Technical Reports of the Institute of Cetacean Research (2018)

pp. 38–49

Technical Report (not peer reviewed)

Biological observations of ﬁn whales sampled by JARPAII in the
Indo-Paciﬁc region of the Antarctic
Toshihiro Mogoe*
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Contact e-mail: mogoe@cetacean.jp

ABSTRACT
A limited number of ﬁn whales (n=17) was sampled during the JARPAII surveys in the Indo-Paciﬁc region of the
Antarctic in the austral summer seasons between 2005/06 and 2010/11. This paper summarizes the biologicalinformation obtained from those whales such as body proportion, reproductive status, age/length relationship, body length/body weight relationship and ecological markers (external parasites). Some of the biologicalinformation was compared with data from the commercial whaling period. The main results were that bodyweights of whales in the JARPAII period are heavier than those reported in the 1950ʼs. Results suggested thepossibility that whales are reaching sexual maturity at younger ages, which is consistent with the reported
increase in the abundance in recent decades. Given the small sample size, these results should be considered
as preliminary.

INTRODUCTION
The ﬁn whale, Balaenoptera physalus (Linnaeus, 1758)
was one of the main target species of commercial whaling during the 20th century, and populations reachedcritical levels after overexploitation. The species was protected in 1976 (IWC, 1977).
More than 40 years have passed since the ban of commercial whaling of ﬁn whales in the Antarctic. As an eﬀectof the protection measures, in recent years abundanceof this species in the Indo-Paciﬁc region of the Antarctic
has been increasing at annual rates of 13–16% based on
JARPA sighting data obtained from the austral summer
season 1987/1988 (Matsuoka et al., 2005; Matsuoka
et al., 2006). Information on biological parameters is important for assessment and management but biological
data of this species have not been available since 1976.
Changes in biological parameters such as pregnancy rate,sexual maturity rate, and age at sexual maturity changes
are density-dependent (Gambell, 1973; Kato, 1986).
A limited number of ﬁn whales (n=17) was sampledduring the JARPAII surveys in the Indo-Paciﬁc region of
the Antarctic in the austral summer seasons between
2005/06 and 2010/11 (GOJ, 2005). Detailed biological examinations were conducted on these whales. The objective of this paper was to summarize the biological information collected. These are the only available biological
data from ﬁn whales in the Antarctic after the commercial
38

whaling operations stopped some 40 years ago. Some of
the biological information was compared with data in thecommercial whaling period.

MATERIALS AND METHODS
SamplesCatch records and biological data of the 17 whales sampled are shown in Table 1. The geographical distributionof the catches is shown in Figure 1. The body weight of
one individual (0506F001) was not obtained because ofsome technical reasons. Another individual (0607F001)
was lost before landing on the deck of the research basevessel and no measurements could be obtained.
Biological data
External measurements
The external measurements were conducted based on
previous protocols (Mackintosh and Wheeler, 1929;
Laws, 1961), modiﬁed by the Institute of Cetacean Research (ICR). Figure 2 shows the external measurements
obtained. Figure 3 shows a ﬁn whale being measured onboard the research base vessel. Body length was deﬁned
as the body axes length from the tip of snout to notch of
ﬂukes in parallel to the plane of the deck.
Ventral grooves
The number of ventral grooves was counted following
Williamson (1973).

Biological observations of fin whales sampled by JARPAII in the Indo-Pacific region of the Antarctic
Table 1
Catch records and biological data of the ﬁn whales sampled in the JARPAII.
Catch
date

LatitudeLongitude

0506F001
0506F002
0506F003
0506F004
0506F005
0506F006
0506F007
0506F008
0506F009
0506F010
0607F001
0607F002
0607F003
0809F001
0910F001
1011F001
1011F002

030206080206090206100206130206140206070306090306100306130306030107050107020207130309030210070111
20011165°44S
65°54S
65°48S
65°37S
65°22S
65°10S
64°34S
64°53S
64°48S
65°36S
63°53S
62°35S
68°46S
65°38S
66°08S
63°28S
66°39S

71°38E
78°06E
78°07E
78°13E
82°00E
81°59E
111°51E
114°06E
114°14E
120°30E
170°44W
174°17W
173°41W
165°08E
62°32E
175°40W
165°32E

Figure 1.

