SC/O05/BWI3

Comments on the hypotheses on stock structure presented at
the pre-implementation assessment of western North PacificBryde’s whale
LUIS A. PASTENEThe Institute of Cetacean Research,
Toyomi 4-5, Chuo-ku, Tokyo 104-0055,
Japan
ABSTRACTThis paper comments on the stock structure hypotheses presented at the pre-implementation assessment ofwestern North Pacific Bryde`s whale in the light of the available scientific data. The hypothesis of a single
stock scenario in sub-areas 1 and 2 (Hypothesis 1) is fully consistent with the available data and deserves tobe considered in the trial specifications as a base case scenario. The hypotheses of two stock- scenario(Hypotheses 2 and 3) should be considered in the trials under a precautionary approach: although there isno scientific evidence supporting the occurrence of a second stock east of 180° (sub-area 2), DNA andmark-recapture data are very limited for that sub-area. The hypotheses involving sub-stocks in sub-area 1(Hypotheses 4 and 5) were already considered by the Workshop on pre-implementation assessment as
having much smaller plausibility than the other hypotheses given the available data, particularly those thathave become available since 1998. The scientific evidence examined here clearly does not support thestock structure hypotheses involving sub-stock scenario. In order to avoid waste of time, hypotheses
involving sub-stocks can be ignored for the trial specifications.
KEYWORDS: BRYDE’S WHALES, STOCK STRUCTURE, IMPLEMENTATION, WESTERN NORTHPACIFICINTRODUCTION
Following the schedule for an Implementation and subsequent Implementation Review recommended in
2004 (IWC, 2005a), the Scientific Committee (SC) completed the pre-implementation assessment ofwestern North Pacific Bryde’s whale during a Workshop carried out early 2005 (IWC, 2005b). The
Workshop considered all the aspects required under the ‘Requirements and Guidelines’ for
Implementations to complete a pre-implementation assessment (IWC, 2005a), specifically a) abundance
estimates; b) catches; c) stock structure hypotheses; d) dispersal rates; and e) data for conditioning. Basedon the results of the examination, the Workshop recommended to the SC that it considered the preimplementation process completed. The SC accepted the Workshop report and agreed that the preimplementation assessment for western North Pacific Bryde’s whales was completed and recommended
that Implementation can commence (IWC, 2005c).
With regard to stock structure of western North Pacific Bryde’s whales, the Workshop had identified fivealternative hypotheses, which considered sufficiently inclusive that collection of new data during the
Implementation process is unlikely to suggest a new stock hypothesis (IWC, 2005b). The Workshop had
agreed that the various stock hypotheses were not equally plausible, but did not assign plausibility weights
to these hypotheses as this is scheduled for the ‘First Annual Meeting’.
The primary objective of the ‘First Intersessional Workshop’ is to develop an appropriate Implementation
Simulation Trials structure and to specify the associated conditioning so that it can be carried out before the‘First Annual Meeting’.

