INFLUENCE OF CHASING TIME TO STOMACH CONTENTS
OF BALEEN AND SPERM WHALESAKITO KAWAMURA
ABSTRACTThe duration of chasing time by catcher boats which might influence on
the fulness of stomach contents of whales was examined on fin, sei, andsperm whales caught in the northern North Pacific during the summer of1969. Of 895 whales observed only 28 whales (3.6%) vomited out theirstomach contents while chasing, and sperm whale vomited most frequently(16.8%) whereas sei and fin whales were 1.1 % and 0.78% respectively. The
diet of the whales concerned was consisted of boarfish, squid, copepods andeuphausiids. It was often observed that the whales likely to vomit out morelarger sized foodstuff such as boarfish than smaller one. The amount of
stomach contents vomited was negligibly few, and has no significant influences on the amount of stomach contents which have been obtained fromcarcasses. Most whales (81 %) were caught within 40 minutes of chasing,and the number of whales which would vomit out their stomach contents
does not always increase in proportion to the prolongation in the duration ofchasing time. It was estimated also that the fully repleted stomach of thebaleen whales would be almost emptied by digestion within 15 hours or so.

INTRODUCTION

The quantity and its fulness of the stomach contents of baleen whales have long been
observed, and a considerable amounts of those knowledges were accumulated in the
pelagic and coastal whaling operations (e.g. Collett, 1911-12; Klumov, 1961;
Nemoto, 1957, 1966, 1970: Brown, 1968; Gambell, 1968; Kawamura, 1970a).
These observations can be considered as one of the very important items in the biological observations of whales to offer basic data for realizing a feeding behavior ofwhales along with the swarm forming mechanisms of prey organisms such as an
estimation of swarm density (Kawamura, l 970b; Omori et al., 1971 ). In addition,
they will give a fundamental material for a nutritional budget between predator
and prey animals as Marr (1962) tried to evaluate an approximate estimation ofquantitative relationships between Euphausia superba, one of a principal food sourcesof the Antarctic baleen whales, and the feeding of baleen whales.
In the post-war years, on the other hand, the proportional increase of vacantstomachs among the whales caught was reported as Mackintosh (1965) denoted(e.g. Nishiwaki and Oye, 1951; Peters, 1955). Nemoto (1957) pointed out thatthe actual fulness of first stomach of the North Pacific fin whale in percentage
figures has been reduced distinctly in accordance with the prolongation of chasingtime of catcher boats, and later, he suggested a possible causative reason on thisSci. Rep. Whales Res. Inst.,
No. 23, 1971. 27-36.

28

KAWAMURA

subject (Nemoto, 1959), i.e. an awful improvements of fishing effort especially in
the greately increased power of modern whalers enabled them to chase the whale
more actively rather than stalk so as to the whales can not swim so powerfuly
anymore. Hence a possible causative factors which may induce the decrease in
the fulness of stomach contents on the whole would be due to a vomit of foodstuff
during those long and restless chasing by the whalers though it seems partly due todigestion. The decrease in the quantity of stomach contents in relation to chasing time can be considered to be caused by both vomit and digestion, although
there still remains some physiological problems whether such a muscle fatigue is
responsible for the vomiting behavior of whales.
In this point of view, the present observations were chiefly focussed on theabove mentioned subject to know how much and often the whales actually vomit
out their stomach contents by chasing in the recent whaling operations. If the actual
amount of stomach contents vomited was negligibly small, it would be needless totake these loss of food into considerations when we measure the whole amountof stomach contents of carcasses. I made a brief analysis on the materials to givesome criterion concerning to those " vomit " problems.
MATERIALS

