SC/D06/J12

WHAT DO WE KNOW ABOUT THE STOCK STRUCTURE
OF THE ANTARCTIC MINKE WHALE? A SUMMARY OF
STUDIES AND HYPOTHESESLUIS A. PASTENEThe Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan
ABSTRACT
A review of the studies on stock structure in the Antarctic minke whale was conducted with the purpose toestablish a plausible hypothesis on stock structure of this species in the JARPA research area (Areas IIIE-VIW).
Studies on stock structure started at the end of the decade of the 70’s and results were revised by the SC during
the comprehensive assessment of the species in 1990. All the analyses were conducted using samples and datafrom commercial pelagic whaling in the Antarctic. Genetic studies were based mainly on allozyme althoughstudies based on mitochondrial and nuclear DNA were also conducted. Most of these analyses involved small
sample sizes from only Areas IV and V. Non-genetic studies revised in 1990 involved morphology, catch andsighting distribution pattern, analysis of Discovery marks and ecological markers. Results from the different
approaches failed to identify unambiguously any isolated population in the Antarctic. Analysis of sighting datasuggested the occurrence of five breeding Areas. Studies on stock structure under the JARPA started after thecomprehensive assessment. It is considered that samples taken by JARPA are more useful for studies on stock
structure given the wider geographical covering of the surveys and because minke whales were taken along
track-lines in a random mode design. Initially the JARPA studies on stock structure were based on mtDNA anda considerable genetic heterogeneity in Areas IV and V was found. More recently the total minke whale samples
taken by JARPA in Areas IIIE, IV, V and VIW were examined by different analytical approaches, genetics andnon-genetics, using the same samples and kind of grouping. The results from the different techniques provide
strong evidence to reject the hypothesis of a single stock in the JARPA research area. The most parsimonious
explanation of the results is that there are at least two stocks present in the research area: an eastern Indian (I)and a western South Pacific (P) stock. These stocks would mix across a soft boundary, which would probably
best be placed near 165ºE. This stock division is adopted for the objective of the estimation of biologicalparameters in JARPA. Although the most recent analyses by JARPA indicated that whales in Area IIIE are
related to the I stock, other analyses suggested some degree of heterogeneity between Areas III and IV.
Therefore the possibility of additional stock structure in Area III (e.g. the occurrence of animals from thewestern Indian Ocean breeding ground) should be investigated in the future. Any stock boundary (orequivalently sectors of mixing) among stocks in the Antarctic are likely to vary according to oceanographic
conditions, which in turn controls the distribution of the key prey species of the Antarctic minke whale, the krill.
Several future research needs on stock structure are identified. The results will inform the specifications andtesting of appropriate management areas under the Revised Management Procedure.
INTRODUCTION
The Antarctic minke whale, like all the other Southern Hemisphere baleen whales species apart from theBryde’s whale, was managed by the International Whaling Commission (IWC) on the basis of six geographical‘Areas’ (Figure 1). The IWC established these Areas from the 1974/75 season, based mainly upon informationfrom Mackintosh (1942; 1966) on distribution of catches of blue, fin and humpback whales (see review by
Donovan, 1991).These Areas were used by the IWC for the implementation of the New Management Procedure(NMP). However, biological evidences for the particular boundaries are weak, especially for those species suchas the minke whale, whose data were not considered when the original management Areas were established.
In this regard, some related and important questions were formulated by Hoelzel and Dover (1989):‘are the whales found in two geographically distinct management Areas from two different genetic stocks? orare individuals from more than one genetic stock present in a particular management Area? If so, what level ofinterchange may have occurred between different genetic stocks?’. Several approaches were used in the past to1try to identify genetic stocks of the Antarctic minke whale and determine to what extent genetic stocks and IWC
management Areas coincide. These approaches included genetics, morphology, analysis of mark-recapture data,
patterns of catch and sighting distribution and ecological markers, and the analyses were conducted using
samples and data derived from past commercial pelagic whaling (CPW) in the Antarctic. The output of most ofthese studies were presented and discussed during the Comprehensive Assessment (CA) of this species
conducted by the IWC Scientific Committee (SC) in 1990 (IWC, 1991). Detailed reviews of studies on stock
identity in the Southern Hemisphere minke whale have been conducted by Horwood (1990), Best (1990) and
Pastene and Goto (1999a).
I present here an update of the information on stock structure in the Antarctic minke whale. The review
is conducted for studies based on CPW samples and JARPA samples, separately. The output of this review isused to formulate a stock structure hypothesis of this species in the feeding ground so that the estimation of
biological parameters, which is the main objective of the JARPA, can be carried out on the basis of thebiological stocks proposed in the hypothesis.
As a background for the review, three related matters are reviewed: abundance, catch history andseasonal movements.
Abundance
Abundance of the Antarctic minke whale was given during the CA of the species in 1990 (IWC, 1991).
Estimates were based on sighting data collected during the IDCR (International Decade for Cetacean Research)
surveys in Antarctic Areas I-VI south of 60°S. Estimates for Area I, which was based on a survey conducted in
1982/83, was 73,302 (CV=0.254). The estimates for Area II, based on a survey conducted in 1986/87, was122,156 (CV=0.190), for Area III (1987/88 survey), was 88,735 (CV=0.273), for Area IV (1988/89 survey), was74,692 (CV=0.257), for Area V (1985/86 survey) was 294, 6.10 (CV=0.138) and the estimates for Area VI,
based on a 1983/84 survey, was 106,901 (CV=0.277). All these estimates were made following ScientificCommittee standard methodology. The IWC/SC is currently conducting an update of these abundance estimates.
Catch history
The total catch of minke whales to 1990 was summarized during the 1990 SC meeting. For Areas I to VI was
12,108, 19,739, 27,541, 34,586, 15,165 and 4,999 whales, respectively (IWC,1991). From 1987/88 to 2005/06
JARPA catches in Areas III, IV, V and VI should be added.
Seasonal movements
The Antarctic minke whale like all the other balaenopterids (except the Bryde’s and pygmy blue whales) are
believed to undertake seasonal migrations between feeding grounds in the Antarctic waters in summer (south of60ºS) and breeding grounds in the tropical or temperate regions in winter. For this species, however, there is
only a single evidence of such linkage, based on mark-recapture data. Two whales that had been marked in the
Antarctic were recovered off Brazil (Buckland and Duff, 1989). There are also a few indirect evidences on thislinkage based on ecological markers (Nemoto et al., 1980; Ohsumi, 1973). Kasuya and Wada (1991) examinedsighting data obtained from Japanese sighting vessels in the Indian Ocean and because of the considerable
sightings in summer to the north of 55°S, they suggested that not all individuals migrate to waters south of the
Antarctic Convergence in summer. On the other hand, it is possible that not all individuals, distributed in the
Antarctic feeding grounds in summer, migrate to lower latitudes in winter. Aguayo (1994) made 37 sightings(211 individuals) of minke whale in Antarctic Area I in winter suggesting that some minke whales stay in the
Antarctic over the winter.
Kasamatsu et al. (1995) investigated breeding areas and southbound migrations of the Antarctic minke
whales using Japanese sighting surveys data obtained during 1976 to 1987. Latitudinal occurrence by monthsuggested that minke whales moved southward from the breeding areas by October-November, and that most ofthem had migrated into Antarctic waters by January. According to the authors, whales tend to move almost
directly south from the breeding areas to feeding areas, and subsequently disperse after arriving at the feedingareas.