Sex

Sexualmaturity

Body
length(m)

Bodyweight
(t)

Age
(yrs)

M
F
F
M
M
F
F
F
M
F
F
M
F
F
M
M
M

Immature
MatureMatureMatureMatureImmature
MatureImmature
Immature
Immature—
MatureMatureImmature
Immature
MatureMature

19.17
20.05
19.47
18.73
19.14
19.15
20.22
18.22
18.30
19.35
—
20.67
21.15
14.79
17.61
19.05
18.99

—
53.48
52.05
41.87
47.28
47.04
61.52
41.06
42.27
47.24
—
51.62
65.02
22.26
34.20
39.63
43.78

9
11
12
22
11
9
7
7
6
8
—
11
10
6
6
12
10

Catch position

SerialNo.

Foetussex

Foetusbody length
(cm)

Male
Female

127.5
280.7

—

—

Male

243.4

Geographical distribution of ﬁn whales sampled during JARPAII surveys. Closed circle: female; open circle: male.

Body weight
Body weights were measured by summing all body parts
using an electronic hanging scale (maximum capacity of30t) and marine scale (M1100, Marel, Iceland).
Reproductive data
Three individuals (0506F002, 0506F003 and 0607F003)
were pregnant. Their foetuses were measured and sampled in the same manner as adult whales.
In females, both ovaries were removed and weighed
together. In males, testes were removed from both sides

and weighed separately. The gonads weight was measured by using the electronic marine scale (S-182, Marel,
Iceland).
The sexual maturity of females was determined by thepresence of corpus luteum or corpus albicans in either
ovary. In the case where no corpus luteum or corpus
albicans was observed in both ovaries, the female wascategorized as sexually immature. Conversely, if at least
one corpus luteum or corpus albicans was observed ineither or both ovaries, the female was categorized as
sexually mature. The counting of the corpus luteum and39

Technical Reports of the Institute of Cetacean Research (2018)

Figure 2.

Measurement points of external proportions of ﬁn whale in the JARPAII. 1: total length; 2: lower jaw, projection beyond tip of snout; 3: tip of snout to blowhole; 4: tip of snout to angle of gape; 5: tip of snout tocentre of eye; 6: tip of snout to tip of ﬂipper; 7: eye to ear; 8: notch of ﬂukes to posterior emarginationof dorsal ﬁn; 9: ﬂukes, width at insertion; 10: notch of ﬂukes to anus; 11: notch of ﬂukes to umbilicus; 12:
notch of ﬂukes to end of ventral grooves; 13: anus to reproductive aperture; 14: dorsal ﬁn, vertical height;
15: dorsal ﬁn, length of base; 16: ﬂipper, tip to axilla; 17: ﬂipper, tip to anterior end of lower border; 18:
ﬂipper, length along curve of lower border; 19: ﬂipper, greatest width; 20: not available; 21: skull, greatest
width; 22: skull length, condyle to tip of premaxilla; 23: ﬂipper, tip to head of humerus; 24: not available;
25: ﬂukes, notch to tip; 26: tip of snout to centre of ear; 27: tip of snout to centre of umbilicus; 28: tip ofsnout to end of ventral grooves; 29: tip of snout to centre of reproductive aperture; 30: tip of snout to anus;
31: notch of ﬂukes to centre of reproductive aperture; 32: tip of snout to posterior emargination of dorsal
ﬁn; 33: width of ﬂukes; 34: girth of chest, half; 35: girth of abdominal, half; 36: girth of buttock, half; 37:
not available; 38: body height of navel; 39: border length posterior end to tip of ﬂipper.