The material used in the present study was compiled by the personnel who belonged
to .six whale catchers which participated in the North Pacific whaling operations
during the summer of 1969. Sending a form to whaling companies, I asked themto fill the following observation items, i.e. date, position at which whale caught,
time (L.T.) of first sight, beginning time of chasing, time of harpooned, occurrenceof vomit, amount and kind of food organisms vomited, chasing speed, and whale
species concerned. Season, localities and whale species were not designated beforehand because any of these were not thought likely to give inherent effects on the
results.
The whale catchers participated in the observations in the whaling ground were
six in all as described below, and I will extend my great appreciations to the whaling
companies and all personnel on boad.
Taiyo Gyogyo K.K. Toshi Mam No. 17 and Toshi Maru No. 18
Nihon Suisan K.K. Konan Mam No. 25 and Konan Mam No. 26
Kyokuyo Hogei K.K. * Kyo Mam No. 12 and Kyo Mam No. 15
RESULTSAn outline ef observations
The general features of the investigation are summarized in Table I. In theseason of 1969 three Japanese whaling fleets operated in the mid-latitudes of thenorthern North Pacific, approximately between 40°N and 50°N. It was 0420 hour

* Present name:

K. K. Kyokuyo.
Sci. Rep. Whales Res. Inst.,
No. 23, 1971.

CHASING TIME AND STOMACH CONTENTS

29

TABLE I. NUMBER OF WHALES OBSERVED BY SIX CATCHER BOATS WHICH
PARTICIPATED IN THE NORTH PACIFIC WHALING OPERATIONS IN 1969.
FleetsCather boats
participated
Duration of operation(day/month)
Sei whale{Vomited
None
Unknown{Vomited
Fin whale
None
Unknown{Vomited
Sperm whale
None
Note:

Kyokuyo Maru No. 3,.-------....

Tonan Maru

Nisshin Maru,.------'..._______,.------'-------

Kyo
Maru
No. 12
18/V25/VI

KyoMaru
No. 15
6/V18/VIII

Ko nanMaru
No. 25
19/V24/VII

Konan
Maru
No. 26
24/V8/VII

22

74

55
15
25
8

4

16
20
81

Toshi
Maru
No. 17
16/V4/VIII

Toshi
Maru
No. 18
17/V4/VIII

Total

102
13

175

5
174
6

6
427
209

16
7

24
28

85
43
21
104

23

Sperm whale was not observed except Kyo Maru No. 15 and Toshi Maru No. 18.

that the whale was sighted at the most earliest in the morning, and 2105 hour forthe latest time of catch. The observations were performed throughout the whole
whaling seasons, May to August, and the material can be considered to represent a
general results of whaling of this season. The total numbers of fin, sei, and sperm
whales concerned to this study were 129, 742, and 125 whales respectively. They
were chased at various ship speed but usually it was 17-18 knots in the first ofchasing then slowed down to 8-12 knots when the whales were harpooned. The
whaling sonar was often used while under chasing. As it is noticed in the resultsof two Konan Maru and Toshi Maru No. 17, there were considerable number of
unknown whales. This fact suggests that there was some difficulties in practicalobservations of whale's vomit from heavily heaving ships. The actual number ofwhales which leaked out their stomach contents to some extent while under chasing
was only 28 whales (or 3.6%) among 895 whales through three whale species
concerned. Kyo Mam No. 15, however, observed one fifth (20.0%) of vomited
sperm whales. The sperm whale on the whole seems more likely to vomit out thestomach contents (16.8% on an average) than fin (0.78%), or sei (1.1 %) whales.
It was suggested from those facts that the whales unlikely to vomit their foodstuff
so frequently by chasing of whale catchers as to have been thought previously.

Kind offood organisms
Table 2 shows the degree of fulness of the first stomach by the kind of foodorganisms along with the time of whale caught, which concerns to only whales
vomited during chasing. Of 28 whales vomited only 3 whales were caught in
the early morning when the degree of fulness of the first stomach is relatively high in
general (Nemoto, 1957, 1959; Kawamura, 1970a). It is suggested on the wholethat both baleen and sperm whales likely to vomit out their stomach contents mucheasier when their stomachs are not so fully repleted. However, as it is noticed in
the table, the acutual fulness of stomachs in percentage figures as being found later
Sci. Rep. Whales Res. Inst.,
No. 23, 1971.

