FURTHER INFORMATION ON BRYDE'S WHALE
FROM THE COAST OF JAPANHIDEO OMURA
Very little has been reported on ecological matters of Bryde's whale(Balaenoptera edeni) from the coast of Japan. In 1960, however,material was collected from about 120 whales from various landstations
at Sanriku and Oshima. The present paper is based on this material aswell as on that collected before, together with catch informations.
EXTERNAL CHARACTER

One striking feature in external character of Bryde's whale is the ridges
on each side of the head which run just posterior to the tip of thesnout to the level of blow-holes, on the mid line
between median line and margin of the snout.
Since there present another ridge on the medianline of the head, from tip of snout to blowholes, there are 3 similar ridges, which run
antero-posteriorly, on the head of the Bryde's
whale. The side-ridges, however, sink abruptly
at a level of or a little infront of the anterior
part of the blow-holes and end with grooves(Fig. 1). Several hairs are present on eachside-ridge.
- - _- '-------2
In sei whale (Balaenoptera borealis) median- -----_- ----------- 3
ridge is present, but prominent side-ridges are
not present (Figs. 2 and 3). This character is, Fig. 1. Schematic drawing ofhead of B. edeni showing
therefore, very useful for identification of theridges.
two species at a glance. Such side-ridges are
1. Ridge
2. Groove
also present on the head of the Bryde's whale
3. Blow-holes
from the coast of Brazil as reported by Omura (1962). This character
was already reported by Omura (1959) in a Japanese journal.

/1\MOVEMENTS

Bryde's whale does not follow long distance migration, being only one
exceptional species among balaenopterid whales. It is believed that
Bryde's whale tends to remain in the same locality throughout the year.
Recently Best (1960) reports that the Bryde's whales on the coast of7

8H.OMURA

Fig.2. Dorsalviewo
fhead.B.edeni. (Onagawalandstation,1960)

︑
守nL、． '・・L？

Fig. 3. Dorsalviewo
fhead.B.boγealis. (Onagawalandstation,1960)r

FURTHER INFORMATION ON BRYDE'S WHALE

9South Africa are participating in either an onshore-off shore or a limited
North-South migration and it is possible that they tend to follow theshoals of fish (South African pilchard) on which they feed for most ofthe year.
On the coast of Japan there are four localities on which Bryde'swhales concentrate. These are the seas around Bonin Island, off Sanriku,
off Oshima (Wakayama prefecture), and west coast of Kyushu (Fig. 4).

35°

30°

r o..
120°

130°

Fig. 4. Main concentrations of Bryde's whales on the coast of Japan.
A. Sanriku
B. Bonin Island
C. Oshima
D. West coast of Kyushu

It was proved by whale marking that the Bryde's whales in the seasaround Bonin Island move to the coast of Sanriku as already reported
by Nemoto (1959). Fujino (unpublished) found that there is no practicaldifference in the frequency occurrence of blood group types between
whales from the coast of Sanriku and off Oshima, using the material
collected in 1960. It is possible, therefore, that the Bryde's whales inthese three localities belong to single group or population. I have nomaterial, except catch information, of the Bryde's whale on the coastH. OMURA

10of west Kyushu. It is probable, however, that they belong to anothergroup or population of Bryde's whales than those occurring on the former
three localities, judged from the size distribution of the catches andfrom the point of view of the geographical separation. They are shorter
than the other by about 3-4 feet (Fig. 5).
Male....

Femate_15,...

~-···.

..:.

...

,.x·~/ \~f\II

A··,.

' .
' 1'fI \10

J: I '.

