SC/63/RMP21

A brief background of the RMP Implementations for western
North Pacific common minke whale: stock structure,plausibility and management implications
Luis A. Pastene and Hiroshi Hatanaka
Institute of Cetacean Research, Toyomi 4-5, Chuo-ku, Tokyo 104-0055, Japan
ABSTRACTThe first RMP Implementation for western North Pacific common minke whale started in 1993 and wascompleted in 2003. The second Implementation started in 2010 and, unlike the previous one, is being
conducted under the new ‘Requirements and Guidelines for Implementations’ agreed by the IWC SC in
2004. Stock structure is a key piece of information for Implementation. Weighting of trials into ‘high’,‘medium’ and ‘no agreement’ depends mainly on the plausibility rank assigned to stock structure
hypotheses (into ‘high’, ‘medium’ ‘low’). On the other hand the output of the Implementations (e.g.
management advice) depends on the conservation performance of trials at its different weights. Four
stock structure hypotheses (A, B, C and D) were adopted in the previous Implementation and the IWC
SC was unable to rank the plausibility of those hypotheses. To complete the Implementation process it
gave ‘high plausibility’ to the four. The implication of this was that the IWC SC was unable to agree ona single management variant to be recommended in case the Commission would decide to implement
the RMP. Therefore the previous RMP Implementation was useless for the objective of management ofcommon minke whale. In the current Implementation three stock structure hypotheses were adopted (I,II and III). Hypotheses I and II are updated versions of hypotheses A and B of the previous
Implementation while Hypothesis III is a new one. There are substantial differences between
Hypotheses I/II and III. These differences are likely to result in very different management advice. In
order to provide proper management advice, it is essential to appropriately assign plausibility rank to
the three hypotheses. If not, the RMP will again become a useless tool for management. To put thediscussions on plausibility in context, this paper presents an outline of the past and current RMP
Implementations of western North Pacific common minke whale with particular emphasis on the stock
structure hypotheses adopted by the IWC SC, and its management implications.
KEYWORDS: COMMON MINKE WHALES, IMPLEMENTATION, WESTERN NORTH PACIFIC,STOCK STRUCTURE HYPOTHESES, PLAUSIBILITY
THE 1993-2003 RMP IMPLEMENTATION
The first RMP Implementation for western North Pacific common minke whale started in 1993.
Previously the IWC SC established a Working Group to start the ISTs for the application of the RMP
for this species in the western North Pacific. The Implementation process took an abnormally long time
to be completed due in part to the long discussions and disagreements among members on stock
structure hypotheses. This abnormally long time motivated the development of specific requirements
and guidelines for RMP Implementations, which were agreed by the IWC SC in 2004, one year after
the first Implementation was completed. Stock structure hypotheses have very important implications
for the output of the RMP Implementation process. Notwithstanding the process the rational to adopt
some stock structure hypotheses has been weak. Some hypotheses and rational, strongly supported bysome members during the Implementation, have been forgotten with the passage of time.
Discussion on stock structure before the 1993-2003 Implementation
Studies on stock structure of common minke whale around Japan started in the 1950’s using a) catch
distribution information, b) differences in body length and c) conception date. Based on that
information the IWC identified three stocks (Sea of Japan-Yellow Sea-East China Sea (J), Okhotsk Sea
West Pacific (O) and remainder stocks) and established boundaries for management of these stocks
following recommendations from the Committee (IWC, 1983).

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The IWC SC addressed the issue of stock structure again during the CA of this species conducted in1991 (IWC, 1992). Regarding stock structure the analyses were based exclusively on samples and datacollected during the period of commercial whaling, therefore, samples were geographically restricted tocoastal areas of Japan. Analyses were focused to compare minke whales from either side of Japan. The
following kinds of data and analyses were discussed during the CA:
a)
b)
c)
d)
e)
f)

Hypothesis testing based on mitochondrial DNA (mtDNA) RFLP
Hypothesis testing based on allozymes
Comparative analysis on external body proportions
Comparative analysis of external coloration (shoulder/flipper coloration pattern)
Pattern of sighting distribution
Pattern of catch distribution