30

KAWAMURA
TABLE 2.

TIME OF WHALES CAUGHT AND THE DEGREE OF THE FULNESSOF STOMACH BY THE KIND OF FOOD ORGANISMS
Fin whale

Sei whale

Sperm whale~~

Boar fish
Cope pod a
Squid
Euphausiids
Squid
Time ofTime ofTime ofTime ofTime ofNo. ofwhale
whale
Stomachwhale
Stomachwhale
Stomach whale
Stomachwhalecaughtfulness
fulnesscaughtfulnesscaughtcaughtfulness
observedcaught
1420
1445
1605
1820

Note:

rrr
rr
rr
R

1210

R

0807

Fulness of stomach in percentage figures
R: 75-100 %, rrr: 50-75 %, rr: 25-50 %,

r

1110

rr

0610
0855
1010
1120
1250
1300
1440
1600
1630

3
3
2
4
1
4
2

r: less than 25 %by flensing carcasses varied from "r" (less than 25%) to "R" (completely full).
There observed no clear trends that well repleted whales do not vomit out thestomach contents much easier but rather moderately repleted whales. It seems
difficult to draw any conclusive tendency from these observations, but it can besaid that there are no clear relationships between vomiting behavior and the degreeof the fulness of whales stomach.
The kind of food organisms found in sei and fin whales was consisted of boarfish(Pseudopentaceros richardsoni), Calanus cristatus, Calanus plumchrus, Euphausia pacijica,
Thysanoessa inermis, and squids. Among these food organisms boarfish and squids

are quite large in body size as the diet of baleen whales usually found. As the size ofboarfish which was found in the whales stomach was varied 22-32 cm in folk length,
its population seems to be consisted of sexualy immature individuals which form adense swarms in the very surface water during the night (Sengoku, 1970). The sei
whale vomited boarfish most frequently than much smaller organisms, i.e. copepods
or euphausiids. However, the very few instances of vomiting those copepods andeuphausiids might be the results partly due to some difficulties to detect the vomit
which is accompanied by so small organisms at the rough high sea only by visualobservations.
Relationship between chasing time and vomit

Table 3 shows the frequency distribution of the number whales of in relation to
the duration of chasing time in 10 minutes intervals. The duration of chasing wasrepresented by the time between beginning of chasing and whale harpooned. There
were no sperm whale being reported as unknown possibly because the observations forsperm whales on this matter would be much easier than the baleen whales due tolarger size of main foodstuff in sperm whales. In the frequency distribution of eachwhale species by the duration of chasing, 10 percent or more of whales were caught
Sci. Rep. Whales Res. Inst.,
No. 23, 1971.

31

CHASING TIME AND STOMACH CONTENTSTABLE 3. OCCURRENCE OF WHALES CONCERNING TO VOMITING BEHAVIORIN RELATION TO THE DURATION OF CHASING BY CATCHR BOATS.
Durationof chasing(min.)

Sei whale
VomitedNone

Unknown

9>

3

68
103
74
53
33
26
20
J4
9
4
6
3
J5
428

60
63
33
19
J4
9
5
2

10

20
30
40
50
60
70
80
90
JOO
JJO
JJO<
Total

6

Sperm whale,,.---------'....________

Fin whale
VomitedNone

Unknown

Vomited

None

10
9
14
13
9
9
6
3

4
12
6

5
4
6

20
30
23
JO
7
3
3

3

2

J
6
83

42

10

2
2

2
3

2
3
210

21

2
104

within 20 minutes to 30 minutes. These percentage figures decreased steadily inproportion to the prolongation of chasing time. There were only 2.9 percent of
whales which were caught after two hours or more of chasing. Sei and sperm whales
as they are shown in the table, it is clear that the whales do not always likely tovomit their stomach contents by the longer chasing time, but they vomit rather
more frequently by very short duration of chasing time within 20 minutes. Thistendency seems to run parallel with the variation in the numbers of whole whale
catch (see also Fig. 3).
TABLE 4.

