Praca licencjacka- Polar bear(Ursus maritimus Phipps) diet
"Polar bear diet: evidence for adaptation to climate change?"
Table of Contents
I Introduction……………3
II Body
Materials and methods…….4-6
Results………………………7-8
Discussion of the results
III Conclusion………………….18
IV References………………….19
Andrew E. Derocher Ć Řystein Wiig Ć Magnus Andersen
Diet composition of polar bears in Svalbard
and the western Barents Sea
Results obtained from polar bear kill sides- very hard and could be a bit biased. Also bear tracking.
During studies of ringed seal
breeding habitat in Svalbard, a discrepancy was noted in
the production of ringed seals and the number of ringed
seals required to support the polar bear population in
the area (Smith and Lydersen 1991). Smith and Lydersen
(1991) suggested that pack-ice production of ringed
seals may be an important contribution to the population.
Our results further confirm the findings of Wiig
et al. (1999) that ringed seals breed in the drifting pack
ice of the Barents Sea, particularly northwest of Hopen
Island. Ringed seals are available to all bears in the
study population.
The only previous study of polar bear diet in the
study area comes from bears harvested throughout the
year near Svalbard; 52 ringed seals, 10 bearded seals and
6 harp seals were found in stomachs (Lřnř 1970). Harp
seals were only found during June/August and most
bearded seals (9/10) were found in the same period. The
prey composition from this study was 76% ringed seal,
15% bearded seal and 9% harp seal, and was very
similar to the composition of the 114 samples of known
species in our study. Numerically, similar to earlier
studies, ringed seals are the dominant prey of polar
bears. However, on a biomass basis, the results from
Lřnř (1970), together with ours, suggest that the diet of
polar bears in Svalbard and the western Barents Sea has
a significant contribution from bearded seals. However,
in the eastern Barents Sea, a Russian study reported
68% ringed seal, 22% walrus and miscellaneous other
items for the diet of polar bears (Parovshchikov 1964)
and may reflect further geographic variation in the same
population. Studies of fatty-acid profiles of polar bears
suggest that geographic variation in diet may be large
(Iverson et al. 1999).
Polar bears in Svalbard and the western Barents Sea
area are part of a common population that extends as
far east as Franz Josef Land (Mauritzen et al. 2002).
Polar bears living in the study area have two different
space use patterns: one group lives near shore and has
small annual ranges whereas the other lives offshore and
has larger ranges (Mauritzen et al. 2001). Annual range
size of adult females ranged from 185 to 373,539 km2
and dietary differences were postulated to explain the
different space use patterns (Mauritzen et al. 2001). In
particular, Mauritzen et al. (2001) suggested that nearshore
bears relied more on the land-fast ice and preyed
largely on ringed seals during spring while pelagic bears
preyed more on bearded and harp seals over a longer
period. Our results support this hypothesis given that
most of the kills observed in June and August were in
multiyear pack-ice where the pelagic bears tend to
summer.
Polar bears are opportunistic
Polar bears are also opportunistic scavengers. In
summer 2001, polar bears were observed feeding on both
a white whale carcass and a sperm whale (Physeter
macrocephalus) carcass in northern Svalbard (J.O.
Scheie, personal communication). In these 2 observations,
up to 14 and 17 bears, respectively, were observed
on the carcasses, suggesting that scavenging is important
for many individuals. Further, observations of predation
and scavenging of reindeer (Rangifer tarandus
platyrhynchus) (Derocher et al. 2000) attest to the
diversity of diet.
Similarly, if climate change alters the distribution
and abundance of prey (Stirling and Derocher 1993),
better documentation of current predation patterns is
essential for understanding the effects of climate change
on polar bears.
In summary, similar to other areas, the diet of polar
bears in Svalbard and the western Barents Sea is dominated
by ringed seals on a numerical basis, but bearded
seals make a significant contribution to the diet when
biomass is considered. Harp seals likely play an important,
but lesser, role in the diet of bears living in more
pelagic habitats, but only during the summer months.
