J-STAGE Advance published date: December 23, 2021

MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALESDWARF MINKE WHALES: MORPHOLOGY,GROWTH AND LIFE HISTORY BASED ON
SAMPLES COLLECTED FROM THE HIGHERLATITUDES IN THE SOUTHERN HEMISPHERE
Hidehiro KATO1, 2*, Yoshihiro FUJISE2, Gen NAKAMURA1,
Takashi HAKAMADA2, Luis A. PASTENE2, 3 and Peter B. BEST4†Tokyo University of Marine Science and Technology, 5–7–1 Konan, Minato-ku, Tokyo 108–8477, Japan
2
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan
3
Project Microbiome as Bioindicators of the Aquatic Ecosystem Health in Chilean Patagonia, Centro deEstudios del Cuaternario de Fuego-Patagonia y Antártica (CEQUA), Punta Arenas, Chile
4
Mammal Research Institute, University of Pretoria, c/o Iziko South Africa Museum,
P. O. Box 61, Cape Town, 8000 South Africa†
deceased on April 22, 2015.
*Corresponding author: katohide@kaiyodai.ac.jp

1

Abstract
This study examined the morphology, growth and life history of dwarf minke whales to
identify and conﬁrm any diﬀerences from other minke whale species and subspecies. The
study was based on biological samples and data obtained from 16 whales (3 males and 13
females) collected through the 1987/88 to 1992/93 austral summer seasons by the Japanese
Whale Research Program under Special Permit in the Antarctic (JARPA). The whales werecollected between latitudes 58°23′S and 65°04′S in the Antarctic area between 90°E and 180°.
Mean body length at physical maturity was estimated to be 7.16 m for females, approximately
1.5 m to 2.0 m smaller than equivalent values of Antarctic minke whales and North Paciﬁc
common minke whales. The characteristic feature of a white shoulder/ﬂipper patch was conﬁrmed and some variations in the overall color pattern was found. Skeletal observations conﬁrmed the previously reported characteristic features on the vertex of the skull. In addition,
this study found a longer rostrum, deeply curved mandible, and narrower nasal bone in dwarf
minke whales in comparison with other minke whales. All pregnant females had conceived
in mid-austral winter (middle of June to early August). Females are likely to attain sexual
maturation at 6–6.5 m and at around 7–10 years of age. Stomach contents indicated that dwarf
minke whales mainly fed on lantern ﬁshes around the Antarctic Convergence in summer. Analyses by ANCOV revealed signiﬁcant diﬀerences in both external body and skull morphology
among diﬀerent species and subspecies. Furthermore, cluster analyses on the skull morphology revealed diﬀerentiation between dwarf minke whales and other common minke whales but
they are more closely related to North Atlantic common minke whales. These analyses concurred with previous genetic analyses results. The results of this study provided support for the
proposed subspeciﬁc status of dwarf minke whales.
Key words:

dwarf minke whale, diminutive minke whale, minke whale clade, morphology,
life history parameters.

Introduction
Early reports suggested the existence of a diﬀerent form of minke whale from the typical southern
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minke whale (now known as the Antarctic minke whale, Balaenoptera bonaerensis) in the Southern
Hemisphere (Kasuya and Ichihara, 1965; Gaskin, 1976; Wada and Numachi, 1979; Best, 1982; Baker,
1983; Singrajah, 1983). Subsequently, Best (1985) described two morphological forms of southernminke whale as being the ordinary and the small (diminutive) forms based on material collected fromboth the South African coast and the Antarctic. He also documented diﬀerences in shoulder/ﬂipper
coloration, type of baleen as well as other diﬀering external morphological features between the twoforms: the smaller (‘dwarf’ or diminutive) and the larger ordinary (B. bonaerensis) forms.
Arnold et al. (1987) further examined the morphology of the small form of minke whales in theAustralian coastal area which he called ‘diminutive’ minke whales. They conducted some preliminary
osteological examination and found some characteristic skull features and distinctive pigmentation
which were additional to those reported in Best (1985). However, their sample sizes were too small
and geographically restricted to reach any deﬁnitive conclusions on their taxonomic status. Subsequently some additional studies were conducted on the Australian diminutive form e.g., Arnold et al.
(2005).
The Japanese Whale Research Program under Special Permit (JARPA) started in the 1987/88 austral summer season and continued until the 2004/05 season. The target species for the sampling was
the southern ‘ordinary’ minke whale. However, at the end of the ﬁrst survey in 1987/88, a minke
whale, having a noticeably clear white patch on the shoulder (Fig. 1) was sampled on 23 March 1988.
Fifteen additional whales with a similar characteristic were sampled in subsequent JARPA surveys
until the 1992/93 season. Those whales were associated with the dwarf minke whales reported byBest (1985) and Arnold et al. (1987). The total 16 dwarf minke whales were examined by two of theauthors (Kato and Fujise) on the deck of the research base vessel. Materials from these dwarf minke
whales were ﬁrst reported by Kato and Fujise (2000), and some of the biological data from their report
was used in Perrin and Brownell (2002, 2009) for their description of diﬀerent types of minke whales.
Wada et al. (1991) and Pastene et al. (1994) conducted the ﬁrst genetic analyses of dwarf minke
whales sampled by the JARPA, based on mitochondrial DNA. They found substantial diﬀerencesamong southern ‘ordinary,’ North Paciﬁc and dwarf minke whales. Their phylogenetic analyses suggested that dwarf minke whales were closer to the North Paciﬁc minke whale than to the southern
ordinary minke whale. North Atlantic minke whale samples were not available for genetic analysis atthat time and the authors recommended additional genetic and non-genetic analyses to elucidate thetaxonomy of the minke whale. Based on the genetic and non-genetic studies summarized above andthe recompilation of Rice (1998), the Committee of Taxonomy of the Society for Marine Mammalogy(SMM, marinemammalscience.org) listed the following species and subspecies of minke whale:
Antarctic minke whale, Balaenoptera bonaerensis Burmeister, 1867 also known as ordinary southern minke whale, Southern Hemisphere minke whale, ordinary form of minke whale, dark shoulder

Fig. 1. A dwarf minke whale (88/89-013) sampled under the JARPA program in the Antarctic, in the 1988/89
season.

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MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALES

form of minke whale.
Common minke whale, B. acutorostrata Lacépède, 1804 having three separate subspecies as below:
North Atlantic minke whale, B. a. acutorostrata Lacépède, 1804.
North Paciﬁc minke whale, B. a. scammoni, Deméré, 1986.
Dwarf minke whale, B. a. un-named subsp. [Rice, 1998] also known as diminutive minke
whale, dwarf form of minke whale.
More recent genetic analyses using samples of minke whale worldwide provided further evidence
for the separation of the two species, and at least three subspecies of the common minke whale using
mtDNA sequences (Pastene et al., 2007, 2010) and microsatellite DNA (Glover et al., 2013). Thesestudies indicated that dwarf minke whales are more closely related to the North Atlantic common minke whale (see also relevant sections in Murase et al., 2020).
The biological samples and data of dwarf minke whales taken by the JARPA were further analyzed
in the present study following the initial analyses conducted by Kato and Fujise (2000) while it is stilla small sample size. The aim of the study is to compare the biological features, including external andskeletal morphologies, with those of other species and sub-species of minke whales in an attempt toelucidate the taxonomic status of the dwarf minke whale. Also, the study provided an opportunity totest the hypothesis derived from recent genetic studies that dwarf minke whales are more closely related to the North Atlantic common minke whale.

Materials and methods
The present paper examined biological features of the dwarf minke whales taken by the Japanese
Whale Research Program under Special Permit in the Antarctic (JARPA). Preliminary results of theprevious analyses of these samples were presented to the IWC Scientiﬁc Committee meeting in 2000
(Kato and Fujise, 2000). The biological features, including external and skeletal morphologies, werecompared in the present study with those of other species and sub-species of minke whales in an attempt to elucidate the taxonomic status of the dwarf minke whale.
Biological materials
The present study primarily used biological samples and information collected from the 16 dwarf
minke whales (3 males and 13 females) sampled under JARPA through 1987/88 to 1992/93, at whichtime the dwarf minke whale was not recognized as a diﬀerent taxon from the Antarctic minke whale,at least at the species level. No dwarf minke whales were sampled after the seasons of 1992/1993. Table 1 summarizes primary biological information used in the present study. The following data werecollected onboard the research base vessel according to the ﬁeld and laboratory protocols provided in
Kato et al. (1989): body length to the nearest cm, sex, number and length of fetus, testes weight, number of corpora in both ovaries, thickness of blubber, and stomach contents.
Sexual maturity was examined by standard methods based on ovary and testis examination. Females were determined as sexually mature animals by the presence of at least one corpus albicans or a
corpus luteum in both ovaries.
Sexual maturity in males was determined by histological examination of the testis. Tissues werecollected from the center of the heavier testis by cutting out a 5 mm square sample. After ﬁxation with
10% neutral buﬀered formalin solution, the tissues were sliced to a thickness of 3 µm. Subsequently
they were stained by Eosin Hematoxylin solution and examined under a light microscope with 400×
magniﬁcation scale. Taking account of the timing of samplings, which were conducted outside of thelikely breeding season, sexual maturity was determined by the presence of spermatids in addition tosperm. If there were neither sperm nor spermatids in the seminiferous tubules, size of the open lumen(minor axis) in the seminiferous tubules was considered, as in other studies for balaenopterids (North
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5.41
6.6
7.01

89/90-199
88/89-014
87/88-273

2.05
2.95
4.66

0.65
0.7
0.85
1
2.25
4.3
5.05
4.2
4
3.79
4.55
5.5
4.45

Male
Male
Male

FemaleFemaleFemaleFemaleFemaleFemaleFemaleFemaleFemaleFemaleFemaleFemaleFemale

Sex

Fish
Fish
Fish

—
Eu
Fish
—
Fish
Fish
Fish
Fish
Fish
—
Fish
Fish
Fish
1
2
1

0
1
1
0
1
1
1
1
1
0
2
1
1
—
—
—

—
S
—
—
—
—
—
—
—
—
—
—
—
F
F
M
F
M
F
M

0
0
0
0
0
1
1
1
1
1
1
1

Age

—
10
21

1
1
3
—
7
98.6
19
111.7
22
119
23
Lost***
10
83.8+**** 17
115
—
169.6
19
102.8
26

Length(cm)

FoetusType Volume Size no. Sex

Stomach contents**: Recorded according to BIWS (Bureau of International Whaling Statistics) format. Eu: Euphasiids.
**: Tp represents age at sexual maturity.
***: Left ovary and foetus lost by harpoon.
****: Ovaries and foetus partly damaged by harpoon.

3.53
3.83
4.29
4.45
5.94
6.61
6.82
6.99
7.02
7.04
7.07
7.17
7.47

Body Body
length weight
(m)
(t)

11

6
6

9
5
11
4
9

Tp

Age and at
its transition
phase (Tp**)

57
195
540

53
182
530

Left Right

Testis wt.
(g)

0
0
10
6
—

0
0
1
1
—

?**** 5+****
1
10
1
4
1
13

0
0

CL+CA

0
0

CL

no. ovulation,
corpus luteum(CL) and
albicans (CA)

Immature
MatureMatureImmature
Immature
Immature
Immature
Immature
MatureMatureMatureMatureMatureMatureMatureMatureSexual status
after present
examination

3.3
3.6
3.7

3.3
3.1
3
3.3
2.4
4.1
4.6
3.7
5.6
4
3.6
5.4
3.1

153
165
201

92
114
115
126
150
204
214
203
192
178
196
214
189

Blubberthickness at
Girth atlateral side umbilicus
below dorsal(cm)
ﬁn (cm)Primary biological information of the sixteen dwarf minke whales which were examined in the present study, listed by order of their body lengths.

92/93-108
90/91-002
89/90-002
88/89-005
88/89-070
90/91-014
90/91-118
88/89-013
88/89-227
92/93-107
89/90-215
92/93-330
90/91-012

SampleNo.

Table 1.

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Paciﬁc sei whale, Masaki, 1976; Antarctic minke whale, Kato, 1986; Inoue et al., 2014). The measurements on the minor axis of the respective seminiferous tubules using the ocular micrometer weretaken by randomly choosing 25 tubules from the respective samples.
Age was determined by counting growth layers on the bisected core surfaces in earplugs under astereoscopic microscope, as detailed by Lockyer (1984), under the assumption that one growth layer(a pair of pale and dark laminae) was deposited per year, as well as establishing the position of a transition phase in the earplug (Locker, 1972; Kato, 1985).
In addition, external measurements (76 points), were obtained according to the protocol of Kato etal. (1992), and comparison of sexually mature individuals was carried out among 10 dwarf minke, 704
Antarctic minke and 161 North Paciﬁc common minke whales (from the ICR data base for JARPA
and the Japanese Whale Research Program under Special Permit in the North Paciﬁc (JARPN).
Skeletal measurements were compared among dwarf, Antarctic minke and North Paciﬁc common
minke whales. Skeletal measurements (21 points) from eight dwarf minke whales and ﬁve Antarctic
minke whales were made based on the protocol of Omura (1975). For North Paciﬁc common minke
whales, skeletal measurements from Nakamura (2012), which followed the same principal method of
Omura (1975), were used.
To compare biological aspects of the dwarf minke whales with other minke whale species andsub-species, published biological information with equivalent quality was used. Details are given in
the relevant sections.
Sighting information of sampled whales
While sighting information was available from 1987/88 onwards under the JARPA program, for thepresent study, only sightings of the dwarf minke whales sampled from 1987/88 to 1992/93 were used.
All dwarf minke whales sighted and recorded during the shipboard surveys were identiﬁed from theircharacteristic white shoulder/ﬂipper patches, which could be easily observed during closing mode surveys (also see Kato et al., in press).
Table 2.

