ON THE FOOD OF BRYDE'S WHALES CAUGHT IN
THE SOUTH PACIFIC AND INDIAN OCEANS
AKITO KAWAMURA*
Whales Research Institute, Tokyo

ABSTRACT

A total of 225 Bryde's whales was caught in the Coral Sea, South Pacificand southwestern Indian Oceans during the 1976/77 Antarctic season under
the scheme of special permission (Figs. lA-B), and their stomach contents alongwith feeding conditions in terms of the state ofrepletion were examined. In theSouth Pacific regions 75% of animals was found to be repleted with under various state whereas it was 46. 7% in the animals caught in the temperate Indian Ocean. (Tables lA-B). The occurrence of fully repleted animal during
the daytime suggests that there seems to exist a considerable availability of
whales food even in the pelagic waters over the tropics (Tables 2A-B). The
stomach contents were solely comprised of three species of euphausiids : Euphausia diomedeae, Euphausia recurva and Thysanoessa gregaria. There found toexist a possible differences in the fashion of geographical distributions among
those euphausiid species as whales food (Table 3). Both E. diomedeae and E.
recurva occurred dominantly over the whaling regions in question with monospecific or mingled composition whereas Th. gregaria alone was completely absent
from the Indian Ocean animals.
INTRODUCTION

During 1976/77 Antarctic season two Japanese whaling fleets, Tonan Maru
No. 2 and Nisshin Maru No. 3, caught a total of 225 southern Bryde's whales in the
Coral Sea, tropical South Pacific and southwestern Indian Oceans under the schemeof special permission for the scientific purpose.
The report on the general topics and some biological observations performed on
those Bryde's whales was preliminarily documented by Ohsumi (IWC/SC/38/1977).
This report deals with the food habits of the Bryde's whales which are identicalto that above mentioned but very briefly since the examination on the stomach contents collected by each factory ship are still halfway of microscopic observations atpresent. Therefore, the argument was focussed on discussing the marine biological purport for taking the whales under special permission rather than describing
the result in detail. However, the article as a whole hopefully be regarded as asupplement to the document by Ohsumi.

* Present address: Faculty of Fisheries, Hokkaido University, Hakodate, Hokkaido.
Sci. Rep. Whales Res. Inst.,

No. 29, 1977, 49-58.

KAWAMURA

50

MATERIAL

Seven Bryde's whales out of 225 animals were caught in the Coral Sea during
October 24-25, 1976, and 113 were caught in the tropical South Pacific between
Fiji Islands and New Zealand during October 30-November 5, 1976. The rest 105
animals came from the catch in the waters off Madagascar, southwestern Indian
Ocean. The approximate locality where the catches took place is demonstrated by
the hatched squares in Figs. IA and lB.
""~01:0,.,_~ ~ <'70./\t
~~

I's

~\,.

CORAL SEA
7 animals

NEW HEBRIDES.cf1 FIJI IS.

q,,

October 24-25, 1976

20·'

NEW CALEDONIA
AUSTRALIA30·~

113 animals

October 30N ovember 5,1976~SOUTH40·

NEW ZEALA~-f/\jFig.IA.
E 120°

140'

130°

150°

160°

PACIFIC

d·
170°

11o·w

180'

lo·
SOUTH AFRICA

20'

r1

MUADAGASCARINDIAN OCEAN
30·

105 animals
March 7-13,1977

Fig.lB.

_ _,
70° E

40°'---'---'---'---"'---'----'-~-'---'-----'----'----'--_,___~__.

S Q°

10'

20·

30"

40'

50°

60°

Figs. IA-B. Whaling ground for the Bryde's whales caught by Japanese whaling
fleets, (IA) Tonan Maru No. 2 and (lB) Nisshin Maru No. 3, under the special
permission for the season of 1976/77. Location of catch is indicated by the hatched squares framed by the farthest extremes of catch positions.
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

