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Observations of a wild polar bear (Ursus maritimus) successfully fishing Arctic char (Salvelinus alpinus) and Fourhorn sculpin (Myoxocephalus quadricornis)

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Polar bears, Ursus maritimus, throughout their range, are nutritionally dependent on ringed (Phoca hispida) and bearded seals (Erignathus barbatus), which are predominantly caught on the sea ice. Other marine prey species are caught and consumed, but less frequently. As the annual sea ice retreats, polar bears throughout their range are forced ashore, where they mostly live off their stored adipose tissue. However, while land-bound they have been observed catching birds and terrestrial mammals. Although polar bears evolved from brown bears (U. arctos), direct observations of polar bears diving for and catching fish have not been reported. Here, we document observations of a young male polar bear catching Arctic charr (Salvelinus alpinus) and Fourhorn sculpin (Myoxocephalus quadricornis) by diving in Creswell Bay, Nunavut. We recorded six search bouts, where six fish were caught during dives, which were preceded by a snorkel. The average dive and snorkel length was (mean±SD) 13±5 and 6±2s, respectively.
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Polar Biol
DOI 10.1007/s00300-007-0338-3
123
SHORT NOTE
Observations of a wild polar bear ( ) successfully
shing Arctic charr ( ) and Fourhorn sculpin
( )
M. G. Dyck · S. Romberg
Received: 1 February 2007 / Revised: 29 June 2007 / Accepted: 2 July 2007
Springer-Verlag 2007
Abstract Polar bears, Ursus maritimus, throughout their
range, are nutritionally dependent on ringed (Phoca hisp-
ida) and bearded seals (Erignathus barbatus), which are
predominantly caught on the sea ice. Other marine prey
species are caught and consumed, but less frequently. As
the annual sea ice retreats, polar bears throughout their
range are forced ashore, where they mostly live oV their
stored adipose tissue. However, while land-bound they
have been observed catching birds and terrestrial mammals.
Although polar bears evolved from brown bears (U. arc-
tos), direct observations of polar bears diving for and catch-
ing Wsh have not been reported. Here, we document
observations of a young male polar bear catching Arctic
charr (Salvelinus alpinus) and Fourhorn sculpin (Myoxo-
cephalus quadricornis) by diving in Creswell Bay,
Nunavut. We recorded six search bouts, where six Wsh were
caught during dives, which were preceded by a snorkel.
The average dive and snorkel length was (mean §SD)
13 §5 and 6 §2 s, respectively.
Keywords Polar bear · Ursus maritimus · Fishing
behaviour · Arctic charr · Fourhorn sculpin · Nunavut
Introduction
Polar bears (Ursus maritimus) need the sea-ice platform
to hunt their prey, primarily ringed (Phoca hispida)
and bearded seals (Erignathus barbatus) (Stirling and
Archibald 1977; Smith 1980; Hammill and Smith 1991;
Derocher et al. 2002). During summer when the sea-ice
disappears, bears can spend up to several months on shore
where they mostly live oV their stored fat reserves (Watts
and Hansen 1987; Ramsay and Stirling 1988). While on
land, they also have been known to consume several alter-
native food sources. Food items that are opportunistically
consumed during the ice-free period range from various
bird species, eggs, and conspeciWcs to vegetation (e.g.,
berries, grass) and garbage (e.g., Russell 1975; Lunn and
Stirling 1985; Derocher et al. 1993; Donaldson et al. 1995;
Dyck 2001; Dyck and Daley 2002; Stempniewicz 2006).
The signiWcance of these dietary components to the overall
energy budget of polar bears was considered to be minor
(Lunn and Stirling 1985; Ramsay and Hobson 1991;
Hobson and Stirling 1997).
In this paper, we report on observations of a subadult
male polar bear and its exhibited behaviour during attempts
to catch Wsh. These observations are unique in that they
diVer from reported brown bear (U. arctos) Wshing behav-
iour, and that these observations are the Wrst of its kind in
over 200 years.