The IWC SC agreed that the data presented confirmed the presence of at least two stocks, J stock on
the western side of Japan (Sea of Japan) and O stock on the eastern side of Japan (Pacific), and that the
combination of genetic, morphological and reproductive data provides strong evidences that seasonal
mixing occurs in some part of the migration and feeding ranges. The SC also noted that no data exist
related to the location of breeding-calving grounds. Arguing the lack of data for some parts of the
migratory corridor and breeding grounds, the IWC SC agreed that the existing stock definition andboundaries did not provide an adequate basis for assessment (IWC, 1992).
Discussions on stock structure during the 1993-2003 Implementation
The Working Group established before 1993 to start the ISTs felt that stock structure information was
not sufficient for the trials and proposed a complicated stock scenario based on three stocks (J, O andW) and 7 sub-stocks (three in J and four in O). The Group established 13 sub-areas for the purpose oftrials. Based on the report of this Working Group, the IWC SC noted the desirability of obtaining
improved data on stock identity and migration pattern in western North Pacific minke whale. In
response Japan started the JARPN (Japanese Whale Research Program under Special Permit in the
North Pacific) with three main objectives: a) clarify whether W stock exists in pelagic areas; b) clarify
the mixing rate of W stock, and c) clarify the validity of sub-stock scenario.
The program was conducted between 1994 and 1999 and a considerable amount of data on stock
structure was accumulated in that period. The most valuable aspects of the JARPN were that: a) it
explored regions from which data were not previously available, particularly from offshore sub-areas 8
and 9; b) samples were collected systematically on predefined track-lines, and c) the new available
samples allowed the comparison among IWC’s sub-areas 7, 8 and 9 using both genetic and non-genetic
approaches.
The IWC SC reviewed partial data obtained by JARPN in a workshop conducted in 1996. The Working
Group agreed that the new data, in conjunction with those reported previously: a) confirmed thedistinction between the J and O stocks; b) the data were compatible with a hypothesis of only one stockin sub-areas 7, 8, 9, 11 and 12 (with allowances for some J stock animals in sub-areas 7, 11 and 12
seasonally), and c) the data were generally inconsistent with there being sub-stocks characterized bydifferent levels of latitudinal migration. With regard the W stock, the Group agreed that no evidence
was presented to support the hypothesis of a W stock. Some members, however, considered that the
information did not exclude this possibility in particular because of concerns about the ability of theavailable data to detect genetic differences (IWC, 1997).
The IWC SC conducted a full review of JARPN during a workshop conducted in 2000. A total of 32
scientific papers were presented and discussed at the workshop. This time the analyses were focused tocompare whales among sub-areas 7, 8 and 9, in the Pacific side of Japan:
a)
b)
c)
d)
e)
f)
g)

Hypothesis testing based on allozymes, mtDNA control region sequences and microsatellites.
Comparative analysis of biological parameters.
Comparative analysis of conception date.
Comparative analysis of external measurements.
Pattern of sighting distribution.
Comparative analysis of pollutant burden.
Comparative analysis of parasite load.

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In general these approaches were consistent with the hypothesis of two stocks, J and O stocks around
Japan, but the analyses failed to detect significant differences between coastal and pelagic localities in
the western North Pacific. In other words these analyses did not provide evidence for the existence ofthe W stock. However, some analyses suggested the occurrence of J stock animals in sub-area 7(Pacific side of Japan) seasonally. The only indication for the occurrence of W stock came from a
mtDNA analysis based on hypothesis testing, which showed some degree of mtDNA heterogeneity insamples taken in the western part of sub-area 9 in 1995. Therefore the possibility of occurrence of W
stock was not completely discarded and the Workshop recommended further studies and samples,
especially from offshore regions (IWC, 2001).
During the Implementation two workshops were conducted, in 2002 (IWC, 2003) and 2003 (IWC,
2004a). During the 2002 workshop some new or updated analyses were presented:
a)
b)
c)
d)

Clustering analysis of mtDNA control region sequence data (Boundary Rank Technique) (BR)
Analysis of geographical distribution by sexual class
Hypothesis testing based on mtDNA control region sequences
Hypothesis testing based on microsatellites

