SC/J09/JR27

Morphometric analysis on stock structure in the western North
Pacific common minke whales (Balaenoptera acutorostrata)
Takashi Hakamada and Takeharu BandoThe Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-Ku, Tokyo 104-0055, Japan.
Contact e-mail: hakamada@cetacenan.jp

ABSTRACTThis study uses morphometric data obtained by JARPN II to investigated differences between “J”
and “O” stocks and the plausibility of four stock structure scenarios adopted by IWC in RMP
Implementation Simulation Trials (ISTs) for western North Pacific “O” stock common minke whales(Balaenoptera acutorostrata), Analysis of covariance (ANCOVA) using body length as a covariate isused to test if there are significant differences in morphometric measurements among the groups
compared. There are some significant differences in morphometric between “J” and “O” stocks, but
no significant differences were found within the “O” stock in sub-areas 7, 8 and 9. Results of themorphometric analysis are consistent with those of the genetic analyses and therefore they provide
support for the single stock structure scenario (Baseline B) used in the ISTs. These results provide no
support for the stock structure scenarios represented by Baselines C and D.

INTRODUCTION
In the western North Pacific two stocks of the common minke whale have been recognized by theInternational Whaling Commission Scientific Committee (IWC SC), the Okhotsk Sea – west Pacificstock (O stock) and Sea of Japan – Yellow Sea – East China Sea stock (J stock). Previous analyses
based on genetics (Goto and Pastene, 1997) and non-genetic (e.g. morphometric, Kato et al., 1992;
Fujise and Kato, 1996) approaches revealed marked differences between these two stocks.

A study based on microsatellite analysis of minke whales sampled by the JARPN and JARPN II in
sub-areas 7, 8 and 9 assigned individual minke whales to either stock (Kanda et al., 2009). These
results provide a unique opportunity to further examine differences between the two stocks using
non-genetic approaches. The first objective of this study was to compare external measurements
between “O” and “J” stock whales as identified by the microsatellite analysis.

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A second objective of this study was to evaluate the plausibility of the four stock structure scenarios
used in the RMP Implementation Simulation Trials (ISTs) for the minke whales in 2003 (IWC,2004), using analysis of morphometric measurements as a non-genetic marker.

The following four stock structure hypotheses were used in the ISTs by the IWC SC:(1) Baseline A: 3-stock scenario (‘J’ ‘O’ and ‘W’) with W found only sporadically in subarea 9W.
(2) Baseline B: 2-stock scenario (‘J’ and ‘O’) with no W stock as a limiting case of Baseline A.
(3) Baseline C: 4-stock scenario (‘J’, ‘Ow’, ‘Oe’ and ‘W’) with fix boundaries at 147°E and 157°E.
(4) Baseline D: 3-stock scenario (‘J’, ‘O’ and ‘W’) with O and W mixing over 147°-162°E, O being
dominant to the west and W to the east.

MATERIALS AND METHODS

Samples
Minke whales sampled by JARPN II surveys in sub-areas 7 (140°-150°E), 8 (150°-157°E), and 9(157°E-170°E) between 2000 and 2007, were used in the analysis. Only mature male animals wereused because body proportion could be different between mature and immature animals and because
the very limited number of mature females in the research area. Males of minke whales were defined
as sexually mature by testis weight (larger side) of more than 290g (Bando et al., unpublished data).

For the first objective of the study whales were separated into two groups, “J” and “O” stocks
according to the results of the microstellite analysis (Kanda et al., 2009). For the second objective of
the study, whales of the “O” stock were divided according to the six longitudinal sectors used during
JARPA surveys: 7W (140°-147°E), 7E (147°-150°E), 8W (150°-153°E), 8E (153°-157°E), 9W(157°E-162°E), 9E (162°-170°E) (Figure 1). Table 1 shows the sample sizes by year andlongitudinal sectors. This geographical division was used for testing the four stock structure
scenarios used in the ISTs.

External measurements
The measurements that were less susceptible to differences among researchers were selected for the
analysis. Selection of these measurements took into consideration the opinion of experienced
researchers. We also excluded girth because they are likely to change in the feeding season,
according to sampling date. The ten external measurements used are shown in Figure 2. Logarithmsof the measurements were used for the analyses.