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STUDIES ON STOCK STRUCTURE BASED ON COMMERCIAL PELAGIC WHALING SAMPLES
Several techniques were used to examine stock structure of Antarctic minke whale based on CPW samples. As
mentioned earlier most of these studies were presented to the CA in 1990. I summarize here only the mainstudies.
Genetics
Several molecular techniques were used to investigate stock structre in the Antarctic minke whale. The mostextensive (geographically) genetic surveys were based on allozymes but also techniques based on restriction
fragment length polymorphism (RFLP) and sequencing of mitochondrial DNA (mtDNA) as well nuclear DNA(nDNA) were used. Table 1 summarizes data and results of the most relevant genetic studies.
Allozymes
Wada and Numachi (1991) conducted an allozyme analysis involving a large sample size of the Antarctic minke
whale. The analysis was part of an extensive allozyme analysis covering minke whales from other localities andother baleen whales species as well.
The authors used 45 allozyme loci to examine a total of 11,414 Antarctic minke whale samples (liver
and muscle) from all the Areas indicated in Figure. 1. In addition they examined 195 samples (liver) fromcoastal Brazil. Samples in the Antarctic were from CPW operations conducted between 1975/76 and 1983/84.
Samples from Brazil were from a commercial coastal whaling (CCW) operation in 1981.
A total of 10 loci (Adh-2, Gdh, Got-I, Idh-l, Me, Mpi, PepD, 6Pgd, Pgm-3 and Sdh) were polymorphic
in the Antarctic sample.
There was not significant departure from the Hardy-Weinberg equilibrium in the Antarctic sample.
Furthermore a homogeneity test based on G-statistics was conducted using the following loci: Adh-1, Adh-2,Gpi, Sdh and 6Pgd. No significant spatial (IWC Areas or 10º sectors) or temporal (between years and between
months within a year) heterogeneity was found in the Antarctic sample. In addition no significant differenceswere found between the Brazilian and Antarctic minke whales.
RFLP analysis of mitochondrial DNA control region
Hoelzel and Dover (1991) analysed variation in the control region of the mtDNA and compared minke whales
from the Antarctic, North Pacific and North Atlantic. From the Antarctic, they used 20 samples from Area IV
and 21 from Area V available from the CPW. They used three kind of four-base restriction enzymes (Ddel,
MhoI and HinfI) to investigate polymorphism in the control region. A total of five haplotypes werediscriminated in the total Antarctic sample. Genetic distance between the two Areas was 0.003 substantiallylower than that found between Southern and Northern Hemispheres minke whales.
RFLP analysis of whole mtDNA
Wada et al. (1991) used a RFLP analysis of whole mtDNA to examine minke whales from
Antarctic Areas IV and V and from the North Pacific. Samples from Areas IV (n=40) and V (n=39) were from a
CPW operation in 1983/84.
Polymorphism in the mtDNA was investigated by using 14 restriction enzymes: AccI, AvaI, BamHI,
BgIII, EcoRI, EcoRJ;; RaeII, HincII, HindIII, HpaI, ScaI, SphI, StuI and XbaI. All but AvaI, BamHI, ScaI, SphIand XbaI showed polymorphism. A total of 15 haplotypes were discriminated in Areas IV and V.
The G-statistics showed no significant heterogeneity between Areas IV and V. MtDNA diversity forthe combined sample was 0.0016.
Repeated DNA sequences
Amos and Dover (1991) used repeated DNA sequences (gene families) to examine minke whales from theNorth Atlantic, North Pacific and Antarctic Areas IV and V. Approximately 50 samples were available fromeach of these Areas. These were available from CPW operations.

3A total of 10 gene families were identified and six uncovered diagnostic differences between North
Atlantic and North Pacific. Three families revealed differences between either or both the Northern Hemisphereand the Antarctic. However no consistent differences were found between Areas IV and V although clone
cl.5M1-19 revealed a polymorphism which had a strongly skewed distribution with respect to these two Areas.
The authors offered three possible explanations for such apparent differences: i) biased sampling due to related
individuals ii) a genuine difference in allele frequencies between the populations and iii) an indication of two
discrete populations which only mix certain times of the year.
Multilocus minisatellite (DNA fingerprinting)van,Pijlen et al. (1991) used this molecular technique to examine minke whales from the North Atlantic, North
Pacific and Antarctic Areas IV and V. Samples from the Antarctic were from CPW operations.
When Jeffreys’ probe 33.15 was used, striking differences were observed between North Atlantic andNorth Pacific and Antarctic minke whales. Such differences disappeared when probe 33.6 was used. No
significant differences between Areas IV and V were found.
Single locus mini- and microsatellite
van Pijlen et al. (1992) used single locus mini and microsatellites to compare minke whales from the North
Pacific, North Atlantic and Antarctic Areas IV and V. Samples from the Antarctic were from the CPW operationof 1982/83.
Three minisatellite loci (cBac02, cBac10 and cBac34) were screened in 24 and 21 whales from Areas
IV and V, respectively. Four microsatellite loci (199/200, 417/418, 464/465 and 415/416) were screened in 19
and 61 whales from Areas IV and V, respectively.
Regarding minisatellite, no significant differences in allele frequencies were found for any of the locibetween Areas IV and V and then these two samples were pooled for further analyses. Striking differences wereobserved among Antarctic, North Pacific and North Atlantic minke whales. No deviations from the HardyWeinberg equilibrium were detected in any population for each of the three loci.
Regarding microsatellite, allele frequencies were homogeneous in Areas IV and V. These two Areas
pooled were substantially different from North Pacific and North Atlantic. For one locus (415/416) a significant
deviation from the Hardy-Weinberg equilibrium was observed for the Antarctic sample.
Clustering analysis of microsatellite showed two sub-clusters in the Antarctic sample in 84% of thetrees. One of them was further divided into two clusters in 86% of the trees. However these clusters were notlinked with catch position, time, date or sex.
The authors noted that the interpretation of their negative results (no significant differences between
Areas) is difficult without further information on movement of whales between Areas during the feeding season.
Furthermore they added that more extensive and synchronized sampling is required before it will be possible todistinguish unequivocally between a truly panmictic population and a subdivided population, which may display
temporal and spatial mixing on the feeding ground.
Morphological and morphometric analyses
Wada and Numachi (1979) examined the morphology in minke whales collected by the CPW in Antarctic Areas
I-VI in the austral summers of the period 1971/72 and 1976/77. The characters used were the following: i) the
relationship between the end of the ventral grooves and umbilicus, ii) flipper coloration and iii) the proportion of
the black band in the largest baleen plate. On these characters two (ventral grooves reaching umbilicus andventral grooves not reaching the umbilicus), four (uniformly black, with dark line, with faint greyish band andwith clear white band) and six (all faint amber, black band occupies l/4 area of baleen plate, black band occupies
1/3 area of baleen plate, black band occupies 2/3 area of baleen plate and all black) items were defined, and eachwhale was classified according them.
The number of whales examined for each of the characters and items were, for character i) 532 and18,692, respectively; for character ii) 8,934, 4,003, 6,147 and 180, respectively and for character iii) 23, 1,459,
7,103, 7,831, 2,703 and 49, respectively.

