FOOD HABITS AND PREY DISTRIBUTIONS OF THREERORQUAL SPECIES IN THE NORTH PACIFIC OCEANAKITO KAWAMURA
Faculty of Fisheries, Hokkaido University, Hakodate, Hokkaido

ABSTRACT

Stomach conditions and a total of 1675 stomach samples of fin, sei and
Bryde's whales caught in the North Pacific during the seasons of 1969-1979
were examined. The percent of filled stomach to all animals examined wasabout 60% with varying fullness; and this figure was considered to be very highnotwithstanding the fact that large number of whales were caught in the subartic to subtropical waters where the zooplankton distribution is poorer than
the northern North Pacific region. Due to southerly shifted whaling groundthere found many warm water prey species in the stomach samples. Of morethan 40 prey species occurred, however, very few number of the species actuallycomprised principal prey items, i.e., Calanus cristatus, C. plumchrus, C. pacificus,
Euphausia pacifica, E. similis, Thysanoessa longipes, T. spinifera, T. inermis, Nematoscelis dijficilis, Sergestes similis, Vinciguerria nimbaria, Scomber japonicus, Cololabis
saira and Pseudopentaceros richardsoni. The composition of stomach contents bywhale species revealed that the fin, sei and Bryde's whales eat mainly euphausiid, copepods, and small gregarious fish species in this order. From thecharacteristics of geographical distributions of the major prey items by eachwhale species, it was suggested that the North Pacific rorqual whales share apossible food species among them by selecting different prey items. Therealso suggested that the feeding conditions in the pelagic waters of the North
Pacific region differ from those in the marginal sea regions such as the Kurile
Islands and/or the Bering Sea in the composition of prey fish species.
INTRODUCTION

Since the establishment of the Whales Research Institute in 194 7, one of main
study areas was to know the food habits of baleen whales of both northern andsouthern species. In the North Pacific region including Japanese coastal waters,
Mizue (1951) was the first who dealt with the food habits oflarger whales caught
by the land-based whaling around Japanese waters during 1946-1948, and pointed
out an extreme importance of krill for fin whales, whilst squid and/or Japanesesardine may contribute as main food items in sei whales. In accordance withthe development of the North Pacific pelagic whaling since 1952, the whaling
ground geographically expanded year after year towards more northern latitudesof the Bering Sea (Omura, 1955; Nasu, 1957; Nemoto, 1957), which caused theshift of main study area from the coastal regions to the pelagic catches of whales.
Studies of the food habits of baleen whales by Nemoto (1957, 1959, 1963) conSci. Rep. Whales Res. Inst.,

No. 34, 1982, 59-91.

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KAWAMURA

tributed to clarify the feeding conditions of baleen whales over the North Pacificand Bering Sea, and the prey items of baleen whales by whale species bacame
clear in detail, although some more earlier Russian works in this field have beenreported (e.g. Zenkovitch, 1937). Nemoto (1959) finally compiled large amountof data that came from a total of 9,270 animals caught in the North Pacific, Bering
Sea, and Okhotsk Sea during 1952-1958. Later, Nemoto (1963) discussed distribution characteristics and importance of two major Calanus species as the preyof whales using additional materials obtained up to the 1961 season.
After a pause of effort to collect the stomach contents of the North Pacificbaleen whales during the 1962-1968 seasons, activity of material collection by the
Whales Research Institute was restored again in 1969, and the effort was continued
until 1979 except 1978 season, while the geographical occupation of whaling groundalong with the composition of exploitable whale species changed considerably during
these periods. However, stomach samples of whales covering last 10 years havenot been examined nor reported todate except several short articles of limited subjects (Omori et al., 1972; Kawamura, 1973; Nemoto & Kawamura, 1977; Kawamura, 1978; Kawamura & Hamaoka, 1981; Kawaguchi & Kawamura, 1981).
Among these reports, Omori et al. ( 1972) reported the mass occurrence of the sergestiid shrimp, Sergestes similis Hansen, and pointed out its importance as whales foodparticularly in the eastern half of the northern North Pacific, while Kawamura (1973)
focussed his discussion on the food conditions of whales in the southern part ofthe subarctic North Pacific region, and he (Kawamura, 1973) pointed out apossible significant ecological role of several commercially important fish species
as food of sei whales.
The long-lasted Japanese activity in the North Pacific pelagic whaling ceased
its 18-year operations in 1979 as it was the final expedition. This report aims toprovide a knowledge about the food habits of the North Pacific baleen whales, fin, sei,and Bryde's that were caught largely in the southern waters from subarctic to subtropical regions. In this point of view, this report can be regarded as a supplement of our earlier knowledge that was obtained in the boreal to arctic regions.
MATERIALS AND METHODS

The stomach contents of whales were collected randomly from the cut opened
first stomach that was found to be containing fresh enough food for the identificationof each prey item. Usually, several hundred grams (wet weight) of stomach contents were collected, and they were preserved in plastic bottles with 10% formalinsolution. The number of samples should be collected by each season and by the
fleet was basically guide lined to take one stomach sample per every ten animals
processed, but actually it varied considerably by situations in the field and by
the fleet participated. However, being independent of the sampling scheme
above mentioned, the materials were collected to meet with the necessity of data
analysis, i.e., to collect the materials so as to totally represent the geographicalexpansion of whaling ground and the month (=season) occupied. Sampling wasSci. Rep. Whales Res. Inst.,
No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

61

TABLE I. NUMBER OF STOMACH SAMPLES COLLECTED IN THE NORTH PACIFIC
AND BERING SEA WHALING DURING THE SEASONS OF 1969-1979.*( ): Number of whales caught
Season

Fin

Sei

1969

56
(576)
32
(518)
62
(542)
14
(426)
24
(256)
46
(216)
31
(118)

316
(3,591)258(3,235)181(2,431)70(2,041)98**(1,710)100(1,190)
52
(454)

1970
1971
1972
1973
1974
1975
1976
1977

No sampling

1978
1979
Total

265
(2,652)

1,075(14,641)

Bryde's

I
(98)

(5)
(2)
46
(522)
51
(688)
56
(578)
97
(424)
(200)
94
(175)
345
(2,694)* A catch of ten minke whales in 1970 was excluded** One unknown stomach sample probably belongs to sei whale stomach was included

also conducted whenever the species of prey items seemed to have changed by avisual observations. Several number of stomach samples were damaged by aleakage and evaporation of preserving solution under an unfavourable conditionsof storage during the past 13 years.
During the summer period of 1969-1979 a total of 19,992 baleen whales
were harvested by the Japanese pelagic whaling in the North Pacific and Bering
Sea regions. The number of materials actually examined in this study was 1,685
stomachs in all as given in Table 1. The whale species treated were fin, sei and
Bryde's. During the study period there were several number of pelagic catchesof minke whales but they were excluded in this study due to small number in theavailable amount of materials.
The traditional catch records (Geirui Hokaku Daicho) on each animal processed along with some results of biological observations in situ by fleet and whaling
season that were compiled by the Far Seas Fisheries Research Laboratory of theFisheries Agency were available, and these statistical data were referred or quoted
whenever it was felt necessary. To construct an approximate expansion of thewhaling ground occupied in the past seasons, I consulted a report series (TheSci. Rep. Whales Res. Inst.,
No. 34, 1982

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KAWAMURA

reports on the biological investigations of the North Pacific whale stocks) publishedby the Japan Whaling Association or the Whales Research Institute, Tokyo.
Since the general methods and items of observations in recording the stomach
conditions of whales in the field have been reported elsewhere (e.g. N emoto, 195 7;
Kawamura, 1974), no details were mentioned in this report.
RESULT

1.

