SC/63/RMP22

Ranking the plausibility of stock structure hypotheses ofwestern North Pacific common minke whale
Luis A. Pastene, Mutsuo Goto, Naohisa Kanda and Hiroshi Hatanaka
The Institute of Cetacean Research, Toyomi 4-5, Chuo-ku, Tokyo 104-0055, Japan
ABSTRACTThis paper ranks the plausibility of the components characterizing the three stock structure hypotheses
agreed for the Implementation of western North Pacific common minke whale. First we determined thecriteria for using different kinds of information to define stocks: genetics, biological, life history,
distribution gaps and migration, ecology and abundance and CPUE trend. In this exercise we took into
account the discussions conducted at the Standing Group on Stock Definition and at the western North
Pacific Bryde’s whale Implementation on the use of different information to define stocks. Then basedon previous IWC SC work we developed a simple procedure to rank hypotheses. Results suggested thefollowing rank of plausibility for the components characterizing the three hypotheses on stock structurein the western North Pacific common minke whale: Hypothesis I: High, Hypotheses II: Low andHypothesis III: Low.
KEYWORDS: COMMON MINKE WHALES, IMPLEMENTATION, WESTERN NORTH PACIFIC,STOCK STRUCTURE HYPOTHESES, PLAUSIBILITYINTRODUCTION
The current Implementation of western North Pacific common minke whales is being conducted under
the new ‘Requirements and Guidelines for Implementations’ developed by the IWC SC in 2004.
The development of the requirements and guideline was a good step forward following the previous
Implementation, which in absence of such guidelines it took an abnormal long period of time to becompleted (1993-2003). However one of the most important tasks of any Implementation is theassignment of plausibility rank to hypotheses on stock structure. Unfortunately the IWC SC has been
unable to develop a procedure that assigns plausibility to hypotheses in an objective and scientificmanner.
In this paper we determined the criteria for using different kind of information to define stocks, both
genetics and non-genetics. In this exercise we took into account the discussions conducted at theStanding Group on Stock Definition on the use of different information to define stocks (IWC, 2002) aswell the discussions held during the Implementation of the western North Pacific Bryde’s whale (seeTable 1 of IWC, 2007). Then based on previous IWC SC work we developed a simple procedure torank the plausibility of the components characterizing the three stock structure hypotheses of western
North Pacific common minke whale.
CRITERIA FOR DIFFERENT APPROACHES TO DEFINE STOCKS
Genetics differences
Examine whether there is genetic differences between stocks, at both maternal inherited and bi-parental
inherited markers, and the extent of such differences. The most used approach is hypothesis testing, inwhich whales from different geographic localities are compared statistically for their allele frequencies
under the null hypothesis of panmixia. It is important to check whether the number of samples is large
enough and if the genetic markers used are sensitive enough to detect differences among weakly
differentiated stocks (sequencing of the mtDNA control region and microsatellite DNA using asufficient number of loci e.g. at least 15 loci are the preferred techniques). If no significant differences
are found check if the power of the statistical analysis has been determined before reach the conclusionof panmixia.

