FOODS AND FEEDING OF BOWHEAD WHALESIN WESTERN AND NORTHERN ALASKALLOYD F. LOWRY AND KATHRYN J. FROST
Alaska Department of Fish and Game, 1300 College Road, Fairbanks, Alaska 99701 USA
ABSTRACTSamples were collected from the gastrointestinal tracts of 20 bowhead
whales taken by Eskimo whalers at several locations on the western and northern coast of Alaska. A probable total of 56 species of prey was found, including 50 species of crustaceans, 3 molluscs, and 3 fishes. Most of the preyspecies (23) were gammarid am phi pods, which occurred in 13 of the samples
examined. Of the individual prey species, the most frequently encountered
were a euphausiid, Th_ysanoessa raschii ( 11 occurrences); a copepod, Calanus
hyperboreus (10 occurrences); and a hyperiid amphipod, Parathemisto libellula (8occurrences).
In samples from stomachs containing appreciable amounts ofrecognizable
food, copepods were the dominant prey in nine, euphausiids in six, and gammarid amphipods in one. The latter was a whale taken at Gambell in May;
the others were all taken at Barrow in May, or at Barrow or Kaktovik in
September-October. Based on volumetric composition of the samples, euphausiids were the dominant (90.3% total contents) prey at Barrow in autumn(n=2). Whales taken there in May (n=4) had eaten substantial amounts ofcopepods (30.7%), as well as euphausiids (59.1%). Copepods (66.1%) andeuphausiids (31.2%) were the dominant prey of whales taken at Kaktovik in
autumn (n=8). The organisms most commonly eaten ranged from about 3
to 30 mm in length.
Based on stomach contents and other information, two important feedingareas in Alaska can at present be identified: the area between Barter Islandand the U.S.-Canada demarcation line, and the region from Point Barrow toapproximately Pitt Point. The organisms eaten in the Beaufort Sea in autumn are extremely high in fat and caloric content when compared to otherspecies and more southern areas. Calculations indicate that prey densities
are adequate for whales to obtain their annual energy needs during a 130-day
feeding season, and that annual production in most years is probably adequate
to support populations of bowheads and other consumers of zooplankton.
Arctic cod are the major consumers of copepods and euphausiids in the area.
Aspects of feeding ecology are obviously of great importance to the recoveryof the presently reduced bowhead whale population. A major question iswhether bowheads can reoccupy portions of the Bering and Chukchi seas thatwere once used as summer feeding areas.

Sci. Rep, Whales Res. Inst.,
No. 35, 1984, 1-16

2

LOWRY AND FROSTINTRODUCTION

Bowheaci whales, Balaena mysticetus, make extensive annual migrations from wintering areas in the Bering Sea to summering grounds in Amundsen Gulf and theBeaufort and Chukchi seas (Braham et al. 1982). It has generally been assumed
that bowheads, like other mysticete cetaceans, feed principally during the summer, and that their migration therefore is undertaken in order to reach preferred
feeding areas. However, aspects of the feeding biology of bowheads are very
poorly known.
The foods of most species of baleen whales are well documented since they
have been the objects of commercial harvests in the 19th and 20th centuries andthe contents of stomachs of harvested whales have been carefully examined (e.g.,
Nemoto 1957, Tomilin 1957). Bowheads were also extensively harvested by commercial whalers in the late 1800's and early 1900's. However, since they usually
were processed only for baleen and sometimes for oil, the contents of stomachs
were rarely, if ever, examined. Tomilin (1957) concluded based on indirect evidence that copepods (Calanus finmarchicus) and pteropods (Limacina helicina) weremajor food items. MacGinitie (1955) in a report based on work done at Point
Barrow indicated that bowheads ate euphausiids, mysids, pteropods, and copepods.
Johnson et al. (1966) examined the stomachs of two bowheads taken at Point Hopein April 1960 and May 1961. One stomach was empty; in the other, they foundfragments of polychaetes, crabs, snails, crustaceans, and echinoderms. Mitchell(1975) stated that bowheads eat principally small and medium-sized zooplankton
but sometimes also eat benthic organisms such as amphipods and mysids.
Since 1976 we have obtained and examined samples of the stomach contents
of bowhead whales taken by Eskimo whalers at several locations on the westernand northern coasts of Alaska. Those samples were collected for us through thecooperation of the Alaska Eskimo Whaling Commission and the National Marine
Fisheries Service. Results of our analyses of the samples have been in part reported (Lowry et al. 1978, Lowry and Burns 1980). In this paper we will report andsummarize all our observations on stomach contents of bowheads, examine theimportance of various prey species in their diet, identify major feeding areas in
Alaskan waters, and discuss the overall feeding strategy of bowheads in the western
Arctic.
METHODS