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As specified in the Workshop report (IWC, 2005b), a plausibility rank would need to be assigned to eachsimulation trial during the ‘First Annual Meeting’. Notwithstanding a review of the hypotheses on stock
structure will be carried out during the ‘First Intersessional Workshop’ with the aim to eliminate any
hypotheses that are inconsistent with the data. This means that only the hypotheses consistent with the data
should be considered for developing Implementation Simulation Trials.
The objective of this paper is to review the hypotheses on stock structure identified during the preimplementation assessment of western North Pacific Bryde’s whale in view of the available data, and toevaluate whether or not these hypotheses deserve to be considered in the trial specifications.
DESCRIPTION OF THE HYPOTHESES ON STOCK STRUCTURE
The five hypotheses on stock structure agreed during the pre-implementation assessment are summarized in
Figure 1.
Hypothesis 1: this is a single stock hypothesis under which only one stock of Bryde’s whale distributes in
the feeding area from 130°E and 160°W (excluding the area of distribution of the East China Sea Stock,around Kochi) as shown in Figure 1(1). Under this hypothesis there is no sub-stock scenario.
Hypothesis 2: this is a two-stock hypothesis under which Stock 1 is found in sub-area 1 and Stock 2 in subarea 2 as shown in Figure 1(2). Sub-areas 1 and 2 are divided at 180° longitude. Under this hypothesis
there is no sub-stock scenario.
Hypothesis 3: this is a two-stock hypothesis under which Stock 1 is found in sub-areas 1 and 2 and Stock 2
only in sub-area 2 as shown in Figure 1(3). Under this hypothesis there is no sub-stock scenario.
Hypothesis 4: this is a two-stock hypothesis under which Stock 1 is found in sub-area 1 and Stock 2 in subarea 2. Stock 1 consists of two sub-stocks that mix in sub-area 1 as shown in Figure 1(4).
Hypothesis 5: this is a two-stock hypothesis under which Stock 1 is found in sub-areas 1 and 2 and Stock 2
in sub-area 2 only. Stock 1 consists of two sub-stocks, one found in sub-area 1 and the other in sub-areas 1
and 2 as shown in Figure 1(5).
EVALUATION OF THE STOCK STRUCTURE HYPOTHESES IN THE CONTEXT OFAVAILABLE DATA
During the pre-implementation assessment Workshop, it was agreed that the various hypotheses shown in
Figure 1 are not equally plausible, particularly given the data and analyses that have become available since1998 (IWC, 2005b). In this section the stock structure hypotheses are reviewed in the context of theavailable scientific data.
Hypothesis 1
Hypothesis 1 is largely supported by the available biological data as shown in Annex E of IWC (2005b).
There is a genetic study, based on allozymes, which covered most of the longitudinal range depicted in
Figure 1 (1) (Wada, 1996). This study showed a notable stability of the frequencies of a particular allozyme(Got-1f) in the area comprised between latitudes 20°N and 40°N and between longitudes 140°E and 160°W(Figure 2). This result provided no evidence of more than one stock in that longitudinal sector. It could beargued on the low power of using just a single locus. However statistical test for heterogeneity using thissingle locus showed significant differences when the sample of the western North Pacific was comparedwith other recognized stocks of Bryde’s whales in the Pacific Ocean (Wada and Numachi, 1991) so if thelevel of genetic differentiation between putative stocks in sub-areas 1 and 2 is similar to that between
Western North Pacific Stock and other Pacific stocks, this single locus should recognize such differences.
Apart from the genetics, analysis of sighting distribution showed no gaps in the longitudinal sector depictedin the Figure 1 (1). Shimada and Miyashita (1996) examined sighting data for western North PacificBryde’s whale obtained between 1988 and 1995. There was no clear discontinuity in distribution in the2pelagic western North Pacific west of 160°W (Figure 3). More recently Shimada (2004) examined sighting
data obtained in the western North Pacific between 1998 and 2002. Distribution of sighting data showed no
discontinuity in the longitudinal sector comprised between 140°E and 160°W (Figure 4).
Other biological information derived from body proportion and biological parameter analyses (Kato andYoshioka, 1995) conducted for whales sampled along all longitudinal range shown in Figure 1 (1) showedno evidence of heterogeneity. Again these data provided no evidence of more than one stock in thelongitudinal range 140°E-160°W.
DNA analyses have been confined to the western part of the area (sub-area 1). Mitochondrial DNA andmicrosatellite data were analyzed using different kinds of clustering methods (Martien and Taylor, 2004)
and hypothesis testing (Pastene et al. 2004a) and none of these methods revealed significant degree ofheterogeneity within that sub-area. During the pre-implementation assessment Workshop three different
methods for evaluating the power of the genetic analyses based on hypothesis testing, were presented. The
Workshop believed that in particular one of these methods (Kitakado et al., 2005) provided a moredefensible means of identifying the power of hypothesis testing (IWC, 2005b). Results from the threemethods showed that for the samples sizes available the power to detect genetic differences for western
North Pacific Bryde’s whale is high.
Same as DNA analyses, mark-recapture analyses have been confined to sub-area 1 (Kishiro, 1996; 1998).
Results were consistent with those from the genetic analysis, and no evidences were found of more than
one stock of Bryde’s whale in sub-area 1.
Hypotheses 2 and 3
These hypotheses involve different stocks in sub-areas 1 and 2. These were proposed under a precautionary
approach. Currently there is no scientific evidence supporting a separate stock east of 180° (sub-area 2). On
the contrary, genetic analyses based on allozymes (Wada, 1996), body proportion and biologicalparameters analyses (Kato and Yoshioka, 1995) and sighting distribution (Shimada and Miyashita, 1996;
Shimada, 2004) showed no differentiation between sub-areas 1 and 2 (see Figures 2, 3 and 4). However it isrecognized that two important information components (genetic analysis based on DNA and markrecapture) are not available for whales in sub-area 2.
Hypotheses 4 and 5
The Workshop on pre-implementation assessment agreed that the currently available data on genetics,
mark-recapture and sightings indicate that the hypotheses in which there are two sub-stocks in sub-area 1(Hypotheses 4 and 5 in Figure 1) are likely to be assigned much smaller plausibility weights than the otherhypotheses (IWC, 2005b). Actually there is no scientific evidence supporting the occurrence of sub-stocks
in sub-area 1.
Argument used in proposing the sub-stock scenario
According to Annex E of IWC (2005b), the possibility of sub-stock structure in sub-area 1 cannot beignored because there are no genetic data for the breeding grounds. If two breeding sub-stocks mix
uniformly to each other in the feeding ground of sub-area 1, then it will be difficult to detect differences inbiological characters, included the genetics, between the west and east part of that sub-area. Such
differences would be detected between different localities in the breeding ground because in those localities
sub-stocks are not mixed.
It could be argued that Hypotheses 2 and 3 (two-stocks in sub-areas 1 and 2) are based on similararguments to those used to postulate Hypotheses 4 and 5 (two sub-stocks in sub-area 1). In the first case it
is argued that no available DNA and mark-recapture data exist for sub-area 2. In the second case it isargued that no available DNA data exist for low latitude breeding grounds. However it is much moreplausible that additional stock structure occur when a wide longitudinal span is involved, as in the case of
Hypotheses 2 and 3.

