RYUKYUAN WHALING IN 1961
MASAHARU NISHIW AKI
In accordance with the invitation from the United States Civil Administration of the Ryukyu Islands, the author had been engaged in thebiological investigation of the Ryukyuan whaling from March 24 toApril 4, 1961.
The scientific study of the composition of whales and the survey on
the migration routes are reported mainly in this paper.
OUTLINE OF THIS WHALING SEASONThe whaling of this year started in the first week of January, and thecatch was started with the sperm whale. Though the humpback whalewas caught in the middle of January, this species of whales are very
scarce at that time.
Even in February the water volume of 20°-22°C which is the suitabletemperature for the humpback whale did not appear in the main whaling
ground but existed in the Miyako area. So the smaller type catcher
boats caught no whales in February. This phenomenon is considered
as follows. According to the weather reports in Far East Asia, theChinese Continent had some copious rains with deluges in the summerof 1960. The author pointed out in his report of the Ryukyuan humpback whaling in 1959 that the Chinese Continent had brought in thesummer of 1958. In that case the decrease of cold water from these
Chinese rivers might probably cause a higher temperature around theRyukyuan Island. The reverse phenomenon occurred this year. Thereis a fact of some floating ice draft in the Korean Channel to the southward, which the author believes was caused by the Tsushima warm
water caurrent that seemed to have weekened this year.
The time of year for the migration of the humpback whale, however,seemed to have made no great difference from the average year. Thattime was pointed out by author in his report of 1960 i. e. about lOthof January.
There is, so to speak, a marching column in the migration of whales.
The order of migration of humpback whale in the Ryukyuan waters is
as follws. The first is some groups of immature male, second is immaturefemale. Then the main groups i. e. the mature male and female come.
Shortly after there are some lactating females mixed in these maingroups. This lactating female delivered a calf this season and was19

M. NISHIWAKI

20

actually lactating at the time. These actually lactating groups are thelast to leave these waters. The males which arive after the main groups
are almost mature.
There were very small number of immature males caught in thecatch of this season. Taking
the above mentioned consideration, the immature~ 60
3male migrated away from...
!1
the Miyako area to the."/>o,.//:5, 40I·//
north-east direction in Janufom•le/ary.
The catcher boats/·l 20'found and caught the imma• Re$tin~ female:'zLactat/ng female'ture females at the time;;,'Pubert;. femaleof their migration in the80
southern parts of the whaling
ground. It is considered~ 70.1!
0 60
that their migration wasFemale* 50
affected by the colder watermass of the East China
Sea. In Fig. 1 the above
43
mentioned facts are shown
as average body length,
sex ratio and compositionof sexual conditions in each] 39
month. These figures fit inwell with the same figures37of the previous years. In
May of this season one
mature female was caught,
Apr.
Total average
Jen.
Feb.
. but the figure does not inFig. 1. Average body length, sex ratio and comclude this whale.
position of sexual conditions in each month.
Nine sperm whales werecaught in the beginning of this whaling season, but in a later period
only a small effort was paid to the sperm whale whaling, because efforts
were concentrated in the humpback whale whaling.
No other species of whales were caught.
0.
0lmniature female' o'"'"f'•Immature maleE

60.

01COMPOSITION OF WHALES CAUGHTIn Table 1 is given the size distribution of the humpback whales caught
according to their physical condition on 90 whales including 31 males
and 59 females.

Sex ratio
Matulity rate
Rate of ovulating
Rate of lactating

4546
47
48
4950
Total
Average length44353637
38
39404142
4334

Body length
in feet

19.4

6
35.3

13
1
180.6

25
40.6
34.4
100.0

31
39.6

1233
244
3
12

Total

13233
32
4
4
3
12,~-~Male
Immature Mature

2136.4

584
3
140.6

338.3

2
1

Immature Puberty

43.5

1842.l11944.0

60.0

222

143
13

123
1~238.511~~

17. l

642.5

1111265.6

15940.4

13543.0

59.3
100.0
100.0

3365353247584Total

2136535324Sum--------------~~-..----------~

MatureOvulatingResting LactatingFirst MultipolaFemale

TABLE 1. SIZE DISTRIBUTION OF HUMPBACK WHALES CAUGHT ACCORDING TO PHYSICAL CONDITIONS

100.0

190
40.1

1810
7106510966524

Grand
total

......

N>......
~......

zc;')
z>
z:?J
:::i::>
t""'c:::><!

:;:::

c:::><!