Sighting information of the dwarf minke whales used in the present study.
Location

Year/Month/
Date sighted

SchoolID no.

Sightingtime

Schoolsize

Estimated
B.L. at sea

Sample no.

1988/3/23

5002

14.47

58

23

S

111

26

E

2

6.8, 6.0

87/88-273

1989/1/13
1989/1/17
1989/1/17
1989/2/4
1989/3/19

8014
5001
8003
5004
1001

14.24
10.27
11.42
8.43
8.13

55
62
62
60
61

22
4
7
38
54

S
S
S
S
S

178
177
177
175
177

10
28
2
7
55

E
E
E
E
E

1
1
1
1
1

5.5
6.2
6.1
5.0
6.0

88/89-005
88/89-013
88/89-014
88/89-070
88/89-227

1989/12/6
1990/1/12
1990/1/15

8004
1001
1002

17.24
7.4
9.41

55
61
60

59
30
59

S
S
S

97
128
116

17
6
6

E
E
E

1
1
1

5.0
6.0
8.3

89/90-002
89/90-199
89/90-215

1990/12/29
1991/1/3
1991/1/3
1991/1/26

1001
1001
5003
8001

6.16
8.13
11.5
9.08

65
61
60
60

4
9
40
34

S
S
S
S

178
175
176
146

12
21
34
49

E
W
W
E

1
1
1
1

4.5
7.0
8.5
7.5

90/91-002
90/91-012
90/91-014
90/91-118

1993/1/10
1993/1/11
1993/3/22

1004
8001
8003

18.00
15.02
15.28

60
60
61

51
31
49

S
S
S

167
166
143

42
5
16

E
E
E

1
1
1

6.5
3.0
6.5

92/93-107
92/93-108
92/93-330

Latitude

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Results
Sighting position of sampled whales
Table 2 indicates relevant sighting information regarding the dwarf minke whales sampled during
the present study.
Fig. 2 plots the 16 dwarf minke whales sampled based on locations of their sightings during the
JARPA surveys from 1987/88 to 1992/93, and by reproductive category. No speciﬁc diﬀerence inlocation between reproductive categories was observed. In the longitudinal sector, searched between
97°17′E and 173°33′W, dwarf minke whales occurred from 48°42′ to 65°04′S. Most animals (75%;n=12 animals) were seen around latitudes 60° to 62°S, but it should be noted that there was limited
sighting eﬀort north of 60°S. Therefore, this result does not necessarily mean they were rare north of
60°S. Rather, these records should be interpreted to represent the likely southern limit for dwarf minke whale distribution in summer. Within the area surveyed there were three regions of relatively highconcentration: 125°–128°E, 141°–146°E, and 177°–179°E at 60–62°S. These areas were located oﬀ theconcaved continental coastlines of Antarctica such as the Ross Sea.
In terms of segregation from Antarctic minke whales, it is noticeable that dwarf minke whales were
distributed in more northern waters than the Antarctic minke whales in summer (Fig. 1). Sightings ofAntarctic minke whales by JARPA surveys from the early 1990s to the present were distributed southof 60°S with their density much higher from 63°S to the ice edge zone (e.g., Hakamada et al., 2005).
Throughout the surveys of the IDCR/SOWER1 programmes, a total of 54 dwarf minke whales,
comprised of two pairs and 50 singletons, were sighted (Kato et al., in press). These sightings were
only 0.13% of the total number of Antarctic minke whale (B. bonaerensis) sightings (41,854 individuals) made during the same searching eﬀort.
Body size and growthAs summarized in Table 1, the 16 dwarf minke whales collected from 1987/88 to 1992/93 comprised three males and 13 females. The smallest (3.53 m) and largest (7.47 m) individuals were both
females. Of the three males, two were sexually mature and their mean body length was 6.81 m. Of theFig. 2. Sighting locations of the dwarf minke whales sampled during JARPA surveys from 1987/88 to 1992/93
and showing the approximate range of Antarctic minke whale in summer (hatched, with darker area indicating
higher sighting density). Immature male (○), mature male (●), immature female (□), mature female (■).
1
International Whaling Commission International Decade for Cetacean Research (IDCR), Southern Ocean Whale and Ecosystem Research (SOWER).

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MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALES

13 females, eight individuals were sexually mature with a mean body length of 7.02 m (SD: 0.249).
Of the 16 animals, the age was successfully determined for 13 (two males and 11 females). Resultant age readabilities were 0.67 (2/3) and 0.85 (11/13) for males and females, respectively. The mean
growth curve of the dwarf minke whales together with that of Antarctic minke whales (Zenitani etal., 1997) and North Paciﬁc common minke whales (Maeda, 2012) are shown in Fig. 3 for both sexes.
Female dwarf minke whales appeared to grow to 3.5–3.7 m at age one and then rapidly reach 6 m atage 10, with an asymptote at around 7.0 m (or slightly more) in body length at about age 20.
Fitting the von Bertalanﬀy growth model to the available data produced the following formula forfemale dwarf minke whales:

Lt = 7.16(1 − e( − 0.19 ( t+2.69)) )(1)

where Lt is body length in meters at age (t).
If the asymptotic length from the equation is taken as a proxy for the mean body length at physicalmaturity, then an interim value of 7.16 m for female dwarf minke whales is obtained. Allowing forpossible errors due to the characteristics of the growth formulae used here and the limitations of thedata (especially small sample size among older animals), a comparison with Antarctic minke whales(Zenitani et al., 1997; Bando et al., 2006) and North Paciﬁc common minke whales (Maeda, 2012)
was carried out using von Bertalanﬀy growth formulae as below:
Lt = 9.16(1 − e( − 0.23( t +2.13)) ) Antarctic minke whale – Female(2)

Lt = 8.61(1  e(  0.27 ( t + 2.00 )) ) Antarctic minke whale – Male(3)

Lt = 8.66(1  e(  0.11( t+ 7.60 )) ) North Pacific common minke whale – Female(4)

Lt = 7.49(1  e(  0.41( t + 0.90 )) ) North Pacific common minke whale – Male

(5)

From the above equations as well as from Fig. 3, it is concluded that dwarf minke whales are signiﬁcantly smaller in body length at least in females than both Antarctic minke whales and North Pacific common minke whales throughout all age classes. The mean asymptotic lengths estimated from thegrowth formulae above indicated that fully grown female dwarf minkes were about 2.0 m shorter than
Antarctic minke whales (Zenitani et al., 1997; Bando et al., 2006) and about 1.5 m shorter than North
Paciﬁc common minke whales (Maeda, 2012). Thus far, under the present analysis, those diﬀerenceswere statistically signiﬁcant (t-test; p<0.001).
Due to the small sample size in all age classes, it was not possible to estimate the mean asymptotic

Fig. 3. Plots of body length at age and growth curves of dwarf minke whales by sex (closed circle, dottedline), in comparison with mean growth curves (length at age) of Antarctic minke whales (solid line) from
Zenitani et al. (1997) and of North Paciﬁc common minke whales (broken line) from Maeda (2012). All the
resultant growth curves were ﬁtted by the von Bertalanﬀy growth formulae.
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length or the length at physical maturity of males under the present study.
Under such limitation of the data, an attempt was made to obtain the range of body length at physical maturity for males by using values from other minke whales. The ratios of asymptotic body lengthof males to those of females are 0.94 (8.61/9.16 m) and 0.86 (7.49/8.66 m) in the Antarctic minke
whales and the North Paciﬁc common minke whales, respectively. These ratios were applied to thedwarf minke whales using the value for females (7.16 m), and the values of 6.73 m and 6.16 m wereobtained from the Antarctic minke whales and the North Paciﬁc common minke whales, respectively.
It is considered inappropriate to narrow down these values further given the limitations of the data.
Thus, mean body length at physical maturity for males in the dwarf minke whales is likely to bearound 6.2–6.7 m.
Body length-weight relationship
Two male and 13 female dwarf minke whales were weighed both before and after ﬂensing(Table 3). Whole body weights before ﬂensing varied from 0.650 tons (3.53 m) to 5.50 tons (7.47 m).
For females, the relationship was examined by ﬁtting an exponential regression of whole-body weight
on body length, as follows:

W = 0.01235 L3.007 ( r = 0.9922, n = 13)(6)where W is whole-body weight in tons and L is body length in meters.
The slope of the regression provides an indication of the relative fatness of the animal shape. The
body weight-length relationship for female Antarctic minke whales (Fujise et al., unpublished), obtained through the same procedure as the present study using whole body weight during the feeding
season, was as follows:

W = 0.019304 L2.792 (r = 0.9741, n = 1,113)(7)

The coeﬃcient for the slope (2.792) was signiﬁcantly smaller than that for dwarf minke whales
Table 3. Body weights of dwarf minke whales by weighing their whole body before ﬂensing and in parts after
ﬂensing.
SampleNo.

Body Body
Foetuslength weight* Sex
number(m)(t)

Blubber**

Muscle**

(kg)

(%)

(kg)

(%) (kg) (%) (kg) (%) (kg) (%)

(kg)

(%)

92/93-108
90/91-002
89/90-002
88/89-005
88/89-070
90/91-014
90/91-118
88/89-013
88/89-227
92/93-107
89/90-215
92/93-330
90/91-012

3.53
3.83
4.29
4.45
5.94
6.61
6.82
6.99
7.02
7.04
7.07
7.17
7.47

0.65
0.70
0.85
1.00
2.25
4.30
5.05
4.20
4.00
3.79
4.55
5.50
4.45

F
F
F
F
F
F
F
F
F
F
F
F
F

146
174
212
225
401
967
1,054
950
984
834
975
1,149
957

26.3
25.7
25.8
21.2
19.1
23.0
21.7
21.9
24.9
22.5
22.0
21.3
21.9

234
333
391
599
1,264
2,350
2,816
2,505
2,278
2,142
2,452
3,073
2,378

42.4
49.3
47.4
56.6
60.2
55.9
58.0
57.8
57.7
57.8
55.2
56.9
54.4

552
676
823
1,057
2,098
4,201
4,857
4,331
3,948
3,705
4,442
5,397
4,368

100
100
100
100
100
100
100
100
100
100
100
100
100

89/90-199
88/89-014
87/88-273

5.41
6.60
7.01

2.05
2.95
—

M
M
M

22 1.1 1,952
47 1.6 2,922
26 0.5 4,684

100
100
100

None
None
None
None
None
1
1
1
Lost
1
1
1
1

Bone**

94
92
112
133
277
447
463
403
411
435
478
511
562

17.0
13.7
13.7
12.6
13.2
10.6
9.5
9.3
10.4
11.8
10.8
9.5
12.9

Viscera**

72
68
90
91
150
392
495
401
263
284
454
517
409

399 20.4 1,156 59.2 211 10.8 165
662 22.6 1,652 56.5 327 11.2 234
960 20.5 2,897 61.9 495 10.6 306

Other**

13.0
7 1.3
10.0
9 1.3
11.0 17 2.1
8.6 10 0.9
7.1
6 0.3
9.3 45 1.1
10.2 30 0.6
9.3 73 1.7
6.7 13 0.3
7.7 10 0.3
10.2 84 1.9
9.6 148 2.7
9.4 62 1.4
8.4
8.0
6.5

Total***: Whole body weighted using a large scale before ﬂensing.
**: Percentage ﬁgures are the proportions to the sums of all parts after ﬂensing.

100

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MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALES(3.007), which suggests that dwarf minke whales tended to be stockier than other minke whale types,
despite both being sampled at the peak of their feeding seasons. This is also endorsed by nature in Fig.
6, which indicates proportion to body length of the dwarf minke whales is higher than of other minkes
at the measurement point P17 of girth at umbilicus.
The proportion of the sum of parts to the whole-body weight before ﬂensing ranged from 0.851 to
1.0582 with a mean of 0.973, indicating an average of only 2.7% weight loss during ﬂensing. Muscle
occupies almost half or more of the sum of parts (mean: 54.58%), with the proportion being higher inthe larger animals, while the proportions of blubber (mean: 22.87%) and bone (mean: 11.92%) werehigher among the smaller animals.
Morphology
External appearance in terms of discriminating the dwarf minke whale from other species andsubspecies of minke whales
Previous authors have reported that dwarf minke whales have distinctive external characteristics,
primarily a white shoulder patch. This distinguishes dwarf minke whales from all other types of minke whales at sea (Best, 1985; Arnold et al., 1987, Kato and Fujise, 2000). Additional features havebeen described for dwarf minke whales such as the dark throat patch and a thorax blaze (Arnold etal., 2005).
From ﬁeld examinations during this study, the following three points by which dwarf minke whales
can be easily distinguished from other types of minke whales were identiﬁed (Fig. 4A and additional
images given in Fig. 4B):
Characteristic (a): A dark throat patch usually extends ventrally as a peninsula of pigmentation on

Fig. 4A. Lateral views of diﬀerent types of minke whales scaled down to the same size; upper: dwarf minke
whale (DWM); middle: North Paciﬁc common minke whale (NPM); bottom: Antarctic minke whale (ATM).
Alphabetical symbols in the upper picture correspond to the explanation of characteristics above.
2

It is unlikely that the value exceeds 1.0, which may be due to logistic errors during the measurement.