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Arguments against the sub-stock scenario based on genetic data
Testing for Hardy-Weinberg (HW) equilibrium in nuclear markers can sometime be useful to detect
situations of mixing of stocks/sub-stocks because deviation from HW provides the evidence of non-randommating as well as selection or migration i.e. the situation at which genetically different populations are
mistakenly sampled as one population. This has been the case of the North Pacific common minke whale
where a significant departure from the HW equilibrium for allozyme loci was found for samples obtainedin the southern part of the Okhotsk Sea where J and O stocks of common minke whale mix to each other insome months (Wada, 1991). By examining microsatellite loci, a significant departure from HW equilibrium
was also found for the autumn samples of the BCB stock of bowhead whale and one of the possible
explanations for such result is that two different stocks mix to each other in Point Barrow during theautumn migration (Pastene et al. 2004b).
Analysis of nuclear markers for western North Pacific Bryde’s whale have been conducted by Wada (1996)
using allozymes and Pastene et al (2004a) using a set of 17 microsatellites. None of these studies detectedsignificant deviation from HW equilibrium for samples in sub-areas 1 providing no support for mixing of
sub-stocks in that sub-area (see also Table 1).
Argument against the sub-stock scenario based on the pattern of mixing
The results of no genetic differences in gene frequencies between Bryde’s whales in sub-areas 1W and 1E(see Table 1) could indicate that two sub-stocks mixed equally in either sub-area. If mixing rates aredifferent it is likely that genetic differences could be detected between the sub-areas, which is not the case(Martien and Taylor, 2004; Pastene et al., 2004a). However, the exactly same mixing rate in two different
sub-areas is implausible considering the knowledge we have on the pattern of movement and mixing oflarge whales. Mixing of genetically differentiated whale stocks has been documented for migratory
corridors and feeding grounds, and a marked variability in the mixing rate has been detected among
geographical regions or among years (e.g. Pastene et al., 1998).
Results for JARPN II samples, which were taken approximately in a same sub-area, showed no significant
genetic differences among years (see Table 4 of Pastene et al., 2004a). In the context of the sub-stock
scenario this results means that the mixing rates of sub-stocks in each sub-area is exactly the same in eachyear. Again by taking into consideration the pattern of movement and mixing of whales this is biologicallyimplausible.
Therefore by considering the pattern of movement and mixing exhibited by whales and the results of thegenetics showing no significant differences between sub-areas 1W and 1E (Table 1), the scenario of substocks in Hypotheses 4 and 5 is considered implausible.
Necessity of samples from the breeding groundIn several opportunities the Scientific Committee has noted the importance of obtaining samples frombreeding grounds for a comprehensive understanding of the stock structure of migratory whales. This
makes sense from the scientific point of view, however the logistic difficulties in getting such samples
should be considered. The case of the B-C-B stock of bowhead whale is mentioned here as an example. As
mentioned earlier, significant genetic heterogeneity has been detected for migrating bowhead whales, forboth mtDNA and microsatellites (e.g. Pastene et al. 2004b). For this specific case samples from thebreeding grounds would assist largely to understand the pattern of genetic differentiation found in the
migratory corridor. By recognizing the logistic difficulties in obtaining samples from the breeding grounds,
the Committee has not insisted in such a sampling neither has adopted stock structure hypotheses to coverfor the lack of samples from the breeding ground. In this particular case analyses and hypothesis on stock
structure are based on samples obtained in the migratory corridor (e.g. Rugh et al., 2003).
Same as in the case of the bowhead whale, the sole reason of absence of samples from low latitude
breeding ground should not be a reason for establishing new stock hypotheses in the case of the North
Pacific Bryde’s whale. Otherwise the Scientific Committee criterion to adopt hypotheses on stock structure
could be considered again as inconsistent (e.g. Pastene, 2003).

