SC/D06/J26

What has happened to the Antarctic Minke Whale Stocks?
- An interprepation of results from JARPA YOSHIHIRO FUJISE, HIROSHI HATANAKA AND SEIJI OHSUMIThe Institute of Cetacean Research, Toyomi-cho 4-5, Chuo-ku, Tokyo 104-0055, JAPAN.
Contact e-mail: fujise@cetacean.jp

ABSTRACT
Historical changes in the Antarctic minke whale stocks were examined based on various
results obtained from JARPA including age at sexual maturity, growth curve, blubber
thickness, prey consumption, and ADAPT-VPA analysis of the stocks as well as research on
mercury accumulation etc. It has been assumed that feeding conditions of the minke whale
improved with the removal of large baleen whales such as the blue whale by commercial
whaling, which promoted rapid growth and younger age at sexual maturity; however, around1970, conditions gradually shifted unfavourably, resulting in slower rates of change in theforegoing parameters. These changes were then arrested by the 1980s to the 1990s.
Reflecting these unfavourable changes, it was observed that blubber thickness and stomach
content weight were reduced, which indicated less prey consumption. There was also adecrease in the accumulation of mercury resulting from less prey consumption. Also, thedistribution area of humpback and fin whales in the feeding season expanded southward in
the Antarctic from around 1990, suggesting further deterioration of feeding conditions for
the Antarctic minke whales.
KEYWORDS: ANTARCTIC MINKE WHALE; BLUE WHALE; FIN WHALE; HUMPBACKWHALE, COMPETITION; LONG-TERM CHANGE; HEAVY METALS; AGE AT SEXUAL
MATURITY; PREGNANCY RATEINTRODUCTION
Abundance and biological parameters of Antarctic minke whales have greatly changed over theyears, and since the late 1970s the IWC/SC has spent considerable time discussing possible reasonsand trying to understand this phenomenon (e.g. IWC, 1985).
Due to uncertainties related to the estimation of biological parameters, there was no agreement atthat time concerning the data necessary for stock management, including natural mortality rate. This
resulted in difficulties in calculating the catch quota and was the primary reason for the moratoriumon commercial whaling. The Government of Japan, therefore, launched a whale research program
under the Article VIII of the International Convention for the Regulation of Whaling (ICRR), in the
Antarctic in 1987/88, with the estimation of biological parameters necessary for the management of
Antarctic minke whales as the first objective. The elucidation of the role of cetaceans in the
Antarctic ecosystem was the secondary objective. The program was called JARPA, and in 1994
and 1995, the elucidation of the effects of environmental changes on cetaceans and, the Antarctic
minke whale stock structure were added to the research objectives.
The JARPA program spanning over eighteen years completed in 2004/05. Research in various
fields were conducted together with surveys and analyses related to the program objectives.
Phenomena suggesting qualitative and quantitative changes in the Antarctic minke whale stocks
have been observed, some of which have been reported at the IWC/SC (e.g. IWC, 1988).
This paper rearranges the results reflecting changes in the Antarctic minke whale stocks, examines
what has happened in these stocks, and propose a hypothesis of changes in the Antarctic ecosystemin the 20th Century.
1

MATERIALS AND METHOD
Examination of the changes in the Antarctic minke whale stocks since whaling began, is based on
analyses of sexual maturity age and growth curve (Kato, 1987; Zenitani et al., 2006), blubber
thickness (Ohsumi et al., 1997; Konishi and Tamura, 2005), and estimated prey consumption(Tamura and Konishi, 2006) using samples from commercial whaling and JARPA, ADAPT-VPA
analysis of the stocks (Butterworth et al., 1999; Mori et al., 2006), and study of mercury
accumulation in the whale body (Honda, 1985; Honda et al., 1987; Fujise et al., 1997; Yasunaga etal., 2006) and other reports.
Age at sexual maturity estimated by the transition phase of the growth layer in cetacean earplugs
has been used here.
Data on age at sexual maturity for fin and Antarctic minke whales used in this study are fromLockyer (1972) and Kato (1987), respectively. Apparent pregnancy rates for blue and fin whales arefrom Gambell (1972). Apparent pregnancy rate for humpback whales are calculated from theInternational Whaling Statistics.
RESULTS AND DISCUSSIONSCatch History and Biomass of Large Cetaceans in the Antarctic Ocean
Commercial whaling began in the Antarctic in 1904. Initially, whaling mainly targeted the blue
whales that had high commercial value and humpback whales that are slow swimmers. Later, theobject of commercial whaling gradually shifted to the fin, sei and Antarctic minke whales with
reduction of the former target whale stocks (Fig. 1).