51

FOOD OF BRYDE'S WHALES

A total of 121 stomach contents was collected from the identical number ofanimals, of which 69 samples were obtained from the South Pacific and Coral Sea
regions, and 52 were from the southwestern Indian Ocean.
The collected stomach contents were preserved in 10% formalin solution. Although a considerable amount of the stomach contents was heavily digested leaving
a very small fraction of the appendages of prey organisms, it was rather easy to identify euphausiid species by the remains of male copulatory organ on the 1 st-2 ndswimming legs and spermatophore in female since there was quite clear biasing insex composition by each euphausiid species.
Apart from sampling the stomach contents, eye observations on the stomach ofeach carcass were made by a personnel on board, and the results were recorded by
the kind of food organisms on all animals. By examining this results, there foundno descriptions of food items other than euphausiids.
RESULT

Stomach condition in general
The overall state concerning the amount of stomach contents was based on eye
observations by classifing it into five quantitative categories. One of summed up figures was given in Tables IA and lB by the whaling ground. In the animals caught
in the Coral Sea and tropical South Pacific waters, 75% of animals were found to
be repleted with food to some extent under varying quantity. Although the majority of those repleted animals showed few in the quantity of stomach contents, say,
57.5% of animals were repleted less than halfofthe stomach volume, it is noteworthy
or even amazing that there occurred 17 .5% of animals which were repleted almost
fully(' Rich' plus 'Full' in the table-A) in those pelagic waters of the tropics where
the quantitative distribution of planktonic organisms is very scarce in general.
TABLES lA-B. THE OVERALL STATE OF THE STOMACH CONDITION IN BRYDE'S
WHALES CAUGHT IN THE CORAL SEA AND SOUTH PACIFIC OCEAN
DURING OCTOBER 24-NOVEMBER 5, 1976 (A), AND IN THE
SOUTHWESTERN INDIAN OCEAN DURING
MARCH 7-13, 1977 (B).
(A)*
Amount ofstomach contents

Empty

Few

Moderate

Rich

Full

No. of animalo/o to total

30
25.0

49
40.8

20
16.7

13
10.8

8
6.7

(= 120)(=100)* catch by the Tonan Maru No. 2 fleet(B) **
Amount ofstomach contents

Empty

Few

Moderate

Rich

Full

No. of animal

56
53.3

21
20.0

10
9.6

1
0.9

17
16.2

% to total** catch by the Nisshin Maru No. 3 fleet
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

(=105)(=100)

52

KAWAMURA

In contrast to the animals in the South Pacific regions, there occurred considerably large number of poorly fed animals in the southwestern Indian Ocean.
The number of whales with empty stomach roughly doubled in this whaling ground.
However, there still exists about 50% of animals of being well repleted stomach,and the percentage figures combined both ' Rich ' and ' Full ' are very similar tothat found in the South Pacific animals.
The stomach conditions in southern blue and fin whales, for instance, show veryfrequent occurrence in the number of animals with empty stomach in the Ross Sea
region, and its percentage figures usually vary between 40% and 57% (Kawamura,1977). By comparing these figures with those found in the southern Bryde's whales,
it may be considered that the relatively frequent occurrence of well fed animals bothin the South Pacific and southwestern Indian Oceans is significant evidence in connection with dealing the ecosystem through food webs in the pelagic waters of thetropics.

Occurrence of stomach contents by the local time
In the animals caught in the South Pacific and Coral Sea regions, there seems
to be no clear trends in the stomach condition by the local time of catch. The
animal caught in October showed somewhat large number in the frequency of empty
stomach (44.4%) while it was reduced to 13.3% in November (Av. 25.0%), butthere was a slight difference in the Indian Ocean. (Tables 2A and 2B).
The number of animals of being repleted stomach in terms of the percentage figures is very large throughout every time series of catch. Both upper and lower mostextremes of the percentage in the South Pacific animals repleted with some amountof food for given time series was 87.5% for 0900 hour and 60.0% for 0800 hour
respectively, while they were 66.7% and 16.7% in the Indian Ocean animals. Thevery high percentage occurrence of animals of repleted stomach through a series ofdaily catch time (0500-1800 hours) suggests that there must be considerably richavailability of food organisms for baleen whales, and that possibly for many other key
members involved in the tropical food webs. No animal with repleted stomach
was found in 0500, 1000 and 1100 hours, but perhaps it was due to poor catch
number during those time zones. One of important facts in Tables 2A and 2B
should be found in the occurrence of ' Rich ' and ' Full ' stomachs during the daytime (1200-1400 hours). These animals undoubtedly preyed upon euphausiids
within the past several hours prior to their capture. This indicates that there
exists an abundant food organisms even during the daytime and that E. diomedeae,
E. recurva and Th. gregaria occur with large biomass by forming the mono-specificsurface swarms instead of remaining in deep waters.
Species ef food organisms
From a total of 121 stomach samples following three species of euphausiid wereindentified:Euphausia diomedeae Ortmann
Euphausia recurva Hansen
Sci. Rep. Whales Res. Inst.,
No 29, 1977.