Age determination
The age was determined by counting of growth layers in
the earplugs (Purves, 1955; Ohsumi, 1964; Lockyer, 1972;
Maeda et al., 2013). The left and right earplugs were collected carefully using scalpel, and immediately ﬁxed in
10% formalin until age determination. After slicing thesurface of earplugs by use of whetstone, the layers werecounted using a stereoscopic microscope under low magniﬁcation (3.15–31.5x, Figure 5). One pair of the light anddark laminae in the core of the earplug corresponds to
one year, according to evidence from Ohumi (1964) and
optimized histochemical method of Maeda et al. (2013).
Figure 3.

Body measurements of ﬁn whale No. 1011F001 on
the deck of the research base vessel.

corpus albicans was not carried out because the ovary
samples were lost after the earthquake and tsunami on
11 March 2011.
The male sexual maturity was determined by theweight of testis. If one testis was over 2.5 kg, the whale
was determined as sexually mature (Ohsumi, 1964).
Figure 4 shows ovaries and testes of Antarctic ﬁnwhales examined in this study.

40

Marine diatom
Quantitative measurements of attached marine diatoms
on the whale body (ﬁve categories) were made following
Omura (1950).
Parasites
Observation of internal/external parasites was carriedout.
Analytical procedures
Fin whale data obtained by JARPAII were compared withpublished Japanese commercial whaling data obtained in
the Antarctic in the late 1940s and early 1950s. Table 2

Biological observations of fin whales sampled by JARPAII in the Indo-Pacific region of the Antarctic

Figure 4.

A pair of ovaries of ﬁn whale individual No. 0506F003 (left) and a pair of testes with epididymis of ﬁn whale
individual No. 0607F002 (right).

from Japanʼs commercial whaling data. These data were
calculated on mean (±SD) value in each class of 1 m bodylength.
In order to check whether there are diﬀerences in reproductive condition, we compared the relationship bodylength/gonad weight using the same data from bodyparts weight.

Figure 5.

Earplug of ﬁn whale individual No. 0506F001 after
slicing the surface.

shows the number of samples used for the comparative
analysis. The following biological data were used in thecomparison.
Body proportion
The mean values (±SD) of JARPAII were calculated andcompared through plotting data on the normalized axis
using Japanese commercial whaling data.
Relationship between body length and body weight/organ weight
The relationship between body length and body weight
was evaluated by applying single nonlinear regression.
The following formula was used (Lockyer, 1976):

Body weight (t) = a Body length (m)bThe coeﬃcient of a and b were estimated by the leastsquares method.
Comparison between body length and body partweights was carried out using samples from 34 ﬁn whales

Relationship between body length and sexual maturity,and between age and sexual maturity
We estimated the age and length at sexual maturity byﬁtting a logistic regression to the proportion of mature
female and male at age (length) x.
For body length and sexual maturity in JARPAII, there
was no signiﬁcant regression coeﬃcient in the logistic
model (p=0.09). Therefore estimates were based only
on commercial whaling data in seasons 1949/1950s,
1950/1951s, and 1951/1952s.
For age and sexual maturity the same approach as
described above was used. In this case the logistic model
was based on both JARPAII and commercial whaling(1956/1957 season; Nishiwaki et al., 1958). Each formulaof logistic regression model was used:p=e β1x1+β2 x2++β p x p+β0
1+ e β1x1+β2 x2++β p x p+β0

p: predicted value, x: independent variable, e: base ofnatural logarithm, β: parameter.

RESULTS
Biological information from JARPAII
Sex ratio and body weight
Of 17 whales sampled nine were females (male sex ratio:0.47). Mean body weight was 46.02t (SD: 10.47). The
maximum and minimum weights for females were 65.02t
41

Technical Reports of the Institute of Cetacean Research (2018)
Table 2
Number of samples, period of sampling and source of data used in the comparative analysis of ﬁn whales between JARPAII and pastcommercial whaling.
Items

JARPAII
SamplesCommercial whaling
Samples

SourceBody proportion

16

16
6
5

1948/1949
1949/1950
1950/1951

Fujino (1954)
Fujino (1954)
Fujino (1954)

Body length and weight

16

16
13
5

1947/1948
1948/1949
1950/1951

Nishiwaki (1950)
Nishiwaki (1950)
Ohno and Fujino (1952)