Considering the results of different kinds of analyses, the workshop defined four baseline stock
structure hypotheses for consideration in the trials, which were accepted subsequently by the IWC SC(Figure 1):a) Scenario A: two main stocks (J and O) allowing the sporadic occurrence of a third stock (W) in partof sub-area 9 (based on the results of genetics and non-genetics approaches presented to the JARPN
review, particularly mtDNA results, by Japanese scientists).
b) Scenario B: two stocks (J and O) (based on the results of the genetic and non-genetic approaches
presented to the JARPN review).
c) Scenario C: four stocks (J, Ow, Oe, W) with three to the eastern side of Japan with hard boundaries
at 147E and 157E (results of the application of the technique Boundary Rank to mtDNA data by US
scientists).
d) Scenario D: three stocks (J, O and W) with mixing gradient between O and W between 147°E and162°E (based on the interpretation of the results of BR and assisted by some oceanographic data by US
and Australian scientists).
These four hypotheses were adopted despite considerable disagreement among IWC SC members on
the plausibility of Hypotheses C and D. Hypotheses A and B were based mainly on hypothesis testingof genetic (mtDNA and microsatellite) and non-genetic data, following suggestions from the IWC SC
since1994. Hypothesis C and in part Hypothesis D were based on the results of the application of the
BR to mtDNA data. The core of Hypothesis C suggested two O stocks (Ow and Oe) divided by a hardboundary at 147°E.
The BR technique has not been published and it has not been used in current IWC SC assessment of
whale stocks. It has not been used in the formulation of the current three stock structure hypotheses ofcommon minke whale (see below). Even the US proponents of Hypothesis III, which were in favor of
the BR technique in the previous Implementation, have opted this time for the hypothesis testing
approach.
Plausibility rank of stock structure hypotheses in the 1993-2003 Implementation
During the 2002 IWC SC meeting Japanese scientists presented the results of an AIC (Akaike’s
Information Criterion)-based evaluation of the plausibility of baseline stock scenarios defined by the2002 workshop. These were based exclusively on mtDNA data. To our knowledge this was the only
attempt to develop a procedure to evaluate plausibility objectively.
Results of the AIC gave a low plausibility to stock structure C and D. However there was no agreement
at the IWC SC on the validity of using AIC for evaluating plausibility therefore the IWC SC agreed toretain the four basic stock structure scenarios.

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Several papers dealing with evaluation of plausibility of the different stock scenarios were prepared by
Japanese scientists for the 2003 IWC SC meeting. However, the IWC SC refused to discuss these
papers and to be able to complete the already long Implementation decided to give these four different
stock structure scenarios the same `high` plausibility (IWC, 2004b) meaning that the IWC SC failed toassign plausibility to different hypotheses in an objective and scientific way. The result of this was thatwhen the Implementation was completed the management implications were flawed.
Management implications
A total of six RMP variants were defined at the 1993-2003 Implementation. Regardless of which stock
structure hypotheses are considered plausible only Variant 1 (Small Areas equal sub-areas. For thisoption, the Small Areas for which catch limits would be set are 7W, 7E, 8W, 8E, 9W, 9E, 11, 12SW
and 12NE) and Variant 5 (7+8+11+12 and 9 are combination areas and catches are Catch-cascaded tothe sub-areas with each combination area i.e. Small Areas are the same as for Variant 1), were
acceptable based on the risk-related statistics. Of these, Variant 5 was preferable based on the catchrelated statistics.
All variants were acceptable under stock structure A and B. Variant 6 (7+8+11+12 and 9 are Small
Areas; catches from the 7+8+11+12 Small Area are taken from sub-areas 7W and 11 using Catchcascading across those two sub-areas) was the preferable based on the catch-related statistics.
Variant 6 (V6) of Scenario A4-J1 (stock scenario A, MSYR: 4% and J catch series 1) gave a mediancatch/year (commercial+incidental) of 132 O stock animals and 21 W stock animals. Under V6 O stock
animals can be taken from sub-areas 7W and 11. The catch for Variant 5 of Scenario C4-J1 was 32 Ow
stock animals, 25 Oe animals and 94 W stock animals e.g. most of the allowed catch quota was inoffshore waters and not accessible to the small coastal whaling (IWC, 2004b).
The views of the IWC SC members were divided in recommending a management variant in 2003:
most members recommended that variant 5 was the preferred management option if the RMP is
implemented. Other members recommended that variant 6 should be the preferred management option
if the RMP is implemented. Such disagreements on management advice could have been avoided if therelevant questions on stock structure had been resolved satisfactorily and plausibility rank assigned in
an appropriate scientific way.
THE CURRENT RMP IMPLEMENTATION
In 2009 instead of conducting the typical Implementation Review (after five years since completion thefirst Implementation) the IWC SC agreed to conduct a pre-implementation assessment, which wascompleted at the 2010 IWC SC meeting. Therefore at this meeting the IWC SC agreed to start the
Implementation process for this stock. This time the IWC SC is conducting the Implementation under
the new ‘Requirements and Guidelines for Implementations’ agreed by the IWC SC in 2004. Under
these guidelines an Implementation should be conducted in a two-year period, during which twointersessional workshops and two annual meetings are carried out. The First Intersessional Workshop
was completed in December 2010. One of the main tasks of the First Annual Meeting in June 2011 is
the assignment of plausibility rank to different stock structure hypotheses. As noted above the IWC SC
is still lacking an appropriate procedure for this important task.
Stock structure hypotheses
Three stock structure hypotheses (Hypotheses I, II and III) were proposed and specified for the
Implementation (see Figure 2 for the new sub-areas).
Hypothesis I (Figure 3a)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 and7CN) and the southern part of the Okhotsk Sea (sub-areas 11 and 12SW).
Hypothesis II (Figure 3b)
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.

