence of their diverse
diets, which include comparatively high levels of both
beluga whale and harp seal.
Dietary diversity was highest in Baffin Bay (Fig. 3), at
least partly because of access to harbor seals along the
nearshore shallow waters of Baffin Island (Mansfield
1967). Ringed seals are the primary prey of polar bears
throughout their circumpolar range, including our study
area, because of their ubiquitous distribution and high
abundance (Stirling and Archibald 1977; Kingsley et al.
1985; Stirling and Øritsland 1995). Bearded seals are also a
common prey species for polar bears (Smith 1980; Dero-
cher et al. 2002; Iverson et al. 2006; Thiemann et al.
2008a), including those in this study (Fig. 3). Predation on
other species may vary as a function of marine mammal
migratory patterns that affect the seasonal availability of
some prey. Thus, polar bears likely exploit locally abun-
dant prey as seasonal conditions allow. Moreover, some
individual bears may specialize in capturing larger prey
species more frequently (Thiemann et al. 2011).
Beluga whales comprised a large portion of the diets of
polar bears in this study. Belugas may be most accessible
to polar bears during winter months because of possible sea
ice entrapments while traveling through the sea ice (Lowry
et al. 1987; Heide-Jørgensen et al. 2003). Other sources
may include natural carrion, or hunting remains from the
Inuit harvest.
Harp seals migrate northward as the sea ice retreats in
summer, reaching Baffin Bay in early July and Lancaster
Sound during the summer months (Finley et al. 1990; DFO
2011). As the sea ice begins to reform in late September,
harp seals migrate back to southern areas (Finley et al.
1990). Polar bears prey on harp seals during the summer in
Svalbard (Derocher et al. 2002) and an increase in harp
seals and hooded seals in the diets of polar bears in East
Greenland (McKinney et al. 2013). The harp seal popula-
tion in eastern Canada has increased over the past four
decades (DFO 2011) and represents an important prey
species for polar bears, particularly in Davis Strait (Iverson
et al. 2006). We found the highest level of harp seal con-
sumption in Baffin Bay, where polar bears would have
access to harp seals during the spring and fall movement
and summer residency (Sergeant 1991). Harp seals were
less abundant in the diets of bears in Lancaster Sound and
Gulf of Boothia where they are less accessible to polar
bears during the ice-free season.
Each of the three subpopulations studied here supports a
high density of polar bears (Obbard et al. 2010). The North
Water Polynya is the largest recurring polynya in the
Canadian Arctic extending from northern Baffin Bay to
eastern Lancaster Sound (Stirling 1997; Born et al. 2004;
Heide-Jørgensen et al. 2013). A variety of marine mam-
mals are attracted to the biologically productive open water
(Stirling 1980; Laidre et al. 2008; Heide-Jørgensen et al.
2013). The similarity of polar bear diets in the High Arctic
may be a consequence of bears from Baffin Bay and
Lancaster Sound targeting this common feeding area.
Moreover, the shallow continental shelf waters and small
polynyas throughout Lancaster Sound and the Gulf of
Boothia (Stirling 1980; Welch et al. 1992; Stirling 1997)
may contribute to a higher diversity and availability of prey
and ultimately higher densities of polar bears in these
areas.
Sex and age variation in polar bear diet
Sex and age class had a significant influence on polar bear
diets in Baffin Bay, although ringed seal consumption was
consistently high in all sex and age classes (Fig. 4a). In
past studies, adult male polar bears have often been found
to have a higher level of bearded seal in their diet (Iverson
et al. 2006; Thiemann et al. 2007,2008a). The larger body
size of adult male bears (Atkinson et al. 1996; Derocher
et al. 2005,2010) potentially allows them to capture larger
prey, like bearded seals. Our results showed a reverse trend
Polar Biol
123
in Baffin Bay where adult females fed more on bearded
seal than adult males. It may be that female bears are tar-
geting younger, smaller bearded seals which may be spa-
tially segregated from dominant adult seals (Young et al.
2010). Alternatively, adult male bears may be targeting
harp seal and beluga whale, and thus, a smaller proportion
of bearded seal is found in their diet.
