SC/J09/JR8

The number of western North Pacific common minke whales(Balaenoptera acutorostrata) distributed in JARPN II coastal
survey areas.
Takashi Hakamada1, Koji Matsuoka1 and Tomio Miyashita2
1

The Institute of Cetacean Research, 4-5, Toyomi-cho, Chuo-Ku, Tokyo, 104-0055, Japan.

2

National Research Institute of Far Seas Fisheries (Yokohama), 2-12-4, Fukuura, Kanagawa,

Yokohama, 236-8648, Japan.
Contact e-mail: hakamada@cetacenan.jp

ABSTRACT
In order to examine an impact of whales on Japanese fisheries in Kushiro and Sanriku regions
through estimating the amount of prey consumed by minke whales or using an ecosystem model, it
was required to estimate the number of the whales distributed in each of the survey areas during the
JARPNII survey periods. The estimated number off Kushiro was 601, 968, 368, 316, 241 and 142 in
2002, 2003, 2004, 2005, 2006 and 2007, respectively. The estimated number off Sanriku was 247 in2005 and 123 in 2006. Note is that these numbers are not abundance estimates of the minke whale
stock in the areas because the sighting data we used for the estimation covered only a part of thestock distribution.

INTRODUCTION
Feeding ecology and ecosystem studies are one of the main objectives of the JARPN II. The
common minke whales consume some of the main Japanese fishery resources off Kushiro and off
Sanriku. An impact of whales on Japanese fisheries in the JARPNII survey area can be assessedfrom estimating the amount of prey consumed by the whales in survey areas (Tamura et al., 2009) or
using an ecosystem model developed for the survey area (e.g. Okamura et al., 2009). For either way,
it is required to estimate the number of the whales distributed in the survey areas.

MATERIALS AND METHODS
Dedicated sighting survey was conducted off Kushiro in September and October every year from2002 to 2007 and off Sanriku in April and May from 2003 to 2006. The survey area off Kushiro wasstratified, except for the 2003 survey, as Offshore (O), coastal-East (E), coastal-Central (C),coastal-West (W), and off Hidaka sub-prefecture (H) (Fig. 1). Distribution of primary sightings ofthe common minke whales and searching effort off Sanriku during the 2005 and 2006 JARPN II
costal component were shown in Fig. 2. Survey area and design off Sanriku in 2003 were different
from those in 2005 and 2006. Although the survey periods were similar in 2003 (8 - 28 April), 2005
(20 April – 2 May), and 2006 (21 April – 3 May), the research area covered by the sighting survey in2003 was quite different from that in 2005 and 2006. Baceause we thought that the number ofwhales obtained from the sighting data in 2003 was not comparable to that in 2005 and 2006, wedidn’t estimate the number of distributed whales from the 2003 data. Survey area off Sanriku was
divided at 141o30’E longitudinal line as coastal area (west) and offshore area (east). The coastal area
was surveyed twice per year in both 2005 and 2006. The first period was 24 - 30 April in 2005 and
25 – 29 April in 2006, and the second period was 30 Apr. – 2 May in 2005 and 29 April – 3 May in2006. We used the data only from the second survey because this period was thought to be closer topeak migration period of the minke whales in the area, likely providing relatively a better estimate of
the whale numbers for estimation of prey consumption by the whales. More details of the sighting
surveys in general are explained in Kiwada et al., (2009), while the details of the 2004 sighting
survey in Sendai Bay in Appendix of this paper.. Distribution of trackline surveyed and primarysightings of the minke whales off Kushiro and off Sanriku by strata were shown in Fig. 1 and 2,
respectively.
The number of minke whales distributed in the area was estimated using the computer program
DISTANCE ver 3.5. The estimated numbers (N) and their CVs (CV(N)) were obtained from thefollowing formulae:N=

AnE ( s )
2 wL

(1)

2

  n 2
2
CV ( N ) = CV   + {CV (w)} + {CV (E ( s ) )}  l (2)

We applied g(0)=0.732 (CV=0.309) for Top barrel and Upper bridge (Okamura et al., 2008).

