SUBSPECIFIC DIFFERENCES OF THE WHITE PATCH ON FLIPPER OF MINKE WHALE

Full paper

COMPARISON OF SHAPES OF THE WHITEFLIPPER PATCH BETWEEN TWO
SUB-SPECIES OF COMMON MINKE WHALES(BALAENOPTERA ACUTOROSTRATA)Gen NAKAMURA1*, Kathrine A. RYENG2, Ichiro KADOWAKI1,Ryotaro HAYASHI1, Shouka NAGATSUKA1,
Ayumi HIROSE1, Yoshihiro FUJISE3 and Tore HAUG2
1
Laboratory of Cetacean Biology, Tokyo University of Marine Science and Technology,
4 – 5 – 7 Konan, Minato-ku, Tokyo 108–8477, Japan *(Corresponding author: gnakam1@kaiyodai.ac.jp)
2Institute of Marine Research, Fram Centre, P.O. Box 6606 Langnes, NO-9296 Tromsø, Norway
3
Institute of Cetacean Research, Toyomi Shinko Building 5F, 4 – 5 Toyomi-cho, Chuo-ku, Tokyo 104 – 0055, JapanAbstract
The North Atlantic and North Pacific minke whales are regarded as two different subspecies.
In this study we aimed to clarify the morphological differences of the white patch on the flipper
between these subspecies. Morphological measurements were taken from the left flipper ofsexually mature animals, collected from the North Atlantic (N= 15) and the North Pacific(N = 16) oceans. The length between the tip of flipper to the distal border of the white patch
relative to the total flipper length showed no statistical differences between the two subspecies.
However, the length between the tip of flipper to the proximal border of white patch relative tothe total flipper length was significantly larger in the North Atlantic (74.31%) as compared to
the North Pacific (63.62%) minke whales. Also, the mean angle between the proximal boundaryline of the white patch and the longitudinal axis of the flipper was significantly differentbetween the North Atlantic (70.05 degrees) and the North Pacific (92.29 degrees) minke whales.
These results show that there are clear morphological differences in the white patch of the flipper between the two minke whale subspecies.
Key words

common minke whale, Balaenoptera acutorostrata, flipper, white patch morphology, subspecies, taxonomy.

Introduction

The common minke whale (Balaenoptera acutorostrata) is distributed worldwide and is regarded
as an important marine resource, particularly in the North Atlantic and North Pacific. Taxonomically,
common minke whales are classified into two subspecies: B. a. acutorostrata in the North Atlantic andB. a. scammoni in the North Pacific. Although a distinctive population exists in the Southern hemisphere, generally known as the “dwarf” minke whale (B. a. subsp.), the taxonomical status of thissubspecies is still under discussion (Rice, 1998). Since external characteristics are important classification criteria for taxonomy, various studies have focused on the differences in these characteristics todistinguish minke whale populations within and between oceans (Omura and Sakiura, 1956; Christensen
et al., 1990; Kato et al., 1992; Nakamura et al., 2014). A unique characteristic of the common minke
whale is the white patch on their flippers. Compared to the North Pacific minke whale, the dwarf minke
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Fig. 1. Examples of typical appearances of minke whale flippers for
the North Atlantic minke whale (top) and the North Pacific minke
whale (bottom). See also photographs in Appendix 1. Scale bars
indicate 10 cm.

whale has much larger white patches which extend to their shoulders. This feature has been used todistinguish these two subspecies (Arnold et al., 1987; Kato and Fujise, 2000; Arnold et al., 2005).
Nakamura et al., (2015) reported that the shape of the white patch would be a powerful taxonomical
character to morphologically distinguish the stocks in the North Pacific. Horwood (1989) reviewed
and described the differences in the shape of the white flipper patch between the North Atlantic andNorth Pacific common minke whales. Notably, the latter has a small central projection of the whitearea into the black area of the flipper, whereas in the former, the white area is more angled with nosuch projection.
Fig. 1 shows the color patterns of flippers from North Atlantic and North Pacific common minke
whales. These different characteristics of the white patches have not yet been thoroughly describedand compared. Using a photogrammetric method, Nakamura et al. (2014) showed that the white patch
is significantly larger in the North Atlantic common minke whale as compared to the North Pacificone. However, to clarify the morphological differences of flipper between the two common minke
whale subspecies, a more detailed analysis based on unified methodologies and controlled conditions
is needed. The aim of this study was to specify the relative size and differences of the white flipper
patch between the North Atlantic and North Pacific common minke whales, now based on measurements made directly on flippers obtained from animals taken in commercial (North Atlantic) andresearch (North Pacific) catches.
Materials and Methods