What can they feed on in Svalbard:
-ringed seals(Phoca hispida)
-bearded seals(Erignathus barbatus
-harp seals(Phoca groenlandica)
-white whales (Delphinapterus leucas)
-narwhal (Monodon monoceros)
-walrus (Odobenus rosmarus)
-little auks (Alle alle)
-pale-bellied brent geese (Branta bernicla hlota)
-Canada geese (Branta canadensis)
-thick-billed mures (Uria lomvia)
-willow ptarmigan (Lagopus lagopus)
-guillemots
-kittiwakes
-vegetation (found from the tidal zone to 200 m above sea level): eaten as source of vitamins and minerals
Mosses: eaten as source of vitamins and minerals
-Svalbard reindeers (Rangifer tarandus platyrhyncus) -> observations and evidence of carcass(especially young reindeers) at notes in the paper “Predation of Svalbard reindeer by polar bears”
-algae: eaten only as a source of vitamins and minerals
-berries: source of carbohydrates
Food eaten in other areas:
-musoxen
-other polar bears
-Ducks (Somateria spp., Clangula hyemalis)
-puffins Fratercufa spp.)
-lemmings
(Lemmus spp., Dicrostonyx spp.)
In year 2000 – 60 % of Svalbald covered in glaciers
Fatty acid composition of the adipose tissue….
Polar bears feed little from late summer through winter, with the peak feeding period occuring in spring
and early summer when substantial adipose deposits
are formed (Watts & Hansen 1987, Ramsay & Stirling
1988).
The diet of polar bears is
obtained principally from the marine food web
(Ramsay & Hobson 1991, Hobson & Stirling 1997).
In the Barents Sea — Svalbard area — the diet is
found to consist almost exclusively of ringed,
bearded and harp seals (Lønø 1970, Derocher et al.
2002). Harp seals have only been found in the diet
during the summer season (April/May to October).
Since the bears in the present project were sampled
in mid-April, we assume they had eaten
mostly ringed and bearded seals during the 6 mo
prior to sampling.
Analiza
Scats collected in august 2004 (6 and half years ago)
Place of collection: Spitsbergen, Horsund
Probably from one individual, close to the place where he rested
Informacja od Nurii:
Dear kaja,
Quite inetersting results and polar bears being more vegetarians than we thought! the white hairs (long, resembling plastic) are for sure from polar bear. The rest of the hairs may be from seals. About feathers, we will neeed to check, but close to the place where scats were collected there was a huge colony of Kittiwakes (Rissa trydactyla)[mewa trójpalczasta) and of Guillemots(nurzyki) (Uria spp., I have to check the exact species). So probably the feathers are from thosen species, eaten as carcasses.
For the plants, we will need to check them in a guide or consult with my colleagues.I pasted below some info they sent me some time ago
"Bear grazing(pasący się) in tundra and especially close to
seabird colony where vegetation is lush(bujny) most probably supplement vitamins
eg. C-vitamin of which Cochleria groenlandica is very rich (it was used
for ages by native people, whalers, trapers and explores as a Vit C
substitute). A lot of Cochleria is at foot of Gnall colony and we observed
bears grazing there regularly."
Gnall is the place in Horsund where the scats were collected.
Pozdrawuiam
Nuria
Literature to find
Polar bears in warming climate
In Svalbard, the number of maternity
dens on the most southern of the denning islands, Hopen,
has varied from 0 to over 35 and was strongly
correlated with the date that the sea ice arrived the
previous autumn (A.E.D., unpublished data). Furthermore,
Comiso (2002b) suggested that by the 2050s,
the mean minimum extent of the sea ice in the polar
basin would be about 600 km from the north coast of
Alaska or western Siberia and 100 or so km north of
Svalbard. Two of the three largest known polar bear
denning areas are on Wrangel Island and the Svalbard
Archipelago. It seems likely that if this prediction is
correct, pregnant females will likely not be able to
reach either of these areas or several other coastal locations
(such as the north slope of Alaska) where polar
bears also have maternity dens, though at much lower
densities.