Blue whales
In the 1911/12 season, more than 1,000 blue whales were taken. In 1928/29, the yearly catchexceeded 10,000, and in the 1930/31 season, 29,410 whales were taken as the largest catch onrecord. Annual catches continued in the tens of thousands until the 1939/40 season. It temporarily
decreased during World War II, but recorded 9,192 in the 1946/47 hunting season, then declined
rapidly (Fig. 1). The take of blue whales was banned in 1964. Total catch amounted to 331,644
whales. In terms of biomass, this means that a maximum of 2,941,000 tons in a year, and an
average of 526,408 tons per year were removed from the stocks, calculated with an average bodyweight of 100 tons (Fig. 2).
Fin whales
Fin whales were also hunted from the initial period. More than 10,000 were taken in the 1929/30
season, and in 1937/38, more than 20,000, exceeding the catch of blue whales, when the fin became
the major target of commercial whaling. As with blue whales, catches temporarily decreased during
World War II, but recovered when whaling was resumed after the end of the War, and in the
1951/52 season it again exceeded 20,000. Annual catches continued in the tens of thousands until
the 1963/64 season (Fig. 1). The largest catch on record was made in the 1960/61 season, when
28,761 whales were taken. Total catches came to 691,890 until the take of fin whales was bannedin 1976. In terms of biomass, this means that a maximum of 1,581,855 tons in a year, and an
average of 528,527 tons per year were removed from the stocks, calculated with an average bodyweight of 55 tons (Fig. 2).
Sei whales
There is a record of the take of sei whales in 1905/06, but full-scale hunting began in the 1957/58
season. Since then annual catches increased to a peak of 20,380 in the 1964/65 season anddecreased rapidly after that (Fig. 1). Total catch till 1977/78 was 149,594 or, an average of 2,301
whales taken annually. In terms of biomass, this means that a total of 2,917,083 tons, a maximum2

of 397,410 tons in a year, and an average of 44,878 tons per year were removed from the stocks,
calculated with an average body weight of 19.5 tons (Fig. 2).
Antarctic minke whales
The take of Antarctic minke whales has been recorded in 1951/52, but it was in the 1971/72 season
that full-scale whaling for them began. About 6,000 whales were taken annually from the 1972/73
to the 1986/87 season, when commercial whaling was suspended. Since then, 330 or less have beentaken under the special permit of the Japanese Government up till 1994/95, and 440 or less till
2003/04 (Fig. 1). The largest catch on record was made in the 1976/77 season, when 7,900 weretaken. Total catch came to 97,810 whales until the 1986/87 season, when commercial whaling wassuspended or, an average of 2,877 whales taken annually (for reference, total catch is 104,165 andyearly average 2,042 whales if those taken under special permit are included). In terms of biomass,
this means that a total of 723,794 tons, a maximum of 58,460 tons in a year, and an average of
21,288 tons per year were removed from the stocks, calculated with an average body weight of 7.4
tons (for reference, total biomass is 770,821 tons, and annual average 15,114 if those taken under
special permit are included) (Fig. 2).
Humpback whales
Humpback whales were taken as the major target species from the 1904/05 season, whencommercial whaling began in the Antarctic Ocean, since they were easy to hunt. Their status as the
major target continued until the 1913/14 season. In the 1910/11 season, more than 8,000 whales
were taken, but after the 1913/14 season, the target shifted to blue and fin whales, and catch
gradually decreased until the 1916/17 season, after which it declined to 1,000 or less. From the1934/35 to 1940/41, and from the 1949/50 to 1959/60 seasons, 1,000 to 2,000 whales were taken,
but the take of humpback whales was banned in 1963 (Fig. 1). The largest catch on record wasmade in the 1936/37 season, when 4,477 whales were taken. Total catch came to 68,294 or, anannual average of 1,102. In terms of biomass, this means that a total of 2,117,114 tons and an
average of 33,605 tons per year were removed from the stock, calculated with an average bodyweight of 31 tons (Fig. 2).
Until around 1970 while fin whales were being hunted, about 2 million tons of whales had been
removed from the stocks. Krill consumed by the whales would have amounted to 60,000 tons perday, assuming that consumption is 3% of body weight of whales. This all became a surplus since
whales were removed by the hunts. If we assume that the blue, fin, humpback and other large
whales stayed in the Antarctic Ocean for one hundred days, as much as 3 million tons of krill would
have been left over as surplus every year.
Age at sexual maturity
Age at sexual maturity of the fin and Antarctic minke whales is discussed here since biological data
for these species are comparatively abundant.