The data from North Atlantic common minke whales were collected during Norwegian commercial
whaling operations conducted south of the Svalbard islands during the summer season in 2016 (Fig.
2). The North Pacific common minke whale data were collected from the survey of the second phaseof the Japanese Whale Research Program under Special Permit in the Western North Pacific (commonly known as JARPN II), conducted in the coastal and offshore waters of Japan in 2012 and 201316

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SUBSPECIFIC DIFFERENCES OF THE WHITE PATCH ON FLIPPER OF MINKE WHALE

Fig. 2. Location where materials of the North Atlantic and North Pacific minke whales were collected.

(Fig. 2). This research was conducted in accordance with Article VIII of the International Convention
for the Regulation of Whaling, and Japanese law.
To minimize the effects of sex-specific and growth-dependent differences on the white patch, weanalyzed sexually mature female whales only. A total of 15 animals, mean body length 8.07 m (range:7.2–8.7 m) from the North Atlantic population, and 16 animals, mean body length 7.96 m (range:7.10–8.68 m) from the North Pacific population were used in this study. Body length was measured
from the tip of the snout to the notch of flukes, rounded to the nearest 10 cm for the North Atlantic
minke whales and the nearest 1 cm for the North Pacific minke whales. Sexual status was determinedby examining ovaries; whales possessing ≥ 1 corpus albicans or corpus luteum were regarded as
sexually mature. The left flipper was removed and photographed. For each photograph, we carefully
ensured that the camera was placed in the upper direction confronting the flipper. Then, the following
lengths were measured in a straight line using a measuring tape to the nearest 0.5 cm: Total flipper
length: The tip of flipper (a) to the end of the articular process of the humerus (c); Measurement point
A: The tip of flipper (a) to the distal border of white patch (A); and Measurement point B: The tip offlipper (a) to the proximal border of white patch (B). Measurement point C (Angle θ) is the angle
between the proximal boundary line of white patch and the longitudinal axis of the flipper. The proximal boundary line of white patch was defined as the line passing from the ventral (B) to dorsal (b)sides of the proximal border of white patch, whereas the longitudinal axis of the flipper is the straightline from the tip of flipper to the end of the articular process of the humerus. This angle was calculated
by a photogrammetric method using the graphic software Canvas X (Fig. 3). T -testing was applied totest the differences between the two subspecies. It was considered that t was significant at P < 0.05.
Standard deviation (S.D.) was adapted to measure the dispersion of the data. All statistical analyses
were carried out using packaged tools in the statistics software R (R Development Core Team 2015).
Results and Discussion

To clarify inter-subspecies differences in the relative size of the white patch, the proportion of Measurement points A and B relative to the Total flipper length in percent, and Measurement point C inCetacean Population Studies (CPOPS)
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Fig. 3. Measurement points of the white patch of the left
flipper from the common minke whale. Total flipper
length: The tip of flipper (a) to the end of the articular
process of the humerus (c), Measurement point A: The tipof flipper to the distal border of white patch (A), Measurement point B: The tip of flipper to the proximal border ofwhite patch (B) and Measurement point C (Angle θ): The
angle between the proximal boundary line of white patch(B-b) and the longitudinal axis of the flipper (a-c) weremeasured.

Fig. 4. Comparison of the mean values of three measurement points of the white patch on the flipper from theNorth Atlantic and North Pacific minke whales. A and B show relative size of the Measurement point A and B(see Fig. 3) to the Total flipper length.