Female polar bears demonstrate a wide range of
space-use patterns, both within and between populations,
with annual home ranges as small as 500 km2
to over 300,000 km2 (Garner et al., 1991; Ferguson et
al., 1997;
Harbour seals, spotted seals (P. largha), ribbon seals
(Histriophoca fasciata), and gray seals (Halichoerus
grypus) populations already exist at the edges of the
range of polar bears and are not currently common
prey. Woolett et al. (2000) showed from archaeological
data that during periods of warmer weather and
presumably less ice, harbour seal bones had a higher
frequency of occurrence relative to ringed seals along
the coast of northern Labrador and south-eastern Baffin
Island and that the opposite was true when the
weather was colder and there was more ice. This suggests
that as the climate warms and there is more open
water in the ice, harbour seals are likely to become
more abundant. In western Hudson Bay, preliminary
data from the Inuit harvest data and fatty acid signatures
in polar bears suggest that harbour seals may
already be increasing (I.S. and S. Iverson, unpublished
data) and becoming more important prey items for the
bears there. Predation attempts on harbour seals have
been also observed in Svalbard (Derocher et al., 2002).
Over the long term, harbour seals are unlikely to replace
ringed and bearded seals as prey for polar bears
because they will become most abundant when open
water predominates in a region. However, if their numbers
increase among the floes and leads as the amount
of open water in winter increases they could become
more important as prey.
We have assumed that a
reduction in sea ice area is largely detrimental to icebreeding
seals but it is conceivable that, similar to their
more temperate relatives, they may move to landbased
haul-outs, moulting, and pupping areas. Using
land may be more likely for bearded seals that occasionally
haul-out on land but how ringed seals, which
rarely haul out on land, would respond is unknown.
Other temperate seals species have a more land-based
life cycle and it is conceivable that the polar bear–seal
system could become more land-based as the climate
warms. Polar bears will use terrestrial resources such
as blueberries (Vaccinium uliginosum) (Derocher et
al., 1993), snow geese (Anser caerulescens) (Russell,
1975), and reindeer (Rangifer tarandus) (Derocher et
al., 2000) but the frequency of occurrence recorded to
date indicate that these are relatively unimportant energy
sources compared to seals.
As noted earlier, much of the most biologically productive
habitat for polar bears is the annual ice overlying
the continental shelf and inter-island channels of
archipelagos around the rim of the arctic basin, and
more southerly relatively shallow water areas such as
Foxe Basin and Hudson Bay. These are the most important
areas for polar bears because that is where biological
productivity, and hence seals, are most abundant.
If as projected by Comiso (2002b), a large
amount of the pack ice in the polar basin retreats to
the north and lies over the deep polar basin, then it is
likely that productivity will be less than over the continental
shelves. However, with thinner ice and more
open water, productivity may be greater than it presently
is. This dichotomy makes accurate predictions
difficult.
Bearded seals and walrus, feed in relatively shallow
waters and rely on benthic prey (Lowry et al., 1980;
Kraft et al., 2000; Hjelset et al., 1999) associated with
continental shelf areas and rely on annual sea ice for
pupping (Burns, 1981). A likely effect of reduced sea
ice over the continental shelf is that bearded seals and
walrus may be forced offshore to try to find ice suitable
for pupping and feeding in areas where the water
may be too deep or lack the productivity of near shore
habitats. The net result may be reduced bearded seal
and walrus abundance and condition with subsequent
negative effects on polar bears.
Over the shorter term at least, if the multiyear ice
that prevails over the relatively shallow waters of the
inter-island channels of the Canadian High Arctic Islands,
including Sverdrup Basin, is largely replaced by
annual ice as suggested by Melling (2002) and the
polynyas in the area (Stirling, 1997) became more numerous
and larger it is likely that biological productivity
might increase. If so, it is likely the resident
populations of ringed seals, bearded seals, and walrus
would increase and the area would become better habitat
for polar bears.
