SC/J09/JR15

Distribution and the number of western North Pacific common
minke, Bryde’s, sei and sperm whales distributed in JARPN II
Offshore component survey area.
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 large whales, such as common minke (Balaenoptera

acutorostrata), Bryde’s (Balaenoptera edeni), sei (Balaenoptera borealis) and sperm whales(Physeter macrocephalus), on Japanese fisheries through estimating the amount of prey consumed
by these whales or using ecosystem models , it was required to estimate the number of these whalesin the JARPN II survey area. Considering the migration pattern of these whales in the area suggested
by our sighting survey data, the number of the whales needed to be estimated separately for the earlyand late seasons for each of the whale species. The estimates were 7,338 in the early and 2,976 in thelate season for the common minke, 7,744 in the early and 5,406 in the late season for the sei whales,
1,677 in the early and 9,797 in the late season for the Bryde’s whales, and 15,929 in the early and20,292 in the late season for the sperm whales. It is important to note that these estimates should not
be used for assessment because the estimated figures represent only a part of the populationconsidered.
INTRODUCTION
Feeding ecology and ecosystem studies are one of the main objectives of JARPN II. An impact ofwhales on Japanese fisheries in the JARPNII survey area can be assessed from estimating theamount of prey consumed by the whales in the areas (Tamura et al, 2009) or applying ecosystemmodels developed for the area (Mori et al., 2009; Kawahara et al., 2009). For either way, it isrequired to estimate the number of whales distributed in the area. Stomach contents and distributionof the whales could differ between early (May – June) and late (July – September) feeding seasonsand therefore the number of whales distributed in JARPN II survey area was estimated separately forthe early and late seasons in this study.
MATERIALS AND METHODS
Dedicated sighting survey was conducted in JARPN II survey from 2002 to 2007. Timing of survey

and surveying order of strata was changed substantially year by year in order to know how thenumber of distributed whales changed and how whales moved seasonally (for more details, see
Kiwada et al., 2009). During 2002-2005, the survey area was planned to be covered for two years
whereas during 2006-2007 the survey area was planned to be covered for a year. Table 1 showssurvey period and survey days in each of the survey years. Table 2 shows survey period bylatitudinal sector for each of the sub-areas. In 2006, the survey was conducted from south to north. In
2007, the survey was conducted from north to south. More details of the sighting survey procedure
are explained in Kiwada et al., (2009). Stratification of the JARPN II survey area is shown in Fig. 1.
Sub-areas 8 and 9 are stratified at 41oN latitudinal line. Distributions of trackline surveyed andprimary sightings for the common minke, the sei, the Bryde’s and the sperm whales are shown in
Figs. 2, 3, 4 and 5, respectively.
Based on sighting data obtained during these surveys, the number of the whales distributed in the
JARPN II survey area and their CVs was estimated from the following formulae;N=

AnE ( s )
2 wl

(1)

2

  n 2
2
CV ( N ) = CV   + {CV (w)} + {CV (E ( s ) )}  l (2),where N was the number of the whales distributed, A was area size of the surveyed area, E(s) was
estimated mean school size, w was effective strip half width and l was searching distance. In casethat data were pooled over multiple strata to estimate w and E(s), CV of the estimated N was
estimated from

 E ( s) n Ai ni  nCV  ∑ N i  = CV ∑i l 
2
w
 i

i


2

  n A n 22
= CV  ∑ i i  + {CV (w)} + {CV (E (s ))}  i li (3), ni n∑ A var l i=i

 i  + {CV (w)}2 + {CV (E (s ))}2
Ai ni
∑i l
i
n

where i was an index of strata. n was the number of strata whose data were pooled. In thiscalculation, it was assumed that n nj 
cov i ,  = 0
l l 
 i j (i ≠ j)(4).