RESULTS
Table 1 shows the estimated number of the minke whales off Kushiro by strata and by year. Table 2
shows the total number of whales off Kushiro assuming g(0)=0.732 for each of the survey years. The
estimated numbers are 601, 968, 368, 316, 241 and 142 in 2002, 2003, 2004, 2005, 2006 and 2007,
respectively. Table 3 shows the estimated number of the minke whales off Sanriku by strata and by
year. The estimated number for coastal stratum of 247 in 2005 and 123 in 2006 was used for
estimating amount of prey consumed by the common minke whales in the survey area. Table 4shows the total number of whales off Sanriku assuming g(0)=0.732 in each year. The estimated2

number in the whole surveyed area of Sanriku region was 437 in 2005 and 236 in 2006. Theseestimates in the whole survey area were not different substantially compared to the estimate inAppendix. Fig. 3 shows plots of detection functions for each of the survey years off Kushiro and off
Sanriku. The fitting of the detection function seemed to be good.

DISUSSIONS
It is important to note that the numbers of the minke whales we estimated in this paper do not
represent the number of the whale in a whole stock because the sighting data we used covered only alimited area of the stock distribution.
The estimated numbers of the whales in this study decreased year by year. We think this isbecause the number of minke whales migrated to the area differed year by year probably due to someenvironmental factors.

It was suggested the number of the minke whales distributed off Kushiro

was influenced by the environmental factors such as sea water temperature or Oyashio extension(Watanabe et al., 2009). In fact, according to Murase et al. (2007), during our surveys in 2002-2006,
the stretch of optimal temperature zone for the minke whales was reduced and this reduction caused
low influx of the common minke whales..

ACKNOWLEDGEMENT
Authors would like to express gratitude for all the researchers and crew involved the JARPN II
coastal component. We also thank Ms. Saeko Kumagai, Mr. Hiroshi Kiwada and Ms. Tomoko
Hasegawa (Institute of Cetacean Research) for their assistance in this study. We also thank Hiroshi
Hatanaka and Naohisa Kanda (Institute of Cetacean Research) for their valuable comments andsuggestions on this study .

REFERENCE
Kiwada, H., Kumagai, S. and Matsuoka, K. Methodology and procedure of the dedicated sighting
surveys in JARPN II –Offshore and coastal component of Sanriku and Kushiro-. Paper
SC/J09/JR2 presented to the JARPN II Review Workshop, Tokyo, January 2009
(unpublished) 16pp.
Murase, H., Kiwada, H., Matsuoka, K. and Nishiwaki, S. 2007. High sea surface temperature caused
low influx of common minke whales to the Kushiro water in September 2006. Appendix 4of paper SC/59/O7 presented to IWC Scientific Committee, May 2007 (unpublished)[Available from IWC Secretariat]. 14pp.
Okamura, H., Miyashita, T. and Kitakado, T. 2008. Abundance estimation on common minke whalesin the Russian waters of sub-area 10 using the IO sighting data in 2006. Paper SC/60/NMP7
presented to IWC Scientific Committee, May 2008 (unpublished). [Available from IWC

3

Secretariat]. 7pp.
Okamura, H., Nagashima, H. and Yonezaki, S. 2009. Preliminary assessment of impacts on thesandlance population by consumption of minke whales off Sanriku region. Paper
SC/J09/JR14 presented to the JARPN II Review Workshop, Tokyo, January 2009
(unpublished). 20pp
Tamura, T., Konishi, K., Goto, M., Bando, T., Kishiro, T., Yoshida, H., Okamoto, R. and Kato, H.
2009. Prey consumption and feeding habits of common minke whales in coastal areas off
Sanriku and Kushiro. Paper SC/J09/JR9 presented to the JARPN II Review Workshop,
Tokyo, January 2009 (unpublished) 18pp.
Watanabe, H., Yonezaki, S., Kiwada, H., Kumagai, S., Kishiro, T., Yoshida, H. and Kawahara, S.
2009. Distribution and abundance of prey species and prey preference of common minke
whale Balaenoptera acutorostrata in the coastal component of JARPN II off Kushiro from2002 to 2007. Paper SC/J09/JR11 presented to the JARPN II Review Workshop, Tokyo,
January 2009 (unpublished) 37pp.