In Gulf of Boothia and Lancaster Sound, there was no
difference in diets between sexes or age classes of polar
bears. The high level of large prey in the diets of adult
males is consistent with studies from other regions (Iverson
et al. 2006; Thiemann et al. 2007,2008a), although larger
prey species were also frequently present in the diet of
adult females and subadults. Subordinate individuals in all
three subpopulations may scavenge the remains of kills
made by larger adult male bears, and previous studies have
suggested that scavenging is an important opportunistic
food source for less experienced bears (Stirling and McE-
wan 1975; Derocher et al. 2002), especially the Canadian
Archipelago (Smith and Sjare 1990).
Seasonal variation in polar bear diet
Seasonal differences in ringed seal, bearded seal, and bel-
uga whale consumption suggest that polar bears in our
study area may capture prey species as they become tem-
porally available. The shift in beluga whale consumption is
the largest seasonal difference in the Gulf of Boothia and
the increase in consumption likely proportionally reduces
ringed seal and bearded seal consumption in early spring
(i.e., March and April).
As sea ice retreats in summer, beluga whales use shore
leads to migrate from the North Water Polynya through
Lancaster Sound and south toward summer feeding
grounds in the Gulf of Boothia (Smith and Martin 1994;
Richard et al. 2001; Heide-Jørgensen et al. 2003). Among
Baffin Bay and Lancaster Sound polar bears, beluga whale
contribution was highest during winter and fall, suggesting
that polar bear foraging is associated with beluga migration
patterns and potentially, entrapment events (Stewart et al.
1995). Harvest seasons in some communities (such as
Clyde River and Arctic Bay) occur in the fall, and thus,
polar bears may have additional access to beluga whale
carcasses to scavenge. In the Gulf of Boothia, polar bear
predation on beluga whales increased in early spring which
likely reflects the frequency of overwinter mortality.
Implications for conservation
Our results provide further support for the designatable
units for conservation first suggested by Thiemann et al.
(2008c). Currently, polar bears in Canada are considered a
single unit in terms of conservation status but are
distributed among 13 subpopulations for harvest manage-
ment (COSEWIC 2008). Ecological factors such as pri-
mary productivity, prey distribution, and sea ice conditions
vary spatially and temporally across the Canadian Arctic
and the rate at which subpopulations will be affected by
climate change is predicted to vary (Stirling and Derocher
2012). Thiemann et al. (2008c) recommended five distinct
designatable units: Beaufort Sea, Central Arctic, High
Arctic, Hudson Bay/Foxe Basin, and Davis Strait. Baffin
Bay, Gulf of Boothia, and Lancaster Sound would com-
prise part of the Central Arctic Unit. The similarity of polar
bear diets, the likely interchange of prey and possibly polar
bears (Peacock et al. 2015), and the regional similarity of
projected sea ice conditions (Hamilton et al. 2014) rein-
force the hypothesis that bears in these three subpopula-
tions share a common conservation status driven by
regionally specific ecological factors.
This study identified the high diversity and seasonal
variability of polar bear diets in the Canadian High Arctic.
Recurring areas of open water and the associated abun-
dance of marine mammals may contribute to the distinct
diets and high density of polar bears in this region. Con-
tinued use of harvest-based sampling and improved
understanding of polar bear movement patterns and habitat
use, will clarify the ecological factors supporting these
subpopulations and how they may be shaped by future
environmental change.
Acknowledgments We are especially grateful to the Hunters and
Trappers Associations and Organizations of Nunavut for collecting fat
samples from polar bears and marine mammals harvested during their
subsistence hunts. A. Coxon and P. Frame (Government of Nunavut–
Department of Environment) helped coordinate the collection, orga-
nization, and shipment of polar bear samples. Thanks to B. Dunn, B.