Whaling ground
Geographical occupation
As it was reported earlier (e.g. Nemoto, 1957, 1959), the fin whales occur
more larger numbers in the Bering Sea and higher latitudes of the northern North
Pacific regions from May to August. Due to reduced catch quotas for fin whales
year after year the catches of this whale species during study period were confinedin small local areas closer to the Pribilof Islands, whereas in the North Pacific the
majority of fin whales were caught in the southeast region off Kamchatka and in
the Gulf of Alaska. However, the trends of their catches on the whole were somewhat sporadic during the l 960's. In contrast to fin, the sei whales, a major exploitable species during the study period, were found to be distributed over a wide
range of the subarctic North Pacific region of north of 40°N. With the change in
exploitable whale species from sei to Bryde's along with the opening of warmer
temperate/subtropical region down to 20°N as a possible whaling ground in thewestern North Pacific, the Bryde's became a major species of pelagic whaling since1971 (Kawamura, 1973).
In order to show approximate trend of the changes in geographical occupations of whaling ground, Fig. I was constructed by selecting several representative
whaling seasons. During the 1950's the expansion of whaling ground was confinedin geographically smaller area of higher latitudes of the North Pacific. The major
whaling ground was established both in the eastern/southeastern waters off Kamchatka Penninsula and in the eastern North Pacific/Bering Sea regions. With
the developments of whaling activity along with the change in exploitable whale
species from fin to sei the whaling ground during the first half of the 1970's became wide ranged occupation where the southern most whaling ground extended
to 40°N such the case as shown in 1971. The trend of more southerly shift ofwhaling ground in 1972 indicates that the movements of whaling fleet were intense
in pursuit of more profitable whaling ground in accordance with lifting of thebanned area, and this along with covering the catch quotas for fin and sei resulted
a largest occupation of whaling ground during the first half of the 1970's throughout the whole North Pacific whaling.
Since the close of hunting fin and sei whales in 1976, there left the Bryde's
alone, a warm water species that inhabits widely the temperate to subtropicalwaters in the North Pacific (Omura & Nemoto, 1955; Kawamura & Satake, 1976).
In order to catch the Bryde's whales there found a new whaling ground in far
southern waters down to 20°N particularly in the western North Pacific. The
Sci. Rep. Whales Res. Inst.,
No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

63

40" .......~~-'-~~-'-~~~'--~~...J_~~l-.....I
N40°.._~~_,_~~~-'--~~---'-~~~-'-~~-'--'

N

50°

50•

160°

180°

160°

140°

120°w

Fig. 1. Geographical occupations of the North Pacific whaling grounds in the pastnine seasons.

geographical changes in the occupation of whaling ground can be comparable withthe changes in the composition of exploited whale species; the fin and blue were themain species during 1952-1962 when they were hunted in somewhat geographicallySci. Rep. Whales Res. Inst.,
No. 34, 1982

64

KAWAMURA(Fig. 1 continued)

N

60°

40°
30°'-------'----'----~---~~--

N

60°
50°

30°1------+-200.L-----'----'----'-----'----~

Nso•

2oo,___ ___.____.._____._____,__ ____
N

1979

60°
50°

30• 1-~~-1---.••--r--1
20°.___ ___.:_____,,,'----''------'------1---~140°E 160°
1eo 0
160°
140°
120° w
Sci. Rep. Whales Res. Inst.,
No. 31:, 1982

FOOD OF NORTH PACIFIC RORQUAL

65

smaller local regions. With larger increase in the number of sei whale catch fromthe 1962-1963 seasons onwards (e.g. 4-945 animals in 1955 vs 1398-3819 animals in
1963-1975, IWS, 1967-1972), the whaling ground began to occupy more larger
sea area into all horizontal directions until 1975. The very small geographicaloccupation of whaling ground in the southern North Pacific came from hunting
a relatively smaller number of Bryde's whales since 1976, and similar situation
continued until 1979, the final whaling season of the long-lasted pelagic whaling in
the North Pacific Ocean.

Monthly changes in geographical occupation
Since pelagic whaling in the North Pacific is usually operated for four months
or more, the main whaling ground changes in its geographical occupation inaccordance with the proceeding of seasons and catch conditions by whale species.
Fig. 2 demonstrates such example of changes as shown by monthly occupation
through the whaling years of 1969-1973. To see the figures, there observed different monthly occupations from one year to another. In some years such thecase as in August of 1970, there were two or more geographically separated whaling
grounds occupied within the same month due to difference in accomplished catch
conditions by each whaling fleet.
2.

Stomach conditions of whales in generalMonthly changes in prey item
Examination of stomach conditions of whales that were processed on thefactory ship is one of the items of biological observations in the field. Due to visualobservations on the ship each prey item was recorded by the larger taxonomicalgroups such as the Euphausiacea, Copepoda, Amphipoda, Pisces, and Cephalopoda.
One of these available data is found in the catch records of whales by the Fisheries
Agency, and a related part of the records were modified to show a monthly changesof prey items in Figs. 3-4, and in appended table, where all data obtained during
the 1969-1979 seasons were combined altogether.
It is observed in Figs. 3-4 that there were no significant monthly changes in
the percent figure of animals with filled stomach to the total catches, where about
60% of stomachs were found to be filled with variable amount of food over thethree whale species and whaling seasons. In the prey items, however, there observed a considerable difference between each whale species. More than 65% of
fin whales feed on the Euphausiacea from May through August without notablemonthly changes in percent figures. The Euphausiacea along with the Copepoda
comprise major food items of the North Pacific fin whales. Towards mid summer,
however, the Cephalopoda (=squid) become to share a similar percent to the
Copepoda. Sei whales, on the other hand, feed almost exclusively on the Copepoda,
and this prey alone accounts for about 75.8% of the animals with filled stomach.
Different from the case found in fin whales, relative importance of the Pisces andEuphausiacea is a characteristic food habits of sei whales. In both fin and sei
whales the major prey item showed a quite high and less varibale percent fugures
Sci. Rep. Whales Res. Inst.,
No. 34, 1982

KAWAMURA

66

N
60°
50°
40°
30°
60°

1973
140°E

rn
MAY

Fig. 2.

160°
100°
160°
140°
~
llilIIIlIIllil t=========dJUNE JULY AUG SEP

120°w

rn

Monthly occupation of the whaling grounds.

Sci. Rep. Whales Res. Inst.,
No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

370 442

100N:

624

67

225

>u

zw

::::>
G

w
fE50

-

'..c::
.8
0
u

0

z

..c
u
0

u

I-

zw

0

z

u
0::
w
0...

0

FIN
1463 3213 2957 1010

100N:

24

>-

zu

w

::::>

..c.
u

@
0::: 50

lJ...

I-

-8
0

z

z

~w

D...

0
151

~uJ

::::>
G

w

[E 50
z
w

1-

~
w

0...

305

76

~1
'

lfil-2
D. -3

ra - 4lillLJJ·-5§-6

Fig. 3. Composition of stomach contents by the larger prey taxa in fin, sei and
Bryde's whales caught during the seasons of 1969-1979.
1-Euphausiacea 2-Copepoda 3-Amphipoda 4-Pisces 5-Cephalopoda(decapoda)
6-Cephalopoda(octopoda)
N: Number of filled stomach

Sci. Rep. Whales Res. Inst.,
No. 34, 1982

68

KAWAMURA

537 697 1085 343

100N:
>-

~
w

:J
G

w

..c
u

I-

u

0:: 50
LL

zw

-

..c
u

0

z

8

Cl

0

z

ii
w

a..
0
100N:

FIN
2303 5375 5232 1688

39

SEI
543 1180 337 452

96

>u

z

uJ
:J
G

w

0::
LL 50
I-

z

..c
u

0

u
0

z

w
~
w

a..

0

>~
w

:J

Q-2

0::
LL

~-3

1-

·-4

@
z

w

ii
w
a..

Fig. 4.

Stomach fullness in fin, sei and Bryde's whales caught during the seasons of

1969-1979.
0-Empty I-Few 2-Moderate 3-Rich 4-Full
N: Number of whales

Sci. Rep. Whales Res. Inst.,
No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

69

throughout the whaling season. In contrast to this, there observed considerable
seasonal changes in the major. prey items in Bryde's whales, where both the
Euphausiacea and Pisces comprised most important prey items. The Copepoda
occurred only in 0.12% of animals with filled stomach, and this prey item alongwith the Amphipoda and Cephalopoda was unlikely to keep any importance inthe food habits of the Bryde's whales. During April the Bryde's feed exclusively
on the Pisces, but the Euphausiacea becomes very important food towards mid
summer, then fish shares 50% again in September. Although there found the occurrence of ' Octopus ' as one of prey items in the catch records of whales, its occurrence seems to be doubtful since none of this prey was collected as the stomach
samples. The overall figures in Fig. 3 clearly show that the major prey items offin, sei and Bryde's whales in the North Pacific region including a part of the Bering Sea are quite different by each whale species. Dominancy of the Euphausiacea
in fin, and the Copepoda in sei whales was seasonally unchanged while that of
the Euphausiacea and Pisces in Bryde's whales showed distinct seasonal changes.
These characteristics of possible selection in prey items by the whale species havebeen pointed out elsewhere (e.g. Nemoto, 1959; Nemoto & Kawamura, 1977,
Kawamura, 1981).