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The following characters were dominant: ventral grooves reaching umbilicus, flipper coloration
uniformly black and baleen plate coloration with black occupying 1/2 area of baleen plate. No relationshipbetween external characters and sex was observed but considerable variation in the observed frequency patterns
between CPW operations was found. Apart from this, remarkable variation even within the same 10º square byexpedition or by season was found. Finally the authors concluded that the data set was not useful to identify
stock units and that criterion classification technique of each observer should be unified.
Doroshenko (1979) examined the morphology of minke whales collected by CPW operations in
Antarctic waters of the Indian Ocean and in the southwest Pacific. He called these as Indian and New Zealand
populations, respectively. A total of 800 whales collected in the austral season 1975/76 were examined for ten
morphological characters as follow: i) shape of the fluke notch, ii) color of flipper on dorsal side, iii) color of thepalate, iv) location of the Jacobson’s organ, v) configuration of the left liver segment, vi) sternum shape, vii)
number of vibrissae, viii) number of ventral grooves on a line with the base of the flippers, ix) number of baleen
plates on one side of the baleen series and x) number of phalanges on the first and fourth digits of the flippers.
For some of these characters items or types were defined, and the frequencies of them were compared among
the two populations.
According to the author the most marked differences between both populations were the frequency ofoccurrence of shapes of fluke notches (character i), color of flippers (character ii), number of baleen plates andnumber of phalanges on the first and fourth digits of the pectoral flipper. He suggested that the Indian
population is thought to inhabit the area between 55°E and 110°E and the New Zealand population between
135°E and 165°W. He further suggested that the border line is limited by latitudes 58°S to 60°S and thesouthern one coincides with the ice-edge.
Bushuev (1990) examined minke whales collected by CPW operations in Areas I, II, III and IV
between 1983/84 and 1985/86. A total of 6,646 whales was examined for different morphological markers.
A total of 34 nonmetric characters were used. These characters were on coloration, derivatives of
cutaneous covering, skeleton, digestive system and circulatory system. In addition the author examined 10
meristic and two linear morphological features. Comparison between the samples by Area and by sex was madeusing the index of similarity r and the significance differences between r and 1 was calculated by J-statistics,
which has a chi-squared distribution. Differences in the mean values of meristic and linear morphologicalcharacters between samples were evaluated using Student’s test.
In relation to the analysis of nonmetric characters the author found specific pattern of variation by sex
in all samples, stability of differences between the sexes over season (years) and significant differences between
sexes for combined data of several seasons in nine characters. For one character only they found a statisticallysignificant age dependent variability. Differences over three successive seasons in a same Antarctic Area wassmall. Comparisons among Areas were made for female and male independently. The results of several
combinations and tests suggested no reason to consider the groupings of minke whales examined to be fromisolated populations.
Regarding meristic and linear characters, statistical significant differences between males and females
were found for four characters. No significant correlation of characters with age was found. Limited variation inthese characters among seasons (years) was found. No significant differences were found among Areas.
Other approaches
Analysis of tagging data
Information on the recovery of 94 Discovery marks from minke whales in the Southern
Hemisphere was reviewed by Best (1990). The main features were the recovery of two marks from whales on
the winter breeding grounds off Brazil. These whales had been marked at locations 54° of longitude apart in the
Antarctic. This was a direct evidence of linkage of breeding areas with feeding areas in the Antarctic. Noting thelong longitudinal distance between marking locations at the Atlantic, and recovery locations at the breeding
ground off Brazil, Best (1990), suggested that whales from different breeding grounds may intermingle on the
Antarctic feeding grounds. Recoveries of the other 92 marked minke whales in the Antarctic indicated a
substantial but limited range of longitudinal movement (up to 40°) for 90% of whales within eight years of5marking. Patterns of dispersal of marked whales suggested a discontinuity around 80°E (western part of Area
IV) (see also Wada, 1984).
Kato et al. (1993) examined all available marks (2,864 mark release and 110 recoveries of Discoverytag) at the Antarctic. Through their analyses it was revealed that: the average distance of longitudinal movement
is about 30º, recaptured animals showed no preferential east or west movement in the Antarctic and no
significant difference were found between sexes in terms of distance moved. Marked movement of whales wasobserved through 130ºE, the boundary between Areas IV and V. Regarding boundaries they noted that theabsence of mark crossing at 80ºE and 160º E suggests the possibility of separate feeding stocks. Following an
examination of mark distribution and catching effort they concluded that discontinuity at 80ºE could be moresuggestive of a boundary between stocks than that at 160ºE.
Pollutant burden
Tatsukawa et al. (1990) examined tissue samples from minke whales taken in Areas IV, V and VI
by CPW operations in 1984/85 and 1985/86. They compared the level of concentration of DDE and PCB among
these Areas using male samples aged over 15 years old. No significant differences among Areas were observedin the concentration of PCB. However, significant higher values of DDE were observed in Area IV than in
Areas V and VI.
Tanabe et al. (1995) conducted an analysis of organochlorines in the blubber of minke whales taken
during a CPW operation in 1984/85 and during a JARPA survey in 1990/91 (Area V). They detected fiveorganochlorine compounds (PCBs, DDTs, HCBs, CHIs and HCHs). No yearly variation was detected in thelevel of concentration of DDTs. However, even considering the age-dependent accumulation characteristics,
they concluded that PCB concentration was higher in 1990/91than in 1984/85.
Fujise et al. (1997) examined the level of accumulation of Hg in liver samples of Antarctic minke
whales. They used a total of 534 samples obtained during CPW and JARPA operations. In their analysis ofgeographical variation they compared level of accumulation among Areas III-VI. No significant differenceswere observed between female and male samples. Also no significant differences were observed among Areas
for different age groups examined.
Ecological markers
Nemoto et al. (1980) reported the presence of diatoms (Cocconeis ceticola) on the skin of minke
whales killed off Durban, South Africa. On the assumption that typical C. ceticola is only
contracted in high latitudes, the authors speculated that its occurrence on whales from Durban
shows that these whales may recently have migrated from higher latitudes.
Ohsumi (1973) reported a broken-off bill of a marlin (Makaira mazara or M. indica) embedded in the
rostrum of a minke whale killed in the Antarctic at 64°06’S, 87°14’E (Area IV). This finding also provides
indirect evidence of a probable linkage between Antarctic and tropical or sub-tropical waters of the Indian
Ocean.
Bushuev (1990) studied several ecological markers on minke whales from Areas I, III and IV. He usedsamples collected by CPW operations in these Areas between 1983/84 and 1985/86. The ecological markers
investigated were: presence (absence) of Xenobalanus globicipitis, presence (absence) and the degree ofoccurrence of Cyamus balaenoptera ,degree of occurrence of ‘white’ scars and degree of occurrence (number)of fresh ‘brightly white’ areas.
The presence/absence of X globicipitis was the most useful marker for stock structure. Differences ininfestation by this parasite among feeding concentrations appeared to be largely unrelated to differences in thetime of whaling. On the other hand, infestation by this parasite was found to be practically the same in different
age groups. In general, females appeared more often infested by this parasite than males and this difference
varied by Area.
Significant differences by Area were found in the frequency of occurrence of X. globicipitis with thelevel of geographical differences far exceeding that of the time differences (seasonal and inter-seasonal). The
author explained such differences saying that the whales feeding in Area III, in the western and central parts of6