Young (Fisheries and Oceans Canada), D. Muir, and X. Wang (En-
vironment Canada) for providing additional marine mammal seal
samples. S. Budge and C. Barry (Dalhousie University) conducted the
gas chromatography. I. Stirling and A. Derocher provided helpful
comments on an earlier version of the manuscript. This project was
funded by the Natural Sciences and Engineering Research Council
(NSERC, Canada), Environment Canada (Grants and Contributions),
Kenneth M. Molson Foundation, Nunavut General Monitoring Plan,
Northern Scientific Training Program, and York University, Faculty
of Graduate Studies.
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... Warming in the Arctic has resulted in rapid deterioration of seasonal sea-ice cover (Stroeve and Notz 2018), which has been particularly detrimental to polar bears (Ursus maritimus Phipps, 1774) throughout their circumpolar range Bromaghin et al. 2015;Lunn et al. 2016). Polar bears primarily hunt marine mammals using the sea-ice (Stirling and Archibald 1977;Galicia et al. 2015), but the amount of time they can access prey is decreasing due to a spatiotemporal decline in sea-ice extent (Stern and Laidre 2016). Concordantly, restricted prey accessibility for polar bears has led to reduced adult body condition (Stirling et al. 1999;Obbard et al. 2016), decreased cub recruitment (Laidre et al. 2020), and population decline Lunn et al. 2016) in parts of their range. ...
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Climate-induced sea-ice loss represents the greatest threat to polar bears (Ursus maritimus), and utilizing drones to characterize behavioural responses to sea-ice loss is valuable to forecasting polar bear persistence. In this manuscript, we review previously published literature and draw on our own experience of using multirotor aerial drones to study polar bear behaviour in the Canadian Arctic. Specifically, we suggest that drones can minimize human-bear conflicts by allowing users to observe bears from a safe vantage point; produce high-quality behavioural data that can be reviewed as many times as needed and shared with multiple stakeholders; and foster knowledge generation through co-production with northern communities. We posit that in some instances drones may be considered as an alternative tool for studying polar bear foraging behaviour, interspecific interactions, human-bear interactions, human safety and conflict mitigation, and den-site location at individual-level, small spatial scales. Finally, we discuss flying techniques to ensure ethical operation around polar bears, regulatory requirements to consider, and recommend that future research focus on understanding polar bears’ behavioural and physiological responses to drones and the efficacy of drones as a deterrent tool for safety purposes.
... For all species of bear, diets vary seasonally, depending on the part of the world they inhabit (sloth bears (Melursus ursinus), Joshi et al., 1997, Mewada & Dharaiya, 2010; Andean bears (Tremarctos ornatus), García-Rangel, 2012; brown bears (Ursus arctos), Mowat & Heard, 2006;Munro et al., 2006; American black bears (Ursus americanus), Lesmerises et al., 2015;Mosnier et al., 2008; polar bears (Ursus maritimus), Galicia et al., 2015; Asiatic black bears (Ursus thibetanus), Ali et al., 2017; sun bears (Helarctos malayanus), Fredriksson et al., 2006; giant pandas (Ailuropoda melanoleuca), Cabana et al., 2020;Li et al., 2017). Home ranges vary as well, as bears migrate to find available food (sloth bears, Joshi et al., 1997;Andean bears, García-Rangel, 2012; brown bears, Mowat & Heard, 2006;Munro et al., 2006; American black bears, Bonin et al., 2020;polar bears, Ferguson et al., 1999;Asiatic black bears, Izumiyama & Shiraishi, 2004;sun bears, Scotson et al., 2017;giant pandas, Yong et al., 2004). ...
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In natural environments, bear behavior follows seasonal patterns but the zoo environment differs from the natural environment in several ways, including the presence of zoo visitors. Although typically difficult to disentangle, we were able to tease apart the effects of seasonal changes and visitor density on the visibility and behavior of 10 bears representing five species housed at Cleveland Metroparks Zoo due to the disruption caused by COVID-19. We conducted a longitudinal bear behavior monitoring project from June, 2017-November, 2020. Bears were more visible in the spring and in the presence of visitors, locomoted more and were less inactive when large crowds were present, foraged and locomoted more when it was earlier in the day, and locomoted more at higher temperatures. There were limited differences in bear visibility to observers between 2020 (when the zoo was temporarily closed to visitors) and the previous three years. There were no differences in rates of stereotypy or social behavior across seasons, crowds, or daily attendance categories. Based on these limited differences, neither season nor visitor density seemed to have an apparent effect on bear behavior or welfare.