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Is the longitudinal line at 155°E biologically plausible?
During the 1998 Scientific Committee meeting there was a concern on an apparent gap in the catch
distribution of Bryde’s whale between 150°E and 160°E (see IWC, 1999 p. 116). Catch distribution
analysis was based on past land-based and pelagic commercial catches (Figure 5). On that opportunity it
was explained that such gap in catch distribution was a result of catch regulations; the western boundary to
pelagic whaling set by the Government of Japan at that time was 159°E and the eastern extent of coastal
whaling was restricted by distance from the land station (IWC, 1999).
Since 2000 JARPN II surveys have covered new regions in the western North Pacific included thelongitudinal sector around 155°E. The catches of Bryde’s whales in the western North Pacific for both pastpelagic commercial operations (1971-1979) and recent JARPN II catches (2000-2005), were plotted(Figure 6). As evident from this figure there is no gap between 150°E and 160°E. Further no discontinuity
in the catch distribution is observed for the sector comprised between approximately 140°E and 160°W,
which cover most of sub-areas 1 and 2. Whales taken by past land-based operations around the Ogasawara
Island (data not shown) would cover the blank space in the south west region in Figure 6. Therefore theexplanation given in 1998 to explain the gap observed in catch distribution between 150°E-160°E has been
corroborated.
A statistical test based on the randomized chi-square (Roff and Bentzen, 1989) was conducted using all
available genetic samples (Figure 6), to test for differences between whales distributed west (sub-area 1W)
and east (sub-area 1E) of 155°E (Table 1). Analysis based on mtDNA involved 261 samples for sub-area
1W and 140 for sub-area 1E. A large P-value resulted from this comparison suggesting no significant
differences between these sub-areas. A similar result was found in the microsatellite analysis for 17 loci(Table 1). This is consistent with the results found by Martien and Taylor (2004) and Pastene et al. (2004a),
which conducted more detailed genetic analyses based in different groupings in sub-area 1
Analysis of sighting distribution (Miyashita and Shimada, 1996; Shimada, 2004, Figures 3 and 4) andmark-recapture (Kishiro, 1996; 1998) suggested no discontinuity around 155°E.
Given these results the longitudinal line at 155°E is not supported by available scientific data.
CONCLUSIONSThe single stock scenario (Hypothesis 1) is fully consistent with the available data. This hypothesis should
be given high plausibility and it should be considered as base case scenario in the trials specifications.
Although DNA and mark-recapture data are limited for sub-area 2, results based on allozymes, sighting andcatch distribution and biological parameters suggest no differences between whales in sub-areas 1 and 2.
Hypotheses 2 and 3 should be considered in the trials under a precautionary approach (to cover for theabsence of DNA and mark-recapture data in sub-area 2). However these hypotheses should not be
considered as base case because there is no scientific evidence supporting the existence of a second stock
east of 180°E.
Hypotheses 4 and 5 are not supported or explained by the available scientific data. Furthermore theapplication of the `simple model filter` to mark-recapture data for western North Pacific Bryde`s whales(Punt et al., 2005) suggested that if there are two sub-stocks in sub-area 1, they are very well mixed. The
high mixing rates implied by the available data meant that trials based on stock hypotheses with two-substocks that mix would behave in a manner very similar to trials based on stock hypotheses with only one
stock in sub-area 1. In order to avoid waste of time, hypotheses involving sub-stocks can be ignored for thetrial specifications.
The possibility of additional stock structure in sub-area 1 emerged during the 1998 Scientific Committee,
not because of supporting evidence but rather by the concern by some members of the Committee that subarea 1 is very large and there is limited information for some part of it (IWC, 1999 p. 14). The spatial
distribution of genetic samples in sub-area 1 has been enhanced since 1998 through the addition of thesamples from the JARPN II. Different genetic methods were used to examine these data and no significant