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Fig. 4B. Variation of shoulder/ﬂipper coloration on the body surface for 15 of the 16 dwarf minke whales
examined in the present study. No photography was taken of 90/91–118 (see also Table 2).

the ventral grooves restricted to the region between the ﬂipper insertion and the angle of the gape. In
the samples for the present study, this dark patch was symmetrically arranged on both sides.
Characteristic (b): Fig. 4B shows the variation in shoulder/ﬂipper pigmentation among the 16 specimens. Best (1985) reported that dwarf minke whales have an entire white patch on the shoulder/ﬂipper
regions. On the other hand, Arnold et al. (1987) found an elongated dark oval patch within it and hidden
when the ﬂipper is held against the body, which they called the “ﬂipper oval.” However, there is muchvariation in this pattern as illustrated in Fig. 4B. The ﬂipper ovals certainly existed in their approximate
position in all specimens, but the ‘arch like white bands’ surrounding the dorsal margin of the ﬂipper
oval were sometimes incomplete so that the white patch on the shoulder region was cut into two in all
but one case. Only one animal (90/91–118) had a complete white patch above the ﬂipper oval on theshoulder region. Unfortunately, no photograph was available in Fig. 4B for this animal.
Characteristic (c): The thorax blaze/patches were principally located above the white patch on the102

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ﬂippers, usually in a somewhat triangular shape. As in Fig. 4B, there were some variations in the pattern of connection between the ﬂipper oval and the thorax blaze/patches being totally connected or
separated by splashed pigmentations.
The present study conﬁrmed the three characteristics noted above as consistent keys to distinguishing dwarf minke whales from other minke whales (Fig. 4A). In addition, the present samples provided
some additional information on blowhole streaks, which Best (1985) reported in a small dwarf minke
whale (about 4 m) from South Africa but were not seen in any dwarf minke whales oﬀ Australia (Arnold et al., 1987, 2005). In the specimens examined in the present study, the blowhole streaks wereabsent or obscure. However, all of the six fetuses larger than 98.6 cm listed in Table 1 had very distinctive parallel streaks in the posterior region of the blowhole. This may indicate changes in coloration
with respect to age that is more distinct in younger stages, or possibly more visible in living animals
or when underwater (Arnold et al., 2005).
Baleen plate coloration
Fig. 5 (A and B) shows a typical baleen plate coloration of dwarf minke whales, which was sharedby all the specimens in the present study. As both Best (1985) and Arnold et al. (1987) noted, the outside view of the baleen plate series is two-tone, being creamy white anteriorly and dark gray or brown
posteriorly. The darker coloration in the posterior portion of the series is due to a thin dark outer border of the plates. As in Fig. 5(B), this baleen plate coloration is diﬀerent from the other minke whales.
The external view of the baleen plate series of Antarctic minke whales is predominantly black on theleft side and creamy white in 1/3 of the anterior portion and black in 2/3 of the posterior portion on theright side while it is usually entirely creamy white for North Paciﬁc common minke whales (though
there are rare cases where animals have plates with a thin dark outer border in the posterior parts ofthe series). Thus, it is evident that the dark outer border is much wider in Antarctic minke whales thanin dwarf minke whales (Best, 1985).
Kato et al. (1992) suggested that the occurrence of a dark outer border to the baleen had some
growth-speciﬁc nature in North Paciﬁc common minke whales, therefore the proportion of anterior
creamy white plates and posterior black outer margined plate in dwarf minke whales was examined.
According to similar statistics (Table 4), the length of the creamy white portion varied from 24 to
115 cm (mean: 67.29, SD: 21.15) and 28–94 cm (mean: 63.21, SD: 16.98) on right and left sides respectively, or 31–85% (mean 53, SD: 13) and 36–85% (mean: 50, SD: 12) of the total length of thebaleen plate series, respectively. The ratio of right side to the left side was 1.06 (SD: 0.13), thus thecreamy white portion of the right side was slightly longer than that of the left, but not signiﬁcantly so.
As to growth speciﬁc changes in proportion of the plates having black outer margin, the samples were
not clear enough for detecting such nature.
In summary, the external view of a baleen plate series of dwarf minke whales is mostly bilaterally
symmetrical in coloration with a creamy white anterior portion that extends for almost half of the en-

Fig. 5. A: Lateral view of left side of dwarf minke whale head showing baleen plates exposed in its slightly
opened mouth. B: Labial view of the baleen plate series removed from both sides of the upper jaw.
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Table 4. Baleen plate series of the dwarf minke whales having measured data, especially the proportion of baleenseries of the plate with creamy white coloured outer margin to the total length of baleen. See also Fig. 5B.
Baleen plate series, length (cm) at outer margin

Sample no.

Samplingdate

Body
length(cm)

Sex

87/88-273
88/89-005
88/89-013
88/89-014
88/89-070
88/89-227
89/90-002
89/90-199
89/90-215
90/91-002
90/91-012
90/91-014
92/93-118
92/93-107

1988/3/23
1989/1/13
1989/1/17
1989/1/17
1989/2/4
1989/3/19
1989/12/6
1990/1/12
1990/1/15
1990/12/29
1991/1/3
1991/1/3
1991/1/26
1993/1/10

701
445
699
66
594
702
429
541
707
383
747
661
682
704

Male
FemaleFemaleMale
FemaleFemaleFemaleMale
FemaleFemaleFemaleFemaleFemaleFemale% of Right sideof creamy
white margin
creamycreamyTotal
R (w/t)* Total
L (w/t)* R (w/t)/L (w/t)
white
white
Right side series

Left side series

145 7288 41
147 65
134 45
118 73148 7986 73
112 60152 8677 24
163 115142 83
139 65
135 61

0.50
0.47
0.44
0.34
0.62
0.53
0.85
0.54
0.57
0.31
0.71
0.58
0.47
0.45

142
89
148
130
118
148
86
112
152
78
166
141
139
135

72
37
78
48
71
71
73
59
76
28
94
70
51
57

0.51
0.42
0.53
0.37
0.60
0.48
0.85
0.53
0.50
0.36
0.57
0.50
0.37
0.42

0.98
1.12
0.84
0.91
1.03
1.11
1.00
1.02
1.13
0.87
1.25
1.18
1.27
1.07

Mean 67.29
S.D. 21.15

0.53
0.13

S.D.

63.21
16.98

0.50
0.12

1.06
0.13

*: Proportion of creamy white length per total length of baleen plate row in each side.

tire length of the baleen plates. With this characteristic, they diﬀer from both Antarctic minke whales(bilaterally asymmetric baleen coloration) and North Paciﬁc common minke whales (usually all
creamy white baleen). In comparison, dwarf minke whales have an intermediate coloration.
External body proportion
Prior to the statistical analyses, the general characteristics of the external body proportions of dwarf
minke whales were examined in comparison with Antarctic minke whales (n=507) and North Paciﬁc
common minke whales (n=91). Fig. 6 shows the body proportions (expressed as a percentage of the
body length from tip of snout to notch of tail ﬂukes) for dwarf minke whales, Antarctic minke whales
and North Paciﬁc common minke whales. The rostrum of the dwarf minke whale is elongated in a
V shape, typical of minke whales. On average the head (P19) comprised 22.90% (min. 21.20–max.
24.10) of the body length. The average length from the tip of snout to the center of the blowhole (P2)comprised 14.50% (12.80–15.60); to the center of the eye (P3) 17.60% (15.50–17.60); and to the external auditory meatus (P4) 22.70% (20.20–24.10) of the body length. The average length from the tipof snout to the posterior end of the ventral grooves (P6) comprised 51.00% (49.10–53.10), to the umbilicus (P7) 54.90% (53.10–56.00), the center of the genital aperture (P8) 71.00% (67.00–72.60), andto the anus (P9) 74.80% (73.80–75.70) of the body length.
The pectoral ﬁn is also an elongated oval shape with tapering tip typical of balaenopterids and its
length (P12, tip to anterior insertion) and breadth (P14) were 16.10% (15.00–17.50) and 4.10% (3.60–
4.30), respectively. The dorsal ﬁn is falcate with a tapering tip of which the height (P11) was 4.30%(3.30–4.30). The tail ﬂukes are leaf-like in shape with a rather straight posterior margin and tapering
tips at both ends, while their width (P16) was relatively broad at 28.10% (24.90–31.10) and depth(P15) was 7.00% (6.40–7.50).

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Fig. 6. Mean external measurements (P2–P20) of sexually mature dwarf (closed circle), Antarctic (open circle)
and North Paciﬁc minke whales (gray colored circle), expressed as respective proportion to the body length.
Abbreviations of respective measurement points correspond to the numbered locations in the illustration.

All the body proportion measurements in the anterior half of the body were highest for Antarctic
minke whales and lowest for North Paciﬁc common minke whales, with dwarf minke whales being
intermediate between the two but somewhat closer to Antarctic minke whales. On the other hand, therelative proportions of the appendages were remarkably close to each other among the three types ofminke whales. Those aspects are further examined by statistical analyses in the later section.
Skeletal features
Skeletal observations were taken from all 16 animals collected, but data from eight sexually mature
animals were to be the base for the present analyses especially on skull, to minimize possible growthdependent changes. Those observations were appropriately compared and veriﬁed with other type ofminke whales in some cases.
1. SkullFirstly, before the statistical analyses, general aspects of the skeleton are presented in this section.
See also details of the skeleton in Appendix 1.
Fig. 7 shows the dorsal view of the skull of a dwarf minke whale as compared to those of North
Paciﬁc common minke whales and Antarctic minke whales. The diagnostic diﬀerences in skull morCetacean Popul. Stud. (CPOPS), Full paper
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Fig. 7. Dorsal view of skulls by photographing (upper) and corresponding contour drawings (bottom) of thedwarf (a: 87/88-273), the North Paciﬁc (b: 08NPCK-M030) and the Antarctic minke whale (c: 93/94-AM287)
showing the principal diﬀerences in morphology among the three diﬀerent types of minke whales of whichwere fully grown animals. The attached bar on the photos is 1.0 m long with a 10 cm scale interval.

phology can be seen among them. As an example of the skeletal specimens, multidimensional viewsof the entire skeleton, including skull and other skeletal parts of a male dwarf minke whale of 7.10 m
in body length registered as specimen MTUM-DW273, are shown in Appendix 1. Details of the skull
measurements are given in Appendix 2.
The vertex of the skull is considered an important taxonomic trait. A distinct interparietal bone
was present in dwarf minke whales (Arnold et al., 1987; Kato and Fujise, 2000). This characteristic
has been identiﬁed in North Paciﬁc common minke whales and in Antarctic minke whales (Nakamura, 2012). Further, the presence of the interparietal in the vertex has also been identiﬁed in North
Atlantic minke whales (Fig. 8). In dwarf minke whales, the posterior end of the nasal bone and theposterior end of the premaxilla are more extended toward the vertex compared with those of North Paciﬁc common minke whales. As a result, the nasal bone of dwarf minke whales is more elongated thanin North Paciﬁc common minke whales, resulting in a signiﬁcantly larger ratio of the length of thenasal bone relative to the anterior width of the nasal bone. In dwarf minke whales, proportional lengthof maxilla and premaxilla to the skull were signiﬁcantly larger than those in North Paciﬁc common
minke whales. On the other hand, the width of the orbit, width and height of the occipital condyle, andthe length and width of the palatine relative to the skull length were all smaller than in North Paciﬁc
common minke whales.
In terms of absolute measurement values, the maximum length and maximum width of the tympanic bullae of dwarf minke whales (7.9±0.3 cm and 6.1±0.2 cm, respectively) were approximately 10%
smaller than in North Paciﬁc common minke whales (9.0±0.4 cm and 6.9±0.3 cm, respectively) andAntarctic minke whales (9.2±0.6 cm and 7.1±0.3 cm, respectively), whereas their maximum width
was close to North Atlantic common minke whales (8.2±0.2 cm).

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Fig. 8. Morphological comparison of the vertex region on the skulls among dwarf, North Paciﬁc, North Atlantic common minke whales and the Antarctic minke whales. Abbreviations represent: Fr, frontal; Int, interparietal; Ma, ascending process of maxilla; Na, nasal; Pa, parietal; Pm, premaxilla.

Fig. 9. Lateral view of mounted complete skeleton of the dwarf minke whale (museum specimen No. MTUM
DW273; ﬁeld sample ID No. 87/88-273). The specimen was mounted under supervision by Kato and is displayed at the Museum of Marine Science, Tokyo University of Marine Science and Technology, Tokyo.

