SC/61/JR6 (additional analysis - SC/J09/JR27)

Further morphometric analysis on stock structure in thewestern North Pacific common minke whales (Balaenopteraacutorostrata)
Takashi Hakamada and Takeharu BandoThe Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan.
Contact e-mail: hakamada@cetacean.jp

ABSTRACT
Morphometric analysis on stock structure in western North Pacific common minke whales was conductedbased on Principal Component Analysis (PCA) and discriminant analysis, following a recommendation fromthe JARPN II Review Workshop. Results of this analysis suggested significant difference in morphometrics
between the ‘J’ and the ‘O’ stocks but no significant differences among ‘O’-stock common minke whales
from longitudinal sectors in the western North Pacific. Results from the PCA are consistent with thosepresented by Hakamada and Bando (2009) to the JARPN II Review Workshop (SC/J09/JR27).
INTRODUCTION
The International Whaling Commission’s Scientific Committee (IWC SC) carried out a Workshop to review
the progress made in the research conducted under the Japanese Whale Research Programme under Special
Permit in the North Pacific-Phase II (JARPN II) in its first six years (2002-2007). The review was carried out
by an Independent Expert Panel (IEP) who examined primary papers related with the research objectives ofJARPN II.
One of the objectives of the JARPN II is the elucidation of stock structure in large whales and regarding tothis objective a total of eight primary papers on common minke, Bryde’s, sei and sperm whales were
presented to the review workshop. Hakamada and Bando (2009) (SC/J09/JR27) presented the results of amorphometric analysis of common minke whales, based on ANCOVA using body length as a covariate.
Differences were found between ‘J’ and ‘O’-stocks animals identified by the genetic analyses, however, nosignificant differences were found among ‘O’-stock animals from sub-areas 7, 8 and 9.
During the review workshop the IEP suggested that another option for the analysis would be to use a Principle
Component (or similar) Analysis (PCA) of individuals that does not require a priori decisions about groupmembership. It noted that PCA does not attempt to define groups but can reveal patterns in the data related totime or place of sampling (IWC, 2009). In response additional morphometric analysis based on PCA wereconducted to investigate further stock structure of western North Pacific common minke whales. The firstobjective of the study was to compare external measurements between ‘O’ and ‘J’-stocks animals as identified
by the microsatellite analysis. The second objective of this study was to compare O-stock minke whales fromseveral longitudinal sectors in the western North Pacific.
MATERIALS AND METHODS
Materials
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 were usedbecause 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 sexually1mature by testis weight (larger side) of more than 290g (Bando et al., unpublished data).Although the effect ofthe difference among researchers has not been fully examined, at this stage the data from a single researcherwho measured samples in all longitudinal sectors in different years, were used. As a consequence sample sizefor ‘J’ stock is small (n=2).
To compare external measurements between ‘O’ and ‘J’ stocks, whales were separated into two groups, ‘J’(n=2) and ‘O’ (n=118) stocks according to the results of the microstellite analysis (Kanda et al., 2009). To
compare O-stock minke whales from different longitudinal sectors the 118 O-stock whales were divided
according to the six longitudinal sectors used during JARPN 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 SC/J09/JR27). Externalmeasurements that were considered to be less susceptible to measuring error 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 of Hakamada and Bando (2009) (SC/J09/JR27).
Logarithms of the measurements were used for the analyses.
Analytical procedure
First PCA was used to extract principal components (PC) from the 11 measurements used in Hakamada andBando (2009) (SC/J09/JR27). A total of 11PCs was obtained from 11 measurements. Component matrix isshown in Table 1. The first PC (PC1) is positively correlated to all measurements V1-V11 and therefore it canbe interpreted as an index of growth. Consequently PC1 was eliminated from the analysis. Second,
discriminant analysis was conducted using the second to the eleventh PCs (PC2-PC11). To determine thediscriminant function, stepwise variable selection was conducted. If F-statistics is more than 3.84, the PC wasincluded in the discriminant function. If F-statistics was less than 2.71, the PC was removed from the function.
This procedure is a combination of forward selection and backward selection (Landau and Everitt, 2001).