Samples of bowhead whale foods were collected for us by a number of different
persons. All samples were from the gastrointestinal tracts, usually the forestomachs, of whales taken by Eskimo subsistence hunters and were generally obtained
within a few hours of the time the whales were killed and landed. The samples
which we obtained were usually preserved in buffered 10% formalin and rangedin volume from a few mL to over 2L. The total volume of food present in theSci. Rep. Whales Res. Inst.,
No. 35, 1984

3

FOODS OF BOWHEAD WHALES

stomach of each whale was usually estimated and recorded in the field.
In the laboratory, samples were drained and gently washed on a 1.00-mm
mesh sieve. Food material was then sorted macroscopically into major taxonomic
groups, and the water displacement volume of each group was determined. The
organisms in each group were examined microscopically when necessary and identified to species if possible. Identifications were made using appropriate keys andreference specimens in collections at the Alaska Department of Fish and Game andthe University of Alaska. The number of individuals and total volume of eachprey species were determined, and lengths of representative specimens were measured. In the case of abundant, small organisms such as copepods, the volume andnumber of the various species were estimated from subsamples.
RESULTSWe examined samples of prey items from the gastrointestinal tracts of 20 bowhead
whales. With three probable exceptions, all were collected from stomach contents. Seven of the samples were from whales taken near Point Barrow, nine fromwhales taken near Kaktovik, two from Point Hope, and one each from Shaktoolik
and Gambell (Table 1 ). All of the samples from Kaktovik and two of those from
Barrow were from whales taken in the autumn (September or October); all of theothers were from whales taken in the spring (May).
TABLE 1. BOWHEAD WHALE SPECIMENS FROM WHICH SAMPLESOF PREY ITEMS WERE OBTAINEDSpecimennumberLocation

Date ofkill

Sex

Total length(m)76-B-6F
76-B-7F
77-B-579-B-380-B-380-B-580-B-979-KK-l
79-KK-2
79-KK-3
79-KK-4
79-KK-5
80-KK-lBarrow
Barrow
Barrow
Barrow
Barrow
Barrow
Barrow
Kaktovik
Kaktovik
Kaktovik
Kaktovik
Kaktovik
Kaktovik

10 Sep 76
20 Sep 76
5 May 77
27 May 79
25 May 80
25 May 80
27 May 80
20 Sep 79
6 Oct 79
8 Oct 79
10 Oct 79
II Oct 79
14 Sep 80

femalefemale
male
male
male
male
femalemale
female
male
male
male
male

16,0
14.3
10.6
8.3
8.5
10.4
13.7
12.7
10.5
10.3
10.6
10.6
9.1-10. 7

81-KK-l
81-KK-2
82-KK-l78-H-2
79-H-380-SH-l82-G-2

Kaktovik
Kaktovik
Kaktovik
Point Hope
Point Hope
Shaktoolik
Gambell

8 Sep 8111 Sep 81
23 Sep 82
4 May 78
6 May 79
9 May 80
1 May 82

female
male
male
male
male
male
female

17.4
14.0
16.0
9.7
9.1
10.1
8.8

Sci. Rep. Whales Res. Inst.,
No. 35, 1984

Comments
reported to be an ingutuk
killed at 1600 hrs local timesample from colon
killed at 0630 hrs local time
killed at 0616 hrs local time
killed at 1800 hrs local time
recovered on 22 September

killed at 1740 hrs local timesample probably from small
intestine
killed at 1430 hrs local time
killed at 1700 hrs local time
killed at 2100 hrs local timesample from colon
killed at 1533 hrs local time4