The whale numbers were estimated using the program DISTANCE ver. 3.5 (Thomas et al., 1998)
g(0) was assumed to be 0.732 (Okamura et al, 2008) for Top barrel and Upper bridge for the minke2whales, 0.64 (Whitehead, 2002) for sperm whales, and 1 for Bryde’s and sei whales.
RESULTS AND DISCUSSIONSDistribution and movement of whales
As shown in Table 3, the numbers of the whales distributed in the survey area fluctuate among years
probably due to the difference in migration pattern among years. As discussed later, the common
minke and sei whales mainly distribute in southern part of the survey area (south of 41oN) in earlyseason (May – June) and migrate to north of 41oN in late season (July – September). In 2006, thesouthern part of the area was surveyed in early season and the northern part of the area was surveyed
in later season. Therefore, our survey vessels likely followed migrating common minke and sei
whales. This survey process should have caused the highest estimate observed for the common
minke and sei whales in 2006. In 2007, northern part of the area was surveyed when the whales had
not migrated there yet and southern part was surveyed in late season after the whales migrated out tonorth. As mentioned later, Bryde’s whales hardly migrate yet in the JARPN II survey area in theearly season and migrate in the southern part of the survey area in the late season. In 2006, because
the southern part of the area was surveyed in the early season, the estimated number was low. In
2007, because the southern part of the area was surveyed in the late season, the estimated number
was high.
Fig. 6 shows monthly searching effort by latitude. Because there was not enough searchingeffort in April and October, we used data from May to September. Fig 7 shows Density Index (DI:the number of the sightings per 100 n.minles) by latitude during the 1994-2007 JARPN and JARPN
II (Matsuoka et al., 2009). Fig 7 suggested that the minke and sei whales were distributed south of
41oN in May and June and north of 41oN in July and August, and that Bryde’s whales were
distributed in south of 38oN in June and south of 41oN in July and August. For the sperm whales,
there distributions did not change from May to September. In summary, distributions of the minke,
sei and Bryde’s whales change substantially from June to July compared to other month.
Estimation of the numbers of whales distributed
Table 3 shows the number of the whales distributed in the research area during the survey period foreach of the survey years. The estimates for the common minke whales and sei whales were high in2006 and low in 2007 for the reason mentioned above. Contrary, the estimates for the Bryde’s
whales were low in 2006 and high in 2007. For sperm whales, the estimates did not fluctuate
substantially year by year. However, as mentioned earlier, these high estimates might have included
positive biases because our survey vessels followed migrating animals, while the low estimatesmight have included negative biases due to mismatching between timing of survey and distributionof whales.
Considering above changes in distribution and migration of whales, data set were selected so as
to include sighting data in the peak migration area in the early (May and June) and late (from Julyand August) seasons, respectively, but not to combine the both data set to avoid double counting due
to migration. The area of low coverage was not selected. The selected data set were obtained and3listed in Table 4. The estimated number of whales distributed in JARPN II survey area in the earlyand late season can be obtained using the data listed in Table 4. Table 5 shows the estimated numberof whales distributed in the JARPN II survey area in the early and late season. The estimates were
6,609 in the early and 2,879 in the late seasons for the common minke, 7,646 in the early and 5,370
in the late seasons for the sei whales, 1,559 in the early and 9,344 in the late seasons for the Bryde’s
whales and 14,987 in the early and 19,185 in the late seasons for the sperm whales. Fig. 8 shows
distributions of primary sightings used for the estimation of the common minke, sei, Bryde’s andsperm whales in the early and late seasons, respectively. For the common minke and sei whales, themain distribution area moves to north of JARPN II survey area.