An entire lateral view of the dwarf minke whale skeleton (87/88-273) is shown in Fig. 9.
2. Vertebral number
The total number of vertebrae in the dwarf minke whales examined ranged from 47 to 50 with amean of 48.6 (SD: 0.9). The ranges were 47–51 with a mean of 49 (SD: 0.9) and 47–51 with a meanof 48.8 (SD: 0.80) in Antarctic minke whales and North Paciﬁc common minke whales, respectively.
Thus, the total number of vertebrae is virtually identical in all three minke whale species or sub-species(Table 5).
The vertebral formula for the dwarf minke whale was C7＋D10–11＋L11–14＋Ca18–20=47–50,
and for the mean values C7＋D10.6＋L11.7＋Ca19.2=48.6 (SD: 0.9). Again, this formation is thesame, or within the known range, to those of other minke whale species and sub-species.

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Table 5. Mean and range of number of vertebrae in each section of the vertebral colum by diﬀerent type ofminke whales.
Dwarf (n=16)

Antarctic (n=42)

North Paciﬁc (n=200) North Atlantic (n=1)

Cervical (C)
Mean
SD
Range

7
0
7

7
0
7

7
0
7

7
0
7

Dorsal (D)
Mean
SD
Range

10.6
0.5
10–11

10.7
0.5
10–12

10.5
0.5
10–11

11
0
11

Lumbar (L)
Mean
SD
Range

11.7
0.9
11–14

11.8
0.8
10–14

12.1
0.6
11–13

12
0
12

Caudal (Ca)
Mean
SD
Range

19.2
0.8
18–20

19.4
0.9
17–22

19.3
0.8
17–23

18
0
18

Total
Mean
SD
Range

48.6
0.9
47–50

49.0
0.9
47–51

48.8
0.8
47–51

48
0
48

3. Number of ribs
For the dwarf minke whales examined, the ribs are relatively thin and broad, and their numbers are
10–11 on each side, with the mean number of ribs being identical on each side as 10.7 (SD: 0.48).
These are slightly fewer than in the Antarctic minke whales (10–12, mean 11.1 (SD: 0.45)) and North
Paciﬁc common minke whale (10–12, mean 10.8 (SD: 0.4)), but not signiﬁcantly so. No ﬂoating rib
was found among the present specimens of dwarf minke whales.
4. Shape of sternum
Three types of sternum shape are observed in species and sub-species of minke whales: Y-shape(looks like a ginkgo leaf), T-shape and an intermediate shape (Fig. 10). The T-shape sternum is common among dwarf minke whales, Antarctic minke whales and North Paciﬁc common minke whales;
the manubrium parts were rather larger in the North Paciﬁc common minke whales. The Y-shape wasonly conﬁrmed in dwarf minke whales with the presence of a hole in the center of the sternum in somewhales. The Y-shape sternum is likely to be rare among balaenopterids and is possibly exhibited onlyin dwarf minke whales and must be closely related to the shape of the associated ribs. This characteristic may suggest some diﬀerences in feeding behavior, but more samples and further examinations
are required to conﬁrm this.
Life history parameters
Females
1. Reproductive status
While ovaries were unfortunately lost from the three females, six of the 13 females of dwarf minke whales were ﬁrstly conﬁrmed to be sexually mature and four were conﬁrmed as immature based

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Fig. 10. Variations in shape of the sternum among dwarf, Antarctic and North Paciﬁc common minke whales
based on contours of the actual sternums in each type of minke whale.

on gonad examination. Of the remaining three females one (88/89-013) was to be mature because of
having a fetus, another (88/89-227) was thought to be mature given its size (7.02 m) and age (10 years
old) as well as the presence of a transition phase as a mark of attainment of sexual maturity in the earplug, and the third (89/90-002) likely to be immature from its size (4.29 m) and age (3 years old), assummarized in Table 1. Resultant sexual status of the present samples was ﬁve sexually immature versus eight mature. All sexually mature females excepting one missing the uterine horns were conﬁrmed
to be pregnant, apparently indicating a 100% pregnancy rate. This ﬁgure should be, however, treatedwith caution because of the small sample size and possible segregation or timings of migration associated with reproduction.
The transition phase in the earplug was used as an indicator of age at sexual maturity while an annual rate of growth layer deposition was assumed (Lockyer, 1972; Kato, 1982). The mean annual ovulation rate after attainment of sexual maturity was estimated as follows:
no. corpora /(total age – transition phase)(8)

Values from four females having both transition phase and number of corpora ranged from 0.31 to
1.00 with a mean of 0.58, which are understood to be annual ovulation rate leading to maximum value of annual pregnancy rate. This result suggests that the apparent 100% pregnancy rate might be toohigh as an annua1 pregnancy rate (true pregnancy rate) and this high value was possibly due to reproductive segregation in relation to latitude, i.e., pregnant females migrate further south as in the case of
Antarctic minke whales (Masaki, 1979; Kato, 1982).
None of the mature females was lactating, but possible milk remnants consisting of transparent yellowish liquid were found in the mammary gland of one female (sample ID number: 92/93-107), suggesting this animal was sampled just after weaning her calf.
2. Fetus and breeding season
The sex ratio in the fetus samples was 3 males to 4 females, and the mean litter size was 1.0 (n=7).
The lengths of the fetuses were relatively similar, ranging from 98.6 to 119 cm with one at 169.6 cm(Table 6).
To investigate the timing and duration of the breeding season, conception dates were estimated byback-calculating from fetus length and date of capture, and applying the fetal growth rate formula for
Antarctic minke whales (Kato and Miyashita, 1991; Kato, 1995), as follows:t = 1.622 L0.892 + 74

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Table 6. Estimated conception date for the pregnant dwarf minke whales based on back-calculating by thefetal growth curve estimated by Kato (1995).
SeasonSpecimen no.

Date

Fetal length (cm)

90/91
90/91
92/93
89/90
88/89
90/91
92/93

012
014
107
215
013
118
330

3 Jan, 1991
3 Jan, 1991
10 Jan, 1993
15 Jan, 1990
17 Jan, 1989
26 Jan, 1991
22 Mar, 1993

102.8
98.6
84.0
115.0
119.0
111.7
169.6

Days after concept. Estimated concept. date*
175
171
158
186
189
183
232

13 Jul, 1990
17 Jul, 1990
6 Aug, 1992
14 Jul, 1989
13 Jul, 1988
28 Jul, 1990
3 Aug, 1992*: Mean=22 July.

where t is time (days) passed since conception and L is fetal body length in cm (Table 6).
Estimated conception dates were concentrated in a very narrow band from the middle of July to early August, that is, over a 25-day period. Thus, provided that southbound migration is not dependent on
reproductive segregation, even with the small sample size, it appears that the breeding season of thedwarf minke whale likely occurs over a few weeks in mid-winter with a peak in middle to late July.
This contrasts with the case of Antarctic minke whales where the breeding season extends over six
months with a weak peak in September/October (Kato, 1995).
3. Body Length and age at sexual maturity
With the present small sample size, it was diﬃcult to estimate lengths or ages at sexual maturity
with accuracy, especially for males.
For females, the smallest mature individual was 6.61 m and the largest immature individual was
5.94 m in length (Table 1), from which body length at sexual maturity is likely to be around these values or around 6.0–6.5 m. In a separate study, Kato (1987) examined the density dependent nature of
temporal changes for parameters related to sexual maturity in Antarctic minke whales and concluded
that the length at sexual maturity remained constant over time, while age at sexual maturity declinedwith density dependence. Thus, length at sexual maturity is a reliable threshold parameter for speciesor subspecies-speciﬁc sexual maturity. For other minke whales, estimates are:
North Paciﬁc common minke whales, female, 7.1 m (Kato, 1992),
North Atlantic common minke whales, female, 7.1–7.5 m (Jonsgard, 1951; Christensen, 1981;
Larsen and Kaple, 1982),
Antarctic minke whales, female, 8.1 m (Best, 1982; Kato, 1982; Zenitani et al., 1997; Bando etal., 2006).
In females, values for dwarf minke whales were much smaller (approximately 1.0–2.0 m smaller)
than the those for Antarctic and North Paciﬁc common minke whales.
The age of the youngest sexually mature female was 10 years and that of the oldest immature female was 7 years. Therefore, their average age at sexual maturity is likely in the range of 7–10 years(Table 1). This result is consistent with the age at sexual maturity estimated from the transition phase(Table 1), which was 4–11 years with a mean of 7.14 years (SD: 1.05).
4. Maximum life span
The oldest whale in the sample was a 26-year-old female (Table 1). This is most likely to be anunder-estimate of longevity due to the small sample size. This parameter can be estimated using theequation of Ohsumi (1979) which was derived from ﬁtting both baleen and toothed whales as below:

T = 31.277e0.05480 L

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MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALES

where T is maximum life span in years and L is body length at physical maturity in meters.
The above equation was applied to the estimated length at physical maturity (asymptotic length forfemales, 7.16 m) in the present study to estimate the approximate value of the maximum life span. The
result was 47 years. This is not so diﬀerent from those of other minke whale species and sub-species
derived from the same equation, e.g., 50 years for the Antarctic minke whale and 48 years for the
North Paciﬁc common minke whale. It is emphasized here that this is an interim value.
Males
It was diﬃcult to estimate any life history parameters in males because of the limited number of
specimens (Table 1). It was considered that the 5.41 m dwarf minke whale with testes weighing 53
and 57 g was an immature animal. The other two whales, a 7.01 m male (age 21) with testes weighing
530 and 540 g (hereafter 87/88–273) and a 6.6 m male (age 10) with testes of 182 and 195 g (hereafter
88/89-014) were presumed to be mature animals. For these two cases, additional analyses based on
histological examinations of the testes were conducted.
Histological sections for those testes are shown in Fig. 11. It was conﬁrmed that numerous spermatocytes were present in most of the seminiferous tubules of both males, but no sperm was present
in both males. The reason why there were no sperm among almost all of the seminiferous tubules is
not a surprising event even for fully sexually mature males. It is thought to be due to timing of thesamplings of the testes (January to March which did not overlap with the likely breeding season in
July–August inferred from conception timing calculated backward from the fetus frequencies in theabove section.
However, it was further noted that some spermatids existed in the seminiferous tubules of the larger male. Some examples of these are shown by the arrows in Fig. 11(B). This suggests the male wasFig. 11. Histological section images of the seminiferous tubules for the males examined. Bars in all three images represent 100 μm. A: large male (87/88-273), body length 7.01 m and age 21 years. B: magniﬁed view of
the 87/88-273 seminiferous tubules indicating spermatids with arrows. C: the second large male (88/89-014)
whose body length was 6.60 m and age 6 years.
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111

KATO, FUJISE, NAKAMURA, HAKAMADA, PASTENE AND BESTin a somewhat sexually active status even if out of the main breeding season. Thus, the larger male
(87/88-273) was deﬁnitely a mature animal. For the second larger male (88/89-014), spermatids could
not be conﬁrmed in any of its seminiferous tubules during the present microscopic observation.
Another measure of male sexual maturity was the size of the seminiferous tubules. Masaki (1976)
examined the diameter (minor axis) of seminiferous tubules in sei whales and found signiﬁcant correlation in relation to sexual maturity. Kato (1986) also found a similar relationship between the diameter and sexual maturity in Antarctic minke whales. The threshold value for sexual maturity was
mostly 100 μm. Inoue et al. (2018) examined the minor axis of the seminiferous tubules in North
Paciﬁc common minke whales and found that over 100 μm would be enough to determine sexual
maturity even when the samples were collected in the non-breeding season. According to the present
measurement of seminiferous tubules, those were 177.6 μm (n=25, SD: 29.49) and 124.4 μm (n=25,
SD: 13.71) for the larger male (87/88-273) and the second larger male (88/89-014) respectively. They
were wider than the threshold value of 100 μm of sexual maturity in other minke whale types even in
non-breeding season. Another measure for sexual maturity in males is the presence of the open lumen
within the respective seminiferous tubules. Masaki (1976) reported that the presence of the open lumen could be used as a criterion for sexual maturity in North Paciﬁc sei whales. In our analyses, asevident in Fig. 11(B), the open lumen can be seen in the majority of the seminiferous tubules for thetwo males.
From the above examinations, it can be conﬁrmed that the two large males (87/88-273, 88/89-014)
were sexually mature.
Food and feeding habits
The stomach contents of 16 dwarf minke whales were examined. 13 individuals contained food,
while the remainder were empty or contained only traces of food (Table 7).
Table 7. Stomach contents, weights and prey species eaten by dwarf minke whales in relation to sampling
location and time.
Location
Sample no.
87/88-273
88/89-005
88/89-013
88/89-014
88/89-070
88/89-227
89/90-002
89/90-199
89/90-215
90/91-002
90/91-012
90/91-014
90/91-118
92/93-107
92/93-108
92/93-330

Latitude
58
55
62
62
60
61
55
61
60
65
61
60
60
60
60
61

23
22
4
7
38
54
59
30
59
4
9
40
34
51
31
49

Longitude
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S

111
178
177
177
175
177
97
128
116
178
175
176
146
167
166
143

26
10
28
2
7
55
17
6
6
12
21
34
49
42
5
16

E
E
E
E
E
E
E
E
E
E
W
W
E
E
E
E

BIWS stomach record Content
Sampling
Prey species
weight in
Relativetime
identiﬁed
Item
Size
kg**
richness*
15.24
14.55
10.54
12.50
9.00
8.40
18.23
9.20
10.51
7.29
8.38
12.36
9.43
18.26
16.16
15.53

Fish
—
Fish
Fish
Fish
Fish
Fish
Fish
Fish
Eu
Fish
Fish
Fish
—
—
Fish

1
0
1
2
1
1
1
1
2
1
1
1
1
0
0
1

—
—
—
—
—
—
—
—
—
small
—
—
—
—
—
—

22.7
4.9
38.3
33.9
5.6
6.8
15.6
14.0
47.3
3.4
29.1
20.7
2.6
0.0
2.5
35.7

Myctophidae
Myctophidae
Myctophidae
Myctophidae
Myctophidae
Myctophidae
Myctophidae
Myctophidae
Euphausiids
Myctophidae
Myctophidae
Myctophidae

Kreﬀtichthys
anderssoni*: Relative richness by the BIWS format: 0, empty; 1, 25%; 2, 26–50%; 3, 51–75%; 4, 76–100%.
**: Combined value for the ﬁrst (fore) and second (main) stomachs.