In addition, polar bear cub mortality was
thought to be high in some areas of Svalbard owing
to extensive areas of open water (Larsen, 1985) in part
due to the rapid chilling of cubs exposed to cold water
(Blix and Lentfer, 1979). If sea ice conditions are poor
and females with new cubs are forced to swim from
den areas to the pack ice then cub mortality may increase.
Of the world’s 20 populations,
2 are of unknown population size, 6 have
poor estimates of size, 8 have fair estimates, and only
4 are classed as having good population estimates
(IUCN/SSC Polar Bear Specialist Group, 2002).
The polar bear populations in Norwegian
Bay, Kane Basin, and Queen Elizabeth are all small
(presently numbering less than 200 bears each)
(IUCN/SSC Polar Bear Specialist Group, 2002). The
current lack of information in these areas means that
any increase in these populations would be difficult to
detect. Further, monitoring the global population size
of polar bears is impractical and not particularly useful
in any case because the bears in different regions and
populations will respond differently. In many areas, it
is likely that the first indications of declining populations,
reduced condition, or disease will come from
local hunters.
It is not possible to confidently
predict whether a reduction in sea ice area
would necessarily result in a corresponding reduction
in the size of polar bear populations or if under some
circumstances, the number might remain similar for
some time. Alternatively, in some areas polar bear
populations may increase if the changes increased seal
populations.
Polar bears make little use of terrestrial food web
Although anecdotal accounts show that some polar
bears eat limited amounts of sedges (Carex spp.) and
berries while on land (Russell 1975; Knudsen 1978 ; Lunn
and Stirling 1985), the importance of terrestrial foods in
their annual diet is not known.
Polar bears, while
retaining the unspecialized gut of bears, have tertiarily
reverted to carnivory and have molariform teeth less well
adapted to mechanically processing plant foods than
other bear species (Hylander 1978). In consequence, polar
bears probably achieve little net energy gain by foraging
during their forced tenure on land (Lunn and Stifling
1985). The inverse relationship between natality rate and
latitude that Bunnell and Tait (1981) noted for polar
bears would seem, therefore, not to be due to increased
access to terrestrial foods in the more southerly limits of
their range.
Food habits of polar bears
A weakness in this method lies in the fact
that the relative amounts of undigested food items found in scats are not always
indicative of the amounts ingested by the animal; for example, muscle and fat
tissues are more completely digested than most vegetation. However, there appears
to ben o more suitable method for analysing the prdeastean.t
Average per cent volume and frequencyo f occurrence were calculated for each
food item. The data from scats collected in 1968 and 1969 were combined because
of the difficulty in determining time lapse from evacuation.
L@n@(1 957) documented the occasional occurrence of grasses in 172 stomach
samples taken in Svalbard. Loughrey (1956) and Pedersen (1962) also mention
grasses as a source of food for polar bears. On several occasions on both North
Twin Island and the mainland the present author has observed bears feeding
on grass.
Polar bears may seek grasses or other vegetation, even when animal foods are
plentiful. Koettlitz (1898) observed a bear which, after feeding on a seal, immediately
travelled five kilometres to eat grass. He also examined the contents of
30 stomachs and recorded grasses in eight, two of which contained grass in combination
with remains of seal.
On Svalbard, L@$ (1970) witnessed a female and a
yearling dive from an ice floe into 3-4 m of water; they hauled large quantities of
seaweed onto the ice, picked through it, and ate only certain parts.
Polar bear feeding on seabird colony
To cover
its daily energy needs, estimated to be 8 kg of seal
meat and blubber (Uspensky 1989), a bear would
have to consume at least 32 adult and nestling
little auks and dig 16 craters overturning several
tonnes of rock debris. For these reasons the
efficiency of polar bear feeding in the little auk
colony, i.e. a relation of energy losses to gains,
doesn't seem high. It is possible that this feeding
method is used only by some specialised and
experienced individuals which are able to detect
dense patches of active nests covered with rock
debris easy to remove, thus improving their hunting
efficiency. Starving, inexperienced individuals
qay try to follow this food searching pattern
especially when other sources of food are not
available.