Fin whales
Fig. 3 shows the changes in the age at sexual maturity of fin whales in the Antarctic (Lockyer,1972). Their catch continued from 1904, when whaling began in the Antarctic, to 1976. Age atsexual maturity declined markedly from year classes in 1920 to 1930 and this trend is observed until
the 1957 year class for which there are data.
Antarctic minke whales
Fig. 4 shows the changes in age at sexual maturity deduced from the transition phase in earplugs offemale Antarctic minke whales (Kato, 1987). Full-scale whaling for the Antarctic minke whales
began in the 1971/72 season, but the age at sexual maturity already began to decline before theseason which full-scale whaling was started. It seems the decline began from around the 1932 year
class. Significant decline was observed from the 1950 to 1977 year classes (Kato, 1987).
3

After the moratorium on commercial whaling was implemented in 1987, samples were collected by
the JARPA, which are shown in Fig. 5 (Zenitani and Kato, 2006). The decline tendency in the age
at sexual maturity gradually slowed down around the 1960s, and almost stopped around 1965 to
1980. In case of females, increasing trends was observed after the 1990 year class.
Pregnancy Rate
Fig. 6 shows the changes in the pregnancy rates of the blue, fin, and humpback whales over theyears. The rates of the three whale species show the tendency to increase from the 1930s, although
there are yearly fluctuations. Pregnancy rates of blue whales increased from about 1930 to 1960,
fin whales from around 1930 to 1970, and humpback whales from about 1930 to 1960, although theyearly fluctuation is great.
It is considered that Antarctic minke whales are capable of reproducing every year, and the apparent
pregnancy rate estimated from those migrating to the Antarctic is high and constantly in theninetieth percentile since 1970s. However, they are segregated by sex and reproductive status, andthe 78% (Best, 1982) estimated in their breeding ground is considered to be appropriate. No
detailed reports are available on the changes over the years.
Growth Curve
The growth curve of Antarctic minke whales using samples from commercial whaling is shown in
Fig. 6 (Kato, 1987). Kato (1987) reported that growth rate increased from year classes in 1940 to1949 and for those in 1970 to 1979, and that they matured at a younger age and became larger insize.
We compared the growth curve after the above period, using JARPA samples, and found that thegrowth rate has slowed down for year classes in the 1990s, compared with those in the 1980s. The
growth curve shows that the 1990s year group tend to be below those for 1980s (Fig. 8).
VPA Analysis of Antarctic Minke Whale Stocks
Catch-at-age analysis using ADAPT-VPA and others have shown that recruitment of Antarctic
minke whales increased from 1944 to 1968 (Sakuramoto and Tanaka, 1985; 1986; Butterworth etal., 1999; Mori, Butterworth and Kitakado, 2006). It then decreased until about 1980, after which
the declining trend has halted. The causes for these changes have long been the subject of
discussion at the IWC (see IWC, 1989; 1990; 1991; 1992a; 1992b; 1995; Sakuramoto and Tanaka,
1986; Butterworth et al., 1999; Butterworth and Punt, 1999).
Accumulation of Pollutants
Honda et al. (1987) analyzed heavy metals in the livers of Antarctic minke whales commerciallytaken in the 1980/81 season. He found that Hg concentration did not increase with age; rather it
decreased after age ten. It is well known that Hg concentration in the liver increases with age inmarine mammals including cetaceans. However, he reported that such age-related accumulation
was not detected in the minke whale samples. Changes in Hg concentration in the prey was not aplausible explanation, since Hg in the environment has not greatly changed, and he considered that
it was a result of an increase in prey consumption, hence the increase of Hg intake. As a factor, hepointed out that feeding conditions had improved for the Antarctic minke, with the decrease in theabundance of larger whales (Honda et al., 1987).
Further, in order to understand the apparent decreasing pattern of Hg concentration, Honda (1985)
estimated the total mercury loads (burdens) accumulated in the whale, and examined conditions thatwould best fit the mercury accumulation age curve using an accumulation model. In this simulation,
he assumed that Hg concentration in the environment (prey) has not greatly changed and used 4.6
years for the biological half-life of mercury as determined in the striped dolphin. The assumed
feeding conditions that fit the curve was that in 1980/81, whales up to ten years old consumed prey4amounting to 15% of body weight, while consumption decreased from 15% to 5% for those fromten to thirty; and for those over thirty, it was 5% (Fig. 11). The trend was observed by analyzing
samples taken during the 1980/81 to 1981/82 whaling seasons, from which can be deduced thatfeeding conditions became favourable around 1950, which is thirty years prior to these sampling
dates.