FOOD OF BRYDE'S WHALES

53

TABLES 2A-B. FREQUENCY DISTRIBUTION OF THE NUMBER OF ANIMALS BY
THE LOCAL TIME OF CATCH AND THE STATE OF STOMACH CONTENTS,(A) OCTOBER-NOVEMBER, 1976 IN THE SOUTH PACIFIC AND CORAL
SEA, AND (B) MARCH, 1977 IN THE SOUTHWESTERN INDIAN OCEAN.
Tonan Maru No. 2 fleet(A)
PeriodAmount ofstomach contents

October 24-30, 1976
Empty

05
06
07
08
09
10
11
12
13
14
15
16
17
18
Total

1
3
3

Total
1
3
5
1
5
1
1
4
3
4
5
6
3
3
45
100.0

2
2
15
33.3

1
2
4.4

5
11.2

3
6.7

Full

Total

Grand
total

November 1-5, 1976
Few

1
2
4

Moderate

6
8
3

2
4
1

3

1
1
3
2
1
2
1

1
4
4
1
1
34
45.3

10
13.3

Full

2
1
1

1
4

20
44.4

continued ...
Empty

Rich

2
1
3

1
1
1
1
1
2
1
4
1

%

Moderate

Few

Rich

2
3
1

18
24.0

06
07
08
09
10
11
12
13
14
15
Total

%
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

5
6.7

8
10.7
(B)

PeriodAmount ofstomach contents

9
18
9
3
1
4
5
4
6
5
8
2
1
75
100.0

3

1
12
23
10
8
2
5
9
7
10
10
14
5
4
120

% animalwith food
66.7
78.3
60.0
87.5
80.0
77.8
85.7
80.0
80.0
71.4
80.0
80.0

Nisshin Maru No. 3 fleet
March 7-13, 1977

Empty

Few

Moderate

1
7
16
6
9
2
7
3
5

1
5
3
6

1
1

56
53.3

l

l

l

2

Full
1
7
3
2
1
2

3

2
2
1
21
20.0

Rich

l

10
9.5

1
1.0

17
16.2

Total
3
14
28
18
11
5
13
6
6
1
105
100.0

% animalwith food
66.7
50.0
42.9
66. 7
18.2
60.0
46.2
50.0
16.7
100.0

54

KAWAMURA

Tlrysanoessa gregaria G.0. Sars
The population of Euphausia diomedeae occurred in the Coral Sea during October was comprised of adult of both sexes except an instance which was solely comprised of female, and there found a single spermatophore attached to the thelycumin female or to the external genital aperture in male in some individuals. In theSouth Pacific and Indian Ocean population of E. diomedeae, however, male individual was complete absent to result complete mono-sexual composition. The stomach contents of Bryde's whales caught in the Coral Sea were represented solely by
E. diomedeae without exception.
In contrast to the case in E. diomedeae, Euphausia recurva population was comprised of adult male. Female did not occur completely in this species. E. recurva
occurred both in the South Pacific and southwestern Indian Ocean, but not in the
Coral Sea. There were no individuals carrying spermatophores in the specimen
came from the tropical Pacific whereas some few individuals from the Indian
Ocean carried a single spermatophore on the genital aperture although the majority was not.
Thysanoessa gregaria was comprised of both adult male and female. Both E.
diomedeae and E. recurva distributed widely over the whaling grounds in question,
TABLE 3. COMPOSITION OF THE FOOD OF BRYDE'S WHALES CAUGHT IN THE
CORAL SEA, SOUTH PACIFIC AND SOUTHWESTERN INDIAN OCEANS
FOR THE 1976/77 ANTARCTIC SEASON. FIGURES IN THE
TABLE INDICATE THE NUMBER OF ANIMALS.
Sea area
Fleet
No. of animals caught
No. of stomach contents examined