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Stomach contents weighed between 2.6 kg and 47.3 kg (n=13) and the contents were partially digested. The species composition of the contents was mainly uniform within each stomach, thus thefood in the stomachs would have been representative of food organisms typically consumed by dwarf
minke whales.
Sampling locations were spread out latitudinally and longitudinally. Except for one sampled further
north from the Antarctic Convergence (with empty stomach), the majority of dwarf minke whales
were sampled in the vicinity of the Antarctic convergence (58–62°S). The species identiﬁcation offood organisms was referred to Mr. Hiromasa Furuhashi (Hokkaido University) a specialist of morphology and taxonomy of myctophid ﬁsh. Observations were made by placing the photophore patternover the ﬁsh body surface, a method which is widely used for species identiﬁcation of myctophid ﬁshes. The specialist inferred that there were remnants of myctophids, including Kreﬀtichthys anderssoni.
This clariﬁed that these dwarf minke whales fed mainly on small ﬁsh in the vicinity of the Antarctic
Convergence.
On the other hand, euphausiids (probably Euphausia superba) were found in the stomach of one
dwarf minke whale sampled at 65°S, which is further south of the Antarctic Convergence and where
dwarf minke whales are known not commonly occur (Kato et al., in press). Euphausiids such as E.
superba are known to be abundant in this region. Thus, it cannot be automatically determined that the
dwarf minke whale is a ﬁsh-feeder. It appears that the dwarf minke whale is more of an opportunistic
feeder and utilizes organisms which are available in abundance as food.
From the above, it can be summarized that dwarf minke whales feed mainly on small gregarious
ﬁsh species such as myctophids in their normal summer habitat, while dwarf minke whales in lower
latitudes oﬀ Brazil feed on euphausiids (Secchi et al., 2003) on an opportunistic basis.
Morphometric analysis
External body proportions
A total of 21 external measurements collected from 16 dwarf minke whales were compared statistically with those from 507 Antarctic minke whales and 91 North Paciﬁc common minke whales. All
measurements were log-transformed prior to the analysis.
The morphometric comparison for the three species and sub-species of minke whales was carriedout using three methods. The ﬁrst was the analysis of covariance (ANCOV). This assumes that theallometric relationship between body length (V01) and each of the remaining measurements holds
irrespective of age, while body length was used as a covariate to the other measurements (Jover, 1992;
Tanaka and Tarumi, 1986). Secondly, measurements showing no signiﬁcant regression with bodylength were also used for the multivariate analysis of variance (MANOVA) (Jover, 1992; Tanaka etal., 1990). The third method was the canonical discriminant analysis (DA) using component scoresfrom a principal component analysis (PCA) (Tanaka et al., 1984a, 1984b; Christensen et al., 1990).
To evaluate morphometric diﬀerences between males and females, 14 measurements of the dwarf
minke whales were analyzed using MANOVA, and a signiﬁcant diﬀerence (Wilks’ Λ=0.17026,
p<0.01) was detected. ANCOV was also carried out using 20 measurements (V02-V09, V11-V20 and
V31-V32) of the dwarf minke whales with body length as a covariate. The analysis indicated no sexual diﬀerence except for one characteristic (V08: from tip of snout to sexual aperture), which is known
to be sexually dimorphic.
To evaluate diﬀerences in external body proportion for dwarf minke whales, Antarctic minke
whales and North Paciﬁc common minke whales, MANOVA was carried out using the 14 measurements, and a signiﬁcant diﬀerence was detected (females: Wilks’ Λ=0.17026, p<0.01; males: Wilks’Λ=0.24714, p<0.01). ANCOV was conducted using 20 measurements from females. The analysis
revealed that 14 of the measurements were signiﬁcantly correlated with body length (Table 8) whilesome of the measurements diﬀered signiﬁcantly in that dwarf minke whales showed larger values in
the posterior parts of the body (V08 and V09), ﬂipper, and dorsal ﬁn (V11 and V12). Antarctic minke
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KATO, FUJISE, NAKAMURA, HAKAMADA, PASTENE AND BEST

Table 8. Results of ANCOV of body proportion with body length (V01) as a covariate for three types of minke whale: dwarf (DWM), Antarctic (ATM) and North Paciﬁc (NPM) minke whales. Upper, for female; bottom for male.
FemaleSample size

V02
V03
V04
V05
V06*
V07*
V08
V09
V11
V12
V13*
V14*
V15
V16
V17*
V18*
V19
V20
V31
V32

Estimated value at mean covariate with 95% CF

DWM

ATM

NPM

n

n

n

13
13
13
13
13
13
13
13
13
13
13
13
13
13
13
13
13
13
11
12

270
270
268
257
270
269
267
270
259
264
267
269
270
266
270
270
265
264
216
247

40
34
9
40
33
33
18
43
30
36
18
33
25
21
29
14
17

Result of
ANCOV
p<0.01p<0.01p<0.01p<0.01p<0.01p<0.01p<0.01
P<0.01p<0.01p<0.01p<0.01p<0.01p<0.05p<0.01p<0.01p<0.01p<0.01p<0.01p<0.01p<0.05

DWM

ATM

NPM

Mean+95%

Mean+95%

Mean+95%

4.732+0.035
4.940+0.031
5.188+0.023
5.856+0.018

4.761+0.007
5.024+0.006
5.258+0.005
5.866+0.004

4.665+0.020
4.847+0.018
5.113+0.027
5.795+0.010

6.345+0.009
6.369+0.008
3.461+0.067
4.850+0.051

6.328+0.002
6.357+0.002
3.362+0.014
4.732+0.011

6.311+0.007
6.348+0.005
3.402+0.042
4.681+0.029

4.038+0.043
5.405+0.039

4.052+0.009
5.384+0.008

4.013+0.029
5.440+0.029

5.192+0.022
4.607+0.025
5.128+0.027
5.120+0.035

5.243+0.005
4.635+0.005
5.169+0.006
5.164+0.007

5.084+0.022
4.460+0.023

Male
Sample size

V02
V03
V04
V05
V06
V07*
V08
V09
V11
V12
V13*
V14
V15
V16
V17
V18*
V19
V20
V31
V32

Estimated value at mean covariate with 95% CF
Result of
ANCOV

DWM

ATM

NPM

n

n

n

3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3

236
235
233
229
237
237
237
237
229
231
232
235
237
236
237
237
236
233
199
218

48
41
15
45
36
36
30
48
40
41
9
41
40
33

p<0.0144
19
20

p<0.01p<0.01p<0.01p<0.01p<0.01p<0.01p<0.01p<0.01p<0.01p<0.01p<0.05p<0.01p<0.01p<0.01

DWM

ATM

NPM

Mean+95%

Mean+95%

Mean+95%

4.723+0.082
4.931+0.055
5.170+0.042
5.837+0.043
5.969+0.041

4.725+0.009
4.986+0.006
5.220+0.005
5.832+0.005
5.955+0.005

4.654+0.021
4.859+0.015
5.072+0.021
5.758+0.012
5.857+0.012

6.266+0.019
6.352+0.016
3.525+0.134
4.849+0.078

6.253+0.002
6.344+0.002
3.370+0.015
4.728+0.009

6.255+0.006
6.335+0.004
3.411+0.038
4.774+0.022

3.450+0.063
3.973+0.075
5.382+0.068
5.327+0.066

3.330+0.007
4.012+0.008
5.365+0.008
5.334+0.007

3.360+0.018
3.994+0.022
5.412+0.021

5.156+0.041
4.572+0.048
5.098+0.043
5.095+0.045

5.210+0.005
4.613+0.005
5.136+0.005
5.138+0.005

5.078+0.018
4.401+0.021*：As the results showed no correlation with body length as a covariate, a multivariated analysis of variance was adopted.

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whales showed larger values in measurements related to head proportion (V03, V04, V19, V31, V32).
North Paciﬁc common minke whales showed wider ﬂukes (V16). In spite of the small sample size,
similar results were observed for males (Table 8).
The result of PCA showed that the ﬁrst Principal Component (PC1) is related to growth, with apositive value observed for all variables. The PC2 seems to be correlated to body appendages such as
ﬂipper, dorsal ﬁn, and ﬂukes. The values were positive for girth (V11) and ﬂukes (V15 and V16) while
negative values were observed in anterior parts of the body (from V02 to V09). Principal componentscores from PCA were examined using the canonical discriminant analysis (DA). Eigenvalues andeigenvectors derived from DA are shown in Table 9 by each canonical variate (CAN) with and without PC1. Plots of the ﬁrst two variates are shown in Fig. 12 for both sexes. For males, irrespective ofwhether PC1 was included or not, the three forms are visibly separate from each other. These results
indicate signiﬁcant diﬀerences in external morphology among the three types of minke whale.
Skull measurements
1. ANCOV analyses
Comparative skull morphology analyses were carried out based on 76 skull measurements from
15 dwarf minke whales, 33 Antarctic minke whales, 27 North Atlantic common minke whales and 29
North Paciﬁc common minke whales. The measurements were log-transformed prior to the analyses.
Because of the small sample size, the analysis was conducted by combining data of both sexes.
The same methods of analysis as those for external morphometry were conducted: MANOVA,ANCOV, PCA, and DA. In ANCOV, condylo-premaxillary length (SK01) was used as the covariate.
Table 10 shows the results of ANCOV. Fifty-nine measurements indicated a signiﬁcant regression
with the SK01. Of these, 46 were signiﬁcantly diﬀerent among the four species and sub-species ofminke whales. For ﬁve measurements (indicated by ** in Table 10) that had no signiﬁcant slope in the
regression line taking the SK01 as a covariate, MANOVA were applied instead of ANCOV, indicating that measurements related to rostrum (SK03, SK05, SK06, SK07, SK08, SK09, SK19, SK21) are
Table 9. Eigenvectors and eigenvalues derived from the canonical discriminant analysis using the PC scoresof PCA for each sex.
FemalePrincipal
Component
PC1
PC2
PC3
PC4
PC5
PC6
PC7
PC8
PC9
PC10
PC11
PC12
PC13
PC14
EigenvalueMale
PC1-PC14
CAN1

CAN2

PC2-PC14
CAN1

CAN2

−1.0647 1.0367
5.8434 −1.8680 4.5469
3.9497
14.1278 −0.6006 12.4648
5.69951.7539 6.3519 3.9619 −5.6118
4.9272 3.2111 5.6326 −1.3752−4.7839 −4.6171 −6.0319
2.8102−2.0632 0.9634 −1.4914 −1.6930
1.0791 −8.8291 −2.3480
9.071915.2995 3.0035 14.8688
2.573216.0063 28.5834 25.1179 −22.3201
14.2007 13.2371 17.7122 −7.9283
11.7966 21.5350 18.7129 −16.8394−13.6419 35.3312 1.0133 −39.6776−12.6909 15.0742 −5.6906 −19.3782
2.08100.90491.6351

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Principal
Component
PC1
PC2
PC3
PC4
PC5
PC6
PC7
PC8
PC9
PC10
PC11
PC12
PC13
PC14

0.5091 Eigenvalue

PC1-PC14
CAN1

CAN2

PC2-PC14
CAN1

CAN2

1.2805 −0.7460−5.8619
1.87795.41622.5298−13.4996 −1.0185 12.7377
0.18220.7162 −6.3630 −0.3579 −6.7861
5.3022 −2.4817 −4.8601 −3.1148
8.53200.8708 −8.0618
0.1251−2.2883
0.1613
2.14210.38360.83909.7660 −1.2719 10.2354−19.5342 −4.2379 18.5691 −2.6552−13.2718 −18.5866 13.3946 −18.3927−2.2114 14.2976
1.3674 15.3041
18.7030
4.3906 −17.7983
2.892912.6217 −30.3189 −10.3333 −33.1692−14.0194 −2.3797 −13.3009 −1.2024
2.46710.16711.75340.1430115

KATO, FUJISE, NAKAMURA, HAKAMADA, PASTENE AND BEST

Fig. 12. Scatter plots of scores on the ﬁrst and second canonical variates derived from external body proportions of dwarf minke whales (DWM), Antarctic minke whales (ATM) and North Paciﬁc common minke
whales (NPM), for females (upper) and males (lower).