LOWRY AND FROST

Depending on the state of digestion of the samples, it was more or less difficult
to determine the specific identity of the prey. Some prey could be identified only
to phylum, family, or genus when only fragments occurred in the samples. Small,fragile organisms such as copepods were difficult to identify to species except incomparatively fresh stomach contents. Larger, more durable organisms such asamphipods and molluscs could generally be identified in mostly digested stomach
or intestinal samples. The presence of euphausiids was easy to detect due to thepersistent and characteristic nature of the eyes which detach from the body during
digestion. Entirely soft-bodied animals such as coelenterates, salps, chaetognaths,
and pteropods may not have been detected in some samples examined, although
they would have been readily observed in those which were in fresh condition.
Eliminating those organisms which could not be identified to species but
which probably represented species found in other samples (e.g., Calanus sp., Gammarus sp., Family Lysianassidae, and Family Crangonidae ), a probable total of 56
prey species was found in the 20 whales containing identifiable food remains (Table2). With the exception of three species each of molluscs and fishes, all identified
prey were crustaceans. The distribution of prey species among the major groupsof crustaceans was: gammarid amphipods-23; copepods-10; hyperiid amphipods-5; shrimps-3; euphausiids, mysids, and crabs-2 each; and isopods, cumaceans, and ostracods-1 each. The number of times each of the major preygroups occurred in the samples was: gammarid amphipods-13; copepods-12;
euphausiids and hyperiid amphipods-11 each; mysids and shrimps-6 each;fishes-5; molluscs--4; crabs and cumaceans-2 each; and isopods and ostracods1 each. Of the individual prey species, the most frequently encountered were
Thysanoessa raschii (11 occurrences), Calanus hyperboreus (10 occurrences), and Parathemisto libellula (8 occurrences). All the remaining prey species occurred in fewer
than five stomachs, while 41 species occurred in only one or two samples. Pebbles,
generally less than 1 cm in size, occurred in six samples.
Copepods or euphausiids were the dominant component of all except five of
the samples we examined (Table 2). Two of those were from colons and contained
shrimp fragments and small clams. Two others contained a single amphipod anda single snail. The fifth contained gammarid amphipods, cumaceans, and otherbenthic organisms. In the other 15 samples, euphausiids were the major food insix, and copepods were dominant in nine. In most of the samples, either Thysanoessa raschii or Calanus hyperboreus was the dominant prey species. At Barrow, T.
raschii was the dominant prey in both whales taken in September, while in samples
from spring T. raschii and copepods (Calanus hyperboreus, Euchaeta glacialis, and Metridea longa) each predominated in two. In samples from whales at Kaktovik, allof which were taken in late September and early October, copepods (principally
C. hyperboreus) were dominant in seven and T. raschii in two.
Eliminating the samples obtained from small intestines or colons and thosefrom stomachs which contained only a single food item, food remains were foundin the stomachs of 15 whales. One of those (82-G-2) was a whale taken in the Bering Sea near Gambell on 1 May 1982. The stomach of that whale was recorded
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

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PREY IDENTIFIED FROM GASTROINTESTINAL TRACTS OF BOWHEAD
WHALES. DOMINANT PREY SPECIES ARE INDICATED BY x x....

COPEPODS
Calanus cristatus
C. finmarchic~s
C. glacialis
C. hyperboreus
Calanus sp.
Chiridius obtusifrons
Euchaeta glacialis
Heterorhabdus sp.
Metridea longa
M. lucens
Pseudocalanus sp.
EUPHAUSIIDS
Thysanoessa inermis
T. raschii
MYSIDS
Mysis litoralis
Neomysis rayi
HYPERIID AMPHIPODSHyperia galba
H. medusarum
Hyperia sp.
Hyperoche medusarum
Parathemisto abyssorum
P. libellula

TABLE 2.

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GAMMARID AMPHIPODS
Acanthostepheia behringiensis
A. incarnata
Ampelisca macrocephala
Anonyx compactus
A. nugax
Apherusa glacialis
Arylus atlassovi
A. carinatus
Bathymedon sp.
Gammaracanthus loricatus
Gammarus zaddachi
Gammarus sp.
Hippomedon denticulatus
Monoculodes zernovi
Monoculodes sp.
Munnopsis c.f. Jv!. typica
Onisimus glacialis
0. litoralis
0. nanseni
Orchonome sp.
Pontoporeia femorata
Rozinante fragilis
W eyprechtia heulgini
W. pinguis
Family Lysianassidae
Family Synopiidae

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colon.
Sample probably from small intestine.

1 Sample fromISOPODS
Saduria entomon
SHRIMP
Eualus fabricii
E. gaimardii
Sabinea septemcarinata
Family Crangonidae
CRABS
Chionoecetes opilio
Family Paguridae]zoea)
CUMACEANS
Diastylis bidentata
Diastylis sp.
OSTRACODS
MOLLUSCS
Limacina helicina
Natica clausa
Nuculana sp.
Order Pelecypoda
FISHES
Boreogadus saida
Myoxocephalus quadricornis
Pungitius pungitius
Family Cottidae
PEBBLES