... An increase in the number of food compounds, up to ~40, may be achieved by using FAs instead of stable isotopes [2,7,13]. For instance, quantitative fatty acid signature analysis (QFASA) was successfully used to study the diets of different seal species [7], spectacled and Steller's eider [9], Atlantic salmon [11], New Zealand sea lions [22], polar bears [23], flatfish [24], and steelhead trout [25]. A modification of the isotope mixing model, MixSIR, referred to as the FASTAR model, has been developed, which calculates the contribution of food sources to predator diets based on their FA composition [2]. ...
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The study of the trophic relationships of aquatic animals requires correct estimates of their diets. We compared the quantitative fatty acid signature analysis (QFASA) and the isotope-mixing model IsoError, based on the compound-specific isotope analysis of fatty acids (CSIA-FA), which are potentially effective models for quantitative diet estimations. In a 21-day experiment, Daphnia was fed a mixture of two food items, Chlorella and Cryptomonas, which were supplied in nearly equal proportions. The percentages and isotope values of the FAs of the algal species and Daphnia were measured. The IsoError based on CSIA-FA gave an estimation of algae consumption using only one FA, 18:3n-3. According to this model, the proportion of consumption of Chlorella decreased while the proportion of consumption of Cryptomonas increased during the experiment. The QFASA model was used for two FA subsets—the extended-dietary subset, which included sixteen FAs, and the dietary one, which included nine FAs. According to both subsets, the portion of consumed Chlorella decreased from Day 5 to 10 and then increased at Day 21. The comparison of the two model approaches showed that the QFASA model is a more reliable method to determine the contribution of different food sources to the diet of zooplankton than the CSIA-based mixing model.
... Obbard et al. 2016), and diet (e.g. Galicia et al. 2015), all of which are essential for understanding this species' adaptability to environmental change. ...
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Changes in sea-ice dynamics are affecting polar bears Ursus maritimus across their circumpolar range, which highlights the importance of periodic demographic assessments to inform management and conservation. We used genetic mark-recapture-recovery to derive estimates of abundance and survival for the Baffin Bay (BB) polar bear subpopulation—the first time this method has been used successfully for this species. Genetic data from tissue samples we collected via biopsy darting were combined with historical physical capture and harvest recovery data. The combined data set consisted of 1410 genetic samples (2011-2013), 914 physical captures (1993-1995, 1997), and 234 harvest returns of marked bears (1993-2013). The estimate of mean subpopulation abundance was 2826 (95% CI = 2284-3367) in 2012-2013. Estimates of annual survival (mean ± SE) were 0.90 ± 0.05 and 0.78 ± 0.06 for females and males age ≥2 yr, respectively. The proportion of total mortality of adult females and males that was attributed to legal harvest was 0.16 ± 0.05 and 0.26 ± 0.06, respectively. Remote sensing sea-ice data, telemetry data, and spatial distribution of onshore sampling indicated that polar bears were more likely to use offshore sea-ice habitat during the 1990s sampling period compared to the 2010s. Furthermore, in the 1990s, sampling of deep fjords and inland areas was limited, and no offshore sampling occurred in either time period, which precluded comparisons of abundance between the 1993-1997 and 2011-2013 study periods. Our findings demonstrate that genetic sampling can be a practical method for demographic assessment of polar bears over large spatial and temporal scales.