smaller in Antarctic minke whales, i.e., Antarctic minke whales seem to possess a relatively shorterand narrower rostrum, and a larger mouth cavity. The analysis also shows that Antarctic minke whales
have a somewhat larger occipital portion of skull (SK30, SK32, and SK63).
From the results of PCA, eigenvalues and eigenvectors were calculated using DA for each canonical covariate CAN (Table 11) with and without PC1. Plots of the ﬁrst two CANs are shown in Fig.
13. Irrespective of whether PC1 was included or not, skull morphology diﬀered among dwarf minke
whales, Antarctic minke whales and North Paciﬁc common minke whales.
CLUSTER analyses for skull morphology
Although the following analysis is not necessarily the most eﬀective approach to advance the investigation on diﬀerences in skull morphology among taxa, cluster type analyses were carried out using
skull data of sexually mature whales, comprising eight dwarf minke whales (present study), 14 North
Atlantic common minke whales (present study and from Tomilin (1967)), ﬁve Antarctic minke whales(from Nakamura, 2012), and 47 North Paciﬁc common minke whales (from Nakamura, 2012).
In earlier analyses, statistical diﬀerences were identiﬁed in 29 of 44 proportions among minke
whale taxa. Furthermore, reliable measurements, which are potentially less subject to technical measuring error, were extracted. These included (1) CBL (condylobasal length), (2) length of tympanic
bulla, (3) pre-maxilla length as proportion of CBL, (4) maxillary length as proportion of CBL, (5)mandible length along its outer margin as proportion of CBL, (6) occipital length as proportion of
CBL.
Among the six variables chosen, (3), (4) and (5) had growth dependent changes in relative values.
For this comparison, only the data obtained from sexually mature animals or those from animals witha CBL >145 cm, which were known to be independent of growth dependent changes, were used. The
values of the respective variants are given in Appendix 2.
In the next step to evaluate degree of similarity among the diﬀerent taxa, the parameter S was esti-

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Table 10. Results of ANCOV of skull measurements with skull length (SK01) as a covariate for minke whales infour types: dwarf form (DWM), North Atlantic (NA), North Paciﬁc (NPM) and Antarctic (ATM) minke whales.
Sample size
Item

SK02
SK03
SK04
SK05
SK06
SK07
SK08
SK09
SK10
SK11
SK12
SK13
SK14*
SK15*
SK16*
SK17*
SK18
SK19
SK20*
SK21
SK22
SK23*
SK24
SK25
SK26*
SK27
SK28*
SK29*
SK30
SK31
SK32
SK33
SK34*
SK35
SK36**
SK37**
SK38**
SK39**
SK40**
SK41
SK42
SK43
SK44*
SK45
SK46
SK47
SK48
SK49*
SK50*
SK51*
SK52
SK53
SK54
SK55
SK56*

Estimated value at mean covariate with SE

DWM

NA

NPM

ATM

n

n

n

n

15
13
13
12
12
13
13
14
15
12
12
15
13
15
14
15
14
15
15
14
13
13
14
13
13
13
14
14
14
13
15
14
14
11
11
10
10
10
14
12
14
14
14
14
13
13
14
14
13
13
14
13
13
12
15

5
8
1
5
2
1
1
1
7
1
1
4
27
1
5
9
5
11
11
—
—
8
3
—
5
5
3
—
—
3
4
—
—
1
1
1
1
1
6
2
—
—
2
—
—

29
25
26
25
24
27
27
29
29
23
23
28
28
26
26
28
25
28
28
25
11
25
24
20
27
28
27
28
28
28
27
28
28
20
22
20
19
19
28
23
26
24
26
25
24
24
28
28
28
21
29
25
26
21
29

32
31
31
28
26
25
25
28
29
25
24
32
29
30
29
32
29
33
32
25
27
28
28
24
32
32
31
30
30
31
29
30
28
26
26
26
26
26
27
28
26
24
25
22
23
24
26
26
30
26
27
24
30
27
30

21
21
3
3
2
2
4
4
2

Result of
ANCOVCetacean Popul. Stud. (CPOPS), Full paper
Vol. 3, 2021, 93–128

DWM

NA

NPM

ATM

Mean+SE

Mean+SE

Mean+SE

Mean+SE

0.450
0.000
0.000
0.000
0.000
0.000
0.000
0.000

4.715+0.009
4.845+0.008
4.857+0.008
4.802+0.008
4.804+0.080
4.851+0.009
4.857+0.009
4.872+0.008

4.703+0.014
4.845+0.009
4.835+0.026
4.818+0.012
4.814+0.019
4.876+0.027
4.891+0.026
4.908+0.024

4.700+0.006
4.831+0.005
4.842+0.006
4.793+0.005
4.795+0.005
4.841+0.006
4.844+0.006
4.865+0.005

4.696+0.007
4.785+0.006
4.797+0.006
4.748+0.006
4.749+0.007
4.799+0.007
4.796+0.007
4.810+0.006

0.048
0.000
0.041

2.098+0.047
2.152+0.043
4.204+0.017

2.370+0.135
2.551+0.122
4.163+0.029

2.204+0.032
2.236+0.028
4.233+0.012

2.127+0.037
2.079+0.034
4.194+0.013

0.045
0.000

4.432+0.028
4.110+0.017

4.439+0.038
4.033+0.017

4.412+0.019
4.052+0.011

4.333+0.022
3.975+0.013

0.000
0.527

2.727+0.068
2.211+0.055

2.838+0.044
2.284+0.054

2.271+0.056
2.235+0.040

0.967
0.244

2.728+0.030
0.991+0.150

2.750+0.054

2.731+0.020
0.987+0.107

2.743+0.023
0.678+0.122

0.000

2.815+0.028

3.025+0.042

2.851+0.018

2.917+0.021

0.000
0.009
0.000
0.000

2.328+0.019
2.834+0.051
3.695+0.017
2.085+0.026

2.679+0.101
3.842+0.030

2.421+0.013
2.650+0.033
3.763+0.012
2.148+0.018

2.479+0.015
2.633+0.039
3.830+0.014
1.913+0.021

0.000
0.000
0.000
0.000
0.000
0.004
0.001
0.000
0.000

2.096+0.019
1.793+0.017
2.040+0.018
1.808+0.016
1.808+0.016
3.316+0.070
2.595+0.039
4.967+0.005
4.926+0.005

2.239+0.014
1.945+0.012
2.220+0.013
1.952+0.011
1.952+0.011
3.325+0.049
2.581+0.026
4.946+0.003
4.908+0.003

2.200+0.015
1.965+0.011
2.235+0.011
1.973+0.010
1.973+0.010
3.475+0.050
2.767+0.029
4.966+0.004
4.927+0.004

0.000
0.000
0.000
0.159

4.927+0.006
4.637+0.010
4.640+0.010
3.692+0.069

3.525+0.058

4.900+0.004
4.571+0.006
4.582+0.006
3.658+0.046

4.919+0.005
4.640+0.008
4.650+0.008
3.667+0.061

0.000
0.000
0.010
0.010

4.696+0.008
4.702+0.008
4.991+0.006
4.994+0.005

4.698+0.018
4.711+0.016
5.006+0.009
5.010+0.007

4.655+0.005
4.653+0.005
4.978+0.004
4.980+0.003

4.712+0.007
4.706+0.006
4.990+0.004
4.991+0.004

2.181+0.051
1.758+0.057
2.140+0.057
1.705+0.049
1.705+0.049
3.056+0.106
2.736+0.078

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KATO, FUJISE, NAKAMURA, HAKAMADA, PASTENE AND BEST

Table 10. Results of ANCOV of skull measurements with skull length (SK01) as a covariate for minke whales infour types:
dwarf form (DWM), North Atlantic (NA), North Paciﬁc (NPM) and Antarctic (ATM) minke whales.
Table
10. Continued.
Sample size
Item

SK57
SK58
SK59
SK60
SK61
SK62
SK63
SK64
SK65
SK66
SK67
SK68
SK69
SK70
SK71
SK72
SK73
SK74
SK75
SK76

Estimated value at mean covariate with SE

DWM

NA

NPM

ATM

n

n

n

n

14
14
15
15
15
15
14
14
14
14
8
8
6
6
6
6
7
7
6
6

4
6
3
5
3
2
6
2
5
—
—
—
—
—
—
—
—
—
—

28
28
27
28
27
28
28
29
29
28
27
25
23
25
25
26
26
24
26
25

28
32
32
32
32
32
31
30
31
31
22
22
24
24
25
25
26
26
25
25

Result of
ANCOV
0.224
0.050
0.000
0.095
0.011
0.093
0.000
0.000
0.708
0.576
0.027
0.035
0.002
0.006
0.000
0.000
0.004
0.009
0.136
0.058

DWM

NA

NPM

ATM

Mean+SE

Mean+SE

Mean+SE

Mean+SE

2.871+0.029
3.028+0.027
5.150+0.008
5.147+0.013
5.111+0.007
5.107+0.010
3.103+0.010
3.103+0.010
2.802+0.017
2.793+0.018
2.589+0.020
2.586+0.021
2.750+0.045
2.759+0.037
2.186+0.037
2.177+0.031
3.044+0.015
3.051+0.016
0.931+0.034
0.928+0.033

2.788+0.036
2.894+0.032
5.143+0.009
5.120+0.015
5.091+0.008
5.076+0.012
3.195+0.012
3.184+0.012
2.828+0.021
2.819+0.021
2.481+0.028
2.482+0.029
2.927+0.050
2.890+0.043
2.031+0.043
2.036+0.037
2.946+0.018
2.960+0.019
1.052+0.042
1.071+0.040

2.899+0.044
3.018+0.040
5.179+0.011
5.164+0.019
5.125+0.010
5.111+0.015
3.129+0.015
3.131+0.015
2.821+0.026
2.829+0.026
2.571+0.038
2.551+0.040
2.506+0.084
2.573+0.071
1.870+0.072
1.883+0.061
3.039+0.032
3.057+0.033
0.957+0.076
0.952+0.075

3.032+0.070
5.215+0.015
5.238+0.040
5.148+0.015
5.168+0.031
3.170+0.037
3.117+0.021
2.770+0.062
2.810+0.040*: Parallel test indicated no signiﬁcance.
**: As the result showed no correlation with skull length as a covariate, a multivariated analysis of variance was adopted.

Table 11. Eigenvectors and eigenvalues derived from the canonical discriminant analysis using the PC scoresof PCA.
PC1-PC5

PC2-PC5

Principal
Component

CAN1

CAN2

CAN1

CAN2

PC1
PC2
PC3
PC4
PC5

−1.5129
1.1734−0.05170.60070.08590.41020.76070.8427−0.3278−0.3668

1.24130.59240.1062−0.18700.3346−0.6666
0.70680.5102

Eigenvalue

3.24170.78541.03650.3831

Fig. 13. Scatter plots of scores on the ﬁrst and second canonical variates derived from skull measurements ofdwarf (DWM), North Atlantic (NA), North Paciﬁc (NPM) and Antarctic minke whales (ATM).

118

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MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALES

Table 12. Estimated value of correction coeﬃcient r and degree of similarity S in the cluster analysis on theskull between diﬀerent types of minke whales.
Type

Estimated (r/S)
Antarctic

North Paciﬁc

Dwarf

North Atlantic

Antarctic
North Paciﬁc

0.99220.0078Dwarf

0.98330.01670.99830.0017

North Atlantic

0.98250.01750.99720.00280.99830.0017

Fig. 14. Dendrogram showing the degree of similarity among the minke whale clade based on cluster analyses
on the skull morphology. ANT, Antarctic minke whale; NPM, North Paciﬁc common minke whale; NA, North
Atlantic common minke whale; DWM, dwarf minke whale. S, see below.

mated as deﬁned below:

S =1 − r(11)where S represents the degree of similarity, r being the correlation coeﬃcient on the variants between
diﬀerent types of minke whales.
Table 12 gives the estimated values for correlation coeﬃcient and degree of similarity for each pairwise comparison. A dendrogram was produced through cluster analyses using the values from the groupaverage method. These represent the interrelationships in diﬀerent minke whale taxa by weighing thedegree of similarity (Fig. 14). From this dendrogram it was clear that the Antarctic minke whales weremost distant, and secondly, the North Paciﬁc common minke whales were relatively distant from theNorth Atlantic common minke whales and dwarf minke whales. In conclusion, in the present cluster
analysis, the dwarf minke whales were closest morphologically to the North Atlantic common minke
whales. This was also genetically supported by the previous analyses such as Pastene et al. (2007).