:;;i22M. NISHIWAKIThe male whose testis weight on either side is 2.0 kg is defined asmature. The number of immature males is fewer in comparison withthe previous years. The reason that the immature males were scarceis as above stated.
The classification of physical conditions in females was the same asin the previous investigations. The female whose ovaries contain neither
new nor old corpus luteum is defined as immature. In these immature
females whose Graafian follicle was more than 30 mm in diameter wasdefined as puberty. The mature females are divided into three stages;
the ovulation stage where the female has a new corpus lute um (sometimes two or more new corpora lutea were found), the resting stage
where the female has some old corpora lutea and her Graafian follicle
is less than 30 mm in diameter, and the lactating stage when they arefound to be capable of secreting milk in the mammary glands and did
not have any new corpus luteum or a Graafian follicle more than 30 mm
m diameter.
TABLE 2. OCCURRENCE OF BODY COLOR OBSERVED
Grade of body colorPeriodSexJanuary{MaleFemale

15February{MaleFemale

1110March{MaleFemale

April{MaleFemale

13296May{MaleFemale

Total% of occurrence{MaleFemale
Animal1110
131568796.7

201
100
10000

1
2

3
3.3

30000
0
000
00000

400000000(}

0000It is impossible to classify the ovulation stage into the ovulation andthe pregnant stages in these breeding areas, because of the very small
embryo. The rate of ovulation is used for the pregnancy rate in thisreport. The ovulation rate therefore, always shows a higher percentage
than the actual pregnancy rate.
On the maturity rate in the female, the higher percentage figure isconcerned with the migration time of this season.
Table 2 shows the occurrence of the white pattern distribution on theabdominal side according to four stages in the same standard in theprevious investigations. There is no significant difference in comparison
with the previous seasons.

RYUKYUAN WHALING IN 1961

23In Table 3 is given the frequency of occurrence of blood types. Theclassification of the blood types was made by investigater Mr. Kazuo
Fujino of our Institute as in the case of the last year by using thesame serum as in 1960. The occurrence between Type 1 and Type 3
were more similar to the 1959 data than the 1960 data. This matter isalso shown in the other results of the biological investigation of thisseason. It may be suggested that the same groups of the humpback
population do not migrate every year to this whaling ground.
TABLE 3. FREQUENCY OF OCCURRENCE OF BLOOD TYPESCOMPARED WITH THE DAT A IN 1959 AND 1960
Occurrence
Blood type1959

1960

1961

~-~~~~

Number
14787
1100

12342 or 3Total%

1.0
4.0
7.0
87.0
1.0

Number28273085

No tested samples because of hemolysis
Number of samples collected
Number of whales caught
TABLE 4.
Body length
in feet37383940
414243

Number12552060

%

2.35
9.4
2.35
85.9
0.0%
1. 7
3.3
8.3
86.7
0.0

268690SIZE DISTRIBUTION OF SPERM WHALES CAUGHT
IN 1959, 1960 AND 1961
Number of mature male1959
12131960
3333111961
132
11

Sum
2
8647
11

1
939.4

130
39.6

4445
Total
Average length

739.3

1439.9Immature male and female whales were not caught in each season.

Thickness of blubber, stomach contents and parasite, etc. were investigated, but the data giving the effective suggestions on composition ofwhales or on migration routes were not available.
Composition of the sperm whale caught in this year was made in
Table 4 with the same data of previous two years. They were matured
young males classified by testis weighing and did not accompanied with24

M. NISHIW AKIfemales. They are not the main group of this species, but usually theforerunners of their migrating column.
CONSIDERATION FOR THE STOCK OF THE HUMPBACK WHALE

The ear plugs that have the most suitable data on the age determination for baleen whales were collected from 92% of the catch of this~ \IIJI I\~

25~~

020

•"\~o---1959

•

1960

"----

1961

11\~

10ID.<>

0e:Z
501I
51121

31

41

51

61

71

I
15I
25

I
35

I45

I
55

I6575

IFig. 2. Survival curve from the ear plug lamination survey of the humpback whalescaught in Okinawa 1961.

year. In Fig. 2 the frequency of the number of ear plug laminations
was shown as a survival curve. The same curves of the previous two
years are shown in the same figure for comparison. These three curves
are very well in accord. Basing on the agreement of these curves thestock of the humpback whales did not suffer heavy damages throughthe whaling.
These curves must be separated into male and female and the gatheringof the class of ear plug lamination numbers must be done more carefully,
but since the data were scanty this method had to be accepted. TheseRYUKYUAN WHALING IN 1961

25results, however, are enough to study some of the tendencies of thestock. The mortality curve that should be calculated from the survival
curve was omitted here.
19 58

Whaling season-a;~c"'"~~4"

19 6 I,IP.... __//

c-"~

~

41..l!

~

196 0

19 59-.... '°"O"' _ _---0

40g>

,..

390m

38
60

0·~

1"500*4080~-;;;
E70·~
f.

.ll0 E'$.

60,.
50/

if

76ci........ ""'<>--- ___ o5z.
"6040

Survival curve fromlaminat:ipn survey of ear plug

Fig. 3.