AMOUNT OF STOMACH CONTENTS VOMITED.

Whale species

Kind of foodAmount of food vomited

Sei whale
Fin whale
Sperm whale

Boarfish
Squid
Squid

3-J5 individuals
ea. 10 individuals
ea. J individual

The actual amount of stomach contents which was vomited out into the sea
by the whale under chase was negligibly small (Table 4). Even the most heavily
vomited cases, the amount was about 15 individuals of boarfish in a sei whale, and10 squids in a fin whale. From those amount of food organisms vomited, it may
be considered that the whales usually do not vomit out any amount of their stomach
contents so as to make under-estimate the whole amount of stomach contents whichis measured on carcasses later when they are £lensed on the deck. Consequently,
the duration of chasing time does not seem so responsible for vomiting be havior
as to result a significant decrease in the degree of the fulness of first stomach.

Possible cause induces a decrease in the fulness of stomach contents
It is well known fact that the more the whales stomach repleted well the more
fresher stomach contents are expected (Nemoto, 1957). The baleen whales likely to
Sci. Rep. Whales Res. Inst.,
No. 23, 1971.

32

KAWAMURA

50- 75 o•
0

...

00
H

+

75- J00

A••

oo:::.ooSunrise - 0900

••

•

+

nl=J •••• •25- 50 •+

... .

••
•:. •••
25> ••• TT
++

••+-

•

A

75-JOO

..c:
0
<O

E

50- 75

0

t)

0
en
en

<D

c

25- 50

OQ

o"

OOo

00

•• .... •••~F• •:£}•• .....
++

25>

lL

•

I

J2.5

I

0

75.0

JOO

0

00

...•• ...
+•

0

..o
00

50- 7500••

25- 50

\·~·
A

•o9o9

•o9o9

25> ~«ii

00

00

0900- J500

•

...

••+

+

75.0

+

••
•
+

•
I

I

vacantStomach(%) 45.5 46.J 52.7 45.8 57.J 25.0 50.0 57.2
00

JOO

•

I

75-100

I

0

•

•

00

i\•.=
:;= -:=.· ·~·· +"'00000 0000

::;

•

•

I

VacantStomach(%) 53.5 45.4 47.6 53.3 83.3~•••• ••

100

I

100

0

••
I

25.0 50.0

1500 - Sunset
0

0

....

•

.. .....,,... . ...•• •• .. •
••

A

A

+

I

VacantStomach 40.6 47.2 58.4 22.J 36.3 59.0 62.5
(%)
JO

20

30

40

50

60

70

0

JOO
80

90

0

JOO

0

JOO

I

I

I

JOO

J JO

120

Duration of Chasing (min.)•Calanus

OFish+ Euphausiid L'>Squid

Fig. 1. Relationship between the duration of chasing and the fulness of stomach by
the kind of food organisms in sei whale.

become so dull when they took much foods as to be caught easily by a slight chasing.
According to Ingebrigtsen (1929), the North Atlantic sei whales with vacant stomach
are so shy, and could not be harpooned easily from a reasonable shooting range.
Figs. 1 and 2 demonstrate the relationship between the duration of chasing time
and the quantitative degree in the fulness of first stomach. The figures are shown
separately in three different time bands which roughly correspond to the generalfeatures of daily change of feeding percentages in the North Pacific baleen whales(Nemoto, 1957). The number ofsei and fin whales well repleted with food decreased
along with the duration of chasing growing longer over 40 minutes regardless thekind of food organisms. The whales with fully repleted stomach were found up to
30 to 40 minutes of chasing time in the morning but they decreased gradually down
to less than 10 minutes chasing in the evening. The whales with moderately repleted stomach, on the other hand, were found up to 70 to 80 minutes of chasingtime in the morning, then it remarkably prolonged to more than 120 minutes ofSci. Rep. Whales Res. Inst.,

No. 23, 1971.