~I'·1\l \ .,.,,,:,xI•
Ifflitff5I:;,;1:,I :!1:,!1I:II(II;1x

4 35 6 7 89 40 1 23 4 45 6 7Body length in feet

789401234456

Fig. 5. Size distribution of Bryde's whales. (1955-1960, Smoothed)• - • Sanriku
x - - - X Oshima•- - - - .a.. West coast of Kyushu

At Saldanha Bay, South Africa, Bryde's whales are taken during
a period of 6 months from May to end of October (Best, 1960). On thecoast of Japan, however, season is shorter than 6 months. On the coastof Sanriku baleen whales are taken from the beginning of May to theend of October yearly, and taking of Bryde's whales last usually about
4 months during this period. At Oshima, Wakayama prefecture, season
does not last longer than 3 months. Usually season at Sanriku begins
one month later than Oshima. The month when season begins differs
yearly, possibly due to the oceanographic condition in that year. InFig. 6 monthly catches of Bryde's whales are shown according to localities
and by months for each year from 1955 to 1960 inclusive. As shownin this figure, at Oshima the peak of the catch is seen in May in 1955
and 1960, while in 1958 and 1959 the peak shifted to June. On thecoast of Sanriku the largest catch was attained in June in the years
1955 and 1960 (and also in 1956), but in 1958 and 1959 (and also in 1957)
the peak of the catch is observed in August. Fig. 7 shows the percentage of females among the monthly catches in these years. It isclear that at Oshima there is a difference of sex ratio and its tendency

11FURTHER INFORMATION ON BRYDE'S WHALE

100 - .

SANRIKU50..."c~·: 150..!!

iOSHIMAj; 100z

5040302010WEST

KYUSHU
MJJASO MJJASO
1956
195 5Fig. 6.

MJJASOMJJASOMJJASOMJJASO. 1957
1958
1959
1960

Monthly catch of Bryde's whales on the coast of Japan.

(1955-1960)

according to these groups of years. In 1955 and 1960, when the season
started earlier, female is dominant in the catch and increases its ratiowith the shifting of the season. In 1958 and 1959, when whaling begun
later, a quite different tendency is clearly demonstrated in the figure.
Also on the coast of Sanriku a similar tendency is observed, but in thislocality female is alway dominant than male and towards the end of
the season such tendency is changed abruptly.
I have no corresponding figure of the Bryde's whales around the Bonin
Island, since whaling in this region has been ceased since 1953. It is
probable, however, from the above that the Bryde's whales on the coastof Japan move from the seas around Bonin Island to the coast ofHonshu, the main island of Japan, seasonally and back again to theformer region, hence migrating, and a segregation between males andfemales taken place during this migration.

H. OMURA

12807060]\I301-)
20
10OSHIMASANRIKU
MJJFig. 7.

AsM

monl:hMonthly change:of sex ratio.

JJAs(% females)

GROWTH OF FETUS

Laws (1959) found that foetal growth in three species of toothed whales
can be described by a linear plot of length and larger neonatal sizes
are attained by increased rates of growth and by extension of thegestation period, and in the baleen whales the first half of pregnancy
follows this law, but thereafter growth can best be described by alogarithmic plot of length or of the cube root of weight. The reason is
not known, but he suggests the fact that the baleen whales subject tovery discontinuous feeding cycle as compared with the toothed whales.
Bryde's whale is presumably different from other species of balaenopterid
whales in this habit. According to Best (1960) it seems that there is
no restricted breeding season in the Bryde' s whales from South Africa
and no fetal growth curve can be drawn from his material.
I have no recent record of fetus of the Bryde's whales from the coastof Japan, except one which was obtained at Oshima in June 1960 andmeasured 1. 78 m in length. This is because almost all f etuses are lost
during the time of towing whales by catcher to landstation. It isFURTHER INFORMATION ON BRYDE'S WHALE

13

an usual practice on catcher to cut open the belly of a whale, just after
taking, and let the internal organs be washed and cooled by sea waterin order to keep freshness of whale meat which is consumed as humanfood. The fetal records from Bonin Island, however, suggests that also
in the Bryde's whales from the coast of Japan exist a breeding season,
similar to that of other species of balaenopterid whales (Table 1). But
these records are limited within two months of May and June and thisis not conclusive.
TABLE 1. RECORDS OF FETAL LENGTHS OF BRYDE'S WHALESFROM THE COAST OF BONIN ISLAND, 1950-52
Length (m)May

0.0~0.2

106
14
16
19
12
14
7
118
6
2
1

0.2~0.4
0.4~0.6

0.6~0.8
0.8~1.0
1.0~1.2
1.2~1.4
1.4~1.6
1.6~1.8
1.8~2.0

2.0~2.2
2.2~2.4
2.4~2.6
2.6~2.8

JuneTotal

16253479611121072018241518
1420
14
7
322

2.8~3.0
3.0~3.2

3.2~3.4
3.4~3.6
3.6~3.8

Total
Mean length (m)2 S. E.