This figure likely well reflects the

distribution pattern suggested by Fig. 7. Fig. 9 shows the detection probability functions for thecommon minke, sei, Bryde’s and sperm whales. The detection probability functions seemed to fit therelative frequency of the distribution of perpendicular distance of the detections.
Coverage of the survey area for each of the sub-areas 7, 8 and 9 was 85.3%, 100% and 100%,
respectively. The estimated numbers divided by these coverage are shown in Table 6.
DISUSSIONSFor the common minke whales, the estimated numbers distributed in the survey area in the lateseason was less than that in the early season. This can be considered that the minke whales migrate
to further north of the JARPN II survey area. In fact, the common minke whales mainly distribute in
the Sea of Okhotsk and in the waters east of the Kamchatka Peninsula and the Kuril Islands inAugust and September (Buckland et al, 1992; Miyashita, 2009). Similarly, in the case of the sei
whales, the estimated number in the late season was much less than that in the early season. This canbe interpreted as that the sei whales may migrate north or east of the survey area. Contrary, for the
Bryde’s whales, the estimated number in the early season was less than that in the late season. Thiscan be interpreted as that the Bryde’s whales distribute mainly in the south of the JARPN II survey
area and migrate to southern part of the survey area (south of 41oN) in summer (June – September).
For the sperm whales, there was no indication that the distribution pattern in the survey area change
substantially during the survey period.
As discussed above paragraph, the distributed whales in the JARPN II survey area were a partof the whole stock and therefore, the estimated numbers of the distributed whales in this study
should not use as the representation of the population size of the stock. In order to obtain abundance
estimates appropriate for assessment of whale stocks, we also need to consider the information
outside of the JARPN II survey area. We will not discuss this matter further in this paper but in theother paper (i.e., re-assessment of effect of research take on the whales stocks).
In this paper, g(0)<0 was assumed for the common minke and sperm whales and the estimateddensity in the sub-area 7 in Table 5 was extrapolated to the unsurveyed stratum in the sub-area 7 (i.e.
7N in Fig. 1). For the estimate of prey consumption of the whales and the use for ecosystem models,the estimates corrected by g(0) and the estimated density extrapolated to unsurveyed area areappropriate rather than the estimates assuming g(0)=1 as well as no whales in the 7N stratum
because the latter combination clearly underestimates the number of the whales.
4In order to avoid the effect caused by disagreement between the survey timing and whales’
migration pattern, the number of the dedicated sighting vessels has been increased from 1 to 2 since2008, and thus northern and southern halves of the research area are now surveyed simultaneously
by two vessels. Better estimates of the whales can be anticipated.
ACKNOWLEGEMENT
Authors would like to express gratitude for all the researchers and crew involved the JARPN II
offshore component. We also thank Saeko Kumagai, Hiroshi Kiwada and Tomoko Hasegawa (TheInstitute of Cetacean Research) for their assistance in this study. We also thank Hiroshi Hatanaka
and Naohisa Kanda (The Institute of Cetacean Research) for their valuable comments andsuggestions on this study.
REFERENCE
Buckland, S. T., Cattanach, K. L. and Miyashita, T. 1992. Minke whale abundance in the northwest
Pacific and the Okhotsk Sea estimated from 1989 and 1990 sighting surveys. Rep. Int. Whal.
Commn. 42: 387-92.
Kawahara, S. 2009. A minimum realistic model in the JARPNII offshore survey area. Paper
SC/J09/JR22 presented to the JARPN II Review Workshop, Tokyo, January 2009
(unpublished).XXpp
Kiwada, H., Kumagai, S. and Matsuoka, K. 2009. Methodology and procedure of the dedicatedsighting surveys in JARPN II –Offshore and coastal component of Sanriku and Kushiro-.
Paper SC/J09JR2 presented to the JARPN II Review Workshop, Tokyo, January 2009
(unpublished).16pp.
Matsuoka, K., Kiwada, H., Fujise, Y. and Miyashita, T. 2009. Distribution of blue (Balaenoptera
musculus), fin (B. physalus), humpback (Megaptera novaeangliae) and north pacific right(Eubalaena japonica) whales in the western North Pacific based on JARPN and JARPN II
sighting surveys (1994 to 2007) . Paper SC/J09/JR35 presented to the JARPN II Review
Workshop, Tokyo, January 2009 (unpublished). 12pp.
Miyashita, T. 2009. Abundance of common minke whales in the Russian EEZ in the Sea of Okhotsk
and east of Kuril Islands - Kamchatka peninsula, estimated from 2003 and 2005 sighting
surveys. Appendix 1 9pp. In: Hakamada, T. Re-assessment of the effect on the stocks of
JARPN II catches. Paper SC/J09/JR36 presented to the JARPN II Review Workshop, Tokyo,
January 2009 (unpublished).
Mori, M., Watanabe, H., Hakamada, T., Tamura, T., Konishi, K., Murase, H. and Matsuoka, K. 2009.
Development of an ecosystem model of the western North Pacific. Paper SC/J09/JR21
presented to the JARPN II Review Workshop, Tokyo, January 2009 (unpublished). 49pp
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
Secretariat]. 7pp.
5