33

CHASING TIME AND STOMACH CONTENTS
75-100++50- 75

+t

+

+

+

++-

Sunrise-0900+•

25- 50

•

•

25>

+

•

.6

+.6

.6

+

•
I

I

Vaoant16.6 37.4 25.0 33.3 33.3
stomach(%)
75· IQQ r

1-

50- 75

•

•

~
.<::
0

"'E
.s
(f)

(f)
(f)

<D

c

100

0
0900-1500

25- 50

•+ +E

++

+

25>

++ +tt •••

••

•

0

0

I

•
•
+

•+

I

+
I

I

Vacant30.0 55.5 33.3 50.0 66.0
stomach(%) 50.0 50.0

I

I

100

0

50.0

100

~

LI..

75· IQQ r++

I SOO-Sunset•

SQ- 75 r
25- 50

-+

25>

••

+

6

+

•+
I

I

Vacantstomach(%)

050.0 66.6
10

20

100
30

I

I

33.3

0

40
60
70
80
90
50
Duration of chasing ( min)•Calanus

OFish+ Euphausiid

100
100

I iO

120

6SquidFig. 2. Relationship between the duration of chasing and the fulness of stomach by
the kind of food organisms in fin whale.

chasing during midday until it was shortened again in the evening. There observed
to present two different kinds of variation patterns in relation to the daily changeof the duration of chasing time and the degree of the fulness of stomach. Oneof possible explanations for those two different patterns would be found in theproceed of digestion, that is, most whales with moderately repleted stomach in
midday might have had been fully repleted in the morning, and such whales would
shift to those moderately repleted stomach by digestion toward midday (Fig. 3).
The duration of chasing time which corresponds to the degree of the fulness of
stomach seems to be shortened from morning toward evening. There observed
more or less inversed relationship between the duration of chasing time and thedegree of the fulness of first stomach through three different time bands, i.e. themore the stomach fully repleted, the more shorter time of chasing is expected. This
fact makes us confirm the former observations (Ingebrigtsen, 1929; Nemoto, 1957).
So often occurrence of well repleted whales in the morning along with relatively
longer duration of chasing time and its hourly change lead to a consideration that
Sci. Rep. Whales Res. Inst.,
No. 23, 1971.

34

KAWAMURA
0

-§

(J)

"'E "'~
0

B .!::

(J)

0

i
i

'- Rp',r~"'-/ .............. \.......

... . . t.........

....................... I......

6_.... .........

""'--------.... . . . . . . . . . . . . . . .

................. _·--.. .. - - . . : ,

----

'hq
. --.. ..__ ___ ~-------------1-~-"'c "'"'"' 5"':.;(J)____ _..:; :;r-------- ------

<D

l..L

6::,

~-~

<D

""O

_L

I

+-+---decrease - -Duration of chasing-

increase- - - · - 0900-1500 -+- !SOO-Sunset
Fulness of stomach: R 75-100, rrr 50-75, rr 25-50, r 25>---<>--- Sunrise-0900

Fig. 3. Schematic curves showing regressive tendency of the fulness of stomach
contents along with the duration of chasing in three different time bands. Curves
with circles and cross by four different degrees of the fulness of stomach show ashift of those degrees toward lesser direction with the lapse of time from sunrise
to sunset.