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Biomagnification of persistent organic pollutants (POPs) is affected by physiochemical properties of POPs and ecological factors of wildlife. In this study, influences on species-specific biomagnification of POPs from aquatic and terrestrial invertebrates to eight songbird species were investigated. The median concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in birds were 175 to 13 200 ng/g lipid weight (lw) and 62.7 to 3710 ng/g lw, respectively. Diet compositions of different invertebrate taxa for songbird species were quantified by quantitative fatty acid signature analysis. Aquatic insects had more contributions of more hydrophobic POPs, while terrestrial invertebrates had more contributions of less hydrophobic PCBs in songbirds. Biomagnification factors (BMFs) and trophic magnification factors had parabolic relationships with log KOW and log KOA. The partition ratios of POPs between bird muscle and air were significantly and positively correlated with log KOA of POPs, indicating respiratory elimination as an important determinant in biomagnification of POPs in songbirds. In this study, the species-specific biomagnification of POPs in songbird species cannot be explained by stable isotopes of carbon and nitrogen and body parameters of bird species. BMFs of most studied POPs were significantly correlated with proportions of polyunsaturated fatty acids in different species of songbirds.
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Individual foraging specialization is a widespread occurrence and has numerous causes and consequences associated with it. However, one key area that has remained largely undiscussed, is the presence of such specialization in group-living species. This warrants special consideration as the behaviour of individuals living in groups is strongly influenced by their social environment, and so may result in distinct mechanisms favouring specialization. Here, we synthesize current theories regarding individual specialization and apply these to group-living species. In doing so we develop a set of testable predictions about the causes and consequences of individual foraging specialization in group-living species. In particular, we conclude that increased local competition between conspecifics will drive the development of individual foraging specialization in group-living species. We hypothesize that ‘one-to-one’ learning will promote individual foraging specialization, whereas learning from multiple role models will erode individual specialization through behavioural conformity. This increase in specialization may also make social groups more resilient to environmental change. We argue that testing predicted causes and consequences of individual specialization in group-living species is an important step in developing our understanding of the evolution of animal societies and how they are likely to be affected by a changing environment.
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Stewart, D.B., A. Akeeagok, R. Amarualik, S. Panipakutsuk, and A. Taqtu. 1995. Local knowledge of beluga and narwhal from four communities in Arctic Canada. Can. Tech. Rep. Fish. Aquat. Sci. 2065: viii + 48 p. + Appendices on disk. Inuit hunters from the communities of Grise Fiord, Arctic Bay, Igloolik, and Hall Beach were interviewed for their knowledge of the seasonal distribution, biology, and Inuit hunting practices of beluga (Delphinapterus leucas) and narwhal (Monodon monoceros). Survey questionnaires were used to gather information on belugas from a total of 19 hunters, and narwhal from 15 of the 19. This report documents their observations for use in resource co-management, and to provide a basis for further discussions between the hunters and resource managers and researchers. It was prepared for the Canada/Greenland Joint Commission for the Conservation and Management of Beluga and Narwhal. The role and effectiveness of the questionnaire method of gathering local or traditional knowledge is discussed. (Copies in Inuktitut will be available from the Department of Fisheries and Oceans, Iqaluit, NT, XOA OHO)
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If climatic warming occurs, the first impacts on Ursus maritimus will be felt at the southern limits of their distribution, such as in James and Hudson bays, where the whole population is already forced to fast for four momths when the sea ice melts during the summer. Prolonging the ice-free period will increase nutritional stress on this population until they are no longer able to store enough fat to survive the ice-free period. Early signs of impact will include declining body condition, lowered reproductive rates, reduced survival of cubs, and an increase in polar bear-human interactions. In the High Arctic, a decrease in ice cover may stimulate an initial increase in biological productivity. Eventually, however, it is likely that seal populations will decline wherever the quality and availability of breeding habitat are reduced. Rain during the late winter may cause polar bear maternity dens to collapse, causing the death of occupants. Human-bear problems will increase as the open water period becomes longer and bears fasting and relying on their fat reserves become food stressed. If climatic warming occurs, the polar bear is an ideal species through which to monitor the cumulative effects in arctic marine ecosysteme because of its position at the top of the arctic marine food chain. -from Authors
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Bear predation may occur when whales are entrapped by ice or while unrestrained whales are passing through leads or surfacing at holes in deteriorating ice sheets. Bear predation probably has little effect on beluga populations. Belugas are large in comparison to other potential prey and may be of some local importance in polar bear diets. -from Authors