Table 1. Mean values of each measurement points of white patch on the flipper of the North Atlantic and North
Pacific minke whales.
Relative length between the tip of B. Relative length between the tip ofof A.
flipper to the distal border of white flipper to the proximal border of white
Subspecies Number
samples patch to the total flipper length (%)
patch to the total flipper length (%)

C. AngleΘ(°)

North
Atlantic

15

33.97 ± 3.96

74.31 ± 2.58

70.05 ± 5.74

NorthPacific1633.08 ± 3.64

63.62 ± 2.91

92.29 ± 10.15

degrees were compared between the two subspecies.
The mean proportion of Measurement point A relative to Total flipper length was 33.97% (S.D. =3.96) and 33.08% (S.D. = 3.64) in the North Atlantic and North Pacific common minke whales,respectively. No significant differences were detected (Fig 4-A, Table 1). The mean proportion ofMeasurement point B relative to the Total flipper length was significantly larger in the North Atlantic(74.31%, S.D. = 2.58) as compared to the North Pacific (63.62%, S.D. = 2.91) common minke whales(P < 0.01; Fig 4-B, Table 1). The mean of Measurement point C was significantly distinct between
the North Atlantic (70.05 degrees, S.D. = 5.74) and the North Pacific (92.29 degrees, S.D. = 10.15)
common minke whales (P < 0.01; Fig 4-C, Table 1).

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The results of our analysis indicate that clear morphological differences exist in the relative size of
the white flipper patch between the two subspecies. Although the mean relative length of Measurement
point A showed almost the same values between the two subspecies, the relative length of Measurement point B was significantly greater in the North Atlantic common minke whales than in the North
Pacific ones. This indicates that overall, the North Atlantic common minke whales have a relativelylarger white patch area than the North Pacific common minke whales. As mentioned above, the whitepatch of the dwarf minke whales covers its shoulder region and is much larger than that of North
Pacific and North Atlantic common minke whales (Best, 1985; Kato and Fujise, 2000; Arnold et al.,2005). Pastene et al. (2007) reported that dwarf minke whales are genetically closer to the North
Atlantic common minke whales than to the North Pacific ones. Therefore, the shape of the white patch
may well serve as a suitable taxonomic feature to distinguish between subspecies of the commonminke whale.
Acknowledgements

We thank the captain, Mr. Dag Myklebust, and the crew of KATO and Mr. Truls Soløy, the Chairman of the Norwegian Whalers Union for their contribution during sampling in the North AtlanticOcean. We also express our gratitude toward the former leaders of the JARPN II Survey; Drs. Genta
Yasunaga and Takeharu Bando of the Institute of Cetacean Research; Chief in biological surveys, Mr.
Shigeo Tabata and Mr. Takahiro Hara of the National Research Institute of Far Seas Fisheries; Mr.
Atsushi Wada and Mr. Tatsuya Isoda of the Institute of Cetacean Research; and the staff of the Kyodo
Senpaku Co., who were largely involved in the offshore surveys. Finally, we sincerely indebted to Dr.
Hidehiro Kato, Professor Emeritus of Tokyo University of Marine Science and Technology for hissupervision throught the present study.
This study was supported by a grant from “Moritani Scholarship Foundation (2018 – 2019)”.