RESULTS AND DISCUSSION
For the comparison between the ‘J’ and ‘O’ stocks, PC2 and PC8 were selected as variants of discriminantfunction. This implies that the score of the 2 PCs significantly differed between ‘J’ and ‘O’ stocks. FromTable 1, PC2 is interpreted an index on whether an animal has smaller heads and longer lower half of thebody and PC8 is interpreted as an index on length between end of ventral gloves and center of umbilicus.
From the results of discriminant analysis, morphological features of ‘J’-stock animals are that they have
longer head and shorter lower half of the body than ‘O’-stock animals and that their lengths between end ofventral gloves and center of umbilicus is longer than those of ‘O’-stock animals.
In order to evaluate the accuracy to correctly discriminate ‘J’ and ‘O’-stocks animals, discriminant function
was applied to the total samples and 88.3% of the original data were discriminated correctly as shown inTable 2. It should be noted that the small sample size of ‘J’-stock animals could overestimate the accuracy ofthe discriminant function. Notwithstanding this result suggest that there are significant differences between
the ‘J’ and ‘O’ stock in morphometric measurement.
It should be noted that 11.9% of ‘O’-stock animals were discriminated incorrectly. This may be because asmall fraction of the ‘O’-stock animals have features of body proportions of ‘J’-stock animals due toindividual differences in morphometric measurements.
With regard to PC2, ‘J’-stock animals have lower score than ‘O’-stock animals. This means that ‘J’-stock
animals have longer heads and shorter half of the body. This agrees with the results of the estimated marginal
mean of external measurements by ANCOVA in Hakamada and Fujise (2000) and Hakamada and Bando(2009) (SC/J09/JR27).

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In the comparison among whales from different longitudinal sectors in the western North Pacific, no PC wasselected for the discriminant function. In other words, there is no significant difference in morphometricmeasurements among O-stock whales from the longitudinal sectors.
In general results of this analysis based on PCA are consistent with those presented by Hakamada and Bando(2009) based on ANCOVA.
REFERENCES
Hakamada, T. and Fujise, Y. 2000. Preliminary examination of the heterogeneity of minke whales in thewestern part of the 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 Programme
under Special Permit for North Pacific minke whales (JARPN), Tokyo, 7-10 February 2000 (unpublished).
12pp.
Hakamada, T. and Bando, T. 2009. Morphometric analysis on stock structure in the western North Pacificcommon minke whales (Balaenoptera acutorostrata). Paper SC/J09/JR27 presented to the JARPN II Review
Workshop, Tokyo, January 2009 (unpublished). 13 pp.
International Whaling Commission. 2009. The Report of the Expert Workshop to review the ongoing JARPNII Programme. Document SC/61/xx presented to this meeting.
Landau, S. and Everritt, B. S. 2001 A handbook of statistical analyses using SPSS. Chapman & Hall/CRC.
354pp.

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Table 1. Component matrix extracted by PCA. Bold letter indicates the PC’s selected for discriminantfunction. PCx indicates the x th PC.
PC1 PC2 PC3PC4
PC5PC6PC7 PC8 PC9 PC10 PC11
V1 0.92 0.30
0.08 0.02
0.12 0.02 -0.06 -0.01 0.04
0.10 0.15
V2 0.81 -0.46 -0.18 -0.30 0.05 -0.03 -0.05 0.01
0.01 -0.01 -0.01
V3 0.83 -0.49 -0.10 0.17 -0.04 -0.14 0.03 -0.03 -0.10 -0.04 0.04
V4 0.88 -0.39 -0.01 0.20 -0.03 -0.13 0.02 -0.01 0.12
0.06 -0.06
V5 0.91 -0.16 0.07 0.21
0.07 0.18 -0.23 0.04 -0.01 -0.04 -0.03
V6 0.71 0.58
0.09 0.01
0.35 -0.09 0.10 0.12 -0.04 0.00 -0.04
V7 0.79 0.56
0.01 -0.03 0.08 0.03
0.02 -0.23 -0.01 -0.01 -0.03
V8 0.75 0.64 -0.07 0.01 -0.10 -0.03 0.02 0.04
0.08 -0.10 0.03
V9 0.74 0.60 -0.19 -0.03 -0.19 0.02 -0.01 0.05 -0.06 0.07 -0.03
V10 0.83 -0.46 0.01 0.02 -0.02 0.23
0.21 0.02
0.01
0.00 0.01
V11 0.71 -0.08 0.67 -0.14 -0.13 -0.05 -0.01 0.01 -0.02 0.00 -0.01
Table 2. Percentage of correction classified the ‘J’ and ‘O’-stocks animals by the discriminant function.

frequensy
original data%

OJOJO
104
088.1
0.0

discriminatedJ142
11.9
100.0

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total
118
2
100100