4

Table 1. The number of the minke whales distributed off Kushiro during the survey period for eachstratum in 2002-2007. O: Offshore, E: coastal-East, C: coastal-Central, W: coastal-West, and H: off
Hidaka sub-prefecture.
year
2002

straum
E
C
W
O

2003
2004

2005

2006

2007

O
E
C
W
H
W
C
E
O
H
W
O
E
C
H
W
O
E
C

Area
1,864.6
2,912.7
2,403.9
5,931.1
9,471.5
5,931.1
1,864.6
2,912.7
2,403.9
2,148.5
2,527.8
2,912.7
1,864.6
5,821.7
2,148.5
2,403.9
5,931.1
1,864.6
2,912.7
2,148.5
2,403.9
8,164.7
1,864.6
2,912.7

n
5.0
32.7
0.0
0.0
52.5
1.0
1.0
12.0
3.0
0.0
1.0
10.0
9.0
0.0
1.0
1.0
0.0
4.0
5.0
0.0
2.0
0.0
1.0
4.0

L
n/L
CV ESWCV
73.5 0.068 1.043 0.570 0.118
272.6 0.120 0.185 0.570 0.118
48.2 0.000 0.000 0.570 0.118
287.2 0.000 0.000 0.570 0.118
533.9 0.098 0.359 0.846 0.122
265.2 0.004 0.989 0.443 0.232
140.6 0.007 1.093 0.443 0.232
238.7 0.050 0.380 0.443 0.232
164.9 0.018 0.349 0.443 0.232
112.1 0.000 0.000 0.513 0.318
169.6 0.006 1.010 0.513 0.318
365.3 0.027 0.633 0.513 0.318
127.7 0.070 0.077 0.513 0.318
41.7 0.000 0.000 0.513 0.318
154.4 0.006 1.021 0.394 0.239
161.9 0.006 0.897 0.394 0.239
285.3 0.000 0.000 0.394 0.239
145.0 0.028 0.623 0.394 0.239
247.4 0.020 0.274 0.394 0.239
105.8 0.000 0.000 0.394 0.239
144.5 0.014 0.805 0.394 0.239
226.3 0.000 0.000 0.394 0.239
158.6 0.006 1.393 0.394 0.239
314.4 0.013 0.764 0.394 0.239

E(s) CV
1.05 0.035
1.05 0.035
1.05 0.035
1.05 0.035
1.29 0.054
1.06 0.056
1.06 0.056
1.06 0.056
1.06 0.056
1.05 0.048
1.05 0.048
1.05 0.048
1.05 0.048
1.05 0.048
1.00 0.000
1.00 0.000
1.00 0.000
1.00 0.000
1.00 0.000
1.00 0.000
1.00 0.000
1.00 0.000
1.00 0.000
1.00 0.000

D
0.063
0.111
0.000
0.000
0.075
0.005
0.008
0.060
0.022
0.000
0.006
0.028
0.072
0.000
0.008
0.008
0.000
0.035
0.026
0.000
0.018
0.000
0.008
0.016

P
117
323
0
0
709
27
16
175
52
0
15
81
135
0
18
19
0
65
75
0
42
0
15
47

CV
1.050
0.222
0.000
0.000
0.383
1.017
1.118
0.448
0.422
0.000
1.060
0.710
0.331
0.322
1.048
0.929
0.239
0.667
0.363
0.239
0.839
0.239
1.413
0.800

Table 2. Total number of the minke whales distributed off Kushiro during the survey period
assuming g(0)=0.732 for each year.

year
2002
2003
2004
2005
2006
2007

P
601
968
368
316
241
142

CV
0.447
0.492
0.449
0.447
0.448
0.619

5

Table 3. The number of the minke whales distributed off Sanriku during the survey period assumingg(0)=0.732 for each stratum in 2005 and 2006.