Area IV and in the eastern part of Area I spend the winter in different areas of the Southern Hemisphere where
the probability of being infested by X globicipitis varies considerably.
Sighting distribution
Kasuya and Wada (1991) examined sighting data obtained from Japanese sighting vessels in the Indian Ocean.
They suggested that density of minke whale is high in the eastern and western sides of the Indian Ocean and low
in the central sectors. The highest minke whale densities are found south of 60°S from November to March withconsiderable sightings north of 55°S.
Kasamatsu et al. (1995) analysed sightings of minke whales collected by Japanese scouting boats andresearch vessels operating in the Southern Hemisphere since 1976. On the basis of this information the authors
identified five areas of higher density north of 20°S in October-November, which were believed to be breeding
grounds.
Kasamatsu et al. (1990) summarize data from the IWC/IDCR minke whale cruises made from 1978/79.
The document showed regions of high and low density in the Antarctic Ocean but some of these appeared tohave shifted in the interval between the surveys. There was consistent discontinuity at 30°E- 70°E and around
100°E.
Catch distribution
van Beek (1983) and Best (1990) examined CPUE series for the Antarctic minke whale. It was noted that
although there was discontinuity in the distribution of catches, it was not clear to what extend this reflected the
distribution of whales rather than the distribution of catching effort. Van Beek (1983) noted that although theinterpretation of these plots was complicated, he suggested that only at around 100°E is there a very minor
indication for a stock boundary.
STUDIES BASED ON PARTIAL JARPA SAMPLES
Partial samples and data obtained during the JARPA surveys were used in different studies on stock structure. I
summarize here only the main studies.
Genetics
Both mtDNA and nDNA have been used to examine stock structure of minke whales sampled by JARPA. Table
1 summarizes data and results of the most relevant studies.
RFLP analysis of whole mtDNA
Pastene et al. (1993) conducted the first mtDNA study using JARPA samples. In the study a total of 318 minke
whales (from seasons 1988/89 and 1990/91 in Area V and 1989/90 in Area IV), was used. Crude mtDNAs weredigested with six-base restriction enzymes: AccI, BanI, BglII, EcoRJ, EcoRV; HaeII, HincII, HindIII, HpaI,
PvuII, SspI and StuI. All of them showed polymorphism, apart one (HaeII). Restriction enzyme digestions of
mtDNA from the total sample revealed a total of 71 mtDNA haplotypes. For the analysis, samples were divided
into three geographical strata, western (70°-110°E), central (110°-150°E) and eastern (150°E-180°). Haplotype
frequencies were employed to determine genetic relationships between the samples of the designed strata.
Genetic relationships were quantified using the chi-square statistics for heterogeneity of mtDNA haplotype
frequencies (Roff and Bentzen, 1989). Heterogeneity chi-square decomposition began by estimating thesignificance of the chi-squares computed from the raw data for all the three strata. This result showed that
mtDNA haplotypes are not randomly distributed in these strata. Results of pair-wise comparisons indicated that
mtDNA frequency distributions in the western and eastern strata were different. However, no significant
differences were found between the haplotype frequencies of the western and central strata nor between central
and eastern strata. The authors interpreted these preliminary results as the occurrence of different stocks in thefeeding grounds of Areas IV and V and a possible mixing of them in the central stratum.
A more extensive study considering both geographical and temporal criteria was conducted by Pastene
et al. (1994). These authors carried out a mtDNA analysis on 1,257 minke whales from Areas IV and V
collected by JARPA. Samples of Area IV were from two seasons, 1989/90 (n=307) and 1991/92 (n= 260) andthose of Area V from three seasons, 1988/89 (n= 77), 1990/91(n= 308) and 1992/93 (n= 305). Digestion with
six restriction enzymes revealed a total of 123 mtDNA haplotypes. As in the previous study, samples were7

arbitrarily divided into four longitudinal sectors (Area IV western and eastern, Area V western and eastern) andtwo time periods, early (December-15 January) and late (16 January-March). Thus a total of eight area/time
strata were examined. Mitochondrial DNA haplotype frequencies and the randomised chi-square statistic wereused to determine relationships between the area/time strata. After pooling samples from different sexes andseasons, a marked spatial and temporal heterogeneity was found. A group of whales sampled in Area IVWE wassignificantly different in haplotype composition from all but once of the other spatial and temporal strata
analysed. Furthermore, a group of whales sampled in Area VEL was significantly different from all but one
other grouping. Of 123 haplotypes identified, 8 were dominant, but were present in all groups, so that no stock
markers could be identified. Again, the results were consistent with the occurrence of different stocks in Areas
IV and V. This information was revised during the 1994 SC meeting. During the discussion it was noted that thedata presented were amenable to more powerful statistical analyses to examine relationships and clustering andanalysis of molecular variance by permutation procedures approaches were suggested (IWC, 1995).
In response to these recommendations, Pastene et al. (1996) conducted a new analysis of mtDNA
variation in Areas IV and V, this time involving a total of 2,124 minke whales collected by the JARPA.
Digestions with the same six restriction enzymes revealed 137 haplotypes. For the analysis samples weregrouped into eight area/time strata as in the previous study. Following the recommendation from the SC, thequantification of the temporal and geographical differentiation of mtDNA was carried out using the analysis ofmolecular variance (AMOV A) of Excoffier et al. (1992). Genetic distance between haplotypes was estimatedusing a maximum-likelihood method (equation 5.55 of Nei, 1987). Samples from different sexes and seasons
were pooled. There was five predominant haplotypes and these were found in all eight strata tested. The
AMOVA test showed that the molecular differences were significantly less within the area/time strata thanbetween them (PHIst=0.001; P=0.0340). Pairwise testing showed that all the PHIst values involving the Area
IVWE were larger than all the other pairwise comparisons and all of them showed P values below 0.01 or 0.05.
The PHIst value obtained between Area IVWE and all the other strata combined was 0.0090 (P=0.0025). The
authors concluded that a significant source of mtDNA heterogeneity was attributable to the group of minke
whales sampled in the western part of Area IV early in the feeding season. This group was composed by minke
whales sampled during the JARPA surveys of 1989/90 and 1991/92.
Pastene and Goto (1999) examined minke whales sampled by the JARPA in Areas IIIE and IV in twosummer seasons, 1995/96 and 1997/98. Criteria for grouping the samples and method used for the statisticalanalysis were the same as in the previous studies. A total of 812 whales were examined into ten area/time/year
groups. The pattern of mtDNA variation in these two surveys was similar. The significant mtDNA heterogeneity
detected in the group Area IVWE in 1989/90 and 1991/92 was not detected in 1995/96 and 1997/98. Samples inAreas IIIE and IV in 1995/96 and 1997/98 were similar in haplotype frequencies to whales of the core stock(Areas IVWL, IVE, VW). In addition an examination of the offshore component of group IVWE of several
surveys was conducted considering the distance from the ice-edge as a factor. Furthermore a mtDNA analysis
considering different categories of school sizes was conducted. No significant differences were found in
haplotype frequencies among school sizes categories.
Sequencing of the mtDNA control region
Bakke et al. (1996) using sequencing analysis examined 13 and 10 minke whale samples from Areas IV and V,
respectively. The analysis also included samples from the North Atlantic. Samples in Areas IV and V were fromthe 1991/92 and 1990/91 JARPA surveys, respectively. They sequenced a 345bp-segment of the mtDNA control
region. The nucleotide diversity in the Antarctic total sample was 0.0159 higher than in the North Atlantic(0.0064). They used a randomization test to estimate the statistical significance of the genetic differences. Areas
IV and V were different at the 10% significance level.
Microsatellites
Abe et al. (1999) used five microsatellites (GT211, GATA098, GT023, EV1 and EV104) to examine 914 minke
whales sampled by the JARPA in Areas IIIE, IV, V and VIW. The mean observed heterozygosity in these Areas
varied from 0.8206 to 0.8906. Allele frequencies of the five loci were very similar among Areas. Using threedifferent statistical methods, a significant deviation from the Hardy-Weinberg equilibrium was found in the total
sample and Area IIIE suggesting some degree of stock structure. A preliminary heterogeneity test suggested
nuclear DNA heterogeneity in Area V.