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8

LOWRY AND FROST

as full and contained an estimated 30L of food. Based on the sample we examined,
the prey was composed of 92% gammarid amphipods, 7% cumaceans, and 1 %other benthic organisms. Four small pebbles also occurred in the sample.
The quantitative composition of stomach contents samples from the remaining
14 whales is shown in Tables 3 and 4. Euphausiids dominated in the stomach
contents of whales taken at Barrow in the autumn. Whales taken at Barrow inthe spring contained principally euphausiids and copepods in variable proportions,with substantial amounts of mysids in three. Total quantities of food in whales
taken during spring were very small. In whales taken in the autumn at Kaktovik,
TABLE 3. QUANTITATIVE DATA(% OF TOTAL SAMPLE VOLUME) ON
STOMACH CONTENTS OF BOWHEAD WHALES TAKEN AT BARROW
AUTUMN 1976
Prey type

Copepod
Euphausiid
Mysid
Hyperiid amphipod
Gammarid amphipod
Other invertebrate
Sample volume (ml)Estimated total volume
of contents (liters)
1
2

SPRING 1977 AND 1980

Whale specimen Overall
numbermean%of contents 1
76-B-6F 76-B-7F
86.7

90.3

3.0
10.3
<0.1
17.5
33.0
unknown 109

2.7
6.9
<0.1

97. I
2.3
0.6

Whale specimen number
77-B-580-B-380-B-5

97.0
I.0

24.2
48.5
15.2
3.0

95.4
3.8

<0.1

2.0
20.0
3.3
unknown "a few
invertebrates"

73.4

80-B-9
1.4
91.6
5.4
1.0
0.6

Overallmean%
of contents 2
30.7
59. l
6.1
1.0
0.2
0.5

139.7
2

Calculated as the percent of combined total volume in the two samples.
Calculated as the average of the percent of total volume in each of the samples.
TABLE 4. QUANTITATIVE DATA(% OF TOTAL SAMPLE VOLUME) ON
STOMACH CONTENTS OF BOWHEAD WHALES TAKEN AT
KAKTOVIK, AUTUMN 1979-1982
Whale specimen number
Prey type
Copepod
Euphausiid
Mysid
Hyperiid amphipod
Gammarid amphipod
Other invertebrate
Fish
Sample volume (ml)Estimated total
volume of contents(liters)

1

79KK-1

79KK-2

79KK-3

79KK-4

79KK-5

81KK-1

81KK-2

82KK-1

99.7

99.0
0.3
0.3
0.1
0.1
<0.1
0.1
545.2
18

23.4
67.8
7.0
0.5
0.3

88.3
4.9

<0.1
97.9
0.8

99.0
0.7

99.0

98.7

<0.1
1.3

<0.1
0.1
<0.1
<0.1
2406.2
44

1.0
399.7
22

0.4
2.4
2.3
I. 7
131.3
18

0.1
I. I

<0.1
0.3
<0.1

1.0

357.9
36

145.5
18

19.2
95.2
3
"a few"

Overallmean%
of contents 1
66.1
31.2
1.2
0.1
0.4
0.5
0.3

Calculated based on the volume and percent composition of each sample and the estimated total
contents volume of stomachs from which samples were taken.
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

FOODS OF BOWHEAD WHALESTABLE 5.

SIZES OF PREY ORGANISMS IN STOMACHS OF BOWHEAD WHALES

Copepods
Euphausiids
MysidsHyperiid amphipods
Gammarid amphipods
I so pods
Fishes1

9

Length (mm)lVolume (mL)

3.5-7.0
18-30
23-33
8-21
7-55
52-86
31-83

0.002-0.02
0.1-0.15
0.1-0.2
0.05-0.1
0.02-4.0
3.4-5. 7
0.1-2.9

Measurements are total length for all groups except copepods, which are cephalothorax length.