Tamura, T., Konishi, K., Isoda, T., Okamoto, R. and Bando, T. 2009. Prey consumption and feeding
habits of common minke, sei and Bryde’s whales in the western North Pacific. Paper
SC/J09/JR16 presented to the JARPN II Review Workshop, Tokyo, January 2009
(unpublished). 36pp
Thomas, L., Laake, J.L., Derry, J.F., Buckland, S.T., Borchers, D.L., Anderson, D.R., Burnham, K.P.,
Strindberg, S., Hedley, S.L., Burt, M.L., Marques, F.F.C., Pollard, J.H. And Fewster, R.M.
1998. Distance 3.5. Release 6. Research Unit for Wildlife Population Assessment,
University of St. Andrews, UK. [Available: from http://www.ruwpa.st-and.ac.uk/distance/ ]Whitehead, H. 2002. Estimates of the current global population size and historical trajectory for
sperm whales. Mar Ecol Prog Ser 242: 295-304.

6

Table 1．Period and days of the sighting survey by dedicated sighting vessel (KS2).
Offshore Component
Dedicated Sighting Vessel
Season Research
ResearchResearch
Area
PeriodVessel(Days)
2002.6.5-9.8
KS2
2002
7,8,9
(96)
2003.5.14-9.5
2003
7,8,9
KS2
(115)
2004.5.14-9.5
2004
7,8,9
KS2
(115)
2005.5.15-8.24
2005
7,8,9
KS2
(102)
2006.5.16-8.29
2006
7,8,9
KS2
(106)
2007.5.13-7.30
2007
7,8,9
KS2
(79)
KS2: Kyoshin-Maru No.2

Table 2. Survey period and latitudinal band within each stratum for sighting survey by year.
year
2002

2003

2004

Sub-area 8
periodlatitudinal band
6/8-6/18
35-40oNo7/25-7/30
north of 40 No
5/14-5/21 37-41oN(west of 144oE） 7/2-7/6
north of 41 No5/21-5/25
north of 41 N
5/28-6/11 38-41oN(east of 144oE）oo
6/10-6/30
5/14-6/8
35-41 Nnorth of 38 N
period8/11-8/20

Sub-area 7
latitudinal band
38-41oNno survey

no survey

5/17-5/19
6/24-7/6

35-38 No38-41 N

7/25-7/30
6/22-6/27

35-38oN
38-41oN

2005

2006

2007

o

6/27-7/5
5/17-5/25
7/12-7/16
5/19-5/25
6/18-6/24
7/11-7/17

35-38oN
38-41oNonorth of 41 No
35-38 No38-41 Nonorth of 41 N

7/20-7/24
6/27-7/2
6/10-6/15

35-38 N
38-41oNonorth of 41 N

7oSub-area 9
periodlatitudinal bando
6/18-7/2
35-40 N
7/3-7/25
40-45oN
7/15-9/5
north of 43oNo6/30-7/31
8/3-8/23
6/12-6/27
5/26-6/11
7/16-8/22
5/27-6/5
6/7-6/18
7/17-8/4
8/5-8/26
7/10-7/20
7/2-7/10
5/29-6/10

38-41 No41-45 No35-38 N
38-41oNo41-45 No35-38 N
38-41oNo41-45 Nonorth of 45 No
35-38 N
38-41oNo41-45 N