126
1.060
0.105

49
1.447
0.191

175

SEXUAL CONDITION OF WHALES TAKEN

In 1960 at landstations at Oshima and Sanriku 81 whales were observedof their reproductive organs during a period from June to middle ofSeptember. The material obtained are tabulated in Table 2. Males witha combined testis weight of 1.5 kg. or over were deemed as sexual
mature and less immature. In females the criterion for mature is thepresence of any corpus luteum or albicans. As stated above only one
fetus was obtained at Oshima, but great majority of females witha functional corpus luteum were deemed as pregnant, judged from thecondition of their uterine cornua. Sometimes one or both testes orovaries were lost before dismembering. There were two cases of pregnant

14H. OMURATABLE 2.

OBSERVATION OF REPRODUCTIVE ORGANS (1960)

Sexual condition

Females

Males

1628
1264625
17

Immature
MaturePregnant or ovulating
Resting
LactatingUnknown I>
1) Because of one ovary lost

TABLE 3. OCCURRENCE OF NUMBERS OF OVULATIONSIN EACH BODY LENGTH GROUP (Female 1960)
Numbers of ovulations

Body length (m)010.6-10.8
10.9-11.1
11.2-11.4
11.5-11.7
11.8-12.0
12.1-12.3
12.4-12.6
12.7-12.9
13.0-13.2
13.3-13.5
13.6-13.8
13.9-14.1
14.2-14.4
Total

12752134567891011127621*11121111111112111116331Total

2121123322311133* One ovary lost(or ovulating) and concurrently recorded as lactating. Table 3 shows
the frequency occurrence of each corpora number group against bodylength. From this table it seems probable that sexual maturity may beattained in average at a body length of around 11.8-12.0 m (39 feet).

AGE
Ear plugs were collected in 1960 from. 64 whales, but among them 19plugs were damaged at the time of taking or in the course of preparation and could not used for determination of age. Thus remaining
45 ear plugs, 13 from males and 32 from females, were used in thepresent study. The results of ear plug examination are tabulated inTable 4 (males) and Table 5 (females). In Table 4 it is noted that maleswith up to 9 laminations are all sexually immature and with 13 laminations and more are all mature, except one whose testes had not been
examined but apparently mature. In Table 5 it is shown that in females

456J--

11-

0113_____12-

14I

015-

16-

17I018I

019,,,.___~·----···-------·--··----------

200
121...

...

1x

33

Maturex Testes lost

0... Immature

Total

13.3~13.5

13.0~13.2

12.7~12.9

3I

1I

11113

13

2

124

Total

-

-

1012.4~12.6

l...19-I

812.1~12.3

17

Numbers of laminations in ear plug-----·---- -----··----

-

...1

1....

...1 ...1 ...1 ...13-----~----------------

OCCURRENCE OF NUMBERS OF LAMINATIONS IN EAR PLUGIN EACH BODY LENGTH GROUP (Male 1960)

11.8~12.0

11.5~11.7

11.2~11.4

10.9~11.l

10.6~10.8

Body length(m)

TABLE 4.

...,

c::::

"rjCJl

.....

t'1

:»
t""':::i::::;:J

r.ii

t'10-<:?:)

t:tl...,:».....
0z0z~?:)

0z"rj

.....

?:)

t'1:::i::?:)

2

lx

1

....

82

10

1

....

91
ox

100x

MatureBoth ovaries lost.... ImmatureTotal

14.2-14.4

13.9-14.1

3I I7

13.6-13.8

1

1....