8Morphometric analyses
Fujise (1995) conducted a preliminary study on morphometry of minke whales from Area IV sampled in the
1989/90 JARPA survey. All the morphological observations and external measurements had been made by theauthor on the field. Following the sampling design used in the genetic analysis (Pastene et al., 1996) the samples(n= 326) were grouped into three strata: Area IV western early, Area IV western late and Area IV eastern early.
A principal component analysis of the log transformed data revealed that most of the morphometric variation
resulted from measurements of overall length, dorsal fin shape, skull size and shape of flukes. An analysis ofcovariance indicated that the length of the dorsal fin base and the width of the flipper significantly differedamong the three strata of males, but in females only the length of the dorsal fin base differed among strata.
Canonical discriminant analysis revealed that the three area/time strata were not separated exactly. It was
concluded that whales from the Area IV western early stratum have different external body proportions.
Although this result tended to support the finding of the genetic analysis (Pastene et al. 1996), the author could
not exclude the possibility that some of the apparent differences were due to seasonal changes in body fatness.
Other approaches
Pollutant burden
Kunito et al. (2002) determined the concentrations of 12 trace elements in 19 liver and 161 skin tissues of minke
whales from various regions in the Antarctic. Minke whales were collected by JARPA in Areas IIIE (1995/96),
IV (1993/94 and 1995/96) and V (1988/89, 1990/91 and 1992/93). The data of elements in the skins were
subjected to principal component analysis (PCA) and discriminant analysis to assess the ability of trace elements
to discriminate among stocks of the Antarctic minke whales. Principal components were derived fromstandardized data via correlation matrix. For this analysis only the whales with body length over 8m were used.
Large interannual variation of the accumulation pattern of trace elements in the skin was observed in
Area V. There were significant differences in the skin element concentrations among Areas III, IV and V,
especially for males. To eliminate the effect of annual variation of concentration in the skin only the data for
1995/96 (Areas IIIE and IV) were analyzed. These samples were grouped into west and east by longitude 80ºE,
which was proposed by mark-recapture studies (Wada, 1984; Best, 1990; Kato et al., 1993). The discriminant
analysis allowed for a correct classification of 90% of these minke whales.
Ecological markers
Sedlak-Weinstein (1990) summarized the incidence of parasites in 241 minke whales sampled during the
1988/89 JARPA survey in Area V. Of the 241 whales captured 102 (42.3%) were infested with parasites asfollows: Cyamid balaenoptera ectoparasite amphipods found on the ventral grooves (36% infestation rate),
Pennella balanae crustacean siphonostomatid ectoparasite (2.1%), Bolbosoma balaenae intestinal
acanthocephalan (1.3%), Tetrabothria sp. Intestinal cestode possibly T. affinis, Phyllobothrium delphini larval
cestode found in the blubber (1.7%), Anisakis sp stomach nematodes (7.5%).
Pastene et al. (2005) examined the prevalence (percentage of infected individuals per host examined)of the gastric nematode Anisakis simplex in the JARPA research area in the context of stock structure. The
minke whale is known to be the most important final host of A. simplex in the northern North Pacific. Combined
female and male samples were used for the analysis. A total of 6,338 minke whales sampled by JARPA in Areas
IIIE, IV, V and VIW between 1987/88 and 2003/04, were examined.
Prevalence is similar between female and males host. Results indicated that prevalence is higher inAreas V and VIW than in Areas IV and IIIE. The higher rates of Anisakis simplex was observed from longitude
155°E to 170°W, with a peak in sector 165°-170°E.
STUDIES BASED ON TOTAL JARPA SAMPLES (FINAL ANALYSES)
A comprehensive study on stock structure involving genetics and non-genetics markers was presented to the
JARPA review meeting sponsored by the Government of Japan in 2005 (Pastene et al., 2005). The analyses
involved sample and data collected by JARPA between 1987/88 and 2003/04. These analyses were updated toincorporate the samples collected during the last JARPA survey of 2004/05. Below a summary of these updated
analyses is presented.

9Genetics
RFLP analysis of whole mtDNA
Pastene et al. (SC/D06/J9 in this meeting) examined Antarctic minke whales sampled by JARPA in Areas IIIE,
IV, V and VIW between 1987/88 and 2004/05 (whole period) using mtDNA RFLP. Samples were grouped
according the longitudinal sectors used by the JARPA surveys and used in previous mtDNA analyses. A total of
6,256 samples were used in the analysis. Consistent with previous JARPA genetic studies a significant genetic
heterogeneity was found. Whales in the most distant sectors (IIIE+IV and V+VIW) were differentiatedgenetically. The pattern of differentiation was similar between sexes. Genetic results were consistent with the
hypothesis of at least two stocks occur in the JARPA research area. A fine-scale mtDNA analysis suggested alongitudinal division between stocks in the sector 150º-160ºE.
Microsatellites
Pastene et al. (SC/D06/J9) examined Antarctic minke whales sampled by JARPA in Areas IIIE, IV, V and VIW
between 1989/90 and 2004/05 using microsatellite variation at six loci (EV1, EV104, GT211, DlrFCB14,
GT195, GT23). Samples were grouped according to the longitudinal sectors used by the JARPA surveys andused in previous mtDNA analyses. A total of 6,260 samples were used in the analysis. No significant deviationfrom Hardy-Weinberg equilibrium was found. Consistent with previous JARPA genetic studies heterogeneity
tests suggested a significant genetic heterogeneity. Heterogeneity test suggested more partitioning I females thanmales. Whales in the most distant sectors (IIIE+IV and V+VIW) were differentiated genetically. Genetic results
were consistent with the hypothesis of at least two stocks occur in the JARPA research area.
Morphometric analyses
Hakamada (SC/D06/J10) conducted a morphometric analysis based on JARPA samples collected in Areas IIIE,
IV, V and VIW between 1987/88 and 2004/05. Grouping for the analysis followed the strata used by the JARPA
survey. In order to eliminate the effect of bias due to difference among researchers, the ten measurements thatwere less susceptible to such differences were selected for the analysis. Selection of these measurements took
into consideration the opinion of experienced researchers.
Only mature animals were used in the analysis because body proportion could be different between
younger and older animals. First the relationship between body length and longitudinal sectors was investigatedusing ANCOVA. After obtaining an estimated average length of measurements, cluster analysis was applied to
examine the degree of relationships among whales in the six longitudinal sectors. Mature males were separated
into two groups at the division between Areas IV and V (130ºE). Mature females were separated into twogroups at the middle of Area V (165ºE).
It should be noted that the analytical approach used in SC/D06/J10 is different to that used in the 2005
analysis (Pastene et al., 2005). The reason is that in the previous analysis many ‘significant’ p values wereobtained in the comparison among longitudinal sectors. This was because the sample size used is large and thenthe statistical approach used detected small differences in measurements as significant. Results obtained by thecluster analysis are considered more reliable.
Other approaches
Mean length of physical maturity
Bando et al. (SC/D06/J11) compared the mean body length of physically matured whales (MBLM) amongwhales sampled by JARPA in Areas IIIE, IV, V and VIW between 1987/88 and 2004/05. Grouping for the
analysis followed the strata used by the JARPA survey. Physically matured individuals were defined as thosewith epiphysis fusion occurring in the 6th thoracic vertebrae. The t-test and ANOVA were used for testing
differences in mean body length among strata. A P-value smaller than 5% was used as a criterion to reject thenull hypothesis of panmixia. LSD (Least Significant Differences) tests were made in case of multiple tests.
Analyses were conducted for males and females separately. A total of 2,359 minke whales were used in theanalysis.
The total P-values were highly significant for both females and males. Results of pairwise comparisonswere similar for females and males. No significant differences were found among IIIE, IVW, IVE and VW.
Also no significant differences were found between VIW and VE. These two strata differed significantly among
them. Although VEN and VES differed in the case of males, both of these strata showed a similar pattern ofvariation in the comparison to other strata.

