SC/J09/JR20

Trend of blubber thickness in common minke, sei andBryde’s whales in the western North Pacific during
JARPN and JARPN II periods
KENJI KONISHI1), TSUTOMU TAMURA1), MUTSUO GOTO1), TAKEHARU BANDO1), TOSHIYA KISHIRO2), HIDEYOSHIYOSHIDA2), AND HIDEHIRO KATO3)
1) The Institute of Cetacean Research, 4-5, Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan.
2) National Research Institute of Far Seas Fisheries, 5-7-1, Shizuoka, 424-8633, Japan.
3) Tokyo University of Marine Science and Technology, Faculty of Marine Science, 4-5-7, Konan, Minato-ku,Tokyo, 108-8477, Japan
Contact e-mail: konishi@cetacean.jp

ABSTRACTThe trend of blubber thickness in common minke whale Balaenoptera acutorostrata, sei whale B. borealis andBryde’s whale B. edeni sampled in the western North Pacific from May to September in 2000-2007 JARPN II
were analyzed. The purposes of this study were to examine the time trends of blubber thickness in commonminke, sei and Bryde’s, and the factors that influence the energy storage of these whales. Minimum AIC model
based on the results of stepwise multiple regressions analysis of the minke whale data from 1994 to 2007 was;
Blubber thickness = -27.48+0.10Year+0.01Date+0.06Latutude-0.01Longitude+1.07 (Sex: male=1, female=2).
Minimum AIC model in the same regression analysis for sei whale was; Blubber thickness = 452.17+0.23Year+0.02Date +0.16Body length (m)+1.72(Sex: male=1, female=2). Minimum AIC model in thesame regression analysis for Bryde’s whale was; Blubber thickness = 135.85-0.07Year+0.01Date 0.10Latitude+0.02Longitude+0.24Body length (m)+1.21(Sex: male=1, female=2). Our study showed that theblubber thickness of minke whale has increased throughout the JARPN and JARPN II period. The results of thestatistical analyses showed that blubber thickness in sei whales has increased during the 5-years of the JARPN IIresearch period, while that in Bryde’s whales have decreased during 7 years. Other explanatory variables, suchas “date”, “body length” and “sex” shows similar results to previous study of the Antarctic minke whale. The
feeding areas of Bryde’s and sei whales show very little overlap, and their distribution is separated by sea surface
temperature (SST). The interpretation of the above results need further study to clarify the role and prey
consumption by the baleen whales in the western North Pacific ecosystem.

INTRODUCTION
Baleen whale stocks energy by food intake into its blubber as lipid, and the blubber thicker increase through thefeeding season (Lockyer 1987; Víkingsson 1995; Næss et al. 1998, Konishi 2006, Konishi et al. 2008). Long
time trend of energy storage sometimes gives very useful information. A recent study demonstrated thatindicators of energy storage, such as the blubber thickness and blubber weight, have deceased in Antarctic minke
whale for nearly two decades (Konishi et al. 2008). Since environmental and biological factors influence thefood availability of animals which is reflected in energy storage, this study could contribute to ecosystem study
and also to management of whales. The purpose of this study is to examine the time trends of blubber thickness
in common minke, sei and Bryde’s, and what the factors influence the energy storage of these whales.

MATERIALS AND METHODS

Sampling and measurements
Blubber thickness used in the present study were measured in common minke, sei and Bryde’s whales taken bythe Japanese Whaling Research Program under Special Permit in the western North Pacific (JARPN) (19941999 for mike whale) and JARPN II (2000-2007 for the minke, sei and Bryde’s whale). To cover the research of1

minke whale in early and late period and coastal area, the JARPN II coastal component of two regions (Sanrikuand Kushiro) has conducted since 2002. For the analyses in the mike whale, we used only O-stock mink whalefrom offshore and coastal components in JARPN II to this analyses, according to the mtDNA definition (Kandaet al., 2009). To avoid any bias resulting from growth or lactation, we used only mature males and pregnant
females, but not lactating females or immature animals, for the present analyses. Males of minke, Bryde's and sei
whales were defined as sexually mature by testis weight (larger side) of more than 290g, 560g and 1,090g,respectively (Bando et al., unpublished data). Female were defined as sexually mature by the occurrence of atleast one corpus luteum or albicans in their ovaries. Data used in this study was listed in Table 1.
Blubber thickness was measured to the nearest mm, by dissecting perpendicularly from skin to muscle without
including connective tissue and black surface skin. The measurement position of blubber thickness was lateralside at the section of dorsal fin where most commonly measured site from commercial whaling period. Sex andmaturity were recorded for each whale on the basis of routine observations of reproductive organs during
dissection and tissue observations in the laboratory.