2Analytical approach
Analysis of covariance (ANCOVA) using body length as a covariate was used to test if there are
significant differences in morphometric measurements among groups. In these analyses, it was
assumed that lengths of the measurements depend on body length and that their relation can be
described by the formula,log( x n ) = α i log( x1 ) + β i(1)where V1 is body length, xn is length of the measurement Vn (n=2,…,11), i is an index representing
group to be compared, α i is the slope and β i is intercept of the formula (1) for group i. Using
formula (1), ANCOVA can be explained as follows. ANCOVA consists of two steps. The first one isto test null hypothesis thatα 1 = α 2 = ... = α m = α(2)where m is the number of the groups to be compared by ANCOVA. If the null hypothesis was
rejected, the second test would be conducted. Assuming that equation (2) is true, formula (1) wouldbelog( x n ) = α log( x1 ) + β i(1)’The second one is to test null hypothesis thatβ1 = β 2 = ... = β m = β(3)in formula (1)’ when the null hypothesis (2) was not rejected at the 5% significant level. When m ismore than 2, multiple comparison tests would be conducted if the null hypothesis (3) was rejected. In
any ANCOVA conducted in this document, the null hypotheses (2) were not rejected. Note thatderivation of β i (i.e. average of β i subtract from β i ) can be regarded as a correction factor toeliminate the biases to due the comparison factor. Especially, in case of comparison among
researchers, they can be used to correct the bias due to difference of researchers.

The steps followed in the analysis were the following: .first, we tested if there is a temporal
heterogeneity within each longitudinal sector. Second, we examined the morphometric differences
between whales identified as “O” stock and “J” stock animals by the microsatellite analysis (firstobjective). Third, we examined morphometric differences among “O” stock whales according togeographical division underlining the stock structure scenarios of the ISTs (second objective).

RESULTS

Temporal heterogeneity in each longitudinal sector
Table 2 shows results of ANCOVA to test if there are any significant differences among years in eachlongitudinal sector. There are some significant differences in most of the longitudinal sectors. Such3

temporal heterogeneity could not have biological basis as genetic analyses based on mtDNA andmicrosatellite showed no significant yearly differences in these sectors. Rather these significant
differences might reflect difference in measurement among the researchers. Assuming this, in order
to eliminate possible effect of these differences among the researchers on the results of analyses, thedata from a single researcher who measured samples in all longitudinal sectors in different years,
were used. Assuming that the averaged measurements of all researchers are unbiased, measurements
by the selected researcher are corrected in the cases that significant temporal heterogeneity wasobserved. Table 3 shows the numbers of samples by the single researcher. Correction factors were
estimated by comparison among the researchers using ANCOVA. Table 4 shows the estimatedcorrection factors.

The difference between “J” and “O” stocks
Two samples from “J” stock and 118 samples from “O” stocks were used for this analysis (Table 3).
The two “J” stock whales were sampled in 2002, one from 7W sector and the other from 9W. Table 3
shows the number of samples “J” and “O” stock samples measured by the single researchers.
There were some significant differences between “J” and “O” stocks (Table 5). This result suggeststhat external measurements can be used as a non-genetic marker to differentiate these stocks. For
example the average marginal mean of the length of the measurements V2-V5 are longer for “J”
animals than for “O” animals. Those of the measurement V6-V9 are shorter for “J” animals than “O”
animals. Those of V10-V11 are longer for “J” animals than “O” animals. These results suggest that“J” animals tend to have bigger heads and shorter lower half of the body than “O” animals.

Evaluation of the plausibility of stock structure scenarios for “O” stock
Baseline A
Data from the single researcher were available for sub-area 9W only for years 2002 and 2003. Table
6 shows that there is no significant difference between 9W (data combined for the two years) andother sectors. Therefore this result provides no support for baseline A.

Baseline B
There is no significant difference in the measurements among whales in 7W, 7E, 8W, 8E, 9W and 9E
as shown Table ７. This result suggests that there is no sub-stock of the O stock in sub-areas 7, 8
and 9 and agrees with the baseline B.

Baseline C
There is no significant difference among 7E, 8W and 8E as shown in Table 8. This means 7E, 8W

4and 8E can be combined as one group. There was no significant among whales in 7W, 7E+8W+8E,
9W and 9E as shown in Table 9. These results provide no support for the occurrence of three stocks(OW, OE and W) with divisions at 147° and 157°E (stock structure baseline C).
Baseline D
There is no significant difference among 7E, 8W, 8E and 9W as shown in Table 10. This means 7E,
8W, 8E and 9W can be combined. There was no significant among 7W, 7E+8W+8E+9W combined,
and 9E as shown in Table 11 This result suggests that the 147-162oE longitudinal sector
hypothesized as a mixing region in baseline D is not significantly different from east and west of thislongitudinal sector. This is inconsistent with baseline D.