10

Analysis of tagging data
Three 410 Discovery marks have been recovered during JARPA surveys in the Antarctic.
The first occurred during the 1991/92 JARPA survey in Area IV (Fujise et al., 1993a). The mark wasrecovered from a whale sighted at position 65°36’S, 79°E on 3 February 1992. The whale was a pregnant female
and the body length and body weight of this individual were 9.0m and 10.4t, respectively (Fujise et al., 1993a).
The whale had been marked during the 1978/79 IWC/IDCR cruise at position 63º11‘S, 100°5’E on 29
December 1978, then the time elapsed between marking and recapture was 13 years. This case was incorporated
into the analysis by Kato et al. (1993).
The second mark was recovered during the 1992/93 JARPA survey in Area V (Fujise et al., 1993b).
The mark was recovered from a whale sighted at position 66°20’S, 153°16’E on 10 February 1993. The whale
was a male and the body length and body weight of this individual were 8.4m and 7.5t, respectively (Fujise etal., 1993b). The whale had been marked during the 1980/81 IWC/IDCR cruise at position 70°57’S, 174°58’W
on 1 February 1981, then the time elapsed between marking and recapture was 12 years.
The third mark was recovered during the 2001/02 JARPA survey in Areas IIIE and IV (Ishikawa et al.,2002). The mark was recovered from a whale sighted at position 66°37’S, 120°47’E on 31 January 2002. The
whale was a pregnant female and the body length and body weight of this individual were 8.9m and 7.7t,
respectively (Ishikawa et al., 2002). The whale had been marked during the 1980/81 IWC/IDCR cruise at
position 65°15’S, 134°24’E on 7 January 1981, then the time elapsed between marking and recapture was 21
years.
DISCUSSION AND HYPOTHESIS ON STOCK SRUCTURE
As indicated earlier the Antarctic minke whale was managed by the IWC on the basis of the six geographicalAreas shown in Figure. 1. These Areas were established based mainly upon information on distribution ordifferent whale species like blue, fin and humpback whales. Then, biological evidences for the particularboundaries for the minke whale are weak. In this paper I reviewed the relevant studies on stock structure for two
different sample/data sets, that derived from past commercial whaling in the Antarctic and that derived from
JARPA.
Studies on stock structure based on samples from commercial pelagic whaling samples
Most of the studies summarized in this paper were presented and discussed during the CA of the species in 1990
(IWC, 1991).
As reviewed in this paper the genetic analyses that used CPW samples involved methods based on bothallozymes and DNA (RFLP analysis of mtDNA control region, repeated DNA sequences, multilocus
minisatellite), which were used to investigate genetic differences mainly between Areas IV and V. None ofthese genetic techniques provided any evidence of unambiguous genetic differences between these Areas.
During the CA, the SC concluded that ‘there must be sufficient interchange between the currently recognised
stocks in the Southern Hemisphere to counteract the effects of genetic drift (which builds up genetic differences
between populations through the random loss of variation). However, this could be achieved by the movementof one reproductively successful individual per generation between neighbouring stocks’ (IWC, 1991). It should
be noted, however, that all of the genetic works apart from the allozyme, were based on very small sample sizes(see Table 1). Furthermore samples available from the past commercial whaling were obtained mainly in areas
near the pack-ice. Probably these samples were not representative of all genetic diversity of whales from Areas
IV and V. Pastene and Goto (1999b) showed that studies based exclusively on samples obtained near the packice are not informative on the stock structure. It should be mentioned also that, apart the allozyme survey of
Wada and Numachi (1991), all the other genetic studies were concentrated to Areas IV and V with no DNA
information from the other Areas.
Morphological analysis provided no evidence of unambiguous genetic differences between Areas.
Although some studies showed some differentiation among longitudinal sectors in the Antarctic (Doroshenko,
1979), the analyses were restricted to some few Areas and the issue of the criteria classification techniqueamong investigators participating in different whaling expeditions was a common problem in these studies.

11Regarding catch distribution, it was noted by the SC in 1990 that although, there was discontinuity in the
distribution of catches, it was not clear to what extend this reflected the distribution of whales rather than the
distribution of catching effort.
The use of ecological markers were more promising as significant differences in the infestation of one
parasite were found among Areas I, III and IV (Bushuev, 1990). However the interpretation of these results inthe context of stock structure is complicated (see Balbuena et al., 1995).
Perhaps the most useful information on stock structure discussed at the 1990 CA was that derived frompattern of sighting distribution in low latitudes (published later by Kasamatsu et al., 1995), which allowed tohypothesize the occurrence of five breeding grounds in the Southern Hemisphere. The other relevant piece of
information came from Discovery marks analyses. The SC noted in 1990 that it is difficult to interpret the
implications of such movement for stock structure due to the small sample size and due to the fact thatmovements indicated by mark recoveries will be influenced by the distribution of marking and catching effort.
Notwithstanding, several authors recognized marked movement of whales through 130ºE, which is the boundary
separating Areas IV and V and a discontinuity at about 80°E, even after giving consideration to distribution ofmarking and catching effort.
In summary all the genetic and non-genetic approaches reviewed by the SC in 1990 failed to identify
unambiguously any isolated stock in the Antarctic. Recognizing that most of the genetic analyses had been
concentrated in Areas IV and V, the SC recommended that further work on the mitochondrial DNA genome ofminke whales from stock Areas other than IV and V should be conducted to examine stock identity, if suitablesamples are available (IWC, 1991). Also recognizing the ecological markers (infestation rate of ectoparasites) as
a promising approach to study stock identity, the SC recommended that Soviet data on the distribution of
ecological markers should be analysed in more detail to provide some measure of the reliability of theconclusions presented (IWC, 1991).
Since 1987/88 austral season the JARPA surveys started in the Antarctic and new samples from Areas
IV and V became available.
Analyses on stock structure based on JARPA samples
JARPA was started in 1987/88 in Areas IV and V with the main objective to estimate some biologicalparameters to improve the management of the Antarctic minke whale. At that time it was assumed that Areas IV
and V were occupied by different genetic stocks. However the evidences supporting such assumption were weak
as showed by the different studies on stock structure based on CPW samples.
The sampling procedure under the JARPA (see SC/D06/J2) allowed for a more extensive geographicaland temporal covering than it was possible under CPW operations. The use of JARPA samples for stock identity
purposes has several advantages in comparison to CPW samples: a) whales are sampled using a random design
described by Kato et al. (1989). Between 1987/88 and 1991/92, the number of whales to be taken from a school
varied with school size: if a solitary whale was found it was sampled; if a pair was encountered, both whales
were planned to be taken, with the first whale to be sampled being chosen randomly; for schools of three or
more, two whales were taken using the random method. From 1992/93, only one whale was randomly takenfrom a school, regardless of school size; b) whales are sampled on pre-determined track lines, which cover bothoffshore and areas near the pack ice and c) detailed sampling and biological information is available for eachspecimen, and this information has been collected by biologists. Therefore samples taken during JARPA should
be more representative of the genetic diversity of the species in the research area. Several techniques were used
to examine stock structure of Antarctic minke whale using JARPA samples.
Earlier analyses based on partial samples
The genetic analyses based on both mtDNA and nDNA consistently showed significant degree of genetic
heterogeneity of Antarctic minke whales, which was attributed to the occurrence of different genetic stocks inthe feeding grounds. The first proposal on stocks structure was provided by Pastene et al. (1993). Theysuggested the occurrence of two stocks in Areas IV and V with a possible overlap region. However the analysis
was based on samples from a few JARPA surveys and involved longitudinal sectors probably too broad.

12

The second proposal on stock structure was based on a larger sample size and more fine-scale grouping(Pastene et al., 1996). A total of eight area-time groups were designed in Areas IV and V. The results wereoriginally presented to the mid-term JARPA review meeting in 1997 and they were summarized as follows:a)A high degree of heterogeneity (as measured by mtDNA) exists with the ordinary form of the minke
whale (Antarctic minke whale) within Areas IV and V.
b) The heterogeneity observed in Areas IV and V is attributable to both longitudinal and temporalcomponents in distribution.
c) The observed pattern of genetic heterogeneity is not consistent with current stock boundaries (i.e.
between Areas IV and V).
d) There are at least two distinct ‘genetic stocks’ in Areas IV and V.