copepods and euphausiids in aggregate comprised 91.2-99.7% of the contents ofindividual samples and 97.3% of the overall prey in all samples combined. The
stomach contents in individual whales varied from 99.7% copepods to 97.9% euphausiids; overall, copepods comprised about twice as much of the stomach contents as did euphausiids. The total volume of stomach contents in the whales
varied from 3 to 44L, with an average of 23L.
Sizes of representative species of the major prey groups eaten by bowheads areshown in Table 5. The organisms most commonly eaten (copepods, euphausiids,
mysids, and amphipods) range from about 3 to 30 mm in length and have a volumeof 0.002 to 0.2 mL. Organisms such as isopods and fishes are considerably larger
but were rarely found in stomach contents samples. The largest item we foundin bowhead stomach contents was the shell of a snail (Natica clausa), 3.4 cm highand 2.6 cm in basal diameter, weighing 8.0 g. The smallest items were Pseudocalanus copepods, which are approximately 1.3 mm in cephalothorax length andweigh about 0.1 mg.
In addition to the whales from which samples were collected, some additional
animals were examined in the field and the presence or absence of food in theirstomachs recorded. Of whales taken in the Bering Sea in spring, two had preyin the stomach: one taken at Gambell (82-G-2) contained gammarid amphipods,
cumaceans, and other benthic organisms; the other (78-S-l) taken at Savoonga
was reported to con.lain "a few euphausiid-like creatures." Three had empty
stomachs: two of those reportedly had material in the intestines, and the third had
crustaceans in the baleen. Of four whales taken in the Chukchi Sea in spring, two
had empty stomachs, one contained a snail, the other a single gammarid amphipod.
Four whales taken at Barrow in spring have contained food remains, and sevenhave been recorded as having empty stomachs. Three of the latter had some foodresidues in the intestines. All whales that have been taken and examined in theautumn (2 at Barrow and 10 at Kaktovik) have contained substantial quantities
of food.
We examined the relationship between whale size and the principal type of
prey found in samples based on 18 animals of known length which contained recognizable prey. Whales that had eaten principally copepods ranged from 10.5
to 17.4 m, with a mean length of 13.1 m (n=7). Those that contained mostly euSci. Rep. Whales Res. Inst.,
No. 35, 1984

10

LOWRY AND FROST

phausiids ranged from 8.5 to 16.0 m, with a mean of 12.0 (n=7). Five whales
in which we found only benthic organisms were 8.3-10.1 m, with a mean lengthof 9.2 m. Only one of the whales that had eaten copepods or euphausiids was lessthan 10.3 m in length.
DISCUSSION

We identified a wide array of organisms from samples taken from the gastrointestinal tracts of bowhead whales. Most of the prey species (53/56) were invertebrates, and most of those (35/53) were primarily benthic organisms. However,with few exceptions, benthic species composed a very small proportion of the overall
stomach contents. Four of the five exceptions were whales taken in spring in the
Bering and Chukchi seas; the fifth was a whale taken at Barrow in spring whosecolon contained three small clams. The two taken in the Chukchi Sea each contained single items. One of those taken in the Bering Sea had an empty stomach
but shrimp fragments in the colon; the other had a stomach filled with benthic
invertebrates. The five whales were all small, the largest being 10.1 m long, andwere undoubtedly subadult animals (Marquette 1978). We conclude, based on
the samples we examined and field records, that some bowheads feed while passing
through the northern Bering Sea in May. The incidence of feeding during thenorthward migration appears to be less in the Chukchi Sea than in the Bering.
Feeding whales may be predominantly juveniles, and their prey are mostly benthic
invertebrates.
Four of 11 whales taken and examined at Barrow in the spring have contained
food in their stomachs, generally a few liters or less of copepods and euphausiids.
We conclude that some feeding occurs near Barrow during the spring migrationand that planktonic organisms are the main prey. However, based on the highproportion of empty stomachs and the small volumes of contents in those containing food, it appears that the main feeding season has not yet commenced.
Many bowhead whales summer in the eastern Beaufort Sea (Fraker andBockstoce 1980), where they are presumed to feed extensively (Griffiths and Buchanan 1982). Whales that have been taken and examined while moving westward
through the Alaskan Beaufort Sea in autumn have all contained food. Whales
taken at Barrow have contained mostly euphausiids, while in those taken near
Kaktovik both copepods and euphausiids occur, with copepods overall predominating in the samples. Benthic organisms are quantitatively unimportant near Kaktovik but comprised a small and perhaps significant proportion of the samples examined from Barrow. Feeding of whales in autumn is obviously directed primarily
at organisms in the water column, with benthic organisms being taken incidentally
during near-bottom feeding.
Several lines of evidence point to the existence of at least two areas of the
Alaskan Beaufort Sea where bowheads regularly feed during September-October.
First, of course, is the occurrence of substantial quantities of food in the stomachs
of all the whales taken and examined at Kaktovik and Barrow during autumn
Sci. Rep. Whales Res. Inst.,
No. 35, 1984