1Biological differences
Examine whether there is morphometric and morphological (e.g. flipper color pattern, fluke color
pattern) differences between stocks. Check whether the number of morphometric traits, and the numberof samples examined are sufficiently large to get conclusions on panmixia with confidence.
Life history parameters differences
Examine whether there is difference in parameters such as age at sexual maturity, age and growth andconception date between stocks. Check whether the number of samples examined is sufficiently large
to get conclusions with confidence.
Completeness of the stock
For some baleen whale species such as the minke whales the spatial and temporal segregation by sex
and reproductive classes is well documented. This could confound the interpretation of stock structure.
All reproductive classes should be represented in a biological stock. Use the available biological data to
examine whether all sexual classes are represented in the proposed spatial and temporal distribution
range of the stock.
Distribution gaps and migration
Examine gaps in distribution. To determine if such gaps can be attributed to stock segregation it isimportant to check whether the discontinuity is stable with no movement between. It is also important
to examine distribution of effort as some gaps can be explained simply by no surveys in particular areas.
Check if the migration pattern proposed for a given stock is consistent with the available sighting,commercial whaling operation and biological data.
Ecological differences
Examine whether there is differences in accumulation level of pollutants (PCB, heavy metals) between
stocks. Check whether such differences are indeed due to stock differences or simply to other
ecological reasons (e.g. differences in the kind and amount of prey consumed, etc.). Check whether thesource, decay rates and effect of contaminants are known. This information is important forinterpreting differences in accumulation.
Examine whether there are differences in parasite load between stocks. Check whether such differences
are indeed due to stock differences. Check whether the life history and movement/distribution of theparasites are known. This information is important for interpreting differences in parasite load.
Abundance and CPUE
Examine whether the abundance and CPUE trends changed accordingly with the pattern of exploitationof the proposed stock. Check whether the assumption made for abundance estimates are appropriate.
Examine whether the results of conditioning for each stock structure hypothesis agree with abundancetrend.
Validity of pure stocks
Under different hypotheses of an Implementation some spatial and temporal delimited samples are
selected as ‘pure stock’ for the purpose of estimating mixing proportion. Definition of pure stock canbe better obtained if samples from breeding grounds are available. Unfortunately in the case of thecommon minke as well other whale species under assessment by the IWC SC such samples are notavailable (the exception is the humpback whale).
The selection of spatial and temporal samples for this purpose should be carefully examined toelucidate whether such groups contain really whales from a single stock rather a mixture of two stocks
or hybrid whales. The spatial and temporal pattern of mixing of stocks should be examined toinvestigate whether such pattern is consistent with the ‘pure stock sample’.
At least Hardy-Weinberg equilibrium should be tested (including power analyses test) to examine thepossibility of a mixture of more than one stock in the selected sample. Because this is not a powerful
test, use alternatives methods to investigate the possibility of mixture of more than one stock2