Monthly changes in stomachfullness
The stomach fullness of killed animal was also available in the catch recordsof whales. Usually, it is recorded in the field by classifying the fullness of stomach into five different categories, being based on approximate volume of stomach
contents against a whole stomach volume, i.e., few (less than 25%), moderate(25-50%), rich (50-75%) and full (more than 75%). To see Fig. 4 and appended
table the fullness of stomach by each volume category does not seem to change
seasonally over the three whale species concerned, but there was slightly higher
percent of empty stomach in July. The percentages of empty stomach throughout the whaling months in the order of fin, sei and Bryde's were 31.1-42.5%,
38.5-43.5%, and 20.8-55.2% respectively. Both fin and sei whales showed nearly
constant fullness during the whole whaling season whereas the Bryde's alone showedseasonally variable figures. This is probably due to the difference in major prey
items of Bryde's whales from fin and sei whales, that is, the Bryde's whales feed
mainly on both the Euphausiacea and Pisces, while the latter two feed almost exclusively on one of the Euphausiacea and Copepoda.
The categories of both ' rich ' and ' full ' among filled stomachs were relatively
fewer than that of' few' and/or 'moderate'. It can be observed over the threewhale species that both 'rich' and 'full' stomach generally increase in theirpercentage figures when the ' empty ' stomach decreases, but no clear relationshipwas observed between the principal prey items and the stomach fullness (Figs. 3-4).
An unusual high percentage of filled stomach of Bryde's whales in September camelargely from the catches in both the 1974 and 1975 seasons when a vast amountof the gonostomatid fish, Vinciguerria nimbaria and euphausiids, Nematoscelis difficilis
comprised major prey items.
Sci. Rep. Whales Res. Inst.,
No. 34, 1982

70

KAWAMURA

3.

Species of prey item
Prey item in general
Because of wider geographical and longer seasonal occupation of whaling
ground, there occurred a considerable large number of prey species throughout
this study. However, some zooplankton and fish species as whales food known fromthe animals caught during past seasons in the waters of higher latitudes did notoccur completely throughout the present study due to very little effort to catch whales
in such regions as reported by Nemoto (1957, 1959). They were: Metridia lucens,
Gnathophausia gigas, cod (Gadus macrocephalus), walleye pollock (Theragra chalcogramma), Atka mackerel (Pleurogrammus monopterygius) Pacific sandlance (Ammodytes
hexapterus hexapterus), capelin (Mallotus villosus), rockfish (Sebastes polyspinis), Pacificherring (Clupea harengus pallasi) and sea lamprey (Entosphenus tridentatus) (Nemoto,1957).
Instead of these northern fish species there found the occurrence of more variable prey items of warm temperate species in the southern whaling ground. Some ofthem composed major prey item but some others were considered to be occasionalor even accidental cn::currence. Table 2 shows all prey items found in the stomach
samples taken from fin, sei and Bryde's whales during the 1969-1979 seasons.
One of characteristics in the composition of prey items is an occurrence of so variablefish species as whales food, among which a mass occurrence of the gonostomatid
fish, Vinciguerria nimbaria (see Kawamura & Hamaoka, 1981) and relative importance of the clupeid, scombrid, pentacerotid, scomberesocid, and engraulid fish
species are noteworthy. Some of these characteristics found in southerly shifted
whaling ground were reported earlier by Kawamura (1973), and he pointed out theecological significance of the juvenile forms of commercially important fish species
for sei whales. The mass occurrence of pelagic armorhead as prey item of sei
whales was another interesting evidence that was firstly reported by Chikuni (1970).
Although relatively large number of fish species were found in the present study,nine species out of 18 occurred with small number of individuals, and were considered to be an occasional or accidental occurrence.
In crustaceans there occurred four species of calanid copepods, Calanus plumchrus, C. cristatus, C. marshallae and C. pacijicus, and natantia shrimp, Sergestes
similis (see Omori et al., 1972). All these five crustacean species were consideredvery important prey items except C. marshallae that was found in one stomach collected in the Alaskan shelf waters in the Bering Sea. In the Euphausiacea, however, the 14 species of euphausiids, which cover such northern temperate species as
Tlrysanoessa group to the southern temperate or even subtropical species as Euphausia
similis and Nematoscelis dijficilis were found to be another important prey items for fin
and Bryde's whales. The luxuarious species composition in euphausiids can be regarded as one of another characteristics that came from the southerly shift of whaling
ground during the last decade. It was noticed that there were no other taxonomicalgroups to be noted as whales food, but locally limited occurrence of the larvae ofa squid, Berryteuthis anonychus.
Sci. Rep. Whales Res. Inst.,
No. 34, 1982

FOOD OF NORTH PACIFIC RORQUALTABLE 2.

71

PREY ITEMS OCCURRED IN THE STOMACHS OF
FIN, SEI AND BRYDE'S WHALESCOPEPODA
Calanus plumchrus MARUKAWA
Calanus cristatus KROYER
Calanus pacijicus BRODSKY*
Calanus marshallae FROSTEUPHAUSIACEA
Euphausia pacijica HANSEN
Euphausia similis G. 0. SARS
Euphausia recurva HANSEN
Euphausia tenera HANSEN
Euphausia gibboides ORTMANN
Euphausia diomedeae ORTMANN
Thysanoessa inermis (KROYER)
Thysanoessa raschii (M. SARS)
Thysanoessa longipes BRANDT
Thysanoessa gregaria G. 0. SARS
Thysanoessa spinifera HOLMES
Nematoscelis difficilis HANSEN
Nematoscelis gracilis HANSEN
Th;ysanopoda monacantha ORTMANN
DECAPODA
Sergestes similis HANSENAMPHIPODA
Themisto sp.
MOLLUSCA
Berryteuthis anonychus (PEARCY & VOSS)**
Gonatus sp. **Limacina helicina helicina (PHIPPS)
COELENTHELATA
Velella sp.
PISCES
Scomber japonicus HOUTTUYN
Maurolicus muelleri (GMERIN)
Tarletonbeania taylori MEAD
Sardinops melanosticta (TEMMINCK & SCHLEGEL)
Engraulis japonica HOUTTUYNCololabis saira (BREVOORT)
Pseudopentaceros richardsoni (SMITH)
Exocoetus volitans LINNAEUS***
Decapterus lajang BLEEKER
Argyropelecus aculeatus CUVIER ET VALENCINNES****
Myctophum asperum (RICHARDSON)****
Diaphus bertelseni NAFPAKTITIS*****
Pof,ypnus matsubarai SCHLUTZ****
Ranzania laevis makua JENKINS
Pleurogrammus azonus JORDAN & METZ
Gasterosteus aculeatus LINNAEUS
Sebastes sp.
Vinciguerria nimbaria (JORDAN & WILLIAMS)* During discussions about this result with Dr A. Fleminger of the Scripps Institute of Oceanography,
it was suggested that there must be some occurrence of Calanus orientalis among C. pacijicus occurredin the northern waters.
** Identified by T. Kubodera***,, K. Amaoka,, H. Nakaya****",, K. Kawaguchi*****
Sci. Rep. Whales Res. Inst.,
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72

KAWAMURA

Some biological notes of the major prey species
Copepoda
C. cristatus: Occurrence of copepodid stage V (CV) alone. The body length
was recorded up to 7. 7 mm.
C. plumchrus: Occurrence of CV with occasional occurrence of CIV. The
former was 41-50 mm with major body size of 41-43 mm, and the latter was about
30mm.
C. pacificus: CIII-CV, and both adult male and female. Usually CV of
33-36 mm was predominated among all. The prey composition by the developmental stages was usually CV alone, but there were also the case of adult male andfemale with a dominancy of male, CV +male+female, CV +female, CV +male+
female, and CIII+CIV+CV+female. CIII was about 25 mm.
Euphausiacea
E. pacijicus: Both adult male and female of 21-22 mm with occasional occurrence of juveniles of 12-17 mm and 6.8-9.3 mm size classes. There was no clear
trend in the dominancy of one of two sexes. Some male and female carried asingle spermatophore.
E. similis: Adult female alone or juveniles of 17-21 mm.
T. longipes: Both male and female of ordinal and spine forms (12-13 mm)
were found. Most example of prey comprised female alone, but sometimes
mixture of very few number of adolescent males, or juveniles of furcilia stages. No
spermatophore was observed.
T. inermis: Both male and female of ordinal and 2-spined forms. Verystrongly biassed in sex composition. Usually, male or female predominates fromanother.
T. spinifera: Female alone, but occassional mixture with very few number ofmales. Body size was 23-30 mm. Two spermatophores were found in both sexes.
T. raschii: Male alone or both sexes with considerable predominancy infemales.
T. gregaria: Male and female of about equal number. Sometimes juvenilesof 9-10 mm were found among adult forms, but lesser extent in quantity. Some
adults of both sexes carried one spermatophore.
N. difficilis: Both male and female with variable predominancy of one oftwo sexes.
T'poda monacantha: Recorded in one sample collected in the northern watersof Hawaii Islands in April 9, 1979.
Decapoda
S. similis: Usually matured adult forms (49-50 mm) and juveniles composed the prey. Occasionally, adolescent forms of 27-35 mm formed the principal prey composition. (see also Omori et al., 1972 ).
Amphipoda
Only unidentifiable small hyperiids including Themisto sp. (4-5 mm). There
was no occurrence of adult forms of any amphipod species.
PiscesSci. Rep. Whales Res. Inst.,
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FOOD OF NORTH PACIFIC RORQUAL