Fujise et al. (1997) continued to monitor Hg accumulation in Antarctic minke whales using JARPA
samples. They clarified the process that reflects an increase in mercury intake for all ages.
Examination of the accumulation changes up to recent years, shows a rise in mercury intake due toincreased consumption of prey. This was found in all age groups. It was confirmed that Hgconcentration also increased in Antarctic minke whales with age as with other cetaceans (Fig. 12).
Furthermore, Hg concentration tends to be lower in the younger age group (one to five year olds),
when the details of these accumulation curves for the most recent (2003/04) JARPA samples are
examined (Fig. 13).
Similar trend of the Hg accumulations in Antarctic minke whales is observed in recent studies using
JARPA samples in 2004/05 season (Yasunaga et al., 2006).
Blubber Thickness
Ohsumi et al. (1997) examined blubber thickness using data from commercial whaling which began
in 1971/72 and the JARPA data from 1987/88 to 1995/96. They reported that a reduction in blubber
thickness was observed after 1978 (Fig. 14).
Konishi and Tamura (2005) analyzed blubber thickness using the JARPA data from 1987/88 to
2003/04, and reported that the decrease in thickness found by Ohsumi et al. (1997) was still inevidence (Fig. 15).
Changes in Stomach Content Weight of Antarctic Minke Whales
Tamura and Konishi (2006) examined the stomach contents of Antarctic minke whales using datafrom the JARPA 1987/88 to 2004/05 seasons. They reported that the decreasing pattern in stomach
content weights of mature minke whales was observed since the 1987/88 season in which JARPA
was started (Fig. 16).
Competition with Larger Baleen Whales (Humpback and Fin Whales)
In recent years, it has become known that larger baleen whale stocks, including humpback whales,
are recovering. Matsuoka et al., (2006) estimated abundance of humpback and fin whales in the
Antarctic Areas III (East), IV, V and VI (West), using the whale sighting data from JARPA. They
reported that the number of humpback and fin whales migrating to Antarctic Areas IV and V havebeen increasing (Fig. 17) and that the biomass of these species has become larger than that of
Antarctic minke whale in recent years (Fig. 18; Matsuoka et al., 2006). In Area IV, especially, thehumpback whale has been seen to be encroaching on the distribution range of Antarctic minke
whales. Many minke whales were sighted in the research area south of 60°S in recent years, but it
was observed in the 2003/04 surveys that they tended to be pushed back into the pack ice (Ishikawa
et al., 2004).
Humpback and fin whales used to be only sighted offshore until the 1990s, but in recent years, theirdistribution range has become overlapped with that of the Antarctic minke whale. The overlappingof two or more whale species in the feeding grounds of the Antarctic suggests competition among
these whale species occurs over krill, which is the key species, especially in a simple marine
ecosystem structure as the Antarctic Ocean. The reduced range of Antarctic minke whales in theirfeeding ground suggests that those niches have become sub-optimal.

5

What Has Happened to the Antarctic Minke Whale Stocks?
The above considerations can be summarized as follows:
Changes found from 1940 to 1970:* Increase in recruitment (VPA)* Acceleration in growth rate (growth curve)* Decrease in the age at sexual maturity (earplug transition phase)* Increase in mercury intake
Changes found from 1970 to 1980:* Decrease in recruitment (VPA)* Halt in the decreasing trend in the age at sexual maturity (earplug transition phase)* Mercury intake stabilizes at fixed level
Changes found from 1980 onwards:* Decreasing growth rate (growth curve)* Decrease in blubber thickness (from 1980 to present)* Decrease in stomach contents weight (from latter half of 1980 to present)* Decrease in mercury intake
Examining the above phenomenon comprehensively, a following history of the ecosystem change
in the 20th century is hypothesized in the Antarctic Ocean.
Feeding conditions became favourable for the Antarctic minke whales around 1940, at the latest,with the depletion in large baleen whales such as blue and other whales due to overhunting, and thenutritional status of each minke whale individual improved. Thus, growth rate increased for theminke, and they grew to mature body length earlier, reaching sexual maturity younger. The
increased breeding capability resulted in increased abundance. Declining age at sexual maturity andincreasing pregnancy rates were also observed in fin, humpback and other large baleen whales,suggesting improved feeding conditions for them as well. Overall improvement in feeding
conditions is indicated, arising from lower population density due to the decrease in the number oflarge baleen whales which consumed huge amounts of krill in the Antarctic Ocean (Kato, 1987).
The amount of available prey (krill) per minke whale as a consumer became restricted about 1970.