A more general criteria applying to all information above is that some weight should be given to resultsof analyses on stock structure recommended by the IWC SC in previous years.
DESCRIPTION OF THE HYPOTHESES ON STOCK STRUCTURE IN WESTERN NORTHPACIFIC COMMON MINKE WHALES
Three stock structure hypotheses (Hypotheses I, II and III) were proposed and specified for the
Implementation (see Figure 1 for the new sub-areas).
Hypothesis I (Figure 2a)Single J stock distributed in the Yellow Sea, Sea of Japan and in the Pacific side of Japan. Single O
stock occurs in sub-areas 7, 8 and 9, which migrate in summer mainly to the Okhotsk Sea (sub-areas
12SW and 12NE). Both J and O stocks overlap temporally in the Pacific coast (sub-areas 7CS, 7CN
and 2C) and the southern part of the Okhotsk Sea (sub-areas 11 and 12SW).
Hypothesis II (Figure 2b)
Same as Hypothesis I but a different stock (Y stock) resides in the Yellow Sea and overlaps
temporarily with the J stock in the south part of sub-area 6W.
Hypothesis III (Figure 2c)
There are five stocks, referred to as Y, JW, JE, OW, and OE, two of which (Y and JW) occur in the Sea
of Japan, and three of which (JE, OW, and OE) are found to the east of Japan. The JE distributes in the
Pacific coast of Japan around the year and mix with the OW in sub-areas 7CS and 7CN between April
and September. The JW distributes in sub-areas 6W, 6E and 10W and mix with the OW and OE in subareas 11 and 12SW. The OW distributes nearshore in sub-area 7W around the year and mix with theoffshore OE there and with the JW and OE in sub-area 12SW. Only the OE migrates into sub-area
12NE.
Stock structure hypotheses I and II are updated versions of the previous Hypotheses A and B, withsome elements of these hypotheses (e.g. Y and C stocks) mimicing some of the aspects of two of thesensitivity tests considered during the 2003 Implementation (IWC, 2004). A difference between
Hypotheses I/II and previous Hypotheses A/B is the more extensive distribution of J stock animals in
the Pacific side of Japan and the spatial and temporal mixing of J and O stock animals in sub-areas 7CS
and 7CN is now more documented under Hypotheses I and II.
Stock structure hypothesis III is new.
RANKING THE PLAUSIBILITY OF THE STOCK STRUCTURE HYPOTHESES OFCOMMON MINKE WHALES
We constructed a table to evaluate the three hypotheses in the context of the available genetic and nongenetic information and the criteria determined above (see Table 1). There are common and uniquecomponents among some hypotheses. For example Hypotheses I and II share the component of
panmixia of J and O stocks. The occurrence of the Y stocks in sub-area 5 is the component
differentiating these hypotheses. On the other hand Hypotheses II and III share the concept of a Y stockin sub-area 5 but differ on the concept for O and J stocks (panmixia of these stocks in case of
Hypothesis II and multiple J and O stocks in the case of Hypothesis III).
We evaluate the components characterizing each of those hypotheses in the context of the available
genetics and non-genetic information and the criteria determined above: Hypothesis I (panmixia of J
and O stocks and spatial/temporal mixing of these two stocks); Hypothesis II (occurrence of Y stock in
sub-area 5) and Hypothesis III (multiple J and O stocks) (Table 1).
Following the previous work of the IWC SC during the western North Pacific Bryde’s whale
Implementation (IWC, 2007, pp 95), we used the following key: ‘+’= indicates evidence in favour of ahypothesis; ‘-‘= indicates evidence against a hypothesis; ‘(+)’= indicate weak evidence in favour of ahypothesis; ‘(-)’= indicate weak evidence against of a hypothesis; ‘(())’= indicates very weakevidences; ‘NIW’= indicates that the evidence is not inconsistent with the hypothesis, and ND=
indicates the absence of particular data to evaluate a hypothesis. The designation ‘NIW’ often reflects
the asymmetrical nature of information on stock structure (i.e. existence of differences can be viewed
as positive evidence for multiple stocks, but absence of differences provides no information, and can3not be viewed as positive evidence for a single stock (IWC, 2007). In using the ‘NIW’ key,consideration should be given to sample sizes used and/or power analysis results. The category ‘ND’
was not considered in the Bryde’s whale Implementation.
During the Bryde’s whale Implementation the key shown above was agreed and used to complete theinformation table. However there was no discussion on how to rank different hypotheses into ‘High’,‘Medium’ and ‘Low’ based on the information from the table. In this paper we used the following
general criteria.
A hypothesis should be ranked ‘High’ if a) data is available for at least 50% of the boxes; AND, b) the‘ND’ key is not in the boxes of key evidence such as the genetics and completeness of the stock; AND,c) there are several evidences in favour (in the three degree of support indicated above) and few ornone evidence against (in the three degree of support indicated above);
A hypothesis should be ranked ‘Low’ if a) data are not available for more than 50% of the boxes; OR,b) the ‘ND’ key is present in the boxes of key evidence such as the genetics and completeness of thestock; OR, c) if there are several evidences against (in the three degree of support indicated above) andfew or none evidence in favour (in the three categories indicated above).
A hypothesis should be ranked ‘Medium’ if it represents a status intermediate between the criteria for‘High’ and ‘Low’ e.g. similar to criteria for ‘High’ but where a similar number of evidences in favour
and against are found.
Accordingly the result on the plausibility rank for the component characterizing stock structure
hypotheses in the western North Pacific minke whale was the following:
Stock Hypothesis I: High
Stock Hypothesis II: Low
Stock Structure Hypothesis III: Low
REFERENCES
Baker, C.S., Slikas, B., Brownell, R.L., and Wade, P. 2010. Stock structure of western North Pacificminke whales based on mtDNA haplotypes from Korean ‘bycatch’ and Japanese bycatch’ andscientific whaling. Paper SC/D10/NPM3.
Bando, T., Miyashita, T., Kishiro, T., Yoshida, H. and Hatanaka, H. 2010a. An analysis of conception
dates of common minke whales sampled by JARPN and JARPN II in the context of stock
structure hypotheses. Paper SC/S10/NPM10.
Bando, T., Kanda, N., Pastene, L.A., Kishiro, T., Yoshida, H. and Hatanaka, H. 2010b. An analysis of
cookie cutter shark-induced body scar marks of common minke whales sampled by JARPN II in
the context of stock structure hypotheses. Paper SC/D10/NPM6.
Bando, T. 2011. Reliability of conception date of yellow Sea common minke whales derived from
Wang (1985). Small fetuses overlooked?
Gaggiotti, O.E. and Gascuel, F. 2011. Stock structure of North Pacific minke whales as revealed by
Principal Component Analyses of microsatellite data. Paper SC/63/RMPxx.
Goto, M., Miyashita, T., Kanda, N., Pastene, L.A. and Hatanaka, H. 2010. A hypothesis on the
migration pattern of J-stock common minke whales. Paper SC/62/NPM1 presented to the IWC
Scientific Committee, June 2010, Agadir, Morocco (unpublished), 14pp.
Hakamada, T. and T. Bando. 2009 Morphometric analysis on stock structure in the western North
Pacific common minke whales (Balaenoptera acutorostrata). Paper SC/J09/JR27.
Hatanaka, H. and Miyashita, T. 1997. On the feeding migration of Okhotsk Sea-West Pacific stock ofminke whales, estimates based on length composition data. Rep. int. Whal. Commn 47:557-564.