Organ weight

15

16
13
5

1947/1948
1948/1949
1950/1951

Nishiwaki (1950)
Nishiwaki (1950)
Ohno and Fujino (1952)

Body length and gonad weight

16

16
13
5

1947/1948
1948/1949
1950/1951

Nishiwaki (1950)
Nishiwaki (1950)
Ohno and Fujino (1952)

Body length and maturity

16

437
2,049
2,583

1949/1950
1950/1951
1951/1952

Mizue and Murata (1951)
Ohno and Fujino (1952)
Kakuwa et al. (1953)

Age and maturity

16

288

1956/1957

Nishiwaki et al. (1958)

Body length

16535,740

1930/1931–1975/1976

International Whaling
Statistics

and 22.26t, respectively. The maximum and minimum
weights for males were 51.62t and 34.20t, respectively(Table 1).
Sexual maturity
Sexual maturity rate was 50.0% (4/8) and 62.5% (5/8)
for female and males, respectively. The three pregnant
whales had a single foetus, and a single corpus luteum
existed on one ovary. During the dissection of all female
whales, no milk was found in the mammary glands. As
shown in Table 1, body lengths of foetuses were 280.7 cm(female), 127.5 cm (male) and 243.4 cm (male). Theirbody weights were 172.0 kg, 20.00 kg, and 141.0 kg,
respectively. No abnormalities were observed in the fetuses.
Ventral grooves
The mean number of ventral grooves was 67 (SD: 10) inmales and 69 (SD: 5) in females.
Marine diatom
In most cases diatom ﬁlm was recognized on the surfaceof the whale body (14 of 16 whales). Adhesions of diatom
ﬁlms were more densely observed in males than females
42

SeasonTable 3
The adhesion level of diatom ﬁlms of the body of ﬁn whales
sampled by JARPAII.
Classiﬁcation1

Female

Male

Total

−
±
+
++
+++

2
0
6
0
0

0
0
6
2
0

2
0
12
2
0

Total

8

8

16

1

−: not infected; ±: with thin ﬁlm; +: with patched; ++: withthick ﬁlm; +++: with thick ﬁlm on whole body.

(category ʻ++ʼ in Table 3).
Parasites
Table 4 shows the frequency of external parasites.
The most observed sessile organisms on the skin were
Cyamus (44.0%). 75.0% of males and 12.5% of females
had Cyamus on the ventral grooves. Chi-square test revealed that the percentage of attachments of Cyamus signiﬁcantly diﬀered by sex (p<0.05). Neither Pennella nor
Conchoderma were observed. Coronula sp. was observed

Biological observations of fin whales sampled by JARPAII in the Indo-Pacific region of the Antarctic

in males and females with the same percentage.
Internal parasites were not observed in the stomachs
of 16 ﬁn whales. Unidentiﬁed parasites were observed in
the Gastroepiploic.
Comparative analyses
Average body length
Mean body length for female whale sampled in JARPAII
was 19.05 m (SD: 1.92) (maximum and minimum lengths
were 21.15 m and 14.79 m, respectively). Mean bodylength for male whales sampled in JARPAII was 18.96 m(SD: 0.87) (maximum and minimum lengths were 20.67 m
and 18.61 m, respectively).
Body length (m) of each ﬁn whale sampled in JARPAII
is plotted in Figure 6 with annual mean length and ±SD of
ﬁn whales captured in Antarctic pelagic whaling during
the periods 1930/1931–1975/1976.
It is diﬃcult to compare the data between the commercial and JARPAII, because there was a regulation forsize limit of 70ft (21.34 m) for the ﬁn whale in pelagic
Table 4
Infection rate of external parasites and diatom ﬁlms in ﬁnwhales collected from JARPAII.
Species

Male1

Female1

Total1

CyamusCoronula sp
Conchoderma sp
Pennella sp
Diatom ﬁlm

6/8 (75.0)
1/8 (12.5)
0/8 (0.0)
0/8 (0.0)
8/8 (100.0)