73

V. nimbaria: Most individual was 46-60 mm (T.L.). Details of this fish andits food habits were reported by Kawamura and Hamaoka (1981).
T. taylori: Recorded body length (T.L.) was 46-75 mm. The prey item
found in 6 individuals (49-60 mm) was very small hyperiids, Ostracoda, young
euphausiids and Copepoda including Euchirella sp.
M. muelleri: Recorded body length was 34-58 mm (T.L.) with dominancy
of 42-48 mm individuals. Prey items found in 42-58 mm individuals were hyperiids, Conchoecia sp., Pareuchaeta sp., Candacia sp. and micro-calanoida.
G. aculeatus: 36-48 mm (T.L.)
P. azonus: 83-115 mm (T.L.).
E. japonica: 60-125 mm (T.L.), but 60-70 mm was the main body length.
Prey item of this fish in June were CV and adult female of C. pacificus, furciliaof eupahusiids, Oikopleura sp. and micro-calanoida.
S. japonicus: 99-188 mm (T.L.). Very variable prey items were found; C.
pacificus (CV), Candacia bipinnata, Candacia sp. Pseudocalanus sp., Oncaea sp., unidentifiable micro-calanoida, Phronima pacifica, Salpa sp., Muggiaea sp. and fish scale.
S. melanosticta: 75-106 mm (T.L.). Prey item was furcilia of euphausiids,
Clausocalanus arcuicornis, Corycaeus sp. and other micro-calanoida.
C. saira: 98-133 mm (T.L.). Prey item was simply composed of CV of
C. plumchrus.
R. laevis makua*: 89-147 mm (T.L.)
E. monicirrhus*: 98 mm (T.L.)
D. lajang*: 118 mm (T.L.)
A. aculeatus*: 56 mm (T.L.)
D. bertelseni*: 100.5 mm (S.L.) Very rare occurrence as reported by Kawaguchi and Kawamura (1981).
Cephalopoda
B. ano11:Jchus: 10-52 mm
4. Geographical distribution of prey organisms
Copepoda
Figure 5 demonstrates the distribution of three copepod species that werepreyed upon by fin, sei and Bryde's whales during the summer seasons of
1969-1977 and 1979. Since the stomach samples collected were combined together
all through the fishing season and month, the geographical distribution of preyorganisms by species showed somewhat complicated features. For example,
northern boundaries of Calanus pacificus distributions in the eastern half of the North
Pacific showed local irregularity, that is, there were several tongue like intrusionsof distribution range and/or even an isolated patches in the region occupied byanother prey species. The southern boundaries of C. plumchrus was the case ofsimilar pattern to C. pacificus. As it was mentioned in Table 2, copepods were

* The number of specimens was single or very few, and their occurrence in whale stomachs was considered
to be accidental.

Sci. Rep. Whales Res. Inst.,
No. 34, 1982

~

~?

~~

'"l{:i..

;_,_, ~

" "'

~~

~

~

::i:i

?:

35°

40°

45°

500

55°

N

I

~

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'

'<·
·~·'
•~
•/>

'

I

~

160°

I •

lj

'
•1
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I' J
lb I

,.

'I
> ,

.... '\! ~·, $~,'·,

170°,.

, ... >

...

,,

,.

I

,

6

:-...\.._..

...

••'

,(

.....

••
',~ u , ' I•

6

170°

~

... ... ...

,.

160°

I

~

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~·~'6

'"'

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I

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i•

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' '

u

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c. cristaus~ ...

:.."~ '~

•

~··

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~t.

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.

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150°

FIN

0

140°

©•
BRYDE'S SE!

130°w

}~

,y.,' , ...

c. pacificus ~c. plurnchrus

'"

I>

._

'
1

6 t\~

,. ,,,. .. \~•
'

Q.

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6 10

Cm: Calanus marshallae.

'. ,. ,,~\: ... '\' ~ ;· "''\ ,,, ':::' \.\~~u •'

,...

I>

6 b

...,
... ""'~.......

,, ,

'~·"
.. t ' '6' '~Distributions of prey copepods.

160°

j, A.

Fig. 5.

,. ,.,. > I ,,,.,. ,.>,I',. ')"
,,,,
I'
,.
,

,.

::~' ...'''~ " ,. . " . ~'n6~4 r ,,. i ~'' :. 4-,..' ~"'" bf ,. ' p" l~h\~;~r:~;· ,•, ' ~" .....,...... t..

1'1

I

j' I

I

•

I

66 ... ,,"O.QO., "• •·6·'l "•~•6,•1i• •'-'iet\-;M~.~ '" ,1' •' •I,·'!~dt'i't' .....
~~t'}'·,•,j' ' I> 0 t 6 >,.o>

:

1,

4

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6

0

Cm

~

~

c

~

~

FOOD OF NORTH PACIFIC RORQUAL

75

largely preyed upon by the sei whales, and this resulted to show an absence ofany copepod food in the Bering Sea, because the sei usually does not enter thisregion (Nemoto, 1959). One of copepod samples collected at the slope region of
the Alaskan Continental Shelf consisted of Calanus marshallae. This evidence isperhaps the first record of the species as whales food from this region. To see
the general distribution pattern over the whole North Pacific, it is clearly observedthat the major occurrence region of Calanus pacificus is concentrated in the western
half of the subarctic North Pacific with two eastern most occurrences in 155°W. C.
cristatus, one of another major prey item was found to be the most important food
copepods both for fin and sei whales in the western half region. C. cristatus,
however, may possibly become important prey item in the northern latitudes in
the Gulf of Alaska.
C. plumchrus, on the other hand, began to occur frequently towards the eastern
half region with most prominent occurrence in the pelagic region of the mid latitudes in the east of 150°W. In the central region of the North Pacific the distributions of C. plumchrus became very scarce or almost absent between 180° andl 70°W, but this species occurred at 37°N as the southern most record throughout
this study. Due to somewhat sporadic whaling effort in the Gulf of Alaska, information of this region is very limited but suggesting a possible importance of C. cristatus
both for fin and sei whales.
In general the characteristics of copepod prey in its distributions are summerized as that C. cristatus+C. pacificus dominate in the western half but they change
to C. cristatus alone or C. cristatus+C. plumchrus community in the middle. Towards
more east, C. cristatus occurs again but it finally changes to C. plumchrus.
Euphausiacea
In contrast to copepod, the prey species of the Euphausiacea comprised atleast 14 species (Fig. 6). Due to smaller number in the catch of fin whales thatfeed mainly on euphausiids, spots of distributions in Fig. 6 showed more dispersed occurrence than the copepod food. In the northern waters north of 50°N
there occurred only fin whales except a very few sei whales, but the fin also occurredconsiderably in the southern waters down to 35°N in the western half region.
In the shelf region of the Bering Sea there were five collections from fin whales,
and Thysanoessa rashii was the major prey item. In the higher latitudes of theNorth Pacific, T. spinifera, T. inermis and T. longipes were found to be the mostimportant prey items, of which T. spinifera showed its importance in the offshore
region of British Columbia, while the latter two species frequented in the pelagic
regions. In the middle latitudes between 40°-50°N, Euphausia pacifica was exceptionally occurred both in fin and sei whales along with two Thysanoessa species.
Towards southern waters, however, the composition of prey became to show more
complexity by the local and sporadic occurrence of many rare species such as
Thysanopoda monacantha, Nematoscelis dijficilis, Euphausia gibboides, E. tenera, E. recurva
and E. diomedeae. Apart from fin and sei whales, the catch of Bryde's whales wasclearly confined in the southwestern region down to 25°N, where E. similis, N.
dijficilis and T. gregaria were found to be most important as the prey items.
Sci. Rep. Whales Res. Inst.,
No. 31, 1982

""~

""'~

~~

--~ ~

~~

~~
c "'

~

~

~

~

E

o-

160°

"'

•

0'9 0-.... •'.

~. . ·ii··

...
6.

II

.

~

<;/

Pl'fi>

<I

'
p

·170°

<;/

0

0

~'l

•:.

n'J

" ::I<

ll

6
6

. '·~

9

~

··~··...0 ·"~!i~' '~.. .....°'1-tg. .,.Jl : ~.II9"-t .,.

.,.
'I'... ~~

2

3 °4

'e 'e

180°

0

Midway

p

b

't

..,.,

13..,
G'Q

9"

"

,. b
••

~\99'

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,_::

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""()

o,<:i'
0,"«;spinifera~T. inermis

••

..,

T.

q ••

•t

• 9'1

~

0 0

140°
130°
160°
150°
170°
Fig. 6. Distributions of prey euphausiids.
I-Euphausia recurva 2-Euphausia similis 3-Euphausia gibboides 4-Nematoscelis gracilis 5-Thysanopoda monacantha 6-Euphausia diomedeae

2o·L__J_ _ _~~--;:w----,:~--16o-""~

25°

30°

35°

40•

45°

N

0

w

s;

i

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08

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g

c

u

E

u

5l

2
·-

170°
180°

./

&,...