5degree of genetic heterogeneity was found. Also JARPN II catches covered for the apparent geographicalgap observed when only past commercial samples were plotted.
The possibility of a sub-stocks occurring in sub-area 1 has been weakened considerably with the new
information accumulated since 1998 and therefore hypotheses based on sub-stocks (Hypotheses 4 and 5)
can be ignored for the process of trial specifications.
REFERENCES
Goto, M., Kanda, N. and Pastene, L.A. 2004. Analysis of mtDNA sequences in Bryde’s whales from thecentral western North Pacific and Baja California Peninsula. Paper SC/56/PFI5 presented to the IWC
Scientific Committee, June 2004 (unpublished). 9pp.
International Whaling Commission. 1999. Report of the Scientific Committee. J Cetacean Res. Manage. 1(Suppl.):1-284.
International Whaling Commission. 2005a. Report of the Scientific Committee. J Cetacean Res. Manage. 7(Suppl.): 1-391
International Whaling Commission. 2005b. Report of the Workshop on the pre-implementation assessmentof western North Pacific Bryde’s whales. IWC Document SC/57/Rep3 (30pp).
International Whaling Commission. 2005c. Report of the Scientific Committee. J. Cetacean Res. Manage.
(Suppl.00): 00-00.
Kato, H. and Yoshioka, M. 1995. Biological parameters and morphology of Bryde’s whales in the western
North Pacific, with reference to stock identification. Paper SC/47/NP11 presented to the IWC
Scientific Committee, May 1995 (unpublished). 19pp.
Kishiro, T. 1996. Movements of marked Bryde’s whales in the western North Pacific. Rep. int. Whal.
Commn 46:421-8.
Kishiro, T. 1998. Further analyses on the mar-recapture data of the western North Pacific Bryde’s whales
by a unit of five degree square latitude-longitude. Paper SC/50/RMP18 presented to the IWC
Scientific Committee, May 1998 (unpublished). 13pp.
Kitakado, T., Kanda, N. and Pastene, L.A. 2005. A prospective evaluation of statistical power for
population identification under island models. Paper SC/M05/BR3 presented to the IWC Workshop
on pre-implementation assessment, March 2005 (unpublished). 14pp.
Martien, K.K. and Taylor, B.L. 2004. Analysis of population structure in western North Pacific Bryde’s
whales using three clustering methods. Paper SC/56/PFI3 presented to the IWC Scientific Committee,
May 2004 (unpublished). 10pp.
Pastene, L.A. 2003. On the different criteria used by the IWC/Scientific Committee for defining stocks inbowhead and western North Pacific minke whales. Paper SC/55/RMP9 presented to the IWC
Scientific Committee, May 2003 (unpublished). 7pp.
Pastene, L.A., Goto, M. and Kishino, H. 1998. An estimate of the mixing proportion of ‘J’ and ‘O’ stocks
minke whales in sub-area 11 based on mitochondrial DNA haplotype data. Rep. int. Whal. Comm
48:471-474.
Pastene, L.A., Goto, M. and Kanda, N. 2004a. An update of the mitochondrial DNA and microsatellite
analyses in western North Pacific Bryde’s whale. Paper SC/56/PFI4 presented to the IWC ScientificCommittee, May 2004 (unpublished). 9pp.