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Discussion
First of all, throughout this study, the scarcity of available samples has become an issue, however,as it is almost impossible to obtain further samples of the same quality, we had to proceed with theanalyses, bearing in mind this sample limitation. Thus, the shortage of an adequate number of samples
should be recognized as a potential problem in all analyses during this study.
There are currently many reports on the occurrence of dwarf minke whales from coastal waters
in low and middle latitudes in the Southern Hemisphere, mainly Brazil and Australia (Zerbini etal., 1996; Acevedo et al., 2006; Meirells et al., 2011, etc.). In higher latitudes, data on dwarf minke whales has only been from sightings (Kato and Fujise, 2000, Acevedo et al., 2011, Kato et al. inpress). Until the present study there was no information on the biology of dwarf minke whales in higher latitudes. Arnold et al. (1987) reported a considerable number of the dwarf minke whale strandings
and sporadic sightings in the austral winter. The 80% of sightings were in the waters oﬀ Queensland,
Australia, in June and July (Arnold, 1997), which would be consistent with the north-south seasonal
movements exhibited by other austral balaenopterids. However, there have also been mid-summer
strandings of dwarf minke whales on the southeast coast of Australia (Arnold et al., 1987; Zerbini etal., 1996; Kemper, pers. comm.) and sightings oﬀ Brazil (at 23°S) during the month of January (Hassel et al., 2003). Therefore, it is possible that migrations are dispersed seasonally but not undertaken
by all individuals.
The relative distributions of dwarf minke whales and Antarctic minke whales in winter are not wellknown, although dwarf minke whales were found closer inshore than Antarctic minke whales in thewaters oﬀ both Brazil as well as the east coast of South Africa (Best, 1985; Zerbini et al., 1996). Published information (Arnold, 1997; Arnold et al., 2005) suggested that a large proportion of dwarf minke whales remain in lower to mid-latitudes during summer, even though they can be found as far south
as the Antarctic Convergence. Kato et al. (in press) examined all of dwarf minke whale sightings
made during the 1994/95 to 2003/04 IDCR/SOWER cruises and reached almost the same conclusionas the present study in terms of sighting distribution. Further sighting information, combined with experiments such as photo-identiﬁcations, will provide a clearer understanding on their distributions andmovements.
The migration of dwarf minke whales as far south as the Antarctic Convergence in summer is latitudinally of a much wider range than generally expected, as dwarf minke whales are thought to prefercoastal zones in low and middle latitudes. However, this may not be unnatural when considered as an
adaptive radiation process of the minke whale clade.
In both hemispheres, minke whales are widely distributed from the ice edge to tropical waters whiledeveloping or dividing into closely related species or subspecies. In this interpretation, they might
further adapt this cline along the allopatric speciation. The minke whale is one of the most cosmopolitan groups and has a clear morphological cline from North Paciﬁc or North Atlantic common minke
whales to Antarctic minke whales. Dwarf minke whales may have evolved in an ecological niche
between Northern Hemisphere common minke whales and Antarctic minke whales. Inferring fromthis relationship, it can be said that the same interpretation is also true morphologically and perhaps
behaviorally for food and feeding habits. Those of the dwarf minke whales are somewhere between
North Paciﬁc or North Atlantic common minke whales and Antarctic minke whales. Both Best (1985)
and Arnold et al. (1987) indicated dwarf minke whales have distinct morphological features and they
bear a closer morphological resemblance to Northern Hemisphere common minke whales rather thanto Antarctic minke whales. The present study also identiﬁed these characteristics in-depth with a larger
sample size and the use of morphometric analyses.
Pastene et al. (2007) provided mtDNA sequence evidence for the separation of the two species, theAntarctic minke whale and the common minke whale, and at least three sub-species of the common
minke whale. They hypothesized that the two species diverged in the Southern Hemisphere less than120

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MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALES

5 million years ago, and that the current subspecies of the common minke whale diverged after the
Pliocene some 1.5 million years ago. Furthermore, Pastene et al. (2010) provided mtDNA sequenceevidence for the genetic separation of the dwarf minke whale in the Southern Hemisphere. The study
used samples from JARPA in the western South Paciﬁc sector of the Antarctic, Tonga and New Zealand (western South Paciﬁc: WSP), as well as from Brazil, Chilean Patagonia and Antarctic Peninsula(western South Atlantic: WSA). They found phylogenetic diﬀerences between dwarf minke whales in
the WSP and WSA, with dwarf minke whales from the WSA being closer to North Atlantic common
minke whales than to dwarf minke whales from the WSP. Glover et al. (2013) provided microsatellite
DNA evidence for the separation of the two species and three subspecies of the common minke whale.
These genetic analyses used the dwarf minke whale specimens from this study.
Nakamura et al., (2018) showed that there were clear morphological diﬀerences in the white patchof the ﬂipper between North Paciﬁc and North Atlantic common minke whales, which have been recently recognized as two distinctively separate subspecies. Further, the length between the tip of ﬂipper to the proximal border of white patch relative to the total ﬂipper length was signiﬁcantly larger in
the North Atlantic (74.31%) as compared to the North Paciﬁc (63.62%) common minke whales. Also,
the mean angle between the proximal boundary line of the white patch and the longitudinal axis of theﬂipper was signiﬁcantly diﬀerent between the North Atlantic (70.05 degrees) and the North Paciﬁc(92.29 degrees) common minke whales. Therefore, a numerical comparison of the white patch on theﬂipper/shoulder should be conducted in the future for the three sub-species of common minke whales.
Morphometric analyses on both the body proportion and the skull revealed at least three types ofcommon minke whale clade can be distinguished. Also, the ﬂipper/shoulder portion is a consistent andreliable characteristic for distinguishing the three types. As examined by Nakamura et al. (2018), thewhite patch of the ﬂipper/shoulder portion is wider in the following order; dwarf minke whale>North
Atlantic common minke whale> North Paciﬁc common minke whale. This is an additional indicationthat the dwarf minke whale is closer to the North Atlantic common minke whale. While it is still inconclusive due to small sample size, the cluster analyses on body proportion and skull morphometry(Fig. 12) in the present study supports this hypothesis. Before reaching the ﬁnal conclusion on thetaxonomic status of dwarf minke whales, there are some outstanding issues to be pursued. Numericalcomparison of the white patch between the dwarf minke whale and the North Atlantic common minke
whale needs to be conducted. In addition, in light of the genetic diﬀerences suggested by several studies, morphological and morphometric comparative analyses among dwarf minke whales from diﬀerent
locations of the Southern Hemisphere should be carried out.
However, there is little doubt that the dwarf minke whales have diverged from other common minke
whales, at least at the subspecies level. Morphometric comparison in both external body and skull proportions in the present study provided reliable evidence to identify and conﬁrm the diﬀerences among
the minke whale clade. The separation of dwarf minke whales from other common minke whale
sub-species is further supported by genetic evidence. Based on such convincing evidence, dwarf minke whales from the Indo-Paciﬁc sector of the Antarctic examined in this study should be formally described as an independent sub-species or species from other common minke whales.
Acknowledgements

During the course of the present study, our co-author, the late Dr. Peter Barrington Best sadly passed away on 22 April
2015. The present study had been initiated by him. His initiative inspired our present study, and he agreed to be one of theco-authors of this study. Further, he undertook the supervision of senior author Kato during the present study and had previously co-authored with the latter (Kato et al., 2015). Also, the late Dr. Seiji Ohsumi, former Director General of the Instituteof Cetacean Research (ICR), sadly passed away on 2 November 2019. He greatly encouraged us to conduct the present study.
We would like to express our sincere gratitude for the work and involvement of these two remarkable scientists. May they
rest in peace. The late Dr. Peter W. Arnold (James Cook University at that time) and Dr. Catherin Kemper (South AustralianMuseum at that time) kindly provided information and great assistance to us regarding dwarf minke whales in the coastalzone of Australia.
We also wish to express our deep appreciation to the many researchers and crew during our study on board of Nisshin-

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KATO, FUJISE, NAKAMURA, HAKAMADA, PASTENE AND BEST
Maru No. 3 and Nisshin-Maru as well as to program leaders under the JARPA program from 1987/88 to 1992/93, especiallythe late Drs. Ikuo Ikeda and Fukuzo Nagasaki who always oﬀered generous support. The present study was technically supported by Drs. Ryoko Zenitani (ex-ICR scientist), Takeharu Bando (ICR), Hikari Maeda, Tomio Miyashita, Toshiya Kishiroand Hideyoshi Yoshida (National Research Institute of Far Seas Fisheries; NRIFSF). Mr. Hiromasa Furuhashi, Hokkaido
University (at that time) kindly identiﬁed prey species from the stomach contents. Dr. Satoko Inoue supported histologicalexamination on the testes collected from the male whales. Ms. Ritsuko Shige (ex-NRISFS staﬀ) and Ms. Yumi Hosone (exICR staﬀ) assisted with the drafting of ﬁgures and tables. Professor Kazumi Sakuramoto (TUMSAT) kindly took charge ofhandling the present paper for the CPOPS journal. Dr. Gabriel Gomez Diaz (CPOPS) coordinated adjusting style format of
the ﬁnal version of the manuscript, as well as English proofreading. Ms. Saemi Baba kindly took charge of English proofreading on the pre-ﬁnal version.
Finally, we wish to express our deep gratitude to Drs. Toshio Kasuya, Robert L. Brownell Jr. and Koichi Kaji who provided critical and highly insightful reviews.

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Received: January 31, 2021
Accepted: August 19, 2021
Published online: December 23, 2021

124

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MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALESAppendices
Appendix 1. Upper: Skull and mandible of the dwarf minke whale (MTUM-DW273); a) skull
dorsal view, b) skull ventral view, c) skull lateral view, d) mandibles dorsal view, e) skull frontal view,f) backward view. Bottom: other bones of the same skeleton; a) cervical, b) dorsal, c) lumber, d) caudal vertebrae, e) chevron, f, g) left and right ribs with lateral surface and h, i) coastal surface of rightand left scapula, j) sternum, k) pelvic bone, l) hyoid, m) humerus, radius, ulna and manus on the left
ﬂipper. Scale bars are 1.00 m size marked with 0.1 m intervals.

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125

126

Condylobasal length
Length of rostrum
Length of premaxillary (L)Length of premaxillary (R)Length of maxillary (L)Length of maxillary (R)Tip of premaxillary to tip of maxillary (L)Tip of premaxillary to tip of maxillary (R)Tip of premaxillary to nares, anterior
Tip of premaxillary to vertex
Tip of premaxillary to palatine, anterior (L)Tip of premaxillary to palatine, anterior (R)Tip of premaxillary to palatine, posterior (L)Tip of premaxillary to palatine, posterior (R)Tip of premaxillary to pterygoid process (L)Tip of premaxillary to pterygoid process (R)Tip of premaxilla to posterior edge of occipitalbone (L)Tip of premaxilla to posterior edge of occipitalbone (R)
Tip of premaxilla to posterior edge of temporalbone (L)Tip of premaxilla to posterior edge of temporalbone (R)
Breadth of maxillary, posterior edge
Breadth of premaxillary, posterior edge
Tip of premaxillary to anterior end of vomer,
medianLength of vomer
Breadth of rostrum at base
Breadth of premaxillary at base
Breadth of rostrum at middle
Breadth of premaxillary at middle
Greatest breadth of premaxillary
Breadth of cranium, maxillaries

Specimen ID
Body length (m)
Sex

106.1
102.8
103.2
11.9
1.9
13.3
76.6 131.3
34.5
50.7
10.8
15.4
19.7
30.7
7.9
12.7
13.9
20.2
49.5
76.0

169.4
164.2
164.8
19.0
3.0
21.2
122.4
55.1
17.3
31.4
12.6
22.2
79.1

14.2
3.4
17.7

171.2

168.7

166.1

165.7

163.4
106.0
119.4
121.3
114.3
114.8
8.4
9.8
106.2
126.5
102.3
105.2
137.4
139.2
146.3

63.5
74.7
75.1
73.4
73.5
2.8
3.1
68.3
77.5
62.3
62.5
84.2
84.2
90.2
90.0
106.4

159.7
101.4
119.3
120.0
117.2
117.3
4.5
4.9
109.0
123.7
99.5
99.8
134.5
134.5
144.0
143.8
170.0

cm

14.3
3.2
18.3

152.2

153.5

155.9

80.4 116.2
31.0
51.2
9.4
12.8
18.8
30.5
7.8
12.7
12.4
19.2
46.5
73.8

8.7
2.1
10.8

104.8

103.2

101.7

14.0
2.1
19.3

136.5

136.5

138.7

133.1
83.4
97.9
98.5
94.3
94.1
8.7
5.7
85.9
103.7
85.8
86.9
111.7
111.7
119.7
119.3
139.1

cm

cm

80.4
37.0
8.8
21.6
8.9
13.1
49.5

10.5
1.6
14.5

102.6

102.6

104.2

93.7
43.8
11.3
23.7
9.8
15.9
57.6

11.6
1.3
17.9

124.0

127.4

19.0
4.8
21.7

168.2

169.4

172.0

173.4

164.7
111.0
120.0
120.8
115.2
115.4
10.7
10.7
109.1
128.3
108.2
107.6
142.2
141.3
150.3

cm

cm

15.3
3.2
18.5

170.7

172.2

176.8

77.5 136.5
32.7
59.3
8.3
12.8
20.8
36.4
9.2
16.5
13.5
22.0
47.8
82.8

11.5
2.9
13.2

102.1

102.9

104.4

17.9
3.0
16.3

162.7

162.7

165.3

156.1
106.8
119.8
120.2
111.4
112.8
10.3
10.5
104.2
125.5
100.2
100.1
135.2
135.5
143.1
143.3
165.3

cm

80.8
37.3
8.5
22.3
9.9
14.6
51.6

11.5
1.9
10.4

104.2

104.2

105.9

68.4
76.7
77.0
71.4
72.3
6.6
6.7
66.8
80.4
64.2
64.1
86.6
86.8
91.7
91.8
105.9

%

92/93 3307.17
F

80.7 126.1
35.0
58.2
7.6
13.2
21.5
34.8
9.8
15.4
13.0
22.8
48.9
80.5

9.0
1.9
10.9

100.9

101.8

104.5

66.2
72.6
72.3
70.5
70.5
5.7
4.9
65.2
77.8
63.8
64.0
85.9
84.6
90.9
90.0
105.1

%

89/90 215
7.07
F

169.2
112.0
122.8
122.4
119.3
119.3
9.6
8.3
110.4
131.7
108.0
108.3
145.3
143.2
153.8
152.3
105.3 177.8
67.4
72.9
73.3
69.9
70.1
6.5
6.5
66.2
77.9
65.7
65.3
86.3
85.8
91.3

%

88/89 227
7.02
F

76.6 127.6
35.8
53.8
9.2
13.7
19.4
34.2
8.0
15.2
13.0
22.3
47.1
78.7

9.5
1.1
14.6

101.4

104.2

88.6

84.1

64.3

67.2
78.7

75.2

66.7

%

89/90 199
5.41
M

122.3
62.7
81.6
73.6
74.0
92.0
70.8
70.7
6.5
4.3
64.5
82.2
77.9
96.3
64.5
65.3
78.7
83.9
83.9 102.8
89.9
89.6 108.4
104.5

%

88/89 070
5.94
F

78.0 107.0
34.4
49.2
8.6
11.7
20.5
28.7
8.5
11.8
12.9
17.4
49.5
65.9

9.6
2.1
12.3

102.1

103.0

104.6

65.6
73.7
73.4
70.8
70.5
5.6
6.2
65.0
77.9
65.6
65.6
86.0
85.6
90.3
90.5
105.2

%

88/89 014
6.6
M

149.0
97.7
109.8
109.3
105.5
105.0
8.3
9.2
96.8
116.0
97.8
97.8
128.1
127.6
134.6
134.8
101.4 156.8
64.9
73.1
74.2
70.0
70.3
5.1
6.0
65.0
77.4
62.6
64.4
84.1
85.2
89.5

%

cm

cm

%

88/89 013
6.99
F

87/88 273
7.01
M

List of skeletal measurements by the standard measuring method for all dwarf minke whales examined in the present skeletal analysis.