Materials and methods
The timing and location to potentially observe polar bear
Wshing behaviour was suggested to us by local traditional
knowledge from Resolute Bay, Nunavut. The Union River
(72°44 08N and 94°19 11W), Sommerset Island, Nunavut
M. G. Dyck
Environmental Technology Program, Nunavut Arctic College,
Box 600, Iqaluit, NU, Canada, X0A 0H0
S. Romberg
Department of Fisheries and Oceans Canada,
Central and Arctic Region, Eastern Arctic Area,
P.O. Box 358, Iqaluit, NU, Canada, X0A 0H0
M. G. Dyck (&)
Department of Environment, Wildlife Research Section,
Government of Nunavut, Box 209, Iglulik,
NU, Canada, X0A 0L0
e-mail: mdyck@gov.nu.ca
Polar Biol
123
is one of several locations where Inuit have been observing
this type of polar bear behaviour for many years. We con-
centrated our observation period between 17 and 30 August
2006 because Arctic charr (Salvelinus alpinus) occur at
high densities at the estuary during fall, getting ready to
migrate up-stream after a summer of feeding in Creswell
Bay, and returning to Stanwell Fletcher Lake for spawning
and wintering (de March et al. 1977).
We used spotting scopes and digital camcorders, usually
at distances of 300–800 m, and between 0700 and
1300 hours to record polar bear behaviour. All observations
of predatory behaviour on Wshes were conducted downwind
of the bear to avoid scent detection.
To determine the catch eVort, we counted the number of
Wsh caught per unit of time. Whenever possible, we
attempted to determine the species of Wsh, either directly by
viewing through the spotting scopes, or by examining the
left-over Wsh carcasses. Moreover, we determined the
amount of Arctic charr biomass consumed based on aver-
age Wsh weights taken during our study (n= 20 for each
gender; mean round weight for charr = 3,417 g).
For every Wshing attempt at the estuary, we quantiWed
the “snorkeling” and “diving” times because this behaviour
was directly associated with predatory behaviour on Wsh.
We deWned a snorkel as swimming with dorsum exposed,
eyes and nose under water, and only the ears above the
waterline. A dive was deWned as being completely sub-
merged below the water surface. We timed a snorkel from
the moment when the nose and eyes were submerged to the
moment when either both were brought above the water
surface, or the bear dove. A dive was timed from the
moment the bear was completely below the water surface
until it re-surfaced. We also timed search bouts in seconds
where timing began after a bear was Wnished feeding on a
carcass and entered the water, and where timing ended
when the bear caught another Wsh, independent of whether
it was dropped into the water or brought to shore for con-
sumption. As soon as the bear vacated the estuary area we
surveyed the shorelines where the bear was Wshing for Wsh
carcasses to ensure we did not miss any Wsh.
All times were measured in seconds with a digital stop-
watch. No statistical tests could be conducted because all
observations were conducted on the same animal. The
research activities were carried out under permits from the
Government of Nunavut and the Department of Fisheries
and Oceans, Canada.
Results
We observed three adult males, one subadult male, one sub-
adult female, and two adult bears of unknown gender
within 1 km of the Union River estuary throughout our
observation period. Only the subadult male was observed
preying on Wshes, whereas the other bears were occasion-
ally observed either scavenging on several narwhal
(Monodon monoceros) and charr carcasses, and/or feeding
on kelp (Laminaria spp.) and Arctic cotton grass (Eriopho-
rum scheuchzeri Hoppe).
We detected the bear around 0900 hours on 28 and 29
August in the water, swimming and wading in the estuary.
We were able to record six search bouts: bouts one to
three on 28 August, and bouts four to six on 29 August.
The average search bout lasted 419 s per Wsh, with an
average of 17 dives (Table 1). The dive lengths ranged from
3 to 29 s (mean §SD: 13 §5s;
n= 66). The mean length
of a snorkel lasted 6 §2 s (range 1–10 s, n= 66). All Wsh
were caught during a dive, where a snorkel preceded the
dive.
Four Wsh (2 charr and 2 sculpin) were caught and con-
sumed on 28 August. Five Wsh (1 charr, 4 sculpin) were
caught on 29 August. Of these, the charr and one sculpin
were completely consumed, two sculpin were partially con-
sumed, and one sculpin was dropped in the water and
escaped. Only the lower jaw remained from one partially
eaten sculpin carcass, whereas most of the body was left
from the second sculpin (remaining round weight 380 g,
fork length 400 mm).
Discussion
This is the Wrst study to our knowledge that recorded polar
bear predatory behaviour on Wshes. Russell (1975) found
traces of Wshes in polar bear scats from James Bay and
southwest Hudson Bay, but it was unclear whether bears
scavenged or actively caught the Wshes. Anecdotal accounts
reported of 32 white bears Wshing salmon at Eagle River,
Labrador, during July of 1778 (Smith et al. 1975), but other
observations have not been published.