1/8 (12.5)
1/8 (12.5)
0/8 (0.0)
0/8 (0.0)
6/8 (75.0)

7/16 (43.8)
2/16 (12.5)
0/16 (0.0)
0/16 (0.0)
14/16 (100.0)

1

infected/investigated (infected rate %)Figure 6.

commercial whaling. On the other hand, for technicalreasons it was not possible to take ﬁn whales of morethan 20 m in JARPAII. Notwithstanding these diﬃculties, adecreasing trend in the average body length is observed
for the years of commercial whaling (Figure 6).
Body proportion
The mean value and body proportion of the externalmeasurements of JARPAII is summarized in Table 5, bysex. As shown in this table, no diﬀerence in proportions
was observed between the sexes except for the reproductive aperture (e.g. measurement point 13).
In order to clarify the JARPAII properties of body proportions, a data chart was created using the mean value
and the standard deviation for 15 measurement locationsof Japanese commercial whaling data (Figure 7). JARPAII
data are smaller than Japanese commercial whaling data
in many parts in both sexes. In measurements points 7,
14, and 21 in JARPAII, males are larger than commercial
whaling data. Females are larger than males in many
points. Excepting for sex diﬀerence, dorsal ﬁn is higher,
and the skull is shorter than commercial whaling data.
This trend was particularly pronounced in males.
Relationship between body length and body weight
Figure 8 shows the relationship between body lengthand body weight for JARPAII and commercially caught ﬁnwhales. Calculated coeﬃcients a and b in the formula are
a=0.005394±0.005329 and b=3.068448±0.332619 in
JARPAII, and a=0.044530±0.027880 and b=2.315830±
0.205040 in commercial data. From the graph, predictedbody weights of ﬁn whale captured in JARPAII tend to beYearly change in average body length of ﬁn whale captured in Antarctic pelagic commercial whaling (opencircle: seasons 1930/1931–1975/1976) and the body lengths of ﬁn whale sampled in JARPAII (closed circle:
seasons 2005/2006–2010/2011). Vertical bars indicate plus/minus one standard error. The data used in
Antarctic pelagic commercial whaling were summarized from International Whaling Statistics.
43

Technical Reports of the Institute of Cetacean Research (2018)
Table 5The external body proportions of the ﬁn whales in the JARPAII (see Figure 2 for details).
Males

1. Body length (0.01 m)
2. Projection of snout (0.1 cm)
3. Snout-blow-hole (1 cm)
4. Snout-angle of gape (1 cm)
5. Snout-eye (1 cm)
6. Snout-tip of ﬂipper (1 cm)
7. Eye-ear (0.1 cm)
8. Notch of ﬂukes-dorsal ﬁn (1 cm)
9. Notch of ﬂukes-root of ﬂukes (1 cm)
10. Notch of ﬂukes-anus (1 cm)
11. Notch of ﬂukes-umbilicus (1 cm)
12. Notch of ﬂukes-ventral grooves (1 cm)
13. Anus-reproductive aperture (0.1 cm)
14. Height of dorsal ﬁn (0.1 cm)
15. Length dorsal ﬁn (0.1 cm)
16. Axilla-tip of ﬂipper (1 cm)
17. Flipper length (1 cm)
18. Border length ﬂipper (1 cm)
19. Width of ﬂipper (0.1 cm)
21. Skull width (0.1 cm)
22. Skull length (0.1 cm)
23. Flipper length (from humerus) (1 cm)
25. Notch of ﬂukes-ﬂukes (1 cm)
26. Snout-ear (1 cm)
27. Snout-umbilicus (1 cm)
28. Snout-ventral grooves (1 cm)
29. Snout-reproductive aperture (1 cm)
30. Snout-anus (1 cm)
31. Notch of ﬂukes-rep. aperture (1 cm)
32. Snout-dorsal ﬁn (1 cm)
33. Width of ﬂukes (1 cm)
34. Chest circumference, half (1 cm)
35. Abdominal circumference, half (1 cm)
36. Buttock circumference, half (1 cm)
37. Body height (0.1 cm)
38. Body height (0.1 cm)
39. Border leng. ﬂipper (posteroior) (1 cm)