Effects of climate change on polar bears
When the ice retreats north in the summer the bears must either
follow the ice or go on land and wait until the sea ice returns in the
autumn. The pattern varies between subpopulations. In Svalbard, for
example, some bears rest on land but most bears follow the ice
north in the Barents Sea11,12. In the western Hudson Bay, all bears
stay on land during the summer13.
We have
observed that the number of maternity dens at the island of Hopen
at Svalbard, the southernmost of the denning islands in this
archipelago, varied between 0 and 35 during 1994–2001. The
number of dens on Hopen was strongly negatively correlated to
the date of sea ice arrival at the island the previous autumn. In the
fall of 1999 when the ice did not arrive until close to Christmas, the
bears were not able to reach the island at all and there were no dens
there (Derocher et al., unpublished).
We do not know if those female bears that presumably would
have denned at Hopen had the ice cover been better in a particular
year, skipped a year or chose to den in other areas with better ice
condition that year. Nevertheless, the example indicates that if the
extent of sea ice decreases significantly in the future, certain areas
with suitable denning habitat will no longer be available to pregnant
female bears.
Possible effects of climate warming on selected populations…
Between the time of the first polar bear studies in Davis
Strait and the Labrador coast in the 1970s and that of the
later, more limited studies in northern Labrador in the
1990s, the abundance of harp seals and hooded seals
increased significantly (Bowen et al., 1987; Stenson et al.,
1997; Healey and Stenson, 2000; Anonymous, 2005). This
is particularly relevant to the likely increase in the size of
the polar bear population between the late 1970s and early
1990s because both these seal species pup in large numbers
near the outer edge of the pack ice in March (Fig. 1),
and are much less wary than other seal species of being
approached to close distances by humans or polar bears
(I. Stirling, unpubl. observations). Furthermore, both harp
and hooded seals are much larger than ringed seals, so each
animal killed, on average, makes much more fat available
to a bear. Fat is the most favored part of a seal to a polar
bear (Stirling and McEwan, 1975) and is digested with a
digestive efficiency of 98% (Best, 1975), after which it can
be stored on the body of the bear for use up to several
months later, when food may not be available (Nelson et
al., 1983). Outside the pupping and breeding season, harp
seals also haul out on the ice in groups of various sizes, and
humans can often approach closely enough to capture
them with a hand-thrown net for tagging. Similarly, periodic
onshore winds along the northern Labrador coast
during winter and spring sometimes compress the ice
sufficiently in some areas to cause harp seals to be temporarily
stranded on the sea ice, with limited access to water
for escape from predators. Lastly, the harp seal population
increased from less than two million in the early 1970s to
over five million by 2000 (Anonymous, 2005). Taken
together, the larger size, reduced wariness, and large
numbers of accessible individual seals have meant that
polar bears in the Davis Strait population have had a very
large, accessible food base for two to three decades that
other populations of polar bears have not had. This is
particularly relevant because, from analysis of fatty acids
from polar bears from Davis Strait, Iverson et al. (2006)
demonstrated that harp seals are by far the most important
species in the diet of polar bears in that area, in contrast to
the predominance of ringed seals in most other areas
(Stirling and Archibald, 1977; Smith, 1980; Stirling and
Øritsland, 1995).
While the present population size
and trend of the Davis Strait polar bear population are
unknown, it seems likely that the population is no longer
increasing and could, in time, be negatively affected by the
trends toward less sea ice, earlier breakup, and possibly a
decline in the total population of harp seals if the climate
continues to warm as is predicted.
Terrestrial foraging
ABSTRACT. Food habits ofp olar bears on land during the ice-free period in western HudsonB ay were examined between1 986 and 1992.