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Pastene, L.A., Goto, M. and Kanda, N. 2004b. Genetic heterogeneity in the B-C-B stock of bowhead whale
as revealed by mitochondrial DNA and microsatellite analyses. Paper SC/56/BRG32 presented to the
IWC Scientific Committee, June 2004 (unpublished). 17pp.
Punt, A.E., Kishiro, T. and Allison, C. 2005. Progress on estimating mixing rates for western North PacificBryde’s whales using a ‘simple model filter’. Paper SC/57/PFI2 presented to the IWC ScientificCommittee, June 2005 (unpublished). 16pp.
Roff, D.A. and Bentzen, P. 1989. The statistical analysis of mtDNA polymorphisms: chi-square and the
problem of small samples. Mol. Biol. Evol. 6:539-45.
Rugh, D., DeMaster, D., Rooney, A., Breiwick, J., Shelden, K. and Moore, S. 2003. A review of bowhead
whale (Balaena mysticetus) stock identity. J. Cetacean Res. Manage 5(3):267-279.
Shimada, H. 2004. Abundance estimate of the western North Pacific stock of Bryde’s whales using sighting
data from 1998 to 2002. Paper SC/56/PFI6 presented to the IWC Scientific Committee, May 2004
(unpublished). 8pp.
Shimada, H. and Miyashita, T. 1996. Further estimation of Bryde’s whale abundance in the western North
Pacific incorporating sighting data in 1995. Paper SC/48/NP17 presented to the IWC ScientificCommittee, June 1996 (unpublished). 8pp.
Wada, S. 1991. Genetic heterogeneity in the Okhotsk Sea-West Pacific stock of minke whales. Paper
SC/43/Mi32 presented to the IWC Scientific Committee, May 1991 (unpublished). 17pp.
Wada, S. 1996. The stability of Got-1f frequencies of the western North Pacific Stock of Bryde’s whales.
Rep. int. Whal. Commn 46: 459-460.
Wada, S. and Numachi, K. 1991. Allozyme analyses of genetic differentiation among the populations andspecies of the Balaenoptera. Rep. int. Whal. Commn (special issue 13): 125-154.
ACKNOWLEDGEMENTS
I would like to thank T. Tamura and K. Konishi (ICR) for their assistance in making Figure 6 and M. Gotoand N. Kanda (ICR) for their help in the update of DNA data. H. Hatanaka and S. Ohsumi (ICR) read themanuscript and provided valuable comments.

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Table 1: Results of a genetic comparison between Bryde’s whales west of 155°E (sub-area 1W) and east of
155°E (sub-area 1E) based on mtDNA and microsatellite, and chi-square test. In parenthesis are the sample
sizes for 1W and 1E, respectively. Results for the Hardy-Weinberg equilibrium test, by sub-area and locus,
are also shown. Figures shown are the P-values after 10,000 randomizations. All the samples involved inthis analysis are from the larger, pelagic form Bryde’s whale (Goto et al., 2004).
Locus
mtDNA (261, 140)
GATA98
EV104
GT011
GATA53
GATA417
DlrFCB14
DlrFCB17
GT23
EV14
GT310
EV1
EV94
GGAA520EV21GT575
GATA28
TAA31
All microsatellite loci(260, 125)

Heterogeneity test
P-value
0.716
0.154
0.764
0.860
0.578
0.784
0.348
0.968
0.488
0.608
0.188
0.455
0.674
0.351
0.430
0.342
0.454
0.740
0.882

Test for Hardy-Weinberg Equilibrium
Sub-area 1W
Sub-area 1E
0.720
0.829
0.958
0.823
0.954
0.619
0.909
0.218
0.731
0.231
0.038
0.792
0.253
0.138
0.607
0.227
0.502
0.737

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0.148
0.671
0.465
0.294
0.504
0.856
0.915
0.328
0.331
0.641
0.360
0.005
0.247
0.250
0.803
0.243
0.232
0.209

Figure 1: Hypotheses on stock structure presented at the pre-implementation assessment of western North
Pacific Bryde’s whale. The illustration was modified from that in the Workshop report for clarity. See text
for explanation.

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Figure 2: Spatial distribution of Got1f frequencies by 10° squares for the western North Pacific Bryde’s
whales. In parenthesis are the sample sizes (taken from Wada, 1996).

10Figure 3: Positions of primary sightings of western North Pacific Bryde’s whales in August and Septemberin the period 1988-1995 (taken from Shimada and Miyashita, 1996).

Figure 4: Distribution of primary sighting of western North Pacific Bryde’s whales and track lines underpassing mode effort for the period 1998-2002 (taken from Shimada, 2004).

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Figure 5: Summary of information for determining stock boundaries for ISTs for western North PacificBryde’s whales and agreed boundaries for the Western Stock and two sub-areas. Note the apparent gap
between 150°E and 160°E in catch distribution (taken from IWC, 1999).

Figure 6: Catch distribution of Bryde’s whales in the western North Pacific. Red corresponds to catch bypelagic whaling operations conducted between 1971 and 1979; blue corresponds to catch by JARPN II
between 2000 and 2005.

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