FOODS OF BOWHEAD WHALES

II

hunts. Whalers from Kaktovik have indicated that they regularly find bowheads
feeding in the area to the east of Barter Island (D. Ljungblad, pers. commun.; G.
Jarrell, pers. commun.). In discussing bowheads in the area to the east of Point
Barrow, Durham (1979) stated that "the hunters sometimes encounter herds of
50 to 60 whales along the Plover Islands (Thomas Brower, pers. commun.). This
area may be a rest stop for the whales and provide an opportunity for them to feed,judging from stomach contents."
The feeding area east of Barrow appears to extend to approximately Pitt
Point. On 18 September 1974, 57 whales were counted in this area (Braham et al.
1982), while on 20 September counts ranged from 81 to 136 (Ray and Wartzok
1980). On 8 August 1976, a single whale was seen just offshore from the Plover
Islands (Lowry, unpublished). Two ringed seals (Phoca hispida) collected in theimmediate area within minutes of sighting the bowhead had been actively feedingon euphausiids (Lowry et al. 1980). On 19 August 1976, four bowheads wereseen northeast of Point Barrow, and on 21 September 47 whales were counted in
the area (Braham et al. 1982). As indicated in this report, whales taken at Barrowon 10 and 20 September 1976 had both been feeding on euphausiids. A group of
20 whales which appeared to be feeding was seen north of Point Barrow on 22
October 1978 (Braham et al. 1982).
The feeding area in the eastern Beaufort Sea extends from Barter Island east
to at least the U.S.-Canada demarcation line (141°W longitude). In 1979, 35
whales were seen milling east of Beaufort Lagoon on 24 September, and 37 wereobserved north of Demarcation Bay on 26 September (Ljungblad et al. 1980). In
1980, single whales that appeared to be feeding were sighted north of Beaufort
Lagoon on several occasions from 9 to 21 September, and a group of nine was seen
east of Barter Island on 14 September (Frost and Lowry 1981, Ljungblad 1981).
On 22 September 1982, 128 bowheads were counted in the area north of Demarcation Bay. Most of the animals were milling around near the surface (S. Johnson,
pers. commun. ).
Although bowheads may feed regularly or occasionally in other parts of the
Alaskan Beaufort Sea, such occurrences cannot be verified by observations of stomach contents since very few whales are taken elsewhere than the areas discussed
above. Ljungblad (pers. commun.) has seen bowheads engaged in behavior thatmight indicate feeding in the areas north of Flaxman Island and northeast of
Pingok Island.
The smallest organisms which are regular foods of bowheads are the copepods
Metridea spp. (cephalothorax length 2.7-3.1 mm) and Calanus glacialis (2.4-3.3 mm).
The most commonly eaten species of copepod, Calanus hyperboreus, is much larger,
ranging in length from 3.6 mm (copepodite stage IV) to 6.4 mm (adult). The
smaller copepods, Pseudocalanus sp. (1.1-1.6 mm long) and Derjuginia tolli (1.41.8 mm long), although very abundant in the Beaufort Sea (Frost and Lowry
1981 ), virtually never occur in bowhead stomach contents. It appears, therefore,that organisms smaller than about 2.5 mm are not effectively retained by bowheadbaleen. The largest prey regularly consumed appear to be about 30 mm long andSci. Rep, Whales Res. Inst.,
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LOWRY AND FROSTTABLE 6. CALORIC VALUES OF REPRESENTATIVE SPECIES OF ARCTICZOOPLANKTON AND BENTHOS, ARRANGED IN ORDER OF DECREASING CALORIC VALUE. ALL VALUES ARE FROM SAMPLES TAKEN
IN SEPTEMBER UNLESS OTHERWISE INDICATED.
(ADAPTED FROM PERCY AND FIFE 1980.)
Taxon
Copepod (Calanus sp.)
September
mid-late August
late July-early August
Euphausiid (Thysanoessa inermis)
Hyperiid amphipod (Parathemisto libellula)
Gammarid amphipod (Anonyx nugax)
Chaetognath (Sagitta elegans)
Isopod (Saduria ( =Mesidotea) sabini)
Pteropod ( Clione limacina)
Ctenophora (Mertensia ovum)
Cnidaria (Aglantha digitale)