5/16-5/29

north of 45 NoTable 3. The estimated number of the whales distributed in JARPN II survey area during the survey
period for each year. g(0) is assumed to be 0.732 (Okamura et al, 2008) for the minke whales, 0.64
(Whitehead, 2002) for sperm whales, and 1 for Bryde’s and sei whales.
common minke whales
sub-area
SA7
SA8
SA9
total
g (0)=0.732

2002&2003
P
CV
1,330
0.431
0
0.000
4,261
0.283
5,591
0.254
7,638
0.400

2004&2005
P
CV
1,147
0.301
173
0.560
514
0.699
1,834
0.280
2,505
0.417

2002&2003
P
CV
52
0.762
262
0.489
4,291
0.323
4,605
0.331

2004&2005
P
CV
0
0.000
1,187
0.822
6,413
0.677
7,600
0.829

2002&2003
P
CV
0
0.000
982
0.393
1,019
0.671
2,001
0.402

2004&2005
P
CV
39
0.896
535
1.296
338
0.732
911
0.853

2002&2003
P
CV
874
0.354
86
0.526
2,931
0.203
3,891
0.191
6,079
0.407

2004&2005
P
CV
100
0.428
1,816
0.489
4,024
0.349
5,939
0.421
9,280
0.554

2006
P
CV
3,104
0.881
480
0.526
2,471
0.392
6,055
0.546
8,272
0.628

2007
P
415
248
227
890
1,216

CV
0.591
0.872
1.022
0.471
0.563

sei whales
sub-area
SA7
SA8
SA9
total

2006
P
570
2,635
6,827
10,032

2007
CV
0.529
0.354
0.280
0.241

P
205
1,106
1,673
2,984

CV
1.148
0.507
0.650
0.445

Bryde’s whales
sub-area
SA7
SA8
SA9
total

2006
P
686
0
178
865

CV
1.593
0.000
1.161
1.406

2007
P
CV
2,637
0.456
2,918
0.466
3,790
0.582
9,344
0.316

sperm whales
sub-area
SA7
SA8
SA9
total
g (0)=0.64

8

2006
P
3,511
1,085
6,895
11,491
17,954

2007
CV
0.491
0.273
0.213
0.250
0.438

P
4,124
1,985
4,271
10,37916,218

CV
0.361
0.281
0.344
0.254
0.440

Table 4. Sighting data used for the estimated number of whales distributed in early and late season.
period
SA 7
SA 8
SA 9
early
2006 *1
South of 41oN in 2006*2 and South of 41oN in 2006*2 andNorth of 41oN in 2007
North of 41oN in 2007
（May-June）
*3
o
late
2007
North of 41 N in 2006 and North of 41oN in 2006 and SouthSouth of 41oN in 2007of 41oN in 2007
（July-August）*1：SA7 was surveyed in several days in early July in 2006.
o*2：For Bryde’s whales, sighting data in the south of 41 N surveyed in 2005 was used.
*3：SA7 was surveyed in several days in late June in 2007.

Table 5．The estimated number of the whales distributed in JARPN II survey area in early and lateseason. g(0) is assumed to be 0.732 with its CV=0.309 (Okamura et al, 2008) for the minke whales,
0.64 with its CV=0.36 (Whitehead, 2002) for sperm whales, and 1 for Bryde’s and sei whales.
speciesperiodCommon
minke

early
late
early
late
early
late
early
late

sei
Bryde's
sperm

SA7
SA8N
SA8S
SA9N
SA9S
total
P
CV
P
CV
P
CV
P
CV
P
CV
P
CV
4,240 0.934 339 0.925 430 0.782
0 0.309 1,600 0.577 6,609 0.691
567 0.667 226 0.746
0 0.309 1,776 0.678 310 1.068 2,879 0.523
570 0.529
61 1.240 2,280 0.342
0 0.000 4,735 0.371 7,646 0.272
205 1.148 355 1.451 1,045 0.532 2,093 0.360 1,673 0.650 5,370 0.300
686 1.593
0 0.000 535 1.296
0 0.000 338 0.732 1,559 0.860
2,637 0.456
0 0.000 2,918 0.466
0 0.000 3,790 0.582 9,344 0.316
5,487 0.609 501 0.424 616 0.618 5,452 0.521 2,930 0.501 14,987 0.439
6,443 0.510 1,079 0.481 2,599 0.490 7,843 0.446 1,221 0.913 19,185 0.409