References
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whale Balaenoptera acutorostrata sensu lato: description, cladistic analysis and taxonomic implications. Mem.
Queensl. Mus. 51: 277–307.
Arnold, P. W., Marsh H. E. and Heinsohn, G. E. 1987. The occurrence of two forms of minke whales in east Australianwaters with a description of external characters and skeleton of the diminutive or dwarf form. Sci. Rep. Whales Res.
Inst. 38: 1–46.
Best, B. P. 1985. External characters of southern minke whales and the existence of a diminutive form. Sci. Rep. Whales
Res. Inst. 36: 1–33.
Christensen, I., Haug, T. and Wiig, Ø. 1990. Morphometric comparison of minke whales Balaenoptera acutorostrata fromdifferent areas of the North Atlantic. Mar. Mam. Sci. 6: 327 – 338.
Horwood, J. W. 1989. Biology and Exploitation of the Minke Whale. CRC Press, Boca Raton, Florida, 248 pp.
Kato, H. and Fujise, Y. 2000. Dwarf minke whales; morphology, growth and life history with some analyses on morphometric variation among the different forms and regions. Paper SC/52/OS3 presented at: 52nd IWC Scientific Committee meeting; June 2000. 30 pp. [Available from the secretariat of IWC]
Kato, H., Kishiro, T., Fujise, Y. and Wada, S. 1992. Morphology of minke whales in Okhotsk sea, Sea of Japan and off
the east coast of Japan, with respect to stock identification. Rep. int. Whal. Common, 42: 437 – 442.
Nakamura, G., Kadowaki, I., Nagatsuka, S., Fujise, Y., Kishiro, T. and Kato, H. 2014. Variation in a color pattern of whitepatch on the flippers of North Pacific common minke whales: Potential application for their interoceanic difference.
La mer 52: 31–47.
Nakamura, G., Kadowaki, I., Nagatsuka, S., Hayashi, R., Kanda, N., Goto, M., Pastene, L. A. and Kato, H. 2016. White
patch on the fore-flipper of common minke whale, as a potential morphological index to identify stocks. Open Journal of Animal Sciences 6: 116–122.
Omura, H. and Sakiura, H. 1956. Studies on the little piked whale from the coast of Japan. Sci. Rep. Whales Res. Inst.
11: 1 – 37.
Pastene, L. A., Goto, M., Kanda, N., Zerbini, A. N., Kerem, D. A., Watanabe, K., Bessho, Y., Hasegawa, M., Nielsen, R.,Larsen, F. and Palsbøll P. J. 2007. Radiation and speciation of pelagic organisms during periods of global warming:
the case of the common minke whale, Balaenoptera acutorostrata. Mol. Ecol. 16: 1481 – 1495.
R Core Team. 2015. R: A language and environment for statistical computing. R Foundation for Statistical Computing,Cetacean Population Studies (CPOPS)
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Vienna, Austria. URL http://www.R-project.org/.
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Received: April 13, 2018
Accepted: November 7, 201820

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Appendices: Appendix 1-1. Pictures of the left flipper of the North Atlantic minke whale.

50cm 50cm

2016Norway_47(7.9m)(7.9m)
2016Norway_47

2016Norway_49(7.7m)(7.7m)
2016Norway_49

2016Norway_50(8.4m)(8.4m)
2016Norway_50

2016Norway_51(8.5m)(8.5m)
2016Norway_51

2016Norway_52(7.2m)(7.2m)
2016Norway_52

2016Norway_53(8.4m)(8.4m)
2016Norway_53

2016Norway_54(7.8m)(7.8m)
2016Norway_54

2016Norway_57(7.3m)(7.3m)
2016Norway_57

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NAKAMURA, RYENG, KADOWAKI, HAYASHI, NAGATSUKA, HIROSE, FUJISE AND HAUG

Appendix 1-2, (continued).

50cm 50cm22

2016Norway_58(7.7m)(7.9m)
2016Norway_472016Norway_59(8.2m)(7.7m)
2016Norway_49

2016Norway_50
2016Norway_60(8.7m)(8.4m)

2016Norway_51
2016Norway_61(8.0m)(8.5m)

2016Norway_52
2016Norway_62(8.5m)(7.2m)

2016Norway_53
2016Norway_63(8.5m)(8.4m)

2016Norway_54
2016Norway_65(8.3m)(7.8m)

2016Norway_57 (7.3m)

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Appendix 1-3. Pictures of the left flipper of the North Pacific minke whale.

50cm 50cm

2016Norway_47
12NPCS-M029(8.1m) (7.9m)

12NPCS-M049(7.1m) (7.7m)
2016Norway_49

2016Norway_50
12NPCK-M011(8.1m) (8.4m)

2016Norway_51
12NPCK-M028(8.1m) (8.5m)

2016Norway_52
12NPCK-M031(8.2m) (7.2m)

2016Norway_53
12NPCK-M037(8.2m) (8.4m)

2016Norway_54
12NP-M014(8.3m) (7.8m)

2016Norway_57
12NP-M046(7.7m) (7.3m)

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Appendix 1-4, (continued).

50cm 50cm

24

2016Norway_47
12NP-M064(7.9m) (7.9m)

13NPCK-M023(7.9m)(7.7m)
2016Norway_49

13NPCK-M028(7.5m) (8.4m)
2016Norway_50

13NPCK-M040(7.7m)(8.5m)
2016Norway_51

2016Norway_52
13NPCK-M049(8.3m) (7.2m)

13NPCK-M052(8.7m)(8.4m)
2016Norway_53

2016Norway_54
13NPCK-M053(7.6m) (7.8m)

13NPCK-M057(8.1m)(7.3m)
2016Norway_57

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