:.-'.!'.

&v

;fr
.<?;,

Fig. 7. Distributions of prey fish. The encircled areas show approximate range of the occurrences of pelagic armorhead andPacific saury that found in the catch records of whales compiled by the Fisheries Agency.
1-Pseudopentaceros richardsoni 2-Exocoetus volitans 3-Decapterus lajang 4-Argyropelecus aculeatus 5-Myctophum asperum 6-Diaphus
bertelseni 7-Polypnus matsubarai 8-Pleurogrammus azonus 9-Sebastes sp. 10-Myctophids(unidentified) 11-Trigger fish(unidentifed)

160°

-\.

~>

:-,c:i._<:}>

10

.

•:

9 ••

~ s. melonosticto

"'v.s

&o

v.t'.

Oc

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•

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(/)

..

20·._~...........~~~~.....~~~~~......~~~~~..._~~~~--''--~-'---~-..L~~~~

25°

30°

35°

40°

45°

N

.

-.J
-.J

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ig

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......
:::1
0

;;;:

~

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"".!

0
0
tl
0

KAWAMURA

78

PiscesThere were very few stomach samples of fin that preyed upon fish, but both sei
and Bryde's whales fed largely on such various kind of fish species as pointed out by
Nemoto & Kawamura (1977). To see Fig. 7 there observed very clear differencein major prey items between western and eastern halves of the North Pacific.
The fin and sei occurring in the western half region of the mid latitudes ate preN

40° .--~~-.-~~~~~~-.-~~~~~~-r~~~~~~-..~~~~~~-....~

May

..

Sep_yl(_Apr
AugYJune.

.'t 0 6 6

4 .i.·

July

q

0-

.

.,.

.., q

qq

-0
0-

0

d

.d

MidwayHawaiio•0oO

BRYDE'S SEI

20°._~~......~~~~~~--"~~~~~~--"~~~~~~--'"--~~~~~......1---1
E
180°
160°
160°W
170°
170°
Fig. 8. Monthly distribution of Vinciguerria nimbaria eaten by the sei and Bryde's
whales.

N55°

s. similis
L. helicina-Q-'.. Ba..

Batt'' ' Ba0FIN BRYDE'
©S e
SEI

oP'

Themisto sp,

Squid

50°

45.0

o•

91
9
0-

..

'l

Ba

.. . '
9'' '....._.Ba

b

''

"'

't ..'I

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.

bi

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b

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' Ve
•o

•
40° E~---1~6~0-_ _ _ _ _ _ _ _ _ _17~0~------~--1~8-0_000 _ _.....__ _ _ _ _ _1~7-00 ------~
Fig. 9.

Distribution of shrimp, Sergestes
Ba: Berryteuthis
Sci. Rep. Whales Res. Inst.,

No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

79

dominantly on mackerel (S. japonicus) among all and both anchovy (E. japonica)
and Japanese sardine (S. melanosticta) came to the next. Towards more northernwaters, however, the major prey item changed to a myctophid fish (T. taylori) andthree spine stickleback (G. aculeatus) while gonostomatid fish (V. nimbaria), M.
muelleri, R. laevis makua and myctophids (M. asperum and Diaphus bertelseni) may
become important prey for the Bryde's whales (see also Fig. 8, and Kawamura &Hamaoka, 1981 ). Among various species of fish prey V. nimbaria is considered mostimportant item for the Bryde's whales occurring in the subtropical regions of theNorth Pacific during April through September (Fig. 8).
In the eastern North Pacific the collection of stomach samples was fewer than
the western region due to difficulty in collecting and preserving such large-sizedfish prey as the pelagic armorhead (P. richardsoni). Being based on the catch recordsof whales by the Fisheries Agency, it was proved that the sei eat mainly Pacificsaury (C. saira) during July to August in the pelagic waters of the eastern halfregion.
One of another important fish species was pelagic armorhead in the Gulf of Alaska
region. Because of its large-sized body length and easiness in identification in thefield, no P. richardsoni was collected as stomach samples, but their occurrence inthe catch records of whales was indicated by the encircles in Fig. 7. Closer towaters off Vancouver Island, there were another possible important prey item, thelarval forms of rock fish (Sebastes sp. ).
OthersAmong several other prey items the sergestid shrimp, S. similis was mostimportant prey both for fin and sei whales in the midst towards eastern region of
the northern latitudes between 40°-50°N as it was reported previously (Omori etal., 1972). To see Fig. 9 along with Figs 5-7 it can be observed that S. similis was0Ba

o'o ,o6 '

' '

0

0

'
',, t'
0'' 't 6f .

9

9

'

'

... 6.

o.&,,.
•'•~•'• l• ~

ci.o

'

6o

'

0

160°

'

150°

similis and other prey species.
anonychus, Ve: Vellela

Sci. Rep. Whales Res. Inst.,
No. 34, 1982

140°

130°

w

80

KAWAMURA

one of very few prey items that was available in the midst of the northern North
Pacific. Towards west, however, larval forms of squid (B. anonychus and Gonatussp.) and hyperiid amphipods were considered to be moderately important.
However, amphipods represented largely by Themisto sp. never showed such importance of appreciable extent as the case known in the southern counter part,
Parathemisto gaudichaudii (Kawamura, 1970, 1974).
5. Species composition of stomach contents
Fin whales
It was indicated in Table 3 that the euphausiids were relatively more important than the copepods as food of fin whales. However, the detailed compositionof prey species being based on the collected material shows that very limited
number of euphausiid species actually comprise a major food of fin whales. The
matrix of prey composition clearly shows a predominant occurrence of three euphausiid species, i.e., E. pacifica, T. longipes, T. spinifera, and T. inermis (Table 3).
Although there were several examples of mixture with other prey species in boththe case of E. pacifica and T. inermis, most stomach contents were found to be monospecific in the composition.
In copepods, C. cristatus was a major prey item, and this species along withsergestid shrimp, S. similis formed additional important prey items. The veryclear monospecific composition in T. spinifera was noteworthy, while there weremany examples of mixed composition in T. inermis. The major prey species thatcomposed a stomach contents was usually monospecific.
In three examples,
however, there found mixed compositon of food with three species such as C.
cristatus+ T. longipes+ T. spinifera, T. inermis+N. difficilis+C. pacificus and T.
inermis+ T. longipes+C. cristatus. There were only four stomachs that were filledwith fish. Although there occurred a considerable number of prey species on
the whole, it can be said that the fin whales in the North Pacific region mainly live
on by eating six species of crustaceans where euphausiids account for a largest partof the prey composition.
Sei whales
In contrast to somewhat simple or poor composition of prey species in fin
whales, a total of 27 prey items were found to be important in sei whales. As
mentioned before, copepod food was found in quite large part of the sei whale
stomachs, and C. cristatus, C. plumchrus and C. pacificus accounted for more than 79%
among all stomachs examined (Table 4 ). One of the characteristics in the copepod food was a frequent occurrence of mixed composition with different prey
items such as with euphausiids particularly the case in C. plumchrus. To see thefrequency in the number of stomachs, relative importance of euphausiid food
reduced largely in sei whales except the case in E. pacifica, but sergestid shrimp,
S. similis that was a very important prey item in fin whales also showed considerable
importance again in sei whales. One of characteristic compositions was the relative importance of commercially important fish species as a major prey cornSci. Rep. Whales Res. Inst.,
No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

viaf!uJ<fs ·J,+sJULtaUJ •J,
wafiuJ<fs ·J,+ sa<fJiluo1 ·J,sa<fJiluo1 ·J,+ sn1v1>'JJJ ·a
JJ1fOSVJ •J,+ sn1v1sJ11 •:J
sm11Jfip .N+ sn1!ft1v<f ·a
P!nbs

c<')

JlOjl(V/ •J,
snuozv ",JN

v.1afiu.zqs ·J,
sa<fJiluOj ·J,l!')

VJ!f!JVq ·g c<')sn1!ft1vq •:J
aVllV1fSJIJW •:J
sn.1111wn1<f ·ar-co ('

Sci. Rep. Whales Res. Inst.,
No. 34, 1982

CO

81

82

KAWAMURA
TABLE 4.