4

International Whaling Commission. 2002. Report of the Working Group on Stock Definition. J
Cetacean Res. Manage 4 (Suppl.): 261-281.
International Whaling Commission. 2004. Report of the Sub-Committee on the Revised Management
Procedure. J Cetacean Res. Manage 4 (Suppl.): 75-184.
International Whaling Commission. 2007. Report of the Sub-Committee on the Revised Management
Procedure. J Cetacean Res. Manage 4 (Suppl.): 88-128.
Kanda, N., Goto, M., Kishiro, T., Yoshida, H., Kato, H., and Pastene, L.A. 2009a. Update of theanalyses on individual identification and mixing of the J and O stocks of common minke whales
around Japanese waters examined by microsatellite analysis. Paper SC/61/JR5 presented to the
IWC Scientific Committee, May 2009, Madeira, Portugal (unpublished), 14pp.
Kanda, N., Goto, M., Kishiro, T., Yoshida, H., Kato, H., and Pastene, L.A. 2009b. Further
microsatellite analysis of minke whales in the western North Pacific. Paper SC/61/JR8 presented
to the IWC Scientific Committee, May 2009, Madeira, Portugal (unpublished), 14pp.
Kanda, N., Park, J.Y., Goto, M., An, Y.R., Choi, S.G., Moon, D.Y., Kishiro, T., Yoshida, H., Kato, H.
and Pastene, L.A. 2010a. Genetic analysis of western North Pacific minke whales from Korea
and Japan based on microsatellite DNA. Paper SC/62/NPM11.
Kanda, N., Goto, M., Nagatsuka, S., Kato, H., Pastene, L.A. and Hatanaka, H. 2010b. Genetic and nongenetic analyses of North Pacific common minke whales under newly defined sub-areas. Paper
SC/D10/NPM8.
Kanda, N., Goto, M., Nagatsuka, S., Kato, H., Pastene, L.A. and Hatanaka, H. 2010c. Analyses ofgenetic and non-genetic data do not support the hypothesis of an intermediate stock in sub-area 7.
Paper SC/S10/NPM9.
Kanda, N., Pastene, L.A. and Hatanaka, H. 2010d. Length composition and sex ratio of western North
Pacific minke whales and their consistencies with stock structure hypotheses. Paper
SC/D10/NPM7.
Kato, H. 1992. Body length, reproduction and stock separation of minke whales off northern Japan.
Rep. Int. Whal. Commn 42: 443-453.
Okamura, H., Matsuoka, K., Hakamada, T., Okazaki, M. and Miyashita, T. 2001. Spatial and temporal
structure of the western North Pacific minke whale distribution inferred from JARPN sighting
data.. J. Cetacean Res. Manage. 3(2):193-200.
Okamura, H. 2004. An assessment of plausibility of sub-stock scenarios on western North Pacificminke whales using the historical CPUE series. Appendix II of Paper SC/61/O15.
Park, J.-Y., Goto, M., Kanda, N., Kishiro, T., Yoshida, H., Kato, H. and Pastene, L.A. 2010.
Mitochondrial DNA analyses of J and O stocks common minke whales in the western North
Pacific. Paper SC/62/NPM21.
Slikas, B and Baker, C.S. 2010. Preliminary investigation of Hardy-Weinberg equilibria and populationdifferentiation in NP minke whales, based on microsatellite data. Paper SC/D10/NPM4.
Wang, P. 1985. Studies on the breeding habits of the minke whale (Balaenoptera acutorostrata) in the
Yellow Sea. Chinese Journal of Oceanology and Limnology 3: 38-47.

5

Table 1. General summary of the information to assess plausibility of components characterizing stock
structure hypotheses. Key: : ‘+’= indicates evidence in favour of a hypothesis; ‘-‘= indicates evidence
against a hypothesis; ‘(+)’= indicate weak evidence in favour of a hypothesis; ‘(-)’= indicate weakevidence against of a hypothesis; ‘(())= indicates very weak evidences; ‘NIW’= indicates that theevidence is not inconsistent with the hypothesis and ND= indicates the absence of particular data toevaluate a hypothesis. The designation ‘NIW’ often reflects the asymmetrical nature of information on
stock structure (i.e. existence of differences can be viewed as positive evidence for multiple stocks, butabsence of differences provides no information, and can not be viewed as positive evidence for a single
stock (IWC, 2007). In using the ‘NIW’ key however consideration should be given to sample sizes
used and/or power analysis results.