The meeting recognized that the available mtDNA data were consistent with the occurrence of morethan one stock in the JARPA research area. However no boundaries were proposed or discussed at that
opportunity. Based mainly on these results, a working hypothesis on stock structure was presented, whichsuggested a main stock (‘core’) distributed in Areas IV and V and an additional stock (‘western’) distributed inwestern part of Area IV only early in the season. The term ‘core stock’ implied the concept of a large stock
occupying all (or most of) Areas IV and V.
To investigate this hypothesis JARPA surveys covered the eastern part of Area III and western part ofArea VI since the austral summer season 1995/96. MtDNA analysis on the new samples obtained from Area
IIIE failed to detect any boundary of the ‘core stock’ to the west as the pattern of mtDNA heterogeneity found in
the western part of Area IV early in the 1989/90 survey (attributed to a hypothetical ‘western stock’) (Pastene etal, 1996) was not found in samples from Area IIIE (Pastene and Goto, 1997). Furthermore the same analysis
conducted by Pastene et al. (1996) was repeated in the present study for the total JARPA samples (1987/882004/05). This time no significant genetic heterogeneity was found for the samples of group IVW taken early inthe season (data not shown). Two possible interpretations are possible for the results of group IVWE in 1989/90,a) heterogeneity observed in that group reflects a biological event e.g. the sporadic (only in some years)
intrusion of a different stock or the mixing of two stocks in Area IVW early in the season, b) the heterogeneity
observed for that group do not reflect a biological event. Rather it is a product of the low effect size and highgenetic diversity of Antarctic minke whales, which produce misleading results for small sample sizes.
In reviewing the results on stock structure derived from JARPA, the SC has noted that only preliminary
conclusions can be drawn at this stage and that more concrete conclusions will be able to be made following thecompletion of different analyses. It further supported the suggestion that additional analyses using alternative
groupings and analytical methods should be conducted (IWC, 2004). On this regard the 1997 JARPA review
meeting recommended that other analyses be conducted (in addition to mtDNA) and the possibility of further
structure in the ‘core stock’ was not discarded. These suggestions are related to the widely accepted concept that themost effective way to address questions on stock identity is to consider results from several techniques, genetics andnon-genetics (Donovan, 1991; Pastene et al., 2000; Perrin, 2001; Rugh et al., 2003). In the case of the Antarctic
minke whale the application of multi-approaches to investigate stock identity was particularly desirable because
previous genetic analysis suggested that the effect size in this species is low and then, results obtained by a single
genetic marker should be checked using independent markers. Consequently the study on stock structure under the
JARPA was extended by the use of several biological markers, both genetics and non-genetics and more detailed
grouping of samples. These approaches were used for examining samples of the JARPA from 1987/88 to 2004/05 asreviewed above.
Analyses based on total samples (final analyses) and hypothesis on stock structure
It is reasonable to conclude that the most plausible hypothesis on stock structure in the Antarctic minke whalesis that derived from the comprehensive analysis of total JARPA samples and data. The same samples and thesame grouping were used by different analytical approaches.
The results of different analytical approaches used by JARPA were presented to this meeting inDocuments SC/D06/J9, J10 and J11, and summarized in this review paper. Table 2 shows a summary of theresults of these approaches. Based on this information it is reasonable to conclude that the single stock scenario
can not be applied to Antarctic minke whales in the Antarctic feeding grounds of Areas IIIE-VIW. Results of thedifferent approaches are consistent with the occurrence of at least two stocks in the research area. Probably these13

stocks are related to the breeding areas in the eastern Indian Ocean and western South Pacific suggested by
Kasamatsu et al. (1995) (Figures 2 and 3). The following names are proposed for these stocks: Eastern Indian
Ocean Stock (I-Stock) and Western South Pacific Ocean Stock (P-Stock).
Because the different analytical approaches were able to differentiate whales from different
longitudinal sector, the extreme scenario of full mixing of stocks in the Antarctic can be discarded because
different stocks can not be discriminated under such level of mixing. The remaining question is whether thesestocks are fully segregated in the feeding ground or if they partially mix. The possibility of mixing can not be
discarded but such possibility can be better explored with analysis of samples from the breeding grounds.
For practical reason (to define a biological unit on which the estimation of biological parameters can be
estimated) stock boundaries among stocks should be identified. While the microsatellites and morphometrics
analyses were unable to identify any boundary between I and P stocks, the analysis of mtDNA suggested aboundary in the sector 150º-160ºE. The mean body length of physically matured whales suggested a possible
stock separation around longitude 165°E, this is between sectors VW and VE. Although there is not a clear
longitudinal ‘cut’, it is reasonable to conclude that the western part of Area V is more related to I-stock than Pstock. Therefore for the objective of the estimation of biological parameters a boundary between I and P stocks
was adopted at the division between Areas VW and VE (165°E). This is consistent with the results of markrecapture that showed marked movements of whales through 130ºE (division between Areas IV and V)
suggesting that whales in Area IV are related to Area VW.
Regarding the western boundary of the I-stock the JARPA analyses based on mtDNA, morphometricand mean body length of physical maturity suggested no significant differences between whales in Areas IV and
IIIE. For this reason it is assumed that whales in Area IIIE belong to the I-stock. It should be noted, however,that the microsatellite analysis showed some degree of genetic heterogeneity between these two Areas(SC/D06/J9). In addition one of the explanations for the heterogeneity observed for group IVWE in 1989/90 in aprevious mtDNA analysis was the sporadic intrusion or mixing with a third stock presumably distributed in
Area III. Also mark-recapture analysis suggested a boundary at 80ºE, near the boundary between Areas III and
IV, which was consistent with the results of a pollutant study (Kunito et al., 2002) and parasite occurrence(Bushuev, 1990) suggesting differences between Areas III and IV (see review above). For the purpose of theestimation of biological parameters whales in Area IIIE are considered as part of the I stock given the results of
JARPA shown in Table 2. However the possibility of additional stock structure in Area III, or the presence of amixing sector around the division between Areas III and IV can not be discarded at this stage given the resultsof some analyses. For the estimation of the biological parameters it is suggested to consider longitude 145ºW as
the eastern boundary of P stock. The extension of the P stock to the east should be investigated in the future.
Analyses based on pollutant accumulation (Kunito et al., 2002) and parasites load (Bushuev, load
suggested differences between Areas III and IV. Interpretation of results from pollutant accumulation andoccurrence of parasites is, however, difficult in the context of stock structure. With regard organochlorines
Aguilar (1987) reviewed the methods of using these pollutants to discriminate marine mammal populations. He
suggested that among other factors, nutritional state, sex, age, trophic level, distance of habitat from mainlandand pollution source, excretion, metabolism and tissue composition should be identified and their effectascertained before attempting any comparison between populations. Regarding the use of differences in theincidence of parasites for stock structure in whales Balbuena et al. (1995) noted that the application of thetechnique to marine mammals is hampered by the lack of control over sampling conditions and the paucity of
information about the biology of their parasites.
Distribution of Antarctic minke whales is related to distribution of their main prey species in the
Antarctic, the krill (Euphausia superba). The distribution of Antarctic krill concentrations has been related tobottom topography, sea-ice and hydrographic features (Ichii, 1990). Yearly variability in these features in the
sector around 165°E could have some effect on annual fluctuation on the distribution of krill concentrations andthis, in turn, could affect the distribution of minke whale around that longitudinal sector. Therefore a boundary
between stocks or equivalently a longitudinal sector of mixing between two stocks is expected to change
according changes in the distribution of krill (see discussion of Document SC/D06/J9).
Results of the different analyses are not consistent with the current boundaries of the IWC Areas. These
results allows for a response to the questions formulated by Hoelzel and Dover (1989): Area IV is occupied

14

mainly by a single stock (I) while Area V is occupied by two different stocks (I and P). Only a partial portion ofArea III has been investigated by JARPA. While results of JARPA suggested that Area III is occupied mainlyby the I stock, we can not discard the possibility of additional stock structure in that Area (e.g. the intrusion andmixing with animals from the western Indian Ocean breeding ground).
The results on stock structure will inform the specifications and testing of appropriate management
areas under the Revised Management Procedure.
Further research needs
The following topics are recommended for future studies on stock structure:a)Yearly changes in stocks distribution and boundaries (or changes in the proportion of stocks in areas of
mixing) in the region 150ºE-180ºshould be investigated in the future in relation to bottom topography,
currents and krill distribution.
b) Western boundary (or areas of mixing) of the stock originating in the eastern Indian Ocean and theeastern boundary (or areas of mixing) of the stock originating in the western Pacific Ocean should be
investigated in the future.
c) To elucidate the possibility of mixing in the feeding ground at a better resolution, samples and genetic
analysis of whales from the breeding grounds are desirable. Experiments of satellite tracking would bevery useful to examine lateral movement and possible mixing in the feeding grounds as well movement
between feeding grounds and lower latitudes wintering grounds.
d) Promising new techniques to investigate stock identity such as the use of ecological markers andpollutant burden should be further investigated and applied in the future.