Statistical analysis
Almost baleen whales accumulate fat during the summer feeding period and migrate to low latitude areas
for reproduction. The time spent in the feeding area and geographical and biological variables which could
be related to blubber thickness should be considered in body condition analysis. To take these factors into
account and possibly exclude some of them, we conducted stepwise multiple linear regression analyses
using Akaike’s information criterion (AIC) for model selection. In these analyses, first step included all
explanatory variables, and stepwise procedure continued when a model without an explanatory variable hadsmaller AIC. Blubber thickness (in cm) was the dependent variable. We allowed the following independent
variables: “year”, “date” (May 1st. = day 1), catching position (Latitude and longitude), sex (male=1,female=2), “body length” (in m).

RESULTS
Common minke whale

Blubber thickness ranged from 1.5 to 6.6 cm in mature males, and from 2.2 to 7.7 cm in pregnant females
over the whole research period. First, we conducted stepwise multiple regressions analysis in the minke whalefrom 1994 to 2007. Minimum AIC model was;
Blubber thickness = -27.48+0.10Year+0.01Date +0.06Latutude-0.01Longitude +1.07 (Sex: male=1, female=2)
Minimum AIC model did not included Body length. The results indicated that blubber thickness increased

with year, time spent feeding and from south to North.
As second run in the minke whale, we also conducted the same analysis with the dataset from 2000 to 2007 to
test if the yearly trend of blubber thickness was constant.
Minimum AIC model in the regression analysis in the minke whale was;
Blubber thickness = -206.46+0.10Year+0.01Date +0.11Latitude-0.02Longitude +1.39 (Sex: male=1, female=2)
Minimum AIC model did not included Body length. The results also indicated that blubber thickness

increased with year, time spent feeding and from south to North.
Sei whale

Blubber thickness ranged from 2.7 to 7.8 cm in mature males, and from 3.7 to 9.3 cm in pregnant females
over the whole research period. Minimum AIC model in the regression analysis in sei whale was;
Blubber thickness = -452.17+0.23Year+0.02Date +0.16Body length (m) +1.72(Sex: male=1, female=2)
Minimum AIC model did not included Latitude and Longitude. The results indicated that blubber thickness

increased with year, and time spent feeding and body length.
Bryde’s whale

Blubber thickness ranged from 2.6 to 6.9 cm in mature males, and from 3.6 to 9.3 cm in pregnant females
over the whole research period. Minimum AIC model in the regression analysis in Bryde’s whale was;2

Blubber thickness = 135.85-0.07Year+0.01Date -0.10Latitude+0.02Longitude+0.24Body length (m) +1.21(Sex:male=1, female=2)
Minimum AIC model included all independent variables. The results indicated that blubber thickness

decreased with year and from North to South and body length.

DISCUSSION

Annual trend in body condition
Our study showed the blubber thickness of minke whale has increased throughout JARPN and JARPN II period.
The results of the statistical analyses showed that blubber thickness in sei whales have increased during the 5years in JARPN II research period, while that in Bryde’s whales have decreased during 7 years. The common
minke whales and sei whales almost distributed in the same area, however Bryde’s whale distributed in the warm
area (Konishi et al. 2009). These results seem to reflect their prey availability in the feeding grounds.

Elucidation of the role of cetaceans in the western North Pacific ecosystem
Other explanatory variables, such as “date”, “body length” and “sex” shows similar results to previous study in
the Antarctic minke whale (Konishi et al. 2008). Sei whales and Bryde’s whales almost do not overlap theirfeeding area, and their distribution is separated by Sea surface temperature (SST) (Konishi et al. 2009). Theinterpretation of above results need further study to clarify the role and consumption of the baleen whales in thewestern North Pacific ecosystem.