S. Pacific & Coral Sea
Tonan Maru No. 2

S. W. Indian Ocean
Nisshin Maru No. 3

120

105
52

Euphausia diomedeae
E diomedeae/E. recurvalJ
E. diomedeae/Th. gregaria
Euphausia recurva
E. recurva""'E. diomedeae 2l
E. recurva/E. diomedeae
E. recurva+E. diomedeae 3l
E. recurvas;,E. diomedeae/Th. gregaria
Euphausia sp. 41
Thysanoessa gregaria
Th. gregaria/E. diomedeae
Th. gregaria/ E. recurva
Th. grPgaria/E. diomedeae+E. recurva

1751

69

12

4
17

l
2

9

15

2

861

3
3
7

5

10
l

3

by the order of dominancy
mixture of closely equal quantity
3l mixture of two species but quantitative share among them is unknown due to heavy digestion<J the fraction of appendages and spermatophore strongly suggest that the species may possibly be composed of E. diomedeae and/or E. recurva
5J of which five animals out of seven in all caught in the Coral Sea are included
6J including one stomach contained a single specimen of hatchetfish
IJ

2l

Sci. Rep. Whales Res. Inst.,

No. 29, 1977.

FOOD OF BRYDE'S WHALES

55

but Th. gregaria tended to show a sporadic occurrence which suggests the presenceof possible five different local groups. There were however, no noticeable indications in the environmental condition which may explain their characteristic occurrence. The occurrence of Th. gregaria was fairly restricted in the whaling groundof the South Pacific regions.
The Bryde's whales caught in the Coral Sea, South Pacific and southwestern
Indian Ocean preyed upon these three euphausiid species with some local differences in the species composition. As it is shown in Table 3 the food of Bryde's whales
which distributes in the pelagic waters of the tropics was found to be comprised ofmonospecific or mixtured swarms of euphausiids. Comparing this with the stomach
contents having been known throughout the so-called boreal and antiboreal feeding
grounds, the revealed composition of prey organisms in terms of the variety of species
in the tropical waters is considered to be rather monotonous. To see Table 3 there
may be found differences but slight between South Pacific and Indian Oceans: Oneof clear differences was complete absence of Th. gregaria from the stomachs in the
Indian Ocean, instead, Euphausia recurva was possibly dominant in this locality. The
result shows in general that both E. diomedeae and E. recurva are considered to bevery important food items among all in a scope of studying the energy flow throughmarine food webs in the tropical seas where micronektonic organisms other thaneuphausiids have been considered likely to be the key biotic group in the ecosystemof those waters.
DISCUSSION

It is well known fact in general that the abundance of zooplankton in the waters
over the tropics is very poor. The stomach contents of surface dwelling fishes suchas albacore, yellowfin and skipjack suggest that micronektonic fishes and squids may
possibly be the key members in the pelagic food webs in those warmer waters (e.g.
Roger and Grandperrin, 1976). Analysing the stomach contents of above mentioned tunas in the tropical Pacific, Roger and Grandperrin (1976) reported that
60% of the diet of tunas was comprised of micronektonic fishes, and euphausiids
accounted only about 12% of the food of preyed fishes or may account only 7% of
the food of tunas through the predation by their prey fishes.
The Bryde's whales have been considered to be the inhabitant of warm watersof the surface temperature higher than 20°C (Omura and Nemoto, 1955). They
possibly share an identical ecosystem with tunas, surface dwelling fishes and othermany micronektons in those tropical waters. The baleen whales undoubtedly feed
to some extent on some organisms while they are in warmer waters. An example
suggesting their active feeding may be found in the behaviour of excreting reddish
faeces by blue whales in the Indian Ocean (Gambell et al., 1974), and the similar
one was observed in Bryde's whales during the marking cruise of Miwa Maru to theequatorial western Pacific (Far Seas Fish. Res. Lab., 197 5; Wada, 197 5 ). By considering those facts along with some speculations, it may be considered quite naturallythat the Bryde's whales are likely to feed mainly on small gregarious fishes, larvae or
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