ACKNOWLEDGEMENTS
I thank to all scientists and crew members that participated in the JARPA research surveys between 1987/88 and2004/05 for the collection of valuable samples and data used in the different studies on stock structure of
Antarctic minke whale.
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17

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18

Table 1: Summary of the main genetic analyses on stock structure in the Antarctic minke whale.
CPW=commercial pelagic whaling; CCW=commercial coastal whaling; HW=Hardy-Weinberg; RE= restriction
enzyme; SE= length of sequence segment. A sign ‘=’ means that the statistical test found no significant
heterogeneity.
Locality
Period ofn
Number of
Statistical
Main Results
Marker/Sampling
SourceLoci/RE/SE
Analysis
SourceAllozyme
Wada andNumachi(1991)Areas
I-VI
BRAZIL

1975/761983/84
1981

11,414
195

CPW
CCW

45 loci(10
polymorp.)

H-W test
Homogeneity test
(G-test)Areas
I=II=III=IV=V=VI
Areas IVI=BRAZIL

20
21

CPW
CPW

3 restriction
enzymes

Genetic distanceArea IV=AreaV

1983/84
1983/84

40
39

CPW
CPW

14 restriction
enzymes(9 polym)

Homogeneity test
(G-test)Area IV=AreaV

1989/90

118

JARPA

1989/90,90/91

93

12 restriction
enzymes(11polym)

Homogeneity test
(Randomized
chi-square test)

1990/91,88/89

107

W=C
C=E
W≠E

RFLP
mtDNA
Control
RegionHoelzel andDover (1991)

Area IV
Area V

RFLP
Whole
mtDNA
Wada et al.
(1991)

Area IV
Area V

Pastene et al.
(1993)

70˚-110˚E(W)
110˚-150E（C）
150˚E-180˚（E）

19

Pastene etal .(1996)

Pastene et al.
(this meeting)20

70˚-100˚E
Early(IVWE)
70˚-100˚E
Late (IVWL)
100˚-130˚E
Early (IVEE)
100˚-130˚E
Late (IVEL)
130˚-160˚E
Early (VWE)
130˚-160˚E
Early (VWL)
160˚E-160˚W
Early (VEE)
160˚E-160˚W
Late (VEL)
35º-70ºE(IIIE)
70˚-100˚E(IVWN)
70˚-100˚E(IVWS)
100˚-130˚E(IVE)
130˚-165ºE(VW)
165˚E-170˚W(VEN)
165˚E-170˚W(VES)
170ºW-145º
W (VIW)

1987/881994/95

160

JARPA

383

6
polymorphic
restriction
enzymes

Homogeneity test
(AMOVA / PHIst)

6
polymorphic
restriction
enzymes

Homogeneity test
(AMOVA / PHIst, Randomized
chi-Square test)

Significant
heterogeneityin Group IV
WE

233
321
208
264
76
479

1987/882004/05

529
462
959
1234
1094
712
790
476

JARPA

IIE=IVW=IVE
VIW=VE
IIIE,IVW,IVE≠VE,VIW
Possibleboundary inthe sector 150º-160ºE

Sequencing
mtDNA
Control Region
Bakke et al.
(1996)

Area IV
Area V

1991/92
1990/91

JARPA
JARPA

345bpsegment

50
50

CPW
CPW

10 genefamilies

Area IV≠
Area Vusing clone
cl.5M1-19

CPW
CPW

2 Jeffreys’probe(33・15;
33・6)

Area IV=AreaV

Homogeneity test
(Randomized Yst
test)

Repeated DNA
Sequences
Amos and
Dover (1991)

Area IV
Area V

Area IV≠
Area V
at 10%
significant
level

13
10

Multilocus
minisatellite
van Pijlen et al.
(1991)

Area IV
Area V

Single locus
minisatellite
Area IV
Area V

1982/83
1982/83

24
21

CPW
CPW

van Pijlen et al.
(1992)

Area IV
Area V

1982/83
1982/83

19
61

CPW
CPW

Pastene et al.
(this meeting)

35º-70ºE(IIIE)
70˚-100˚E(IVWN)
70˚-100˚E(IVWS)
100˚-130˚E(IVE)
130˚-165ºE(VW)
165˚E-170˚W(VEN)
165˚E-170˚W(VES)
170ºW-145º
W (VIW)

1989/902004/05

JARPA
549

van Pijlen et al.
(1992)

H-W test
Homogeneity test
clustering analysis

Area IV=AreaV

4 lociH-W test
Homogeneity test
clustering analysis

Departurefrom H-W
equilibrium in
one locus Area
IV=Area V

6 lociH-W test
Homogeneity test

3 lociMicrosatell

21

484
1022
1084
1164
675
784
498

IVWN,IVWS≠VE,VIW
Some degreeofheterogeneity
between Areas
IVW and IIIE
(females)Table 2: Summary of the results on stock structure in JARPA. MBLM= Mean body length of physicallymatured whales. A sign ‘=’ means that the statistical test found no significant heterogeneity.
Method

Sex

mtDNA

F+M

Microsatellites

MBLM

Morphometrics

22

JARPA
samples
1987/882004/05

Pattern of Geographical variation

F

1989/902003/04

IVWN,IVWS ≠VE,VIW
Some degree of heterogeneity between Areas IVW andIIIE

M

1989/902004/05

No significant heterogeneity

F+M

1989/902004/05

IVW≠ VE

F

1987/882004/05

IIIE=IVW=IVE=VW
VIW=VE
IIIE,IVW,IVE,VW≠VE,VIW

M

1987/882004/05

VEN≠VES
IIIE=IVW=IVE=VW
VIW=VEN,VES
IIIE,IVW,IVE,VW≠VEN,VES,VIW

F

1987/882004/05

M

1987/882004/05

IIIE=IVW=IVE=VW
VIW=VE
IIIE,IVW, IVE, VW≠VE,VIW
IIIE=IVW=IVE
VIW=VE
IIIE,IVW, IVE≠VW,VE,VIW

IIIE=IVW=IVE
VIW=VE
IIIE,IVW,IVE≠VE,VIW
Possible boundary in the sector 150º-160ºE

Figure 1: IWC Antarctic Areas for the management of baleen whale species (except Bryde’s whale).

23

Figure 2: Encounter rates of Antarctic minke whales in 10º squares of latitude and longitude in waters 0º-30ºS in
October (from Kasamatsu et al., 1995).

Figure 3: Hypothesis on stock structure in the Antarctic minke whale in the JARPA research area. The mostparsimonious explanation of the results is that there are at least two stocks present in the research area: aneastern Indian (I) and a western South Pacific (P) stock. These stocks would mix across a soft boundary, which
would probably best be placed near 165ºE. These stocks could be related to the breeding areas proposed for theeastern Indian Ocean and western South Pacific (Figure 2) (see text for details).

24