Cal/g wet weight% of maximum

2,983
2,660
2,018
1,974
1,364
1,299
517
367
296
98
89

100
90
69
67
46
44
18
12
10
3
3

include euphausiids, mysids, and amphipods.
The fact that bowheads migrate several thousands of kilometers annually tosummer and feed in the Beaufort Sea implies that the quantities and kinds of foodavailable to them there are adequate, and also perhaps that feeding conditions aresuperior to those found in other areas. The abundance of copepods in the Beaufort Sea is not remarkably high (Griffiths and Buchanan 1982). The abundanceof euphausiids is extremely difficult to quantify (Brodie et al. 1978), but observations of predator stomach contents indicate that they may be locally abundant(Frost and Lowry 1981 ). One way in which arctic marine zooplankton are remarkable is their tendency to accumulate storage lipids during the summer which
are used for maintenance and reproduction during winter months (Lee 1975). In
samples of Calanus hyperboreus collected from Fletcher's Ice Island in October, lipids
comprised 64% of the dry weight (Lee 1975). In samples collected in September
at Frobisher Bay, lipids comprised 52.4% of the dry weight of Thysanoessa inermis
and 57.4% of Calanus spp. (Percy and Fife 1980). Caloric values of representative
species of arctic marine zooplankton and benthos are shown in Table 6. Values
are expressed in terms of calories per gram wet weight, which is the most appropriate consideration from the perspective of a consumer. Organisms which are
the primary foods of bowheads (copepods and euphausiids) have very high caloric
values. Those eaten with some frequency (hyperiid and gammarid amphipods)
have intermediate values. Those organisms which are rarely or never consumed
have very low caloric values. Of interest also is the fact that copepods in September contain almost 50% more calories than those sampled in late July and earlyAugust. Therefore, given equivalent prey densities, late summer feeding may beof greater value to the whales than that which occurs earlier in the year.
Although it is probably true in general that arctic zooplankton are richer incalories than those in more southern latitudes (Percy and Fife 1981), there are few
Sci. Rep. Whales Res. Inst.,

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13

data available with which to verify this hypothesis. Nishiyama (1977) sampledzooplankton in Bristol Bay, Alaska and determined the caloric value of Calanus andThysanoessa to be 5,512 and 5,554 cal/g ash-free dry weight. Those values are 44%
and 19% lower than comparable measurements for the same species collected at
Frobisher Bay (Percy and Fife 1980). The values for caloric content of Frobisher
Bay copepods are the highest published values for any marine organism (e.g., see
Braun et al. 1968, Tyler 1973, Laurence 1976).
Several authors have attempted to assess the relationship between availabilityof food in the marine environment and the food requirements of whales. Studies
dealing with fin whales (Balaenoptera physalus) have concluded that either whales
swim exceedingly fast, or densities of prey are much greater than those found using standard sampling techniques (Klumov 1961, Brodie et al. 1978). Similar results were derived by Brodie (1980) and Griffiths and Buchanan (1982), dealing
with bowheads. However, those studies did not take into account the energetic
richness of prey available in the Arctic.
We have made similar calculations, starting with the energetic assumptions
used by Brodie (1980), who concluded that a bowhead 13.72 m long would need toingest approximately 4,000 kg of lipids during the feeding season in order to maintain itself throughout the year. Based on data in Percy and Fife (1980), 16.8%of the wet weight of Calanus copepods collected in late July and August is lipid;
therefore, a whale would need to consume 23,810 kg of copepods during thefeeding,season. A bowhead 13.72 m long would have baleen approximately 2.4 m
long (Alaska Eskimo Whaling Commission, unpubl. data). We assume that whilefeeding the mouth opening is 2.4 m high and tapers from 2.0 m wide at the bottom
to 1.0 m at the top and a whale swims at about 4.2 km/hour (2.8-5.6 km/hr in
Ljungblad et al. 1981). Using those assumptions, 15,120 m 3 of water would be
filtered each hour. Griffiths and Buchanan (1982) observed biomasses of Calanus
ranging from 0.623-0.903 g/m 3 at certain depths in areas of the Canadian Beaufort
Sea where bowheads appeared to be feeding on organisms in the water column.
To acquire 23,810 kg of copepods would require filtering 26,367,000-38,218,000 m 3
of water (assuming the above prey densities and 100% filtering efficiency), which
would involve 1,744-2,528 hours of feeding. Frost and Lowry (1981) estimated afeeding season of 105 days in the Canadian Beaufort and 25 days in the Alaskan
Beaufort Sea, which suggests 3,120 hours available for feeding. Therefore, it appears that bowheads can obtain their annual food requirements with a 130-day
feeding season in the Beaufort Sea, if they feed for somewhat over half the timethey are on the feeding grounds and concentrate their efforts in areas where prey
are relatively abundant. Based on the above assumptions and an average weightfor copepods of 0.004 g (Bain et al. 1977), the ingestion rate of copepods would beapproximately 50,000 individuals per minute.
A further consideration with respect to the bowhead whale stock in the western Arctic is whether the total annual production of prey in the feeding areas issufficient to supply the energetic requirements of all the whales summering in thearea. Although the summer feeding range of the bowhead once included much
Sci. Rep. Whales Res. Inst.,
Na. 35, 1984