Information
Genetics markers
Mitochondria DNA1
Microsatellite2
Biological markers
Morphometric3
Flipper color pattern4
Fluke color pattern5Life history markers
Conception date6
Completeness of the stock7
Distribution gaps and migration
Distribution gaps8
Migration9
Ecology
PCB accumulation10
Heavy metal
accumulation11
Cookie cutter shark scars12
Abundance and CPUE
Trend13
Conditioning14‘Pure’ stock15

HYPOTHESIS I
J/O and mixing

HYPOTHESIS II
Y stock

HYPOTHESIS III
JW/JE and OW/OE

+
+

((+))
(+)

((+))
((+))

(+)
(+)
(+)

ND
ND
ND

NIW
(-)
(-)

+
+

(+)
ND

-

NIW
+

ND
ND

NIW
-

NIW
NIW

NIW
NIW

NIW
NIW

NIW

ND

NIW

(+)

ND

(-)

+

(+)

(-)

6

1,2

Some mtDNA and microsatellite analyses in the Pacific side of Japan were conducted separately for J
and O stocks as recommended by the IWC SC since 2002. This was possible after the microsatellite
work to assign individuals to O and J stocks (Kanda et al., 2009a), which was updated following
recommendations from the IWC SC (Kanda et al. 2010a).

No significant mtDNA differences were found among O stock animals in the Pacific side of Japan
providing no support for sub-structuring in this stock; weak mtDNA differences between Japanese andKorean J stock animals disappeared when whales from the Yellow Sea were excluded from the analysis.
No significant mtDNA differences were found when samples from sub-area 5 were compared withthose from sub-area 6 (Park et al., 2010; Baker et al., 2010).
No significant microsatellite DNA differences were found among O stock animals in the Pacific side ofJapan providing no support for sub-structuring in this stock; weak differences were found within the J
stock animals, which were attributed to a temporal mix of two stocks in sub-area 6W (Kanda et al.,2010a). Additional microsatellite analyses conducted on the basis of the new sub-areas (Figure 1)
showed no significant heterogeneity among J stock animals from sub-areas 1E, 6E, 10E, 2C, 7CS and
7CN; and no significant heterogeneity among O stock animals from sub-areas 2C, 7CS, 7CN, 7W, 7E,
8 and 9) (Kanda et al., 2010b). Slikas and Baker (2010) found significant deviation from HardyWeinberg equilibrium along the Korean coast of the Sea of Japan in summer. However such deviation
was very strong compared to slight or not differences (based on Fst) found between sub-areas 5 and 6
for both mtDNA and microsatellite DNA.
Mixing of two stocks (O and J) in sub-area 7 was suggested based on STRUCTURE analyses (Kanda
et al., 2009a) with the proportion of the J stock decreasing from the coast to offshore waters (higher
proportion within the 10n miles from the coast but also occurring in smaller proportion until 60n miles
from the coast (Kanda et al., 2010c).
The number of samples used in those analyses is large and the genetic markers sensitive (more than
400bp of the control region and 17 microsatellite loci). Furthermore the power of the microsatellite
analyses was estimated to be high (Kanda et al., 2009b).
Principal Component Analysis revealed some sub-structuring within the O stock of sub-areas 7, 8 and 9
but such suggested structuring was not related with body length and geographical position and theauthors noted that such result does not have clear biological interpretation (Gaggiotti and Gascuel,2011). The same analysis showed not genetic structuring among J stock animals east and west of Japan.
Other analyses in the Pacific side of Japan (e.g. mtDNA analysis by Baker et al., 2010 andmicrosatellite analysis by Slikas and Baker, 2010) were conducted for all samples combined (J and O
stock animals). Several ‘significant’ differences among sub-areas were found but it is difficult tointerpret such differences in the context of stock structure. No effort was made to differentiate between
the two possibilities of O/J mixing and independent stock with intermediate characteristics.
In summary analyses conducted separately for J and O stocks followed previous recommendations
from the IWC SC. These showed no significant differences within J and within O stocks animals.
Analyses were based on large sample size and the genetic markers are considered sensitive. The powerof the microsatellite analyses was estimated high. For these reasons we considered that mtDNA andmicrosatellite provide evidence in favour of Hypothesis I. There are some signals of heterogeneity thatcan be interpreted as the occurrence of a Y stock in sub-area 5. However such signals are weak,particularly for mtDNA where no significant differences were found between sub-areas 5 and 6. The
Fst obtained in the comparison between these sub-areas are very small for both mtDNA andmicrosatellite DNA. For these reasons we considered that the evidence provides weak support in caseof microsatellite and very weak support in the case of mtDNA in case of Hypothesis II. No effort wasmade to differentiate between the two possibilities of O/J mixing and independent stock withintermediate characteristics in the mtDNA (Baker et al., 2010) and microsatellite (Slikas and Baker,2010) and then several interpretations are possible for such results. Consequently we considered thatthe genetic evidence provide very weak support in case of Hypothesis III.
3