COMPOSITION OF THE STOMACH
Minor

]
tj

o~
t)

C,j

C. cristatus
C. plumchrus
C. pacificus
E. pacifica
E. diomedeae
E. recurva
E. tenera
T. longipes
T. spinifera
T. inermis
T. gregaria
N. difficilis
N. glacilis
S. similis
G. aculeatus
P. azonus
C. saira
S. japonicus
S. melanosticta
E.japonica
Sebastes sp.
M. muelleri
T. taylori
myctophido
P. richardsoni ( ?)SquidL. helicina~ ~ o~

~ w~

-~
·~ ~
.~ ~ .§-.§ ~ ~ .~ f5 ~ ~C,j ki ki

ki kiv)C!i~C,jv)v)ki~~$~E~~;;i ~ ~]

V)

-Q..-Q.,.~~~--

C,j

398
3
9
10 270 3 5
3 89 255 4 37;;;~tj~ ·~ ~ ·~

1

1

3

11

2

4

3

4

3
7

2
2
4

48

2
5

1 2

33 2
5
3

5
5

* Since the occurrence of the pelagic armorhead, P. richardsoni was based on the catch records of whales
excluded from this table.

ponent. They were, Japanese mackerel, Sebastes sp., Pacific saury, Japanesesardine, Japanese anchovy, and lanternfish, M. muelleri. These greater variety
of prey composition in sei whales is the refiexion of larger geographical occupationof whaling ground along with longer duration in sei whale catches. There wereseveral records of mixed stomachs composed of more than three prey items; theywere, E. pacifica+C. cristatus+ T. taylori, E. pacifica+S. similis+ Vellela sp., T.
longipes+C. plumchrus+ T. inermis, T. longipes+ T. inermis+ T. spinifera, E. pacifica+
C. pacificus+C. cristatus, C. plumchrus+C. pacijicus+C. cristatus, and S. similis+C.
plumchrus+C. cristatus. Although prey composition showed greater variety in sei
whales, but it can be said that the sei in general feeds largely on three species ofcopepods, one species of euphausiids, sergestid shrimp, and scombrid fish.
Sci. Rep. Whales Res. Inst.,
No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

83

CONTENTS IN SEI WHALES* (NUMBER OF STOMACHS)
components

5

5

427
318
103
60

2

12

1.1

7
1

0.6
0.09
0.18
0.18
0.09
4.9
0.18
0.09
0.47
3.6
0.47
0.28
0.56
0.56
0.09
0.09
0.09
1.11
0.09

2
3

1

2
2
53
2
5
39
5
3
6
6

1

3

8

12

39.8
29.7
9.6
5.6
0.09
0.09
0.09

alone, the actual composition of stomach contents was unknown, and consequently this fish species was

Bryde' s whales
Due to different geographical occupation of whaling ground in the case of
the Bryde's whales, the composition of major prey item for this whale species was
far different from that in fin and sei whales (Table 5 ). Most important prey
item was a gonostomatid fish, V. nimbaria which accounted for more than 55%
among all instance, and E. similis came to the next (25.2%). N. dijjicilis was
also important member of the prey composition (10.8%). Except a single record of multispecific prey composition (V. nimbaria+E. gibboides+N. gracilis), thefood of Bryde's whales can be considered quite monospecific with stronger trendsof eating small and gregarious fish species in the pelagic waters.
Sci. Rep. Whales Res. Inst.,
No. 34, 1982

84

KAWAMURA
TABLE 5.

COMPOSITION OF THE STOMACH CONTENTS IN BRYDE'S WHALES(NUMBER OF STOMACHS)
Minor components~.::i ] ..
·~

...
"'

...,

cj ~ ~

C. cristatus
E. pacifica
E. similis
E. recurva
T. gregaria
T. inermis
Thysanoessa sp.
"E"'<I) N. difficilis.::0 T' da monacantha
S. similis0
u V. nimbaria.... M. muelleri
0S. japonicus
S. melanosticta
T. taylori
L. laevis makua
E. volitans
D. lajang

+...,

...,~

.Et

•s

~

.::i

h h ~~~c,)

.~

•s

.

•s

~

::.: ~ c,) c,) h

~ ~

2

2

5

35

8'

i

3

1 1

175
3
4

4

Fish bones

"@

0

E-<

.::

<I)

....<I)(.)
P-c~ t:i.; ...: ~ ~ ~

1
80

.....

·,;

f(J
~
~ ~
" ...,... ... 03 -~...,
c·- .~.,.,. " 2l -~ ~ ~... .::i " 2f ~" -!:l i'! ~" .::""... "... ~ ~::; ~~0"" t::" .0'E}i~ ·~ ~""' " "~
~ .5 ~~]] .~ ~ ·~ ~ ~ ~"" " .....
"'~ """'"'" "~ A"" """"'::; "
"
.~

0.03
0.03
84 25.2
0.03
5 1.5
1 0.030.03
36 10.8
0.03
0.03
184 55.1
4 1.2
4 1.2
0.03
0.03
5 1.5
1 0.03
1 0.03
0.03
334

DISCUSSION

The whaling ground during the seasons of 1969-1979 was occupied in the more
southern sea regions than that occupied during the I 950's to early I 960's. This
geographical difference along with somewhat seasonally longer whaling operation
resulted to show a wide ranged variety in the taxon of prey items, particularly
in species composition of the Euphausiacea and Pisces. The conditions of surface
sea temperature in general over the whaling ground is considered to be somewhere
between about 26°C and I0°C in August (Sverdrup et al. 1942), and from thezoogeographical point of view in zooplankton communities, the whaling ground ofunder consideration includes the region of boreal complex, zone of mixing andeven tropical complex (Zenkevitch, 1963).
The stomach condition of whales in general revealed that about 60% ormore stomachs of fin, sei and Bryde's were filled with variable amount of food without showing any notable seasonal changes in the percent figures of filled stomach.
According to Nemoto (1957), 52% of fin and 44% of sei caught in the northern
North Pacific during the 1952-1956 seasons were found to be filled stomachs. These
percentages seem to be considerably lower than the above mentioned figures (ea.
Sci. Rep. Whales Res. Inst.,

No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

8560%) found in this study. During the years of 1952-1971 when the whaling
ground began to expand southwards, the corresponding percentages for fin and sei
were 60% and 55.5% respectively (Nemoto & Kawamura, 1977), while it was
94% and 81 % respectively in the Kurile region (after Sleptsov, 1955). Thesefigures seem to be high enough when it is compared with that found in the present
study and also in the Antarctic feeding grounds (Kawamura, 1978). Usually the
distribution of zooplankton biomass in the boreal region of the northwestern North
Pacific decreases to about l / 5 or 20% towards the tropical region (Zenkevitch, 1963 ).
According to Odate (1966), the wet zooplankton biomass in the south of 40°N of
the western North Pacific was 20-30 gr/1000 m 3 while it was 200-400 gr/1000 m 3
in the boreal regions of the North Pacific and Bering Sea. Notwithstanding thesefacts the comparisons mentioned above strongly suggest that the boreal or subarctic
North Pacific to the subtropical or even tropical regions may provide very important feeding ground for the baleen whales as well as the northern North Pacificregion. One of possible, but important explanations for this is the local and extremely biassed patchy distributions of prey species (e.g. Brodie et al. 1978;
Kawamura, 1979). The occurrence of fish prey in the southwestern North Pacificmay come from the scarceness of patch-forming zooplankton species in this region since those fish species can eat and survive on such variable zoo plankton
species as studied in Vinciguerria nimbaria (Kawamura & Hamaoka, 1981).
As it was shown in Fig. 4 the stomach fullness by the quantity of contents did
not change seasonally in its general pattern over the three whale species. However,stomachs combined both ' full ' and ' rich ' showed relatively higher figures in fin
and Bryde's than sei whales. This evidence seems to be related to the differenceof major prey items between whale species as shown in Fig. 3, where it was suggested that the larger the size of prey organisms, the larger percent of well filled
stomachs were expected (Nemoto, 1963). Similarly, the smaller percent figures of' full ' and ' rich ' stomach in sei whales that feeds mainly on copepods are resulted
from more smaller size of prey, since the biomass of prey organisms may become
smaller in accordance with the reduction of their body size (Nemoto & Kawamura,1977). The prey items which occurred in boreal regions of the North Pacific wereagreed on the whole to those known previously in the pelagic waters (e.g. Nemoto,1959), and distributions of Thysanoessa species and copepods were agreed well tothat found in the Olyutorsky and Commandorsky regions (Ponomareva, 1949).
However, when each prey item is compared with the case found in marginal seassuch as the Kuril or Bering Sea regions, there were considerable difference in thecomposition of prey fish species. As mentioned before, there occurred no common
fish species between the results from the Bering Sea and the present study (seeKawamura, 1980, Table 17), while only two species, Pacific saury and anchovy
were common with the Kurile region (Betesheva, 1954, 1955). In the Far Eastern
Seas, of 14 prey fish species only Pacific sardine and Pacific saury were common
with the present study (Sleptsov, 1955; Tomilin, 1967). These characteristics inthe prey composition suggest that the feeding conditions of whales in the North
Pacific may differ considerably from place to place especially in the marginal sea
Sci. Rep. Whales Res. Inst.,
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86