56

KAWAMURA

juvenile oflarger fishes and/or micronektonic organisms. However, one of the evidences revealed in the present study on the feeding of Bryde's whales that inhabit
in the tropical South Pacific and southwestern Indian Oceans suggested somewhat
different from that have been considered previously. The Bryde's whales underconsideration preyed exclusively upon euphausiids. There occurred no other kindof food organisms. Although the importance of euphausiids as food ofBryde's whalesin the tropical seas is still obscure since the material did not cover over the sufficient period and amounts. However, the fact that euphausiids occurred significantly
over the different time and space suggests their importance as the stable foodstuff not
only for Bryde's whale but also perhaps for all other baleen whale species occurringin those warm waters regardless the origin of whales whether the animals were endemic or migrants. In this respect the Bryde's whales in the tropics are by nomeans at higher trophic level than any other migrating baleen whale species, andthe ecological niche for those Bryde's whales is considered very similar to thatknown throughout balaenopterid whales.
The euphausiids species, E. diomedeae, E. recurva and Th. gregaria are very
common over the waters from tropics toward the warm temperate regions. Usuallythese euphausiids migrate vertically for a considerable distance of about several
hundred meters and are considered seldom to occur in the near surface during thedaytime (e.g. Boden et al., 1955; Ponomareva, 1963; Mauchline and Fisher,1969). According to Roger and Grandperrin (1976), only Stylocheiron species may
become available for its predators during daytime in the tropical Pacific. Euphausia species, on the other hand, may become more important at night (Roger,
1973a, b). However, the occurrence of E. diomedeae, E. recurva and Th. gregaria
largely in the stomach contents of Bryde's whales even in the daytime suggests theprimary importance of these food species at some restricted time and space overthe pelagic waters of the tropics. Apart from the diurnal behaviour pattern, theformation of swarms at this time of the season in these euphausiid species might
relate to their reproduction, which is indicated by an extremely biased sexual composition occurring only male for E. recurva and female for E. diomedeae of the South
Pacific populations, and several other characteristics such as that the spermatophore frequents in E. diomedeae.
The mass occurrence of euphausiids in the tropical seas so abundant as to be utilized by the predators is again significant phenomenon in considering the energy
budget of baleen whales. Through the calculation of energetic budget in the southern baleen whales, Kawamura (1975) suggested that the overall estimations may fulfill the energetic requirements by migrating animals, but at the sametime there exists
very ill fed animals with thin blubber, and these animals perhaps must to feed on
the way to and from the so-called breeding ground in the warmer waters. One ofquestions arose from the discussion was whether there were any possibility to comeacross suitable feeding place for those stenophagous filter feeders in the tropicalseas, and the failure in this may suggests a critical situation for the mulnutritioned
animals. Although the mass occurrence of euphausiids in the austral spring as was
suggested through this study did not coincide with a possible seasons of appearing
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