Morphometric analyses in sub-areas 7, 8 and 9 were conducted separately for J and O stocks based on
genetics. A total of 10 measurements were used and the sample size was two J stock animals and 118 O
stock animals. Despite the small J stock sample size, significant differences in morphometric7

measurements were found between J and O stocks animals, and no significant differences were foundamong O stock animals from sub-areas 7, 8 and 9 in the Pacific side of Japan (Hakamada and Bando,2009).
We considered that morphometric data provide weak support in case of Hypothesis I due to the limited
sample size of J stock. No data is available to evaluate Hypothesis II and the data is not inconsistent
with Hypothesis III.
4

Flipper color pattern analyses in sub-areas 7, 8 and 9 were conducted separately for J and O stocks.
The sample size was 23 J stock animals and 166 O stock animals. Differences were found between J
and O stock animals. No differences between 7CN, 7CS, 7WR, 8, and 9 O stock animals (Kanda et al.,2010b).
We considered that flipper color pattern data provide weak support in case of Hypothesis I. No data isavailable to evaluate Hypothesis II and the data are weak evidence against Hypothesis III, at least for
the OW/OE component of this hypothesis (sample sizes are larger than in the case of morphometric).
5

Fluke color pattern analyses in sub-areas 7, 8 and 9 were conducted separately for J and O stocks. The
sample size was 14 J stock animals and 155 O stock animals. Differences were found between J and O
stock animals. No differences were found between 7CN, 7CS, 7WR, 8, and 9 O stock animals (Kanda
et al., 2010b).
We considered that fluke color pattern data provide weak support in case of Hypothesis I. No data isavailable to evaluate Hypothesis II and the data are weak evidence against Hypothesis III, at least for
the OW/OE component of this hypothesis (sample sizes are larger than in the case of morphometric).

6

Conception date analyses in sub-areas 7, 8, 9 and 11 conducted separately for J and O stocks. Sample
size for J stock animals was eleven while that for the O stock was 96. Differences found between J andO stock animals. No differences among O stock animals (Bando et al., 2010a). Furthermore theseauthors found that the sample of J stock from the Pacific side of Japan have two conception dates, apattern as in the sample of eight individuals examined by Kato (1992). Then the pattern of conception
date of J stock animals on both sides of Japan is similar. Some differences have been found inconception date between the Yellow Sea animals and those in other areas (Wang, 1985). However data
are limited in quantity and quality to reach a sound interpretation of those differences (Bando, personalcommunication).
We considered that conception date data provide support in case of Hypothesis I; weakly support
Hypothesis II (due to the nature of the data examined by Wang, 1985) and the data indicate evidence
against against Hypothesis III (sample sizes are larger than in the case of morphometric).
7

Length composition and sex ratio in the Pacific side of Japan and Sea of Japan analyses was conducted
separately for J and O stocks. Large sample sizes were used. At the Pacific side of Japan O stock
immature animals distributed mainly in coastal areas whereas O stock mature animals distribute mainly
in offshore areas, which is consistent with a single O stock with spatial segregation by sex and maturity
classes. J stock animals from the Sea of Japan and Pacific coast showed quite similar characteristics inthe data (Kanda et al., 2010d). The analyses were based on large sample size.
We considered that these data provide support in case of Hypothesis I; no data to evaluate Hypothesis
II and the data indicate evidence against Hypothesis III because under this hypothesis a stock would becomposed exclusively by a single reproductive class (e.g OW by immature animals, OE by mature
animals and JE by immature animals), which is not biologically plausible.