Table 1 Observed search bout length, number and type of Wsh caught,
and number of dives per search bout for a subadult male polar bear
preying on Wshes at Union River, Nunavut
Search
bout
Search bout
length (s)
Fish caught Number
of dives
1 149 One Arctic charr Not recorded
2 764 One Fourhorn sculpin 36
3 247 One Arctic charr 12
4 298 One Fourhorn sculpin
(dropped)
15
5 79 One Fourhorn sculpin 3
6 975 One Arctic charr Not recorded
Mean §SD 419 §364 17 §14
Polar Biol
123
It is likely that some polar bears supplement their diet
with charr and sculpin while fasting because streams and
rivers inhabited by these Wsh species occur in many areas
where polar bears are forced on land during the ice-free
period. Inuit people camping or hunting in areas occupied
by polar bears have reported observations of Wshing bears.
Until now, however, successful Wshing by polar bears has
not been reported for over 200 years.
The observed polar bear behaviour is quite diVerent from
what has been reported for Wshing brown bears. Brown
bears catch salmon usually at shallow streams (depth
< 0.5 m; Quinn and Kinnison 1999; Gende et al. 2001) by
running, plunging, or standing (Klinka and Reimchen
2002). Although this polar bear snorkeled and dove to prey
on Wshes, it is very likely that polar bears also catch Wsh
similar to brown bears if the river geomorphology allows it.
Immature polar bears are usually more inexperienced
and ineVective at catching prey than older bears (Stirling
and Latour 1978). However, young bears seem to learn
from older bears how to catch prey eVectively (Stirling
1974). We also believe this to be true for predatory behav-
iour on Wshes. Arctic charr are fast swimmers (several body
lengths per second; Adams et al. 1995), and are confronted
with strong water currents at the Union River estuary. Scul-
pin are benthic Wsh, and use rocks for shelter. The observed
polar bear had to dive in order to locate and catch charr and
sculpin. Additionally, it employed a speciWc skill set (i.e.,
combined snorkel and dive) and underwater agility (e.g.,
move rocks) to capture fast-swimming Wsh like charr, and
inconspicuous Wsh like sculpin. Whether the bear learned
these behaviours from his mother or other conspeciWcs
remains speculation.
Although we observed predatory behaviour toward
Wshes by only one subadult polar bear, we believe that this
behaviour may occur more often across much of the polar
bears’ range. Because of the low human presence in the
areas, over which polar bears range, we suggest that the
best way to collect this speciWc bear behaviour is to record
Inuit Qaujimajatuqangiit (Inuit traditional knowledge)
from people living on the land.
It is well-documented that salmon (Oncorhynchus spp.)
play important ecological roles, which include providing
high energy food sources for brown bears during fall to
accumulate necessary energy reserves needed for hiberna-
tion and cub production (Farley and Robbins 1995; Hilder-
brand et al. 1999, 2000). Until more conclusive food trials
with polar bears have been conducted, the energetic contri-
bution of charr (or other Wshes) to the summer energy bud-
get of polar bears remains speculative.
Acknowledgments Many thanks to the residents of Resolute Bay
and S. Akeeagok for sharing their knowledge about where polar bears
catch Wsh in Nunavut. We also appreciate support contributed by Polar
Continental Shelf Project (PCSP), Nunavut Arctic College, North-
winds, Leica Germany, and R. Romberg. Comments by K. Rhode and
3 anonymous reviewers were helpful to improve the quality of the
manuscript. This is PCSP ÉPCP contribution publication # 019-07.
This paper is dedicated to Atsuli, who was MGD’s loyal companion.
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Analysing the physiological adaptations of marine mammals and seabirds, this book provides a comprehensive overview of what allows these species to overcome the challenges of diving to depth on a single breath of air. Through comparative reviews of texts on diving physiology and behaviour from the last seventy-five years, Ponganis combines this research into one succinct volume. Investigating the diving performance of marine mammals and seabirds, this book illustrates how physiological processes to extreme hypoxia and pressure are relevant to the advancement of our understanding of basic cellular processes and human pathologies. This book underscores the biomedical and ecological relevance of the anatomical, physiological and molecular/biophysical adaptations of these animals to enable further research in this area. An important resource for students and researchers, this text not only provides an essential overview of recent research in the field, but will stimulate further research into the behaviour and physiology of diving.