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Hypothesis III (Figure 3c)
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 side 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 in sub-area 7W around the year and mix with the OE there andwith 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, 2004b). 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.
Hypotheses I and II derived from several analyses, genetics and non-genetics, recommended by the
IWC SC since 1994.
Stock structure hypothesis III is new. It derives mainly from hypothesis testing analyses of mtDNA andmicrosatellites data of O and J stock animals pooled.
Therefore we have the situation that the ‘high plausibility’ hypotheses C and D of the 1993-2003
Implementation are not supported by the new samples and analyses. Furthermore hypothesis testing is
the approach used by the proponents of Hypothesis III, and the BR method used to propose Hypothesis
C in the previous Implementation is no longer used in the current Implementation. An updated analyses
based on BR provided no support for Hypothesis C (Gaggiotti and Durand, 2010)
The key issues to resolve and implications for management
As noted above stock structure is critical information for Implementation. Weighting of trials into‘high’, ‘medium’ and ‘no agreement’ depends mainly on the plausibility rank assigned to stock
structure hypotheses (into ‘high’, ‘medium’ ‘low’). On the other the hand the output of the
Implementations (e.g. management advice) depends on the conservation performance of trials at its
different weights.
A major source of disagreement within the Committee during the 2010 Annual Meeting related towhether common minke whales in sub-areas 7 and 2 represented a mixture of O- and J-stock animals(Hypotheses I/II) or a single stock with ‘intermediate characteristics’ (e.g. OW under Hypothesis III).
The Committee consequently agreed that resolving this issue, using genetic and non-genetic data, was ahigh priority for discussion at the First Intersessional Workshop and beyond (IWC, 2011).
One of the differences between the analytical approach used by the proponents of Hypotheses I/II and
those of Hypotheses III is related to the way they treated samples identified as J and O stocks animals.
Proponents of Hypotheses I/II followed the instructions from the IWC SC to conduct the analyses
separately for J and O stock animals. This was possible due to the microsatellite genotyping study
presented originally by Kanda et al. (2009). These analyses were subsequently refined in response to
IWC SC suggestions (Kanda et al., 2010). On the other hand the proponents of Hypothesis III based
their analyses on total samples and no effort was made to separate J and O stock animals in theiranalyses. Grouping of the total samples in different spatial and temporal strata resulted in several‘significant’ p values that the authors interpreted as sign of multiple O and J stocks (independent stocks
with intermediate characteristics). Results of the analyses conducted in this way might have several
interpretations, which are difficult to verify with new data and analyses.
By taking into account the output of the 1993-2003 Implementation, it is likely that management advice
would differ substantially between Hypotheses I/II and Hypothesis III scenarios. Similar to the case offormer Hypothesis C, management advice under current Hypothesis III would imply that the coreallowed catch be taken in offshore waters.
Therefore it is very important that before the IWC SC advances to the next step (the step after theplausibility ranking in the process of Implementation), the key questions on stock structure
differentiating Hypotheses I/II from III should be resolved adequately.