Females

n

Mean

%BL

n

Mean

%BL

8
4
8
8
8
8
8
8
7
8
8
8
8
8
8
8
8
8
8
8
8
8
4
8
8
8
8
8
8
8
8
8
8
8
7
8
8

18.96
9.9
344
365
372
777
91.4
429
98
535
860
833
131.3
47.9
108.3
149
230
237
52.8
220.6
464.5
239
215
461
1032
1061
1227
1358
664
1460
407
436
345
260
182.6
246.6
154

100.0
0.5
18.2
19.2
19.6
41.0
4.8
22.6
5.1
28.2
45.4
44.0
6.9
2.5
5.7
7.9
12.1
12.5
2.8
11.6
24.5
12.6
11.3
24.3
54.5
56.0
64.7
71.6
35.0
77.0
21.5
23.0
18.2
13.7
9.6
13.0
8.1

8
6
8
8
8
8
8
8
9
8
8
8
8
8
8
8
8
8
8
6
8
5
3
8
8
8
8
8
8
8
8
8
8
8
8
8
8

19.05
7.2
353
371
382
779
91.1
435
100
532
860
835
59
45
102.1
151
230
236
52.3
205.4
475.6
245
226
470
1056
1055
1311
1370
589
1467
426
452
366
277
195.4
254.8
156

100.0
0.4
18.5
19.5
20.1
40.9
4.8
22.8
5.2
27.9
45.1
43.8
3.1
2.4
5.4
7.9
12.1
12.4
2.7
10.8
25.0
12.9
11.9
24.6
55.4
55.4
68.8
71.9
30.9
77.0
22.4
23.7
19.2
14.5
10.3
13.4
8.2

Remarks. n: number of samples; %BL: percentage to body length; Mean: mean length.

heavier than that of the commercial whaling for the same
body length.
Relationship between body length and organ weights
Figure 9 shows the relationship between body lengthand gonad weight. The relationship is very similar
between JARPAII and commercially caught ﬁn whale
samples.
44

Tables 6a–b and 7a–b, and Figure 10 show the mean
weights of each body part, by body length. Figure 10
shows that the body parts weight increase with bodylength. This increase is more pronounced in the case of
the JARPAII whales for blubber (Figure 10b) and meat
(Figure 10c). For bones and viscera the increasing pattern is similar between JARPAII and commercially caught
whales.

Biological observations of fin whales sampled by JARPAII in the Indo-Pacific region of the Antarctic

Relationship between body length and sexual maturity
Figure 11 shows the relationship between body lengthand maturity rate of ﬁn whales sampled by commercial
whaling during the seasons 1949/1950, 1950/1951,
and 1951/1952, for female and males. JARPAII samples

Figure 7.

Body proportions of the JARPAII sample (closed
circles and solid line: male; open circle and broken line: female). The data are plotted on thenormalized axis using the data of Japanese commercial whaling (seasons 1948/1949–1950/1951).
Measurement point key are shown in Figure 2. μ j:
mean value of JARPAII data; μ c: mean value of thecommercial whaling data; σ c: standard deviation of
the commercial whaling data.

Figure 9.

are plotted for both immature (0 rate) and mature (1.0rate) individuals. Immature individuals of JARPAII ranged
from 14.79 m to 19.35 m (17.61–19.17 m in males,
14.79–19.35 m in females). Mature individuals ranged
from 18.73 m to 21.15 m (18.73–20.67 m in male, 19.47–
21.15 m in female respectively).
It is estimated that the body length at 50% sexual maturity is 18.99 m (18.69 m in male and 19.90 m in female)in commercial whaling samples. Regression coeﬃcient

Figure 8.

Relationships between body length and bodyweight in ﬁn whales. Closed circles and solid line:
JARPAII; open circles and broken line: Japanesecommercial whaling (Nishiwaki, 1950; Ohno andFujino, 1952: seasons 1947/1948–1950/1951).