DISCUSSIONS

Difference between “J” and “O” stocks
Marked morphometric differences found between “J” and “O” whales (Table 5) confirmed thefinding of previous JARPN studies. . Hakamada and Fujise (2000) examine the difference between
the “J” and “O” stocks using JARPN external measurement data obtained during 1994-1999 andsuggested significant differences between the two stocks, and a tendency that “J” animals haveshorter lower half of the body than “O” stock animals (Table 12).

Evaluation of the stock structure scenarios of “O” used in the RMP ISTs
The only source of morphometric heterogeneity was due to differences among years in sub-areas,
which was assumed to reflect differences among researchers obtaining the measures in different
years. It should be noted that the genetic analyses based on mtDNA (Goto et al., 2009) andmicrosatellites (Kanda et al., 2009) found no differences among years in the sub-areas, which
provide support for the assumption of differences among researchers rather a biological event. In
general results of the genetic and morphometric analyses were consistent and they provided no
support for stock structure scenarios C and D used in ISTs. They were consistent with the view of asingle “O” stock in sub-areas 7, 8 and 9 (stock structure scenario B).

ACKNOWLEDGEMENT
We would like to thank researchers and crew involved the JARPN II offshore and coastal component.
We would like to express our gratitude Hiroshi Hatanaka and Luis A. Pastene (Institute of Cetacean
Research), Lars Walløe (University of Oslo) and Toshiya Kishiro (National Research Institute of Far
Seas Fisheries) for their valuable comments on this study.

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REFERENCE
Fujise, Y. and Kato, H. 1996. Some morphological aspects of the western North Pacific minke
whales; Preliminary Analyses of materials from JARPN surveys in 1994-5. Paper
SC/48/NP11 presented to IWC Scientific Committee, May 1996 (unpublished). [Available
from IWC Secretariat]. 10pp.
Goto, M and Pastene, L. A. 1997. RFLP analysis of the mitochondrial DNA control region in minke
whales sampled during the 1996 JARPN. Paper SC/49/NP10 presented to IWC ScientificCommittee, September, 1997. (unpublished). [Available from IWC Secretariat]. 10pp
Goto, M., Kanda, N., Kishiro, T., Yoshida, H., Kato, H. and Pastene, L.A. 2009. Mitochondrial DNA
analysis on stock structure in the western North Pacific common minke whales. Paper
SC/J09/JR29 presented to the JARPN II Review Workshop, Tokyo, January 2009
(unpublished). 10pp.
Hakamada, T. and Fujise, Y. 2000. Preliminary Examination of the heterogeneity of externalmeasurements of minke whales in the western North Pacific, using data collected during
1994-1999 JARPN surveys. Paper SC/F2K/J15 presented to the IWC Scientific Committee
Workshop to Review the Japanese Whale Research Program under Special Permit for North
Pacific Minke Whales (JARPN), Tokyo, 7-10 February 2000 (unpublished). 12pp.
International Whaling Commission. 2004. Report of the Scientific Committee. J.Cetacean Res.
Manege. 6: 1-60.
Kanda, N., Goto, M., Kishiro, T., Yoshida, H., Kato, H. and Pastene, L. A. 2009. Individual
identification and mixing of the J and O stocks around Japanese waters examined by
microsatellite analysis. Paper SC/J09/JR26 presented to the JARPN II Review Workshop,
Tokyo, January 2009 (unpublished). 9pp.
Kato, H., Kishiro, T., Fujise, Y. and Wada, S. 1992. Morphology of minke whales in the Okhotsk Sea,
Sea of Japan and off the East Coast of Japan, with respect to stock identification. Rep. Int.
Whal. Commn. 42: 437-442.

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Table 1. The numbers of samples of the “O” stock used in the morphometric analysis, bylongitudinal sectors for each year (see text for explanation).

7W
Kushiro Sanriku offshore total
4
0
0
4
0
0
21
21
11
0
30
41
0
7
4
11
23
0
7
30
24
3
18
45
10
8
14
32
11
8
39
58
79
26
137
242

year
2000
2001
2002
2003
2004
2005
2006
2007
total

7E

8W
0
4
0
5
0
0
0
0
9

8E

0
0
0
12
0
2
6
1
21

9W

0
13
5
11
0
0
20
9
58

9E

10
19
19
18
25
8
14
2
115

0
0
0
11
23
19
0
2
55

total
14
57
65
68
78
74
72
72
500

Table 2. Temporal heterogeneity of the external measurement examined by ANCOVA. Bold letters
indicate the differences are significant at 5% level. “n.s.” is abbreviation for no significant.

measurement
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11

7W
n.s.
p <0.001
p <0.001
0.012
n.s.
0.034
0.001
p <0.001
0.047
n.s.

p -value
8W
8E
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
0.005

7E
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
0.015
n.s.
n.s.
0.021

9W
0.043
n.s.
n.s.
n.s.
0.001
p <0.001
0.032
0.010
n.s.
p <0.001

9E
n.s.
n.s.
n.s.
n.s.
n.s.
0.021
0.001
0.007
n.s.
n.s.