2005
2006

straumoffshorecoastaloffshorecoastalArea
2,777.7772.2
2,777.7
2,172.4

n
9.0
24.9
6.0
11.0

L
282.7
167.1
260.7
341.1

n/L
CV
0.032 0.364
0.149 0.315
0.023 0.508
0.032 0.333

ESW
0.318
0.318
0.388
0.388

CV
0.237
0.237
0.341
0.341

E(s)
1.00
1.00
1.00
1.00

CV
0.000
0.000
0.000
0.000

D
0.068
0.320
0.040
0.057

P
190
247
112
123

CV
0.533
0.501
0.685
0.568

Table 4. Total number of the minke whales distributed off Sanriku during the survey period assumingg(0)=0.732 for each year. More details of the estimate in 2004 is provided in Appendix..

year
2004
2005
2006

P
283
437
236

CV
0.623
0.425
0.493

ref.
2
1
1

ref. 1: This paper, 2: Appendix

6

2002

2003
E
C
W

H

O

2004

2005
E

E
C

C
W

W
H

H

O

O

2006

2007
E

E

C

C
W

W
H

H

O

O

Fig. 1. Distribution of primary sightings of the common minke whales and searching effort off
Kushiro in the survey of JARPN II costal component. There are five survey strata:; O: Offshore, E:
coastal-East, C: coastal-Central, W: coastal-West, and H: off Hidaka sub-prefecture.

7

2005

2006

offshorecoastalcoastaloffshore

Fig. 2. Distribution of primary sightings of the common minke whales and searching effort off
Sanriku during JARPN II costal component.

8

2002
n =37

Detection probability

1

Kushiro

2003

2004

2005
n =17

n =52

2006
n =18

n =19

2006&2007

0
0

1.5 0

1.5 0

1.5 0

1.5 0

n =47

1

1.5

n =27

Sanriku

0
0

1.5

0

1.5 0

1.5

Fig. 3. Plot of detection probability functions for the common minke whales during the sighting survey off
Kushiro in 2002-2007 and off Sanriku in 2005 and 2006. n is the number of the primary sightings to estimate thedetection probability functions.

9Appendix.
Abundance estimate of common minke whales in the Sendai Bay, estimated from 2004 sighting survey
Tomio Miyashita
National Research Institute of Far Seas Fisheries
2-12-4 Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa 236-8648, Japan
Contact e-mail: miyachan@fra.affrc.go.jp

Survey outline
Period: 12 April – 11 May, 2004
Area : Block and pre-determined track line (Fig. 1)
Research vessel: Kurosaki
Scientists onboard: T. Ebusui and S. Yonezaki
Whale observers onboard: T. Okumura, T. Okumura and Y. Tanaka
Research method: Closing mode (the first half), Passing mode (the second half)
Research distance: 694.3nmi (closing mode), 607.0nmi (passing mode)
Track line traversed with sighting effort: (Fig. 2).
Common minke whale sighting results :Closing mode
Passing mode

Primary sighting
schoolanimal67
22
22Secondary sighting
schoolanimal1
1-

Sighting positions of common minke whale: (Fig. 2)
Abundance estimate
Method: Traditional line transect method using the program DISTANCE 4.1 (Thomas et al., 2003).
Detection curve fitting: Because secondary sightings was very small number and the school size was notdifferent between two research methods, all primary sighting are used for fitting ted and the detection curve wasfitted (Fig. 3).
Abundance: 273 (CV 0.57, 95%C.I. 96 – 774) assuming g(0)= 0.756（CV 0.179）which was provisionallyestimated from the IO sighting survey in the Sea of Okhotsk (Miyashita, 2004).
References.
Miyashita, T. 2004. Report of the common minke whale sighting surveys in the sea of Okhotsk in 2003.
Document SC/56/MP1. 10pp.
Thomas, L., Laake, J.L., Strindberg, S., Marques, F.F.C., Buckland, S.T., Borchers, D.L., Anderson, D.R.,
Burnham, K.P., Hedley, S.L., Pollard, J.H. and Bishop, J.R.B. 2003. Distance 4.1. Release 2.
Research Unit for Wildlife Population Assessment, University of St. Andrews, UK.
http://www.ruwpa.stand.ac.uk/distance/

10

Fig. 1. Block and pre-determined track line for 2004 survey.

Fig. 2. Track line traversed with sighting effort
and sighting positions of common minke whale school (white circle).
11

Fig. 3. Detection curve fitted to the sighting data of Kurosaki
in the Sendai Bay sighting survey in 2004.

12