Relationship between body length and gonad weight. A: ovary weight; B: testis weight; closed circle:
JARPAII; open circle: Japanese commercial whaling (Nishiwaki, 1950; Ohno and Fujino, 1952: seasons
1947/1948–1950/1951).
45

Technical Reports of the Institute of Cetacean Research (2018)
Table 6a
Average body parts weight (kg) of the ﬁn whales in the JARPAII.
Class of bodylength (m)Samples(female/male)

Total parts
weightBlubber

Meat

Bone

Viscera andothers

14.0–
17.0–
18.0–
19.0–
20.0–
21.0–

1 (1/0)1 (0/1)4 (1/3)5 (3/2)3 (2/1)1 (1/0)21,982.0
33,996.0
41,837.1
46,090.3
54,992.7
63,999.3

5,505.8
7,779.1
10,317.3
11,678.0
13,587.8
16,745.8

10,700.8
17,080.4
20,463.3
22,318.7
27,499.9
31,439.0

2,783.2
4,879.5
5,370.9
5,918.1
7,195.1
7,287.7

2,992.2
4,257.1
5,685.6
6,175.5
6,709.9
8,526.8

Total

15 (8/7)

45,517.0

11,363.5

22,344.4

5,840.7

5,968.4

Table 6b
Percentage of body parts weight of the ﬁn whales in the JARPAII.
Class of bodylength (m)Samples(female/male)

Total parts
weightBlubber

Meat

Bone

Viscera andothers

14.0–
17.0–
18.0–
19.0–
20.0–
21.0–

1 (1/0)1 (0/1)4 (1/3)5 (3/2)3 (2/1)1 (1/0)

100.0
100.0
100.0
100.0
100.0
100.0

25.0
22.9
24.7
25.3
24.7
26.2

48.7
50.2
48.9
48.5
50.0
49.1

12.7
14.4
12.8
12.8
13.1
11.4

13.6
12.5
13.6
13.4
12.2
13.3

Total

15 (8/7)

100.0

25.0

49.1

12.8

13.1

Table 7a
Average body parts weight (kg) of the ﬁn whales in commercial whaling data during the seasons 1947/1948–1950/1951.
Class of bodylength (m)Samples(female/male)

Total parts
weightBlubber

Meat

Bone

Viscera andothers

17.0–
18.0–
19.0–
20.0–
21.0–
22.0–
23.0–

1 (1/0)1 (1/0)5 (0/5)
12 (6/6)
8 (8/0)6 (6/0)1 (1/0)33,817.0
37,367.0
43,712.0
48,652.7
55,629.7
60,966.0
57,487.6

6,953.0
8,270.0
10,263.8
11,289.8
12,761.0
15,897.7
13,319.0

16,875.0
18,391.0
19,473.6
21,971.2
25,914.0
27,398.5
24,093.0

4,899.0
5,906.0
7,760.2
8,264.3
8,856.8
10,284.7
9,132.0

5,123.04,800.0
6,214.4
7,127.5
8,098.0
7,385.1
10,943.6

Total

34 (23/11)

51,232.3

12,141.5

23,296.6

8,543.3

7,251.9

Table 7b
Percentage of body parts weight of the ﬁn whales in commercial whaling data during the seasons 1947/1948–1950/1951.

46

Class of bodylength (m)Samples(female/male)

Total parts
weightBlubber

Meat

Bone

Viscera and others

17.0–
18.0–
19.0–
20.0–
21.0–
22.0–
23.0–

1 (1/0)1 (1/0)5 (0/5)
12 (6/6)
8 (8/0)6 (6/0)1 (1/0)

100.0
100.0
100.0
100.0
100.0
100.0
100.0

20.5
22.1
23.5
23.2
22.9
26.1
23.2

49.9
49.3
44.5
45.2
46.6
44.9
41.9

14.5
15.8
17.8
17.0
15.9
16.9
15.9

15.1
12.8
14.2
14.6
14.6
12.1
19.0

Total

34 (23/11)

100.0

23.7

45.4

16.7

14.2

Biological observations of fin whales sampled by JARPAII in the Indo-Pacific region of the Antarctic

Figure 10.