KAWAMURA

regions, but they also differ in several prey taxa even in the pelagic waters.
Distributions of each prey species showed very interesting results (Figs. 5-9).
Since stomach samples obtained during 1969-1977 and 1979 seasons were plotted
altogether simply by separating each major prey species, the number of plots do
not agree with the number of stomachs sampled because there were many examplesof mixed stomach composition of two or more species. Figures 5-9 however, demonstrate a zoogeographical pattern of ditribution of each prey item during April to
September, where variable density of plot distribution suggests relative abundanceof whale distribution by sea regions. To see through Figs. 5-9 the overall distribution pattern of each prey species agrees well with the generally known zoogeography of planktonic animals such as the distribution boundary of Calanus species(e.g. Minoda, 1958; Omori, 1965 Frost, 1974), euphausiids (e.g. Boden et al., 1955;
Mauchline and Fisher, 1969) and lanternfishes (e.g. Wisner, 1974; Gjosaeter and
Kawaguchi, 1980). However, important evidence is that the plotted region indicates more possible area of frequent occurrence of plankton aggregations that are
preferable food condition for baleen whales, and a vacancy of the plots never means
negative distribution of each corresponding prey species. In this connection, thelack of amphipods as whales food in the North Pacific must be noteworthy, while
Parathemisto gaudichaudii constitutes important prey item in the southern sei whales(Kawamura, 1974). Actually several number of Themisto species are known toform dense swarms, but they were not eaten by the whales.
The characteristic of the stomach contents as shown in Tables 3-5 is such an
extremely predominant occurrence of monospecific composition over the stomachs ofthree whale species as it was reported by Kawamura (1974, 1980) for the southernsei and Bryde's whales. Although data on the freshness of stomach contents by eachprey species were not shown in this study, it was observed that the freshness of preyspecies which occurred together in a stomach such as the case of C. plumchrus andC. pacijicus, was different from one to another. Similarly the different freshness canbe observed in many stomachs when their contents were composed of more than
two prey species. As it was discussed on the mixed prey with C. cristatus and C.
plumchrus (Nemoto, 1963), these phenomenon was perhaps caused by the time-lag
in picking up each prey species due to horizontal and vertical differences in the
distribution of prey organisms. Occurrence of the Siphonophora, Velella sp.,
however, indicates that the whales often feed in the very surface waters. The plot
in Figs. 5-9 consequently, suggests that how frequently each prey organism occurs
patchily in the region by forming dense monospecific swarms, aggregations, and/or
schools. After analysing a small scale of distributions of whales and their stomach contents observed within a short enough period, Kawamura (1978) estimateda spacial scale of patchiness of prey species as less than 5-6 km as an estimateddiameter of patches in C. cristatus, C. plumchrus and C. pacijicus complex whereas it wasslightly larger in E. pacifica, T. inermis, T. raschii, T. longipes, T. spinijera and possibly in N. dijficilis.
To conclude the geographical distributions of prey species that form dense
swarms or aggregations, it can be summerized that the North Pacific fin, sei andSci. Rep. Whales Res. Inst.,
No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

87

N
60°----...,...,...r-"'T~~..--~~~M"'-,"72'~--.~....,----,

50°
40°
30°
E 160°

180°

160°

140°

120°W

Fig. 10. Approximate geographical occupations of the principal prey species.
1-Calanus marshallae
2-Thysanoessa inermis / T. longipes
3-Calanus cristatus
4Tarletonbeania tqylori 5-Calanus plumchrus 6-Cololabis saira 7-Sergestes similis 8Pseudopentaceros richardsoni
9-Thysanoessa spinifera
10-Euphausia pacijica
llCalanus pacijicus
12-Nematoscelis difficilis
13-Vinciguerria nimbaria 14-Euphausia
similisBryde's whales share a possible prey species each other by selecting euphausiids, copepods and fish communities respectively. Among so many variable prey
items, the distribution ranges of major prey species over the whole North Pacific
can be demonstrated in schema (Fig. 10). Although C. cristatus, C. plumchrus andC. pacificus are known to distribute widely over the whole North Pacific, the mainoccurrence of their patchy swarms show different geographical distributions, i.e.,
both C. cristatus and C. pacificus predominantly form their patches more frequently or
intensively in the northwestern to western North Pacific whereas C. plumchrus doesin the eastern North Pacific. Although physical and chemical conditions of thesea surface in the northern North Pacific shows very homogeneous features fromthe west to the east in general, the distributions of many prey species on the wholesuggest that there seems to exist geographically discontinuous region somewehere
between 160°-l 70°W where the variety of prey species is very poor.
ACKNOWLEDGMENTS

I am very grateful to Dr. H. Omura and his staff of the Whales Research Institutefor their support and encouragement throughout my 10-year sampling scheme.
Thanks are also due to Dr. S. Ohsumi and his colleagues of the Far Seas
Fisheries Research Laboratory for their welltimed supervision and advice throughwhich the collection of stomach samples was implemented. Data in the CatchRecords of Whales by the Fisheries Agency become also available by their
Sci. Rep. Whales Res. Inst.,
No. 34, 1982

88

KAWAMURA

courtesy, and all these support that facilitated the present study is greatly
acknowledged. I am grateful, as well, to all personnel who belonged to whaling division of the Nippon Suisan K.K., Taiyo Gyogyo K.K., K.K. Kyokuyo
and Nippon Kyodo Hogei K.K. for their long-term cooperation in collecting alarge part of the stomach materials during the seasons of 1969-1979.
REFERENCES
BETESHEVA, E. I., 1954. Data on the feeding of baleen whales in the Kurile region. Trans. Inst. Oceanogr.
Acad. Sci. USSR, 11: 238-245 (in Russian)
BETESHEVA, E. I., 1955. Food of whalebone whales in the Kurile Island region. Trans. Inst. Oceanogr.
Acad. Sci. USSR, 18: 78-85 (in Russian)
BoDEN, B. P., M. W. JOHNSON, and E. BRINTON, 1955. The Euphausiacea (Crustacea) of the North Pacific.
Bull. Scripps Inst. Oceanogr., 6: 287-400.
BRODIE, P. F., D. D. SAMEOTO, and R. W. SHELDON, 1978. Population densities of euphausiids off Nova
Scotia as indicated by net samples, whale stomach contents, and sonar. Limnol. Oceanogr., 23: 12641267.
CHIKUNI, S., 1970. On the occurrence of a phantasmal fish, pelagic armorhead. Enyo, 3: 1-4 (in Japanese)
GJOSAETER, J. and K. KAWAGUCHI, 1980. A review of the world resources of mesopelagic fish. FAO Fisheries Tech. Pap., 193: 1-151.
IWS, 1967-1972. International Whaling Statistics. Sandefjord.
KAWAMURA, A., 1970. Food of sei whale taken by Japanese whaling expeditions in the Antarctic season
1967/68. Sci. Rep. Whales Res. Inst., 22: 127-152.
KAWAMURA, A., 1973. Food and feeding of sei whale caught in the waters south of 40°N in the North Pacific.
Sci. Rep. Whales Res. Inst., 25: 219-236.
KAWAMURA, A., 1974. Food and feeding ecology in the southern sei whale. Sci. Rep. Whales Res. Inst., 26:
25-144.
KAWAMURA, A., 1978. An interim consideration on a possible interspecific relation in southern baleen
whales from the viewpoint of their food habits. Rep. int. Whal. Commn, 28: 411-419.
KAWAMURA, A., 1979. An extremely biassed distribution of marine zooplankton. An estimation of their
spacial scale of patchiness. Marine Science Monthly, 10: 877-888 (in Japanese).
KAWAMURA, A., 1980. A review of food of balaenopterid whales. Sci. Rep. Whales Res. Inst., 32: 155-197.
KAWAMURA, A. and Y. SATAKE, 1976. Preliminary report on the geographical distribution of the Bryde's
whale in the North Pacific with special reference to the structure of filtering apparatus. Sci. Rep.
Whales Res. Inst., 28:1-35.
KAWAMURA, A. and S. HAMAOKA, 1981. Feeding habits of the gonostomatid fish, Vinciguerria nimbaria
collected from the stomach of Bryde's whales in the southwestern North Pacific. Bull. Plankton Soc.
Japan, 28: 141-151.
KAWAGUCHI, K. and A. KAWAMURA, 1981. A rare myctophid fish, Diaphus bertelseni from the stomach of
Bryde's whale captured in the subtropical western North Pacific. Jap. ]our. Ichthyol., 28: 169-170.
MAuCHLINE, J. and L. R. FrsHER, 1969. The biology of euphausiids. Advances Mar. Biol., 7: 1-454.
MrnoDA, T., 1958. Report from the Oshoro Maru on oceanographic and biological investigations in the
Bering Sea and northern North Pacific in the summer of 1955. V. Observations on copepod community. Bull. Fae. Fish. Hokkaido Univ., 8: 253-263.
MrNODA, T., 1971. Pelagic copepoda in the Bering Sea and the western North Pacific with special reference
to their vertical distribution. Mem. Fae. Fish. Hokkaido Univ., 18: 1-74.
MrzuE, K., 1951. Food of whales (In the adjacent waters of Japan). Sci. Rep. Whales Res. Inst., .5: 81-90.
NASu, K., 1957. Oceanographic conditions of the whaling grounds in the waters adjacent to Aleutian Islands
and the Bering Sea in summer of 1955. Sci. Rep. Whales Res. Inst., 12: 91-101.
NEMOTO, T., 1957. Food of baleen whales in the northern Pacific. Sci. Rep. Whales Res. Inst., 12: 33-89.
NEMOTO, T., 1959. Food of baleen whales with reference to whale movements. Sci. Rep. Whales Res. Inst.,
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89