the most whales take a bulk of foodstuff once a day in the morning.
The copepod and euphausiid foods were found in the whales which werecaught after more or less longer duration of chasing than those fed on squid orboarfish. This may be the result partly due to vomit, i.e. the large sized food organisms likely to be vomited much easier than the smaller one.
It is also supposed from the figures that an approximate time required for thedigestion of foods may be estimated. The whales which carry a well repleted
stomach were found most frequently in the morning, and consequently they were
found being widely scattered up to the duration of 30 to 40 minutes chasing before
0900 hour. However, these whales were greatly decreased in the late afternoon,
and they were only found in 10 to 20 minutes chasing after 1500 hour. This must
be a result of decrease in the absolute number of whales which are well repleted withfood. If it is assumed that the whales with fully repleted stomach could be expected
to be caught by the same difficulties throughout the day, the time being required tocatch them would give an index for estimating the speed of digestion. The number of whales with fully repleted stomach reduce down to about 70 percent in thefirst half of day and then to 50 percent in the afternoon; the relative abundance ofwhale with fully repleted stomach is considered to have decreased down to about
half in a day time. In another words, 25 to 30 percent of their stomach contents
would be digested within 5 hours or thereabouts, and these whales should beshifted to the stomach conditions of " r " to "rrr " of degrees. The fully repleted
stomach with foods would be emptied in this way by the proceed of digestion in thefollowing 14-15 hours.
DISCUSSION
The aim of this study was to know whether the duration of chasing time by catcher
boats has any influences on the decrease in the fulness of first stomach of whales inSci. Rep. Whales Res. Inst.,
No. 23, 1971.

CHASING TIME AND STOMACH CONTENTS

35

relation to vomiting behavior induced by the chasing as has been suggested previously (Nemoto, 1957, 1959). The sei, fin, and sperm whales were vomited theirstomach contents more or les by the restless chasing of catcher boats. The numberof those vomited whales to total catch, and their amount of stomach contents were
negligibly few. Relatively larger sized food organisms such as boarfish are considered to be vomited more easier than the foods consisted of copepods or euphausiids.
Vomiting of stomach contents was not always occurred along with the longer duration of chasing. Most whales vomited were moderately repleted with foods rather
than those fully repleted. So it is supposed that there are no obvious and causal
relation between vomiting behavior and degree of the stomach fulness. Accordingly, it is supposed that the decrease in the degree of the fulness of stomach
contents which have been found in recent whaling operations does not seem to be
explained fully only by those vomiting behavior of whales which might be induced
by some improvements in fishing ability of modern whalers. The amounts ofstomach contents which has been measured (Nemoto, 1959; Klumov, 1961; Kawamura, 1970a) can be considered reasonable as they are, and there seems little possibility to give a significant under-estimation on to those measurements.
There are one possibility left behind that whales may vomit the stomach
contents in the subsurface waters during long restless chasing by catcher boats,since it must be fairly difficult to detect any vomited foodstuff from the boats.
The behavior of vomiting a bulk of foodstuff in the subsurface waters, however, presumably causes heavy muscular activity for those whales, and they would not vomit
any foodstuff in the subsurface waters since the whales under diving likely to minimize the oxygen consumption as little as possible (Scholander, 1940; Slijper, 1962).
It was observed that the whales concerned were caught or at least in visible
during 0420-2105 hours throughout the operations, and accordingly 16-17 hours
are the upper most extreme of the duration elapsed as far as Figs. 1 and 2 concerned. From the regressive trends in the number of whales fully repleted withfoods as time goes by, it was estimated that 25-30 percent of stomach contents
seems to be digested in 5 hours or so, and the fully repleted stomach would be almost
emptied in the following 15 hours or thereabouts. It is known in the blue whitedolphin (Stenella caeruleoalba) and Gill's bottle nosed dolphin (Tursiops gilli) whichwere kept alive in aquarium that their stomachs likely to be emptied within 10 hours
or more (Tobayama, personal communication). He also observed that a small
instrument swallowed by mistake was excreted after 17 hours. The digesting speed
proposed above for baleen whales as found in this study does not seem unreasonable estimations by taking account of the fact that high feeding rates in percentage
figures are usually found twice a day with intervals of 10 to 15 hours.
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No. 23, 1971.

36

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Sci. Rep. Whales Res. Inst.,

No. 23, 1971.