Comparison of the relationship body parts weight/
body length between JARPAII (closed circle and solidline) and commercial whaling (open circle and broken
line: seasons 1947/1948–1950/1951). A: body weight;
B: blubber; C: meat; D: bones; E: viscera and others.

Figure 11.

Relationship between body length and sexual
maturity rate of the ﬁn whales sampled by JARPAII(closed circle), and comparison of that with thatfrom commercial whaling (broken line: female; dot
line: male; seasons 1949/1950–1951/1952).

Figure 12.

Relationship between age and sexual maturity rateof the ﬁn whales sampled by JARPAII (closed circle
and solid line), and comparison with that by commercial whaling (broken line: season 1956/1957).

between sexual maturity and body length of JARPAII did
not reach statistical signiﬁcance, possibly due to the small
sample size. From the plotting, JARPAII data were equallydistributed besides the rise of predicted probability ofmaturity rate in commercial whaling data except for immature one (body length=14.79 m).

47

Technical Reports of the Institute of Cetacean Research (2018)

Relationship between age and sexual maturity
Figure 12 shows the relationship between age and sexual
maturity rate of ﬁn whales sampled by JARPAII and commercial whaling during the season 1956/1957, for both
sexes combined. Immature individuals of JARPAII ranged
from 6 to 9 years old, and mature individuals ranged from
7 to 22 years old. It is estimated that the 50% sexual maturity age are 8.8 years old in JARPAII and 11.0 years oldin commercial whaling, respectively. The minimum age ofa pregnant whale obtained in JARPAII was 10 years old.
Age at 50% sexual maturity of JARPAII is 2.2 years younger
than Japanese commercial whaling data.

DISCUSSION
This study provided new biological information of ﬁnwhales in the Antarctic after 36 years of protection fromcommercial whaling. Although the number of whales
examined was small some new and interesting results
such as body proportion and parasites were obtained.
During the commercial whaling period only large whales
were taken. During the JARPAII survey there was the opportunity of sampling small animals for the ﬁrst time. Infact the smallest whale was a 14.79 m whale and several
biological data were obtained from this whale. The limitation of JARPAII, however, was for animals larger than
20.0 m which usually were not sampled because technicaldiﬃculties.
Body length/ body weight
It was found that Antarctic ﬁn whales collected by JARPAII
were heavier than those taken by commercial whaling in
the 1950s. This might suggest that the feeding condition
for the Antarctic ﬁn whale has improved in recent years.
It was also found that the relative weights of the blubber and the meat are heavier for ﬁn whales sampled by
JARPAII (Figure 10). The increase in body weight of ﬁnwhales, particularly in weight of meat and blubber, might
indicate faster growth which was derived from better nutritional condition in recent years.
Body length and age at sexual maturity
There is the possibility that the age at sexual maturity of
the ﬁn whale has decreased in the 2000s. Decline in theage at sexual maturity in whales in response to substantial decrease in the abundance (for example due to overexploitation) has been reported for sei and ﬁn whales inpart of the Indian Ocean and the Antarctic Ocean, andfor ﬁn whales in the northwest Paciﬁc Ocean (Gambell,
1973; Lockyer, 1979; Ohsumi, 1986). Our study provided
evidence that the age at sexual maturity of ﬁn whales
48

sampled by JARPAII has decreased about 2.2 years fromthe 1950s.
The number of pregnant whales among the ﬁn whales
sampled by JARPAII was three out of four matured whales(75.0%). This high pregnancy rate was similar to the1970s (Gambell, 1973).
All this evidence suggests improved nutritional conditions for ﬁn whales in recent years. The biological studies
based on JARPAII data were based on a small sample size.
Further biological samples and data from this species will
be needed to conﬁrm the results found in this study.

ACKNOWLEDGEMENTS
I express my gratitude to the crew members and researchers that participated in the JARPAII surveys forhard work and excellent technical assistance. I also thankseveral ICR colleagues for providing suggestions on theanalyses in this study.

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