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SUMMARY
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The IWC SC conducted the first Implementation on western North Pacific common minke
whales between 1993 and 2003.
Four stock structure hypotheses were adopted in the first Implementation: Hypotheses A, B, C
and D. Hypothesis C proposed the occurrence of a small coastal O stock (Ow) and it was
based on the results of the Boundary Rank technique applied to mtDNA data. Hypotheses A
and B were based on the results of genetic and non-genetic analyses that followed
recommendations from the IWC SC since 1994.
No procedure is available for the IWC SC to assign plausibility to stock structure hypotheses
in an objective and scientific way.
Consequently in 2003 the IWC SC was unable to assign plausibility to the four hypotheses ina scientific manner. In order to complete the already long Implementation it assigned ‘highplausibility’ to all four hypotheses.
Because the difficulty to assign plausibility ranks in an objective manner, the views of the
IWC SC members were divided in recommending a management variant in 2003: mostmembers recommended that variant 5 was the preferred management option if the RMP is
implemented. Other members recommended that variant 6 should be the preferredmanagement option if the RMP is implemented. Variant 5 was not acceptable from theperspective of coastal whaling.
A new Implementation is being conducted currently under the new ‘Requirements andGuidelines for Implementations’ agreed by the IWC SC in 2004. However the IWC SC is stilllacking a procedure to assign plausibility to stock structure hypotheses in an objective andscientific way.
Three stock structure hypotheses (Hypotheses I, II and III) were adopted and specified for thecurrent Implementation. Hypotheses I and II are improved versions of previous Hypotheses A
and B. Hypothesis III is a new hypothesis.
Previous ‘high plausibility’ Hypotheses C and D have been abandoned and the analyticalprocedure on which Hypothesis C was based (BR), is no longer used in the current
Implementation. All analyses related to the three hypotheses are based on hypothesis testing.
The key question on stock structure is whether common minke whales in sub-areas 7 and 2
represented a mixture of O- and J-stock animals (Hypotheses I/II) or a single stock with‘intermediate characteristics’ (e.g. OW under Hypothesis III).
By taking into account the output of the 1993-2003 Implementation it is likely thatmanagement advice would differ substantially between Hypotheses I/II and Hypothesis III
scenarios. Therefore it is very important that before the IWC SC continues with the current
Implementation the key questions differentiating Hypotheses I/II from III should be resolved
adequately.

REFERENCES
Gaggiotti, O. and Durand, E. 2010. Update analyses of the genetic structure of western North Pacificminke whales. Paper SC/62/NPM30 presented to the IWC Scientific Committee, June 2010
(unpublished).
International Whaling Commission. 1983. Report of the Scientific Committee. Rep. int. Whal. Commn
33: 43-190.
International Whaling Commission. 1992. Report of the Sub-Committee on North Pacific minke
whales. Rep. int. Whal. Commn 42:156-177.
International Whaling Commission. 1997. Report of the Working Group on North Pacific minke whale
trials. Rep. int. Whal. Commn 45: 203-226.
International Whaling Commission. 2001. Report of the workshop to review the Japanese Whale
Research Programme under Special Permit for North Pacific minke whales (JARPN). J. Cetacean
Res. Manage. 3 (Suppl.): 377-413.
International Whaling Commission. 2003. Report of the workshop on North Pacific Common minke
whale (Balaenoptera acutorostrata) Implementation Simulation Trials. J. Cetacean Res. Manage.
5 (Suppl.): 455-469.
International Whaling Commision. 2004a. Report of the second workshop on North Pacific Common
minke whale (Balaenoptera acutorostrata) Implementation Simulation Trials. J. Cetacean Res.
Manage. 6 (Suppl.): 427-468.

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International Whaling Commision. 2004b. Report of the Scientific Committee. J. Cetacean Res.
Manage. 6 (Suppl.): 1-411.
Kanda, N., Goto, M., Kishiro, T., Yoshida, H., Kato, H. and Pastene, L.A. 2009. Update of the analyses
on individual identification and mixing of J and O stocks of common minke whale around
Japanese waters examined by microsatellite analysis. Paper SC/61/JR5 presented to the IWC
Scientific Committee, June 2009 (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. 2010. Genetic analysis of western North Pacific minke whales from Korea andJapan based on microsatellite DNA. Paper SC/62/NPM11 presented to the IWC ScientificCommittee, June 2010 (unpublished). 13pp.

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Figure 1. Hypotheses on stock structure of North Pacific common minke whale used during the 19932003 RMP Implementation (IWC, 2004). See text for details.

8Figure 2. New sub-areas defined in the current RMP Implementation of western North Pacific common
minke whales.

Figure 3a. 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.

9Figure 3b. 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 3c. Schematic representation of Hypothesis III of the current RMP Implementation (taken from
SC/63/RMP8)10