AKNOWLEDGEMENTS
We would like to thank all the captains and crews of the ships that took part and the scientists who were involved
in JARPN and JARPN II surveys. Thanks are also due to N. Kanda for providing stock information of minke
whales, H. Okamura for helping analysis and Y. Hosone for helping us to organize the data set. We would also
like to thank L.Walløe, H. Hatanaka, and other people who have helped with and made valuable comments on
this paper. The JARPN and JARPN II programs were conducted with permission from the Japanese Fisheries
Agency.

REFERENCES
Kanda, N., Goto, M., Kishiro, T., Yoshida, H., Kato, H. and Pastene, L.A. (2009) Individual identification andmixing of the J and O stocks around Japanese waters examined by microsatellite analysis SC/J09/JR26
presented to the JARPN II Review Workshop, Tokyo, January 2009 (unpublished). 9pp.
Konishi K (2006) Characteristics of the blubber and body condition indicator for the Antarctic minke whales(Balaenoptera bonaerensis). Mamm Study 31:14–22.
Konishi K, Tamura T, Zenitani R, Bando T, Kato H, Walløe L. (2008) Decline in energy storage in the Antarcticminke whale (Balaenoptera bonaerensis) in the Southern Ocean. Polar Biol
Konishi, K., Kiwada, H., Matsuoka, K., Hakamada, T. and Tamura, T. (2009) Density prediction modeling andmapping of common minke, sei and Bryde’s whales distribution in the western North Pacific using JARPN II(2000-2007) data set. SC/J09/JR19 presented to the JARPN II Review Workshop, Tokyo, January 2009
(unpublished). 20pp.
Lockyer C (1987) The relationship between body fat, food resource and reproductive energy costs in northAtlantic ﬁn whales (Balaenoptera physalus). Symp Zool Soc Lond 57:343–361
Næss A, Haug T, Nilssen M (1998) Seasonal variation in body condition and muscular lipid contents inNortheast Atlantic minke whale Balaenoptera acutorostrata. Sarsia 83:211–218
Víkingsson G A (1995) Body condition of fin whales during summer off Icelnad. In: A. S. Blix, L. Walløe and Ø.
Ulltang (eds). Whales, seals, fish and man. Elsevier, Amsterdam. p361-369.

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Table 1 Data used in this study
Minke whale

Mature Male
N=842

Pregnant female
N=86

Bryde's whale Mature Male
N=85

Pregnant female
N=93

Sei whaleMature Male
N=157

Pregnant female
N=142

Variables
Date (May 1st=1)
Latitude (deg)Longitude (deg)Body length (m)Blubber thickness (cm)Date May 1st=1
Latitude (deg)Longitude (deg)Body length (m)Blubber thickness (cm)Date (May 1st=1)
Latitude (deg)Longitude (deg)Body length (m)Blubber thickness (cm)Date (May 1st=1)
Latitude (deg)Longitude (deg)Body length (m)Blubber thickness (cm)Date (May 1st=1)
Latitude (deg)Longitude (deg)Body length (m)Blubber thickness (cm)Date (May 1st=1)
Latitude (deg)Longitude (deg)Body length (m)Blubber thickness (cm)

4

Mean
75.99
42.18
152.05
7.46
3.14
53.35
41.41
149.01
7.89
4.04
80.79
37.40
152.93
12.46
4.55
76.08
37.29
154.70
12.94
5.87
68.61
40.83
160.20
13.77
4.83
63.53
40.47
159.98
14.58
6.55

SD
41.78
2.44
8.17
0.30
0.81
48.71
3.14
9.44
0.43
1.00
28.58
1.46
6.03
0.47
0.87
28.66
1.48
6.40
0.61
1.26
29.09
2.54
5.56
0.51
0.89
28.97
2.51
5.36
0.63
1.18

min
-15
37.13
141.10
6.58
1.5
-20
36.95
141.106.852.2
38
35.02
144.85
11.27
2.6
29
35.00
141.87
11.16
3.6
21
35.30
144.65
12.28
2.7
19
35.08
149.67
13.01
3.7

max
181
48.90
169.76
8.62
6.6
159
47.23
168.88
8.8
7.7
135
40.27
167.67
13.3
6.9
135
40.23
168.75
14.14
9.3
131
47.08
169.67
15
7.8
129
45.87
169.83
16.32
9.3