Survey was Almost same Curve just:. sta.rtedin this year

figure in1959~~:~e1 9b59
and 1960

Data of interpretation on the movement of the humpback whale population.

The annual variations of the above mentioned results are shown inFig. 3.

26M. NISHIWAKIIn the case of decrease in stock, the following phenomena are observedusually.
1. Decrease of average body length.
2. Decrease of male in sex ratio.
3. Decrease of sexual maturity rate.
4. Decrease of average ovulation number in mature female.
5. Decrease in survival curve.
6. Increase of sight catch ratio.
7. Increase of pregnancy rate in mature female.
According to Fig. 3 the stock of the humpback whale seems to bestable except in the item 2. It is considered that the effect of thepresent whaling do not cause considerable decrease in the stock.
Also in this season one of the whale marks that were marked in theAleutian waters was recovered. This fact bear witness to the fact thatthe humpback whales in the Ryukyuan waters are closely connectedwith the stock of all North Pacific. By the observation of the Japanesewhaling fleet operating in the Aleutian waters more than 300 of thehumpback whales are found every season. Nevertheless the catch isdecreasing annually. That is caused by the bad weather and the strong
winds. The second reason, it must be acknowledged, is that the humpback whales are intelligent enough to change their migration routes
because of the increase in the catching intensity.
MIGRATION ROUTES OF THE HUMPBACK WHALESThis is a very difficult problem, and in a word it still remains unexplained.
For information, however, the author enumerates some evidences as
the following.
1. The whale marks tagged in the Aleutian waters are recovered in
the Ryukyuan waters every season and the total number of recoveries
reached six marks.
2. Numerous humpback whales are observed between February andMarch and also in October in the waters of the Midway and the Hawaii
Islands.
3. From January to March many humpback whales are observed in
the Ogasawara waters (area of Bonin Is.). Whale marking on thehumpbrck whales was carried out in March 1961 by the Fisheries Agencyof the Japanese Government in the Ogasawara waters.
4. The number of humpback whales caught in the Japanese coastal
whaling were very scarce after the World War II.

RYUKYUAN WHALING IN 1961

27

SUMMARY

Some considerations and results are made hereinafter based on the data
already mentioned above.
1. The number humpback whales caught in this year has decreased
compared with the last year. The colder waters of the East China Sea,
that was caused by the downpour in the summer of 1960, obstructed
the migration way of the humpback whales.
2. The number of humpback whales sighted have not decreased incomparison with the last season, but the weather and the strong winds
have obstructed the successful catch. The next reason is the factor
depended on the catcher boat.
3. Judging from the results of the biological survey the stock of thehumpback whales did not suffer heavy damages through whaling. Asis shown by the recoveries of the whale marks, the migration groupsof the Ryukyuan waters are closely connected with the stock in theAleutian waters i. e. all the North Pacific stock. It is considered, therefore, that the data of investigation shows the increase and the decreaseof the North Pacific stock.
4. It is still unknown where the migration routes of the humpback
whales are. Further investigation is necessary to solve this problem. It
seems that the whale marking on the humpback whales in the Ogasawara
waters by the Japanese Government is a very valuable action.
5. As was mentioned above, the stock of the humpbak whales isconsidered as a fairly stable condition. It is suitable to give the highest
limit of the number of catch as the quota.
6. Though small in number the sperm whales are caught every
season. The author does not consider that the actual scouting of thisspecies is carried out. The Ryukyuan Whaling industry should not relyon the catch of the humpback whales only, but try to catch other speciesof whales also in order to decrease the catch of the humpback whales.
7. The water temperature around the Okinawa Island, the author
believes, is dependent on the climatical precipitation on the ChineseContinent. Close study of the weather of the last year on the ChineseContinent will be, therefore, essential in deciding the most suitable timefor starting the whaling season and the direction of scouting the whales.
ACKNOWLEDGEMENT

In concluding the report for the Ryukyuan whaling season of 1961,
the author wishes to thanks every person concerned for his kindnesses
suggestions and assistances. The author must particularly acknowledge

M. NISHIWAKI

28

to the appointment for the whaling investigation of this season by theUnited States Civil Administration of the Ryukyu Islands.
The author is quite indebted to the officials of USCAR, the American
Embassy in Tokyo, the Government of the Ryukyu Islands and theFisheries Agency of the Japanese Government who have given a accomodation on the invitation to the Ryukyu whaling.
Grateful thanks are due to the members of the Ryukyuan Whaling
Industry who have always given a big favor.

REFERENCESNISHIWAKI, M. (1959).

Humpback whales in Ryukyuan waters.

Sci. Rept. Whales Res.

Inst., no. 14.
- - - (1960).
15.

Ryukyuan humpback whaling in 1960.

Sci. Rept. Whales Res. Inst., no.