In contrast to previous studies, feeding on vegetation during the ice-free period was common. Between August and October, evidence of
feeding was foundin 34%o f the females an2d6 %o f the males captureodv er 10 km inland from the coast. The primary forage wVasa ccinium
uliginosum and Empetrum nigrum berries. Feeding was most common in subadults and femaleTs.h e incidence of feedingo n berries varied
annually from 2 to 41 %. We were not able to determine the energetic importance of terrestrial foraging, but the intake may reduce the
rate of weight loss of bears on land, particularly in years when berries are abundant.
polar
bears consumed a negligible amount of food frotmer restrial
food webs. However, marine algae, grasses, sedges, mosses,
lichen, berries, and various vertebrates were found in the
scats of polar bears on land along the coast of Hudson Bay
(Russell, 1975). Although unable to determine the frequency
of feeding or the nutritive importance of these food items,
Russell (1975) concluded thatth e caloric intakeo f terrestrial
food was not significant.
Our data indicate that a substantiapl roportion of the polar
bears inland from the coast of western Hudson Bay feed on
plant matter during the ice-free period. The berries of both
were particularly
common. Terrestrial feeding was noted in approximately
40% of cubs and yearlings, but it was also common in
subadults of both sexes and adult females. In comparison,
less than 10% of the adult males examined showed signs of
feeding. These differences may reflect the greater energetic
demands of pregnancy and lactation in adult females and
growth in younger bears.
At present, we cannot quantify the amount of time
individual bears spend feeding or the energy contribution
of vegetation to the total energy used during the ice-free
period. Nevertheless, the proportion of bears feeding is
inconsistent with the conclusions of previous studies based
on observations of bear behavior, analyses of scats, the
concentration of urea and creatinine in the blood, and stablecarbon
isotope ratios (Russell1, 975; Knudsen, 1978; Latour,
1981; Lunn and Stirling, 1985; Ramsay etal., 1991; Ramsay
and Hobson, 1991).
Several important differences in wthaey data were collected
for the various studies may account for the inconsistencies
in the conclusions. Most of the data in the previous studies
were collected along the coast, wherbee rries are not present,
bears spend most of their time inactive (Knudson, 1978;
Latour, 1981; Lunn and Stirling, 1985), and adult males,
which feed less than all other age classes (Fig. 2), are most
abundant (Derocher and Stirling, 1990). For the most part,
bears in the inland area in late summer and autumn were
not represented. In addition, some of the previous studies
were conducted when berries were largely unavailable and
our data indicated monthly variation in feeding. The proportion
of bears that showed signs of feeding in September was
roughly two to three times the proportion in August and
October. Consequently, observations or samples collected
before or after September would have a lower probability
of detecting feeding.
It is clear from our data that polar
bears inland from the western coast of Hudson Bay during
the late summer and early autumn eat terrestrial vegetation.
For females with offspring and young bears athrea tg rowing
rapidly, both of which have high metabolic requirements,
foraging on berriems ay reduce ther ate of weight loss through
the autumn. We have documented mother bears that have
ceased lactation well before freeze-up (Deroceht earl ., 1993)
and feeding on berries may allow mothers to lactate longer
into the ice-free period. If so, terrestrial feeding could
significantly influence the condition of bears and in turn
influence survival, particularly of cubs. However, the
question cannot be resolved until the caloric contribution of
terrestrial feeding to the total energy budget of polar bears
is determined.
Lead-an open way in an ice field
Bathmetry- measuring the depths of the oceans
Plan of work
Introduction
- the problem: are polar bears adapted to climate change
-hypothesis: yes, it is supposed that they are
-importance of research done
-purpose of research: find out if polar bears are adapted to climate change
Materials and methods
Scats were collected
-what was collected and place of collection
-how was it analyzed
-biology of polar bear: range, home range, number of individuals worldwide
Statistical analysis of data
Results
Types of food found in scats
Discussion
What polar bears consume, as compared to results obtained
Conclusions and recommendations
References