FOOD OF BRYDE'S WHALEb

57

the migrating whales, it can be said that the swarms of euphausiids may occur over
the whole warmer season at least in some restricted localities. The occurrence of
euphausiids both in October-November and March with considerable availability
may support this, and there have been reported a considerable amount of halfgrown to adult specimens of E. diomedeae occurred during the austral winter in
Siboga-Expedition (Hansen, 1910).
In concluding with the discussion, the occurrence of euphausiid swarms in thetropical South Pacific and in the southwestern Indian Ocean strongly suggests its
importance in considering the pelagic ecosystem through the food webs in the tropics
as well as the identical subject taking place in the feeding ground of the mid~ to higher
latitudes. The consumption of planktonic crustaceans by baleen whales may
amount significantly among many other predators even if the whale does not feedso much as to fulfill its nutritional daily ration. Although the role of euphausiids
in the tropical marine ecosystem does not seem such magnitude as to noticeable
extent in the overall energetic flows, the swarming of these crustaceans may be oneof the phenomena that can not be overlooked from the ecological aspects. The
swarms of euphausiids possibly be utilized largely by many kind of predators in
addition to the Bryde's whales, and the latter undoubtedly accounts an indispensablerole as the biotic members in the tropical marine ecosystem. More accumulation ofthis kind of knowledge is therefore needed to fulfill the biased knowledge both thebiology of whales and biological oceanography since many similar evidences forthe latter topics have been known solely by studying on the food of baleen whales(e.g. Nemoto, 1962; Omori et al., 1972; Kawamura, 1974).
REFERENCES
BODEN, B. P., M. W. JoHNSON, and E. BRINTON, 1955. The Euphausiacea (Crustacea) of the North Pacific. Bull. Scripps Instn. Oceanogr., 6(8): 287-400.
FAR SEAS FISHERIES RESEARCH LABORATORY, 1975. Progress report on whale research. IWC/SC/27/Progress Report, Japan.
GAMBELL, R., P. B. BEST, and D. W. RICE, 1974. Report on the international Indian Ocean whale marking cruise, 24 November 1973-3 February 1974. IWC/SC/26/37.
HANSEN, H.J., 1910. The Schizopoda of the Siboga-Expedition. Siboga Exped., 37: 1-123.
KAWAMURA, A., 1974. Food and feeding ecology in the southern sei whale. Sci. Rep. Whales Res. Inst.,
26: 25-144.
KAWAMURA, A., 1975. A consideration on an available source of energy and its cost for locomotion in fin
whales with special reference to the seasonal migrations. Sci. Rep. Whales Res. Inst., 27: 61-79.
KAWAMURA, A., 1977. An interim consideration on a possible interspecific relation in southern baleen
whales from the viewpoint of their food habits. IWC/SC/12, Special Meeting on southern sei whales,
Tokyo, April 20-27, 1977.
MAUCHLINE, J. and L. R. FISHER, 1969. The Biology of Euphausiids. Advances in Marine Biology, 7. Sir
F. S. Russell and Sir M. Yonge (ed.), Academic Press, London, 454 p.
NEMOTO, T., 1962. Food of baleen whales collected in recent Japanese Antarctic whaling expeditions.
Sci. Rep. Whales Res. Inst., 16: 89-103.
0HSUMI, S., 1977. Provisional report on the Bryde's whales caught under special permit in the southernhemisphere. IWC/SC/38/1977.
0MORI, M., A. KAWAMURA, and Y. ArzAwA, 1972. Sergestes similis Hansen, its distribution and importanceSci. Rep. Whales Res. Inst.,

No. 29, I977.

58

KAWAMURA

as food of fin and sei whales in the North Pacific Ocean. In : Biological Oceanography of the Northern
North Pacific Ocean. Takenouti et al. (ed.), Idemitsu Shoten, Tokyo, 626 p.
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., 1963. The euphausiids of the North Pacific, their distribution and ecology. Dokl.
Akad. Nauk. SSSR, 1-142. IPST, 1966.
RoGER, C., 1973a. Recherches sur la stituation trophique d'un groupe d'organismes pelagiques (Euphausiacea). II. Comportements nutritionnels. Marine Biology, 18: 317-320.
RoGER, C., 1973b. Ditto. III. Petentiel alimentaire du groupe. Ibid., 18: 321-326.
ROGER, C. and R. GRANDPERRIN, 1976. Pelagic food webs in the tropical Pacific. Limnol. Oceanogr., 21(5); 731-735.
WADA, S., 1975. (Whale marking in the southwestern North Pacific.) Geiken Tsushin, 284: 27-34. (in Japanese).

Note: According to Best (1974) there exist clear difference in the dietary habit of Brycte's whales in theSouth African waters : his ' inshore form ' feeds mainly on fish (Engraulis capensis, Trachurus trachurus,
Sardinops ocellata) whereas 'offshore form' does euphausiids (Euphausia lucens, E. recurva, Nyctiphanes
capensis, Thysanoessa gregaria). As far as this result is concerned, the animals caught in the Coral Sea,
tropical South Pacific, and Indian Ocean seem to represent his ' offshore form '. Although Best's result
provides very important knowledge on the southern Bryde's whales, there was no other way but exclude
his result throughout my discussion since the document (Best, P. B., 1974 : IWC/SC/SP/74/DOC4) has
not been published yet at the moment of publishing this article.

Sci. Rep. Wha!es Res. Inst.,
No. 29, 1977.