Measurement points

Appendix 2.

78.9±1.86
34.7±2.1
8.9±0.97
20.6±1.21
8.7±0.83
13.3±0.7
48.8±1.62

10.3±1.24
1.9±0.52
12.5±1.65

102.7±1.34102.9±0.74

104.4±1.35

65.7±1.94
73.9±1.4474.3±1.44
71±1.1871.1±1.26
5.5±1.33
5.4±1.34
66±1.3178.2±0.98
64.1±1.33
64.5±185.3±1.16
85±1.0190.5±0.76
90.1±1.04
104.8±1.63

Mean±S.D. %KATO, FUJISE, NAKAMURA, HAKAMADA, PASTENE AND BEST

Cetacean Popul. Stud. (CPOPS), Full paper
Vol. 3, 2021, 93–128

Breadth of cranium, anterior edge of zygomatic
process
Breadth of cranium, middle of orbital foramen
Breadth of occipital bone
Breadth of cranium, middle of zygomatic
process
Length from upper ridge of foramen magnum tosuperior part of occipital bone
Greatest breadth of palatine
Length of palatine (L)Length of palatine (R)Breadth of palatine, posterior
Breadth across hamular processes of pterygoid
Length of orbit (L)Length of orbit (R)Height of cranium
Length of nasals
Breadth of nasal, posterior
Breadth of nasal at middle
Minimum breadth of parietal bones
Height of foramen magnum
Breadth of foramen magnum
Breadth across occipital condyles
Breadth of occipital condyle (L)Breadth of occipital condyle (R)Height of occipital condyle (L)Height of occipital condyle (R)Length of tympanic bulla (L)Minimum breadth of tympanic bulla (L)Greatest breadth of tympanic bulla (L)Thickness of tympanic bulla at middle (L)Skull height
Minimum width of the skull at squamous
temporalMeasurement points

Specimen ID
Body length (m)
Sex

55.8
50.2
43.5
55.9
25.3
15.5
23.0
23.2
15.8
8.1
10.6
10.3
9.3
0.7
2.8
11.6
4.0
5.1
10.6
4.3
4.3
6.8
7.0
5.2
3.0
3.8

89.1
80.1
69.5
89.3
40.4
24.8
36.8
37.1
25.3
12.9
17.0
16.5
14.9
1.1
4.4
18.5
6.4
8.2
17.0
6.8
6.9
10.9
11.1
8.3
4.8
6.1

14.3
22.9
22.1
14.0
7.8
9.2
9.8
30.6
10.0
1.2
3.5
10.0
3.6
4.8
10.2
4.3
4.3
6.0
6.1
5.0
3.1
3.9
30.6
10.6

50.0
17.4

24.7

47.4
38.7
50.2

51.7

23.3
37.4
36.1
22.8
12.7
15.0
16.0
50.0
16.3
2.0
5.8
16.4
5.9
7.8
16.7
7.0
7.0
9.8
10.0
8.2
5.1
6.3

40.4

77.5
63.3
82.1

84.5

%

cm

cm

%

88/89 013
6.99
F

87/88 273
7.01
M

23.8
32.3
32.3
23.1
11.7
16.5
15.5
45.1
14.5
1.3
4.9
15.3
7.3
6.0
15.7
6.2
6.5
10.1
10.0
7.9
4.9
6.1
4.3
45.1
15.8

36.4

72.3
59.3
79.4

80.8

cm

16.0
21.7
21.7
15.5
7.9
11.1
10.4
30.3
9.7
0.9
3.3
10.3
4.9
4.0
10.5
4.2
4.4
6.8
6.7
5.3
3.3
4.1
2.9
30.3
10.6

24.4

48.5
39.8
53.3

54.2

%

88/89 014
6.6
M

21.8
28.3
27.3
21.3
11.3
15.5
15.5
34.3
14.0
1.1
4.5
16.5
6.6
7.3
15.8
6.6
6.2
9.2
9.2
8.2
5.2
6.2
4.5
34.3
14.9

31.4

66.7
51.2
71.8

72.8

cm

16.4
21.3
20.5
16.0
8.5
11.6
11.6
25.8
10.5
0.8
3.4
12.4
5.0
5.5
11.9
5.0
4.7
6.9
6.9
6.2
3.9
4.7
3.4
25.8
11.2

23.6

50.1
38.5
53.9

54.7

%

88/89 070
5.94
F

18.5
26.6
27.0
21.7
11.6
14.5
14.0
37.2
10.8
0.8
3.3
12.8
6.3
7.4
13.3
5.3
5.3
8.6
8.4
7.3
4.5
5.7
3.8
37.2
13.6

27.7

58.6
49.4
64.6

64.7

cm

15.1
21.7
22.1
17.7
9.5
11.9
11.4
30.4
8.8
0.7
2.7
10.5
5.2
6.1
10.9
4.3
4.3
7.0
6.9
6.0
3.7
4.7
3.1
30.4
11.1

22.6

47.9
40.4
52.8

52.9

%

89/90 199
5.41
M

22.7
36.2
35.8
27.3
13.8
16.5
17.0
49.4
17.8
2.6
7.1
20.1
6.3
7.1
14.3
6.8
6.3
8.8
8.9
7.7
5.1
5.9
4.3
49.4
17.1

40.2

77.7
66.4
85.3

86.3

cm

13.8
22.0
21.7
16.6
8.4
10.0
10.3
30.0
10.8
1.6
4.3
12.2
3.8
4.3
8.7
4.1
3.8
5.3
5.4
4.7
3.1
3.6
2.6
30.0
10.4

24.4

47.2
40.3
51.8

52.4

%

88/89 227
7.02
F

15.7
22.3
21.5
16.4
8.5
9.8
9.5
30.4
11.1
0.7
3.8
11.5
3.7
3.8
9.9
4.0
3.8
5.9
5.9
4.9

2.5
30.4
8.7

4.2
51.5
14.8

25.5

49.1
37.0
52.3

54.1

%

26.5
37.8
36.4
27.7
14.4
16.5
16.0
51.5
18.7
1.2
6.5
19.4
6.3
6.5
16.8
6.7
6.5
10.0
10.0
8.3

43.2

83.0
62.6
88.5

91.5

cm

89/90 215
7.07
F

25.3
37.7
37.1
26.7
12.8
16.5
16.5
53.4
17.8
1.9
5.3
20.0
6.7
7.3
17.2
6.3
6.8
9.8
9.8
7.6
4.8
5.9
4.0
56.4
17.2

37.3

80.4
61.7
87.7

89.4

cm

16.2
24.2
23.8
17.1
8.2
10.6
10.6
34.2
11.4
1.2
3.4
12.8
4.3
4.7
11.0
4.0
4.4
6.3
6.3
4.9
3.1
3.8
2.6
36.1
11.0

23.9

51.5
39.5
56.2

57.3

%

92/93 330
7.17
F

Appendix 2. (Continued.)
List of skeletal measurements by the standard measuring method for all dwarf minke whales examined in the present skeletal analysis.

15.4±0.93
22.4±0.94
22.1±1.02
16.1±1.14
8.3±0.54
10.6±0.92
10.5±0.74
30.2±2.45
10.2±0.89
1±0.333.4±0.53
11.4±1.05
4.3±0.61
4.8±0.75
10.5±0.93
4.3±0.31
4.2±0.28
6.4±0.6
6.4±0.56
5.3±0.53
3.3±0.35
4.1±0.43
2.8±0.3530.5±3.01
10.5±0.84

24.3±0.93

49±1.5139.7±1.953.3±2.01

54.1±1.82

Mean±S.D. %MORPHOLOGY, GROWTH AND LIFE HISTORY OF DWARF MINKE WHALES

Cetacean Popul. Stud. (CPOPS), Full paper
Vol. 3, 2021, 93–128

127

128

Occipital bone width at jugal process
Length of mandible, straight (L)Length of mandible, straight (R)Length of mandible, curved (L)Length of mandible, curved (R)Breadth of mandible at middle (L)Breadth of mandible at middle (R)Height of mandible at middle (L)Height of mandible at middle (R)Height of mandible at coronoid process (L)Height of mandible at coronoid process (R)Height of mandible at coronoid (L)Height of mandible at coronoid (R)Breadth of mandible at coronoid (L)Breadth of mandible at coronoid (R)Specimen ID
Body length (m)Sex

164.5 103.0
155.4
97.3
156.2
97.8
164.5 103.0
7.0
4.4
7.0
4.4
10.4
6.5
10.5
6.6
21.5
13.5
21.4
13.4
16.8
10.5
16.4
10.3
10.2
6.4
11.0
6.9

36.8
22.5
167.0 102.2
157.4
96.3
158.0
96.7
166.4 101.8
6.8
4.2
7.1
4.3
10.0
6.1
10.3
6.3
21.0
12.9
21.2
13.0
16.1
9.9
16.1
9.9
10.0
6.1
9.9
6.1

%

cm

cm

%

88/89 013
6.99
F

87/88 273
7.01
M
%

36.2
24.3
155.0 104.0
146.0
98.0
145.8
97.9
154.0 103.4
6.4
4.3
6.5
4.4
9.8
6.6
10.2
6.8
19.3
13.0
19.4
13.0
14.3
9.6
14.8
9.9
9.4
6.3
9.3
6.2

cm

88/89 014
6.6
M

36.2
140.0
133.5
133.5
139.9
6.0
6.2
9.7
9.5
18.4
18.5
14.4
14.4
9.3
9.1

cm
27.2
105.2
100.3
100.3
105.1
4.5
4.7
7.3
7.1
13.8
13.9
10.8
10.8
7.0
6.8

%

88/89 070
5.94
F
%

21.7
17.7
127.0 103.8
120.7
98.7
121.5
99.3
126.0 103.0
4.7
3.8
4.7
3.8
7.6
6.2
7.7
6.3
16.0
13.1
16.3
13.3
12.1
9.9
12.3
10.1
7.7
6.3
8.0
6.5

cm

89/90 199
5.41
M
%

cm

98.7
99.0
4.0
4.0
7.0
7.1
13.7
14.0
10.2
10.8
6.8
6.7

25.6

%

89/90 215
7.07
F

46.6
28.3
43.3
170.8 103.7
161.0
97.8
162.0
98.4 167.0
170.8 103.7 167.5
7.5
4.6
6.8
7.3
4.4
6.8
11.1
6.7
11.8
11.2
6.8
12.0
23.3
14.1
23.2
23.2
14.1
23.7
18.3
11.1
17.3
18.5
11.2
18.3
10.7
6.5
11.5
10.7
6.5
11.3

cm

88/89 227
7.02
F

%

Mean±S.D. %

41.3
26.5 24.6±3.56
165.0 105.7
104±1.2
154.8
99.2 98.2±1.3
154.5
99.0 98.5±1.1
165.5 106.0 103.1±2.126.84.4
4.3±0.24
7.0
4.5
4.3±0.26
10.6
6.8
6.7±0.38
10.7
6.9
6.7±0.32
21.4
13.7 13.5±0.46
21.6
13.8 13.6±0.4417.7
11.3 10.4±0.63
17.3
11.1 10.5±0.5411.77.5
6.6±0.46
11.2
7.2
6.6±0.36cm

92/93 330
7.17
F

List of skeletal measurements by the standard measuring method for all dwarf minke whales examined in the present skeletal analysis.
(Continued.)

Measurement points

Appendix 2.

KATO, FUJISE, NAKAMURA, HAKAMADA, PASTENE AND BEST

Cetacean Popul. Stud. (CPOPS), Full paper
Vol. 3, 2021, 93–128