Table 3. The number of samples of the “J” and “O” stocks by the researcher who measured samples
all the longitudinal sectors.

year
2002
2003
2006
total

7W
O
30
4
0
34

7E
J
1
0
0
1

O
0
5
0
5

8W
J
0
0
0
0

O
0
12
1
13

8E
J
0
0
0
0

O
5
11
2
18

9W
J
0
0
0
0

7

O
19
18
0
37

9E
J
1
0
0
1

O
0
11
0
11

J
0
0
0
0

total
O
J
54
2
61
0
3
0
118 2

Table 4. Estimated biases for the researcher who measured samples all the longitudinal sectors using
ANCOVA. Positive number indicates the measurement was overestimated. Negative number
indicates the measurement was underestimated. “-“ indicates there were no significant differences inTable 2 and therefore no correction was made.

measurement 7W
7E
log(V2)log(V3)-0.004log(V4)-0.001log(V5)-0.002log(V6)log(V7)0.007
log(V8)0.001 -0.011
log(V9)0.007
log(V10) -0.004
log(V11) 0.002 -0.021

8W
-

8E
9W
9E
0.004
-0.001-0.004 -0.012
0.000 -0.028
0.004 -0.027-0.001 0.022-

Table 5. Comparison between “O” and “J” stocks identified by microsatellite and estimated marginal
mean of length of measurements for average body length (750.4cm). Bold letters indicate thedifferences are significant at 5% level. “n.s.” is abbreviation for no significant.

measurement

p- value

V2
V3
V4
V5
V6
V7
V8
V9
V10
V11

n.s.
0.041
0.032
n.s.
n.s.
0.036
n.s.
n.s.
0.017
0.035

"J stock" "O stock"(n =2)(n =118)
100.1
94.2
119.9
112.8
159.4
151.6
319.7
310.2
408.7
410.8
345.1
355.2
236.5
243.7
191.8
195.7
162.0
152.1
88.3
84.0

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Table 6. Results of test if there is any significant difference between 9W and other longitudinal
sector in 2002 and 2003.

year
measurement
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11

2002
p- value
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.

2003
p- value
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.

Table 7. Results of test if there is significant difference among 7W, 7E, 8W, 8E, 9W and 9E inmorphometric measurements by ANCOVA. “n.s.” is abbreviation for no significant at 5% level.

measurement
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11

p- value
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.

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Table 8 Results of test if there is significant difference among 7E, 8W and 8E in morphometricmeasurements by ANCOVA. “n.s.” is abbreviation for no significant at 5% level.

measurement
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11

p- value
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.

Table 9. Results of test if there is significant difference among 7W, 7E+8W+8E, 9W and 9E inmorphometric measurements by ANCOVA. “n.s.” is abbreviation for no significant at 5% level.

measurement
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11

p- value
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.

Table 10. Results of test if there is significant difference among 7E, 8W, 8E and 9W inmorphometric measurements by ANCOVA.

measurement
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11

p- value
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.

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Table 11. Results of test if there is significant difference among 7W, 7E+8W+8E+9W and 9E inmorphometric measurements by ANCOVA.

measurement
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11

p- value
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.

Table 12. Morphometric comparison between “J” and “O” stock using JARPN data (Hakamada andFujise, 2000). Measurements that were not used in this study were omitted to facilitate comparison.

measurement
V2
V3
V4
V5
V6
V7
V8
V9

p- valuep <0.05
p <0.05
p <0.05
n.s.
n.s.
n.s.
n.s.
n.s.

"J stock" "O stock"
95.0
91.0
114.1
109.8
151.0
146.8
305.0
299.8
398.1
399.6
344.9
345.5
236.5
238.0
190.6
191.0

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7W

7E

8W

8E

Fig. 1. Geography of the six longitudinal sectors.

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9W

9E

V5
V4
V3
V2

V9
V8
V7
V6
V1

V11

V10

V1: Body length
V2: From the tip of snout to blow hole
V3: From the tip of snout to center of eye
V4: From the tip of snout to ear
V5: From the tip of snout to tip of flipper
V6: From notch of flukes to end of ventral gloves
V7: From notch of flukes to center of umbilicus
V8: From notch of flukes to sexual apparatus
V9: From notch of flukes to anus
V10: Length of skull
V11: Maximum width of skull

Fig. 2. External measurements of western north Pacific common minke whale used in this study.

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