6....

110

540
20
10
1112

1 13Ix

10Ix

13-------~2Ix

Ix

14-- -----·-

I

101521x

Ix16]

01172

10Ix

182Ix

Ix

19

Numbers of laminations in ear plug12-ox---

20

J

1x

21

OCCURRENCE OF NUMBERS OF LAMINATIONS IN EAR PLUGIN EACH BODY LENGTH GROUP (Female 1960)

13.3-13.5

1'3.0-13.2

12.7-12.9

12.4-12.6

12.1-12.3

11.8-12.0

11.5-11.7

11.2-11.4

10.9-11.1

10.6-10.8

Body length(m)TABLE 5.

...

...

1\i1241Ix27

11x28

32

36233541121

Totale?;)>:s::0;:qO>,...

FURTHER INFORMATION ON BRYDE'S WHALE

17sexual maturity will probably be attained when 9 or 10 laminations areaccumulated in the ear plug. If we assume that two laminations arelaid down each year, as in the case of other balaenopterid whales, it isprobable that Bryde's whales attain their sexual maturity after fiveyears from birth.
TABLE 6.

CORRELATION BETWEEN NUMBERS OF OVULATIONSAND LAMINATIONS (Female 1960)
Numbers of laminations in ear plug

Numbers ofovulations

5012345678910Total

678910 1112 13 14 15 16 17 18... 24 Total
43

2

1

11-

1

2

1

2

1-

-

1-

1
111

1

2
13In Table 6 is shown the correlation betweeen ovulation numbers andnumber of laminations. The material is very small, but it is probablethat the increment of ovulation can be described by a linear plot of
number of laminations in the ear plug.
FOODAs already stated whales are cut open of their belly just after taking
in order to keep freshness of meat. Concurrently stomachs are also
cut very often and their contents are washed away during the courseof towing, especially in cases stomachs were full of food. Even in thesecases, however, it is possible to ascertain the kind of food eaten, byinspection of the second stomach and others. In this way 27 whales
were observed of their stomach contents at landstations in Sanriku and55 whales at Oshima in 1960. The results of observation are shown in
Table 7. At Sanriku it is noted that most of the food were consisted ofTABLE 7.

STOMACH CONTENTS OF BRYDE'S WHALE (1960)
Anchovy

Locality
Sanriku
Oshima

Empty
625

Krill
217Anchovy
1111&Mackerel
21

Sand
lance

Saury
pike

Small
fishTotal

114
1

2755

18H. OMURA

fish and among them anchovy is very dominant, while at Oshima higher
percentage of krill than anchovy is observed.
OTHER INFORMATION

Nearly all Bryde's whales taken on the coast of Japan bear marks causedby the healing of the open pits in the skin, of unknown origin, which
are aquired by whales in warmer waters. In addition to these whitescars whales treated at Oshima bear very frequently fresh open pits on
their skin, which numbers from one to 17 on one side of the body.
These open pits were also observed at Bonin Island, but never at Sanriku.
If we assame that the whales in the waters off Oshima move to theoffing of Sanriku, these open pits are healed during this period ofmovement, which is supposed as about one month as already stated.
REFERENCES
BEST, P. B. (1960). Further information on Bryde's whale (Balaenoptera edeni Anderson)from Saldanha Bay, South Africa. Norsk Hvalfangst-Tid., 49 (5): 201-15.
LAWS, R. M. (1959). The foetal growth rates of whales with special reference to the fin
whale, Balaenoptera physalus Linn. Discovery Rep., 29: 281-308.
NEMOTO, K. (1959). Food of baleen whales with reference to whale movements. Sci. Rep.
Whales Res. Inst., no. 14: 149-290.
OMURA, H. (1959). NITARI-KUJIRA NO HANASHI (On Bryde's whales). GEIKEN
TSUSHIN, no. 99: 787-801. (In Japanese).
- - - (1962). Bryde's whale occurs on the coast of Brazil. Sci. Rep. Whales Res. Inst.,
no. 16: 1-5.