14

LOWRY AND FROSTof the Bering and Chukchi seas as well as the Beaufort Sea (Bockstoce and Botkin1980), at present the Beaufort Sea is the primary feeding area, although some lateseason feeding may occur in the Chukchi Sea (Frost and Lowry 1981). Calculations such as those done for an individual whale feeding on copepods cannot be
expanded to the entire population because euphausiids, a major prey species, havenot been quantitatively sampled properly in the Beaufort Sea (see Frost and Lowry
1981 and Griffiths and Buchanan 1982) and bowhead prey are also eaten by otherconsumers in the Beaufort Sea. Frost and Lowry (1983) estimated the quantities
of prey eaten on an annual basis by populations of major vertebrate consumers in
the Alaskan Beaufort Sea. They considered only species which feed primarily onorganisms connected to the pelagic/planktonic food web-bowhead whales, white
whales (Delphinapterus leucas), ringed seals, seabirds, and arctic cod (Boreogadus
saida). Results indicated that arctic cod are by far the major consumer of zooplankton. They were estimated to eat 97.8% of the total copepod and 65.8% of
the total euphausiid biomass consumed annually by all species of predators combined. Estimates for bowhead consumption were 2.2% of the total copepod biomass and 31.5% of the total euphausiid biomass consumed. Although these results suggest the possibility of considerable competition for food, some resource
partitioning occurs since many of the copepods eaten by arctic cod are small forms(Der}uginia and Pseudocalanus), which are not major foods of bowheads (Frost and
Lowry in press). Based on extrapolations from measurements of primary production, Frost and Lowry (1981) estimated that 0.3-4.4 million t of zooplankton are
produced annually in the Alaskan Beaufort Sea. When compared to the estimatedtotal amount ofzooplankton consumed annually (approximately 1.1 million t (Frostand Lowry in press)), this suggests that food availability may be limiting in years of
low production, while in other years a surplus of food may be available. Causesof annual variations in productivity and their effects on consumer populations arelargely unknown.
What then is the feeding strategy of western arctic bowhead whales? Bowhead whales are robust-bodied animals, possessing long baleen with fine fringes
capable of efficiently retaining very small prey. Although our study has shownthat some feeding occurs in the northern Bering and Chukchi seas during the springnorthward migration, the major known summer feeding grounds are in the Beaufort Sea. The quantities and kinds of organisms there are adequate, and the extraordinarily high fat content (and caloric value) of prey facilitates accumulation of
blubber reserves necessary to maintain the animals during periods of fasting. Extensive blubber reserves may help sustain animals through years of low summer
productivity which may occasionally occur.
Some late summer and early autumn feeding may occur in the Chukchi Sea.
There is no direct information to indicate whether bowheads feed on their wintering grounds in the Bering Sea. However, based on considerations such as theseasonal distribution and abundance of prey, and their probable caloric content,
we speculate that winter feeding in the Bering Sea, if it occurs, is of little significance in the annual nutrition of bowheads. Bowhead whales swim from the BerSci. Rep. Whales Res. Inst.,
No. 35, 1984

FOODS OF BOWHEAD WHALES

15

ing Sea to the Beaufort Sea to feed because of the high-energy foods available there,
and perhaps also because competition for food from other organisms occurs at tolerable levels. No other baleen whale penetrates northward into what is presently
the principal feeding grounds for bowheads. In years past, bowheads mingledwith other species in the Bering Sea in summer until they were eliminated by predation from commercial whalers. Whether the portions of their feeding rangethat were lost decades ago will ever be regained is a most interesting question, andone of great significance when contemplating the ability of the western arctic bowhead population to regain its former abundance.
ACKNOWLEDGMENTS

The samples which were used in this study were collected for us by a number ofpeople working for the Alaska Eskimo Whaling Commission, the North Slope
Borough, the National Marine Fisheries Service, and the Naval Arctic ResearchLaboratory. We are grateful to all who helped in the collection, preservation,and transport of specimens. Mr Robert Nelson and Mr Barry Lopez provided
invaluable help during field studies related to bowhead whale feeding. Mr
Kenneth Coyle and Mr George Mueller of the University of Alaska, Institute ofMarine Science, provided expert identifications of many prey organisms. Dr
Thomas Albert, Mr John Burns, and Dr Howard Braham assisted with manyof the financial and technical aspects of the study. Dr Paul Brodie made helpfulcomments on a draft of the manuscript. The manuscript was typed and editedby Mrs Kathleen Pearse.
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