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Although the Arctic has experienced previous periods of warmer climate, the rate of sea ice loss in recent decades is likely faster than polar bears have ever experienced. The rapidly changing climate means that any response in polar bear behavior is unlikely to be driven by microevolution, but rather it will depend on behavioral plasticity. Fortunately, studies indicate high behavioral plasticity in polar bears despite their marked specialization as a marine predator. Although seals are their primary prey, polar bears feed opportunistically on a variety of marine and terrestrial prey and vegetation. Recently, the greatest change in their feeding behavior has resulted from spending more time on land as seasonal sea ice recedes. Additionally, polar bears will encounter new prey as some temperate species extend their ranges northward. Changes in polar bear movements and habitat associations because of climate change vary among subpopulations. In several areas, the loss of sea ice has altered migration routes, required long-distance swimming between hunting and denning areas, and resulted in some denning areas becoming inaccessible. Because polar bears do not occur in regions without sea ice for a significant part of the year, a diet of seals may not be fully replaceable with alternative terrestrial food, which poses a serious conservation concern.
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Once ashore, Thalassarctos maritimus became segregated by age and sex; family groups and pregnant females moved inland into a denning area, while single bears, especially adult males, remained along the coast. Bears were inactive and fed little. Analysis of blood samples taken from bears in the denning area suggested that they also were not feeding. By remaining inactive, they minimize energetic demands and the change of hyperthermia. After 2 months ashore, some bears, mainly family groups and subadults, fed in the Churchill, Manitoba, dump. Individual needs and learning were major factors determining which bears used the dump. Adult males did not feed there even though they may have been there previously as cubs or subadults. Bears which fed in the dump were significantly heavier than those which did not. There was no evidence that bears using the dump gained either reproductive or survival advantages. Thus, while polar bears will use supplemental food sources which are available or if they have previously learned their location, it is not necessary for survival.-from Authors
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Food habits of polar bears on land during the ice-free period in western Hudson Bay were examined between 1986 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 found in 34% of the females and 26% of the males captured over 10 km inland from the coast. The primary forage was Vaccinium uliginosum and Empetrum nigrum berries. Feeding was most common in subadults and females. The incidence of feeding on 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.
Article
Milk composition and intake, cub growth, and mass loss of hibernating lactating and nonlactating American black bears (Ursus americanus) and grizzly bears (Ursus arctos horribilis) were investigated. Except for ash content, milk composition was similar between species. Lipid content varied only slightly throughout lactation, whereas carbohydrate content increased from 1 to 3% during hibernation before decreasing to less than 0.5% at the end of lactation. Protein and dry matter content increased from 6.6 +/- 0.4 and 29.8 +/- 3.9% during hibernation to 13.7 +/- 1.1 and 34.4 +/- 3.7% post hibernation, respectively. The ash content of black bear milk increased from 1% during hibernation to 2% after den emergence, but the ash content of grizzly bear milk (1.3 +/- 0.1%) did not fluctuate. Mean milk intake and growth during hibernation were 185 +/- 89 and 49 +/- 9 g/day for black bear cubs and 353 +/- 54 and 98 +/- 22 g/day for grizzly bear cubs, respectively, which accounted for about 9% of the estimated yearly milk consumption by the cubs. Milk intake peaked during the summer at levels approximately 4 times higher than those occurring in the winter den. The mass lost by older, hibernating, nonlactating bears was proportional to their metabolic body mass and was almost exclusively lipid. The rate of mass loss by denning, lactating females relative to nonlactating bears was 45% higher for black bears and 95% higher for grizzly bears. The less costly black bear cub may be at an important competitive advantage when both species occupy nutritionally limited habitat.
Article
We investigated the effect of hibernation and reproductive status on changes in body mass and composition of adult female brown bears (Ursus arctos) on the Kenai Peninsula, Alaska. This information is fundamental to understanding nutritional ecology of wild brown bear populations. Six adult females handled in the fall and following spring (paired samples) lost 73 ± 22 kg (x̄ ± SD; 32 ± 10%) of fall body mass over 208 ± 19 days. Of this mass loss, 56 ± 22% (55 ± 22 kg) was lipid and 44 ± 22% (43 ± 21 kg) was lean body mass. Catabolism of lipid stores accounted for 88.4 ± 8.1% of the body energy used to meet maintenance demands. Overwinter differences in body composition of adult females assessed only once in either the fall (n = 21) or spring (n = 32) were similar to those of paired samples. Relative fatness of bears entering the den was positively related to the contribution of fat (%) to body mass (P < 0.01) and body energy (P < 0.01) losses during hibernation. Thus, relative fatness at the onset of fasting influences the relative proportion of lipid stores and lean body mass catabolized to meet protein and energy demands during hibernation. In the spring, lone females had greater body and lean masses than females with cubs of the year or yearlings. Lipid content was greatest in lone females in the fall. Studies using body mass and composition as indices of population health should consider season or reproductive class.
