SC/62/NPM27
Initial comments on paper by Baker et al. ‘Stock structure of western North Pacificminke whales based on mtDNA haplogroups from bycatch and scientific whaling’(SC/62/NPM20)
Luis A. Pastene and Naohisa Kanda
Institute of Cetacean Research
SC/62/NPM20 presented an analysis of 4 mtDNA haplogroups in the western North
Pacific common minke whale. Three of these haplogroups are informative (but notdiagnostic) of the J stock, and one is informative of the O stock. Analyses are based on237 samples obtained in the Korean market and 2,551 samples obtained from Japanesebycatches and scientific whaling (JARPN and JARPN II). Pairwise tests ofdifferentiation for mtDNA haplogroups were conducted for sub-areas and sample
sources, using both the randomized chi-square and Fst. Based on the results of theseanalyses the authors reached four main conclusions, which are listed in page 4 of thetheir paper. Here we provide some initial comments on the samples, analyses andconclusions of NPM20
Market samples• Interpretation of results of market samples is difficult as the date and location of
the samples are unknown, and the dynamic of the whale products in the market
is undocumented. For this reason the IWC SC has not agreed yet on the use ofmarket samples for management purposes. I am afraid why the authors did not
make use of Korean bycatch data of known origin, made available underProcedure A.
Quality control• Quality control of market DNA samples are according to Morin et al. (2010). It
seems to me that the guidelines agreed by the IWC Scientific Committee should
be followed.
Haplogroups• 4 haplogroups are identified, one is informative of the O stock and three areinformative of the J stock. As noted by the authors these markers are notdiagnostic of these stocks, e.g. the haplogroup identifying the O stock also occur
in the J stock although in smaller proportion, and the haplogroups identifying theJ stock also occur in the O stock although in smaller proportion. It should be
noted that haplogroup AA in Table 2 (informative of the J stock according to theauthors) occur in higher frequencies in the samples of the O stock in coastal andoffshore samples. It seems that this haplogroup can not be consideredinformative of the J stock.
• There was a good concordance between the haplogroups and individualassignment by microsatellite (Kanda et al., 2009) (93% agreement in the totalsamples). This just confirm that several of the ‘sub-areas’ and ‘source’ used in
the pairwise comparisons of Table 3 are composed by samples with different
proportions of J and O stocks.
Hypothesis test
• As noted above several statistical comparisons are made for strata where J and O
stock animals mix in different proportions. Then it is not surprising thatsignificant differences are found when these strata are compared. For examplemixing rate of J stock is different among BC7, 7W and 7E, and consequently
haplogroup composition changes correspondingly. This is the reason for thesignificant differences. In the same line it is not surprising that in comparisonsamong strata where only one stock is suspected no significant differences arefound (e.g. between sub-areas 8 and 9 and between BC6 and Korean market).
On the conclusions• The authors criticize the lack of consistent sampling across strata, which makedifficult conclusions on stock structure. The important point is that no data set isperfect and that hypotheses should be defined based on the best available data,
not on the perfect set of data. For comparison the authors could refer to otherdata sets used by the IWC SC for the assessment of other whale species.
• Conclusion 1) by the authors is reasonable as the strata BC6 and Korean market
are composed of only J stock animals. However the genetic data from theKorean market are uninformative of the possibility of a second J stock in theYellow Sea as speculated by the authors.
• To our view the author’s interpretation of results leading to conclusions 2), 3)and 4) are not correct. For a better interpretation of the genetic results:a) Statistical tests comparing strata and source could be carried out separately for Oand J stock samples (as defined by the haplogroups), and results could becompared with those of the microsatellite analyses.
b) Seasonal changes along the Japanese coast could be better studied in the context
of a hypothesis on the migration pattern and segregation of the stocks.
c) Seasonal changes of stocks along the Japanese coast could be compared with theinformation provided by Kanda et al. (2009) for microsatellites.
Regarding the Pacific side of Japan the authors provided two explanations for theirresults: a) complex seasonal mixing of two stocks (e.g. O and J) and b) whales in subarea 7W represent a third stock (e.g. Ow). They considered explanation b) moreplausible however they do not provide any evidence for assigning such plausibility. To
our view their results provided no evidence on the occurrence of an Ow stock.