8

The trend surface of the transformed density predicted by each month revealed no clear gaps in the
Pacific side of Japan (sub-areas 7, 8 and 9) (Okamura et al., 2001).
Evidence of spatial (permanent) discontinuity would be viewed as positive evidence for multiple stocks,
but absence of discontinuity is viewed as neutral information, as there is no expectation that their prey
would have a discontinous distribution (IWC, 2007). Given this we considered that the information is
not inconsistent with the data in case of Hypotheses I and III (at least for the OW/OE component of thishypothesis). No data is available to evaluate Hypothesis II.

8

9

The only reports documenting the consistency of different kind of information (sighting, pattern ofwhaling operation, body length and sex ratio distribution) are those by Goto et al. (2010) and Hatanaka
and Miyashita (1997). The information examined was consistent with the migration and mixing of two
stocks along the coast of Japan.
We considered that migration pattern provides support in case of Hypothesis I, no data is available toevaluate Hypothesis II and provide evidence against Hypothesis III (see also footnote 7 above).

10,11

There is limited information on the source, decay rate and accumulation pattern of PCB and heavy
metals. This makes difficult the interpretation of different level of accumulation among groups ofwhales.
We considered that these data are not inconsistent with the three hypotheses.

12

Cookie cutter shark scars analyses in 7CN+7CS and 7E+8+9 were conducted separately for J and O
stocks. Differences were found between J and O stock animals. No differences were found among O
stock animals (Bando et al., 2010b). However there is limited information on the life history andmovement of the cookie cutter shark, which make difficult the interpretation of differences amonggroups of whales.
We considered that these data are not inconsistent with the three hypotheses.
13

CPUE time series data were not consistent with existence of small coastal O stock, similar to the caseproposed in Hypothesis III (Okamura et al 2004).
We considered that these data provide weak support in case of Hypothesis I, no data is available toevaluate Hypothesis II and provide weak evidence against Hypothesis III. We assigned these as weakbecause there some pending question on the operational data for the CPUE.
14

Result of conditioning will be available ate the SC63.

15

Under Hypothesis III the pure stock sample for the JE are the by-catch samples of sub-area 2C; for
OW the JARPNII samples from sub-areas 7CS (April and May) and 7CN (September and October),
excluding samples within 10n miles of the coast. In the first case there are genetic evidences of theoccurrence of O stock animals in sub-area 2C (Kanda et al., 2009a). Results of the Hardy-Weinberg
equilibrium test for those ‘pure stock’ samples resulted in no significant departure, however the powerof this test has not been determined. Furthermore those ‘pure stock’ samples only include a single
component of the assumed stocks (see completeness of the stock mentioned above).
The composition of J and O type animals in 7CN+CS changes with distance from the coast, with theproportion of the J stock decreasing from the coast to offshore waters (higher proportion within the 10n
miles from the coast but also occurring in smaller proportion until 60n miles from the coast (limit for
7CS and 7CN)) (Kanda et al., 2010c).
Under Hypotheses I and II genetic and biological data support the selection of sub-area 6E (all months)
as the pure sample of the J stock and 7WR+7E+8 as the pure sample of the O stock. J stock animals
occur until the limit of sub-areas 7CS and 7CN (Kanda et al., 2010c). Sub-area 9 was excluded to avoid
any confounding effect of the sporadic C stock in that area.

We considered that the definition of pure stock sample migration pattern provides support in case of
Hypothesis I, weak support in the case of Hypothesis II and provide evidence against Hypothesis III(see also footnote 7 above).

9

Figure 1. New sub-areas defined in the current RMP Implementation of western North Pacific common
minke whales.

Figure 2a. Schematic representation of Hypothesis I of the current RMP Implementation (modified
from Hatanaka and Miyashita, 1997).
MM=mature males, MF=mature females, IMF=immature males and females.

10Figure 2b. Schematic representation of Hypothesis II of the current RMP Implementation (modified
from Hatanaka and Miyashita, 1997).
MM=mature males, MF=mature females, IMF=immature males and females. Y stock residing in the
Yellow Sea and mixing with the J stock in the southern part of sub-area 6W in summer.

Figure 2c. Schematic representation of Hypothesis III of the current RMP Implementation (taken from
SC/63/RMP8).

11