14: 149-290.
NEMOTO, T., 1963. Some aspects of the distribution of Calanus cristatus and C. plumchrus in the Beringand its neighbouring waters, with reference to the feeding of baleen whales. Sci. Rep. Whales Res.
Inst., 17: 157-170.
NEMOTo, T. and A. KAWAMURA, 1977. Characteristics of food habits and distribution of baleen whales
with special reference to the abundance of North Pacific sei and Bryde's whales. Rep. int. Whal. Commn(Special Issue I): 80-87.
0DATE, K., 1966. On the comparative study of volumes of zooplankton distributions in the Oyashio area
and in the seas adjacent to that area. Bull. Tohoku Reg. Fish. Res. Lab., 26: 45-53.
0MORI, M., A. KAWAMURA, and Y. ArzAwA, 1972. Sergestes similis Hansen, its distribution and importanceas food of fin and sei whales in the North Pacific Ocean. In: A. Y. Takenouti, M. Anraku, K. Banse,
T. Kawamura, S. Nishizawa, T. R. Parsons, T. Tsujita, (ed.), Biological Oceanography ef the Northern
North Pacific Ocean, Idemitsu Shoten, Tokyo, 626 pp.
0MORI, M., 1965. The distribution of zooplankton in the Bering Sea and northern North Pacific, as observed by high-speed sampling of the surface waters, with special reference to the copepoda. ]our.
Oceanogr. Soc. Japan, 21: 18-27.
OMURA, H. and T. NEMOTo, 1955. Sei whales in the adjacent waters of Japan. III. Relation between
movement and water temperature of the sea. Sci. Rep. Whales Res. Inst., 10: 79-87.
PoNOMAREVA, L. A., 1949. On the food plankton of baleen whales in the Bering Sea. Doklady Acad. Nauk,
USSR, 68: 401-403 (in Russian).
SVERDRUP, H. U., M. W. JOHNSON, and R.H. FLEMING, 1942. The Oceans. Their physics, chemistry and general
biology. Prentice Hall, Inc., N.Y., 1042 pp.
SLEPTsov, M. M., 1955. Biology and.fishing of whales in the Far Eastern Seas. (Translated from the Russianby H. Sakiura, 1955), Whales Res. Inst., Tokyo, 51 pp . .(in Japanese).
ToMILIN, A. G., 1967. Cetacea. Vol. 9. Mammals of the U.S.S.R. and adjacent countries. Heptner, V. G. (ed.)
Israel Prog. Sci. Transl.,Jersalem, 717 p.
WISNER, R. L., 1974. The taxonomy and distribution of lanternfishes (Family Myctophidae) of the eastern
Pacific Ocean. NORDA Rep. 3. Navy Ocean Res. Develop. Activity, Bay St. Louis, 229 p.
ZENKEVITCH, L., 1963. Biology of the seas of the U.S.S.R. Trans!. S. Botcharskaya, George Allen & Unwin,
London, 955 p.
ZENKOVITCH, B. A., 1937. The food of the Far-Eastern whales. Doklady Acad. Sci. S.S.S.R., 16: 231-234(in Russian).

Sci. Rep. Whales Res. Inst.,
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KAWAMURA90
APPENDIX I.

STOMACH CONDITIONS OF FIN, SEI AND BRYDE'S WHALESCATCH RECORDS OF WHALES COMPILED BY THE FAR SEAS
Food item

Catch
Euphausiacea

Copepoda Amphipoda

PiscesSquidl (0.3)l (0.2)
92 (14.7)
61 (27.1)
154
9.32

May
June
July
AugustTotal% to total

537
697
1,085
343
2,662

268 (72.4)
281 (63.6)
410 (65.7)
128 (56.9)
1,080
65.4

101 (27.3)
139 (31.4)
115 (18.4)
35 (15.6)388
23.5

6 (1.4)5 (0.8)l (0.4)
12
0.7

May
June
July
AugustSeptember
Total% to total

2,303
5,375
5,232
1,688
39
14,637293 (20.0)
169 (5.3)
278 (9.4)
123 (12.2)
l (4.2)864
9.97

1,092 (74.6)
2,574 (80.1)
2,080 (70.3)
800 (79.2)
22 (91.7)
6,568
75.8

69 (4.7)456 (14.2)
523 (17.7)
48 (4.8)l (4.2)
1,097
12.66

Bryde's April
May
June
July
AugustSeptember
Total% to total

93
543
1,180
337
452
96
2,703*

1 (2.1)191 (53.4)
274 (37.6)
22 (14.6)274 (89.8)
38 (50.0)
800
47.99

Fin

Sei

(0.3)

2 (0.07)

I (0.3)I (0.3)

(0.7)

2
0.12

2
0.12

9 (0.6)8 (0.3)65 (2.2)
38 (3.8)120
1.38

47 (97.9)
165 (46.l)
454 (62.3)
128 (84.8)
31 (10.2)
38 (50.0)
863
51.76

* Two Bryde's whales that were unknown their catch month were excluded

Sci. Rep. Whales Res. Inst.,.No. 34, 1982

FOOD OF NORTH PACIFIC RORQUAL

91

CAUGHT DURING THE SEASONS OF 1969-1979. (CONSTRUCTED USINGFISHERIES RESEARCH LABORATORY OF THE FISHERIES AGENCY)
Total
of filled
Octopus stomach
15 (3.4)
2 (0.3)17
1.02
6 (0.2)9 (0.3)1 (0.1)
16
0.18

% of

Stomach fullness

filledstomachto total

Few

Moderate

Rich

Full

Empty

370
442
624
225
1,661
62.39

68.90
63.41
57.51
65.60
62.39

167 (31.1)
188 (27.0)
265 (24.4)
83 (24.2)
703 (26.4)

115 (21.4)
146 (20.9). 190 (17.5)
64 (18.7)515 (19.3)

39 (7.3)
55 (7.9)
84 (7.7)35(10.2)
213 (8.0)

49 (9.1)
53 (7.6)
85 (7.8)43(12.5)230 (8.6)

167 (31.l)
255 (36.6)
461 (42.5)
118 (34.4)
1,001 (37.6)

1,463
3,213
2,957
1,010
24
8,667
59.21

63.53
59.78
56.52
59.83
61.54
59.21

824 (35.8)
1,731 (32.2)
1,625 (31.l)
587 (34.8)
8 (20.5)
4,775 (32.6)

393 (17.1)
974 (18.1)
834 (15.9)297 (17.6)
3 (7.7)2,501 (17.1)

128 (5.6)
265 (4.9)
254 (4.9)
72 (4.3)
7(17.9)726 (4.9)

118 (5.1)
243 (4.5)
244 (4.7)
54 (3.2)
6(15.4)665 (4.5)

840 (36.5)
2,162 (40.2)
2,275 (43.5)
678 (40.2)
15 (38.5)
5,970 (40.8)

48
358
729
151
305
76
1,667

51.61
65.93
61.78
44.81
67.48
79.17
61.67

34 (36.6)
141 (26.0)
361 (30.6)
88 (26.1)
80 (17.7)
39 (40.6)743 (27.5)

10 (10.8)66 (12.2)
181 (15.3)
43 ( 12.8)
99 (21.9)
17 (17.7)
416 (15.4)

4 (4.3)66(12.2)
68 (5.8)
7 (2.1)57(12.6)
10(10.4)
212 (7.8)

85 (15.7)
119 (10.1)
13 (3.9)69 (15.3)
10 (10.4)296 (11.0)

45 (48.4)
185 (34.1)
451 (38.2)
186 (55.2)
147 (32.5)
20 (20.8)
1,034 (38.3)

Sci. Rep. Whales Res. Inst.,
No. 34, 1982