Article
A study of summer and autumn food habits of polar bears (Ursus maritimus Phipps) on some islands of James Bay and the coastal mainland of southwest Hudson Bay was conducted in 1968 and 1969. Analyses were made of 233 scats collected from islands in James Bay and 212 scats gathered on the southwest coast of Hudson Bay. Birds, primarily Anatidae, were the most commonly used summer and autumn food of bears in James Bay. Marine algae and grasses were the foods most often eaten by bears on the mainland. The diet of the bears from James Bay probably provides a better preparation for winter than the diet of those from the mainland, but evidence suggests that bears in both regions are generally in good physical condition.
Article
Brown bears (Ursus arctos) have been reported to be primarily diurnal throughout their range in North America. Recent studies of black bears during salmon migration indicate high levels of nocturnal foraging with high capture efficiencies during darkness. We investigated the extent of nocturnal foraging by brown bears during a salmon spawning migration at Knight Inlet in coastal British Columbia, using night-vision goggles. Adult brown bears were observed foraging equally during daylight and darkness, while adult females with cubs, as well as subadults, were most prevalent during daylight and twilight but uncommon during darkness. We observed a marginal trend of increased capture efficiency with reduced light levels (day, 20%; night, 36%) that was probably due to the reduced evasive behaviour of the salmon. Capture rates averaged 3.9 fish/h and differed among photic regimes (daylight, 2.1 fish/h; twilight, 4.3 fish/h; darkness, 8.3 fish/h). These results indicate that brown bears are highly successful during nocturnal foraging and exploit this period during spawning migration to maximize their consumption rates of an ephemeral resource.
Article
The influence of seasonal dietary meat intake on changes in body mass and composition in wild and captive brown bears (Ursus arctos) was investigated because the importance and availability of meat to brown bear populations is currently an important management consideration in several North American ecosystems. Adult female brown bears on the Kenai Peninsula, Alaska, utilized meat heavily in both spring and fall. Meat accounted for 76.2 +/- 26.0% (mean +/- 1 SD; primarily moose carrion and calves) of assimilated carbon and nitrogen in the spring and 80.4 +/- 22.2% (primarily salmon) in the fall. Mass increases in the spring (71.8 +/- 28.2%) were mostly lean body mass, but increases in the fall (81.0 +/- 19.5%) were primarily fat. Daily intake by captive brown bears fed meat ad libitum during 12-day trials was positively related to body mass. Mass change was positively related to intake in both seasons, but the composition of the gain varied by season, with spring gains primarily lean body mass (64.2 +/- 9.4%), while fall gains were 78.8 +/- 19.6% lipid. Absolute rates of gain by wild bears occasionally equaled, but were usually much less than, those of captive bears. This was likely due to a combination of factors, which included the time required to locate and handle meat resources, the limited availability of or access to meat resources, and (or) the duration of meat resource availability. Estimated intake by bears not feeding selectively on high-energy components of moose and salmon were 8.5 +/- 1.5 kg/day and 541 +/- 156 kg/year and 10.8 +/- 4.6 kg/day and 1003 +/- 489 kg/year, respectively. Intake would drop by as much as 58% for bears feeding exclusively on salmon roe. Management strategies for areas with brown bears that consume significant amounts of meat should address the perpetuation and availability of these meat resources.
Article
Predation of seals by the polar bear, Ursus maritimus, was not significant in the Western Arctic. In the High Central and Eastern Arctic, and along southeastern Baffin Island, bear predation of the subnivean lairs of ringed seals, Phoca hispida, was common. The ice types hunted by bears differed between the High Arctic and southeastern Baffin Island. However, no difference was seen in the proportion of successful kills. There is strong evidence that the bearded seal, Erignathus barbatus, is an important prey species of the polar bear in southeastern Baffin Island. Polar bears mainly kill newborn pups in their birth lairs. The prime breeding habitat of ringed seals located in ice hummock areas is less successfully preyed upon by bears than other ice types. Several factors such as the complexity of birth lairs and possible olfactory confusion might account for this. Seals under 2 years of age are those most frequently killed by bears. Data are presented to show that harvesting these age-classes provides the maximum return of energy to the bear and results in the least harm to the prey population.