Table 6. The estimated numbers in Table 5 divided by coverage for sub-area 7 (85.4%). The
estimated numbers in sub-areas 8N, 8S, 9N and 9S are same as those in Table 5.
speciesperiodCommon
minke

early
late
early
late
early
late
early
late

sei
Bryde's
sperm

SA7
SA8N
SA8S
SA9N
SA9S
total
P
CV
P
CV
P
CV
P
CV
P
CV
P
CV
4,969 0.934 339 0.925 430 0.782
0 0.309 1,600 0.577 7,338 0.712
665 0.667 226 0.746
0 0.309 1,776 0.678 310 1.068 2,976 0.517
668 0.529
61 1.240 2,280 0.342
0 0.000 4,735 0.371 7,744 0.270
241 1.148 355 1.45 1,045 0.532 2,093 0.360 1,673 0.650 5,406 0.300
804 1.593
0 0.000 535 1.296
0 0.000 338 0.732 1,677 0.893
3,090 0.456
0 0.000 2,918 0.466
0 0.000 3,790 0.582 9,797 0.311
6,429 0.609 501 0.424 616 0.618 5,452 0.521 2,930 0.501 15,929 0.444
7,550 0.510 1,079 0.481 2,599 0.490 7,843 0.446 1,221 0.913 20,292 0.411

9

Fig. 1. JARPN II survey area and its stratification.

10

Fig. 2. Distribution of the effort and primary sightings of western North Pacific common minke
whales by dedicated sighting vessel during JARPN II

11

Fig. 3. Distribution of the effort and primary sightings of western North Pacific sei whales bydedicated sighting vessel during JARPN II

12

Fig. 4. Distribution of the effort and primary sightings of western North Pacific Bryde’s whales bydedicated sighting vessel during JARPN II. In 2003, there was no primary sighting.

13

Fig. 5. Distribution of the effort and primary sightings of western North Pacific sperm whales bydedicated sighting vessel during JARPN II

14

10000ALL AREAEFFORT

9000

Apr

Effort [n.m.]

8000
7000

May

6000

Jun

5000

Jul
4000

Aug

3000
2000

Sep

1000

Oct

0
35

36

37

38

39

40

41

42

43

44

45

46

Latitude [deg N]

Fig. 6. Effort by latitude from April to October during 1994-2007.

15

47

48

49

50

51

ALL AREA
Minke

2.5

DI (sighting per Effort 100n.m.)common minke whales
2

May

1.5

Jun

1

Jul
0.5

Aug
0
35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

Latitude [deg N]

ALL AREA
Sei

6

sei whales
DI (sighting per Effort 100n.m.)

5

May
4

Jun
3

Jul

2

1

Aug
0
35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

Latitude [deg N]

10

DI (sighting per Effort 100n.m.)

ALL AREA
Bryde's

Bryde’s whales

9
8

May

7
6

Jun

5
4

Jul
3
2

Aug

1
0
35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

Latitude [deg N]
16

ALL AREA
Sperm

sperm whales

DI (sighting per Effort 100n.m.)

14

May

12
10

Jun
8
6

Jul

4

Aug

2
0
35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

Latitude [deg N]

Fig. 7. DI (whale/100n.mile) by latitude from May to September during 1994-2007 for the common
minke, sei, Bryde’s and sperm whales.

16common minke whales

common minke whales

early

late

sei whales

sei whales

early

late

Bryde’s whales

Bryde’s whales

early

late

sperm whales

sperm whales

early

late

Fig. 8. Distribution of primary sightings of the common minke, sei, Bryde’s and sperm whales inearly and late seasons. Left panels are figures in early season and right ones are in late season.

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Fig. 9. Plot of detection probability functions for the common minke, sei, Bryde’s and sperm whales.
n is the number of the primary sightings to estimate the detection probability functions.

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