Around that time, growth rate and the declining the age at sexual maturity slowed down. By 1980 a
halt in the latter trend was observed. It seems that the growth rate of whales in year classes of the
1990s was lower than that of those in year classes of the 1980s. The change in feeding conditions
was reflected in blubber thickness. Blubber thickness of Antarctic minke whale has shown aconstant decline since 1978/88. Also, the number of humpback and fin whales which are higher intheir niches than the number of Antarctic minke whales, migrating to the Antarctic increased from1990. This suggests the recovery of these stocks, while indicating a further deterioration in feeding
conditions for Antarctic minke whales.
Other factors that may have contributed to the changes in feeding conditions include environmental
changes such as global warming. Melting of fast ice in the seas around the Antarctic Peninsula has
been reported, and a decrease in the number of penguins which incubate on ice has been observed(Croxall et al., 2002). However, Areas IV and V of the Antarctic Ocean, which are the concern of6this paper, are on the opposite side of the Antarctic Peninsula and no major melting of fast ice has
been reported to date. Analysis of satellite data and oceanographic observations carried out in the
JARPA programs have not shown any constant change in the marine environment, although annual
fluctuations due to El Nino and La Nina have been observed (Watanabe et al., 2006).
It is highly possible that nutritional conditions for the Antarctic minke whales have changed due tocompetition with other whale species such as the humpback whale, and possibly the change incarrying capacity, in the Antarctic marine ecosystem.
For the appropriate management and sustainable use of Antarctic minke whale stocks, we would
need to collect not only data on abundance and biological parameters of major whale species, butalso data on their habitat environment and their responses to environmental changes.
ACKNOWLEDGMENTS
We thank Dr. Hidehiro Kato, Tokyo University of Marine Science and Technology, Ms. Ryoko Zenitani, theInstitute of Cetacean Research (ICR), for preparing the information on sexual maturity of whale samples. We
also thank Mr. Koji Matsuoka, ICR, Dr. Tsutomu Tamura, ICR, Mr. Takeharu Bando, ICR, Dr. Kenji
Konishi, ICR, and Dr. Mitsuyo Mori, ICR, for providing the information in the referenced researchdocuments. Our sincere thanks are also due to all researchers and crews who were participated in the JARPA
surveys from 1987/88 to 2004/05 seasons.

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whale based on materials collected by the JARPA survey in 1987/88 to 2004/05. Paper SC/D06/J17
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Best, P.B. 1982. Seasonal abundance, feeding, reproduction, age and growth in minke whales off Durban(with incidental observations from the Antarctic). Rep. int Whal. Commn 32: 759-786.
Butterworth, D.S., Punt, A.E., Geromont, H.F., Kato, H. and Fujise, Y. 1999. Inferences on the dynamics ofSouthern Hemisphere minke whales from ADAPT analyses of catch-at-age information. J. Cetacean Res.
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Butterworth, D.S. and Punt, A.E. 1999. An initial examination of possible inferences concerning MSYR for
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Science, 297: 1510-1514.
Fujise, Y., Honda, K., Yamamoto, Y., Kato, H., Zenitani, R. and Tatsukawa, R. 1997. Changes of hepatic
mercury accumulations of Southern minke whales in past fifteen years. Paper SC/M97/20 presented to the
IWC Intersessional Working Group to Review Data and Results from Special Permit Research on Minke
whales in the Antarctic, May 1997 (unpublished). 16pp.
Gambell, R. 1973. Some effects of exploitation on reproduction in whales. J. Reprod. Fert., Suppl. 19: 533553.
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bioaccumulations of heavy metals in marine mammals). Ph. D. thesis, Univ. Tokyo, 101p.
Honda, K., Yamamoto, Y., Kato, H. and Tatsukawa, R. 1987. Heavy met al. accumulations and their recentchanges in southern minke whales Balaenoptera acutorostrata. Arch. Environ. Contam. Toxicol. 16:209216.
International Whaling Commission. 1985. Report of Scientific Committee. Rep. int. Whal. Commn 35:31152.
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International Whaling Commission. 1995. Report of Scientific Committee. Rep. int. Whal. Commn 45:53103.
Ishikawa, H., Otani, S., Kiwada, H., Isoda, T., Tohyama, D., Honjo, K., Hasegawa, A., Terao, T., Kushimoto,T., Ohshima, K., Sugiyama, K., Sasaki, T., Itoh, S., Takamatsu, T. and Yoshida, T. 2004. Cruise Report of
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JARPA Review Meeting, December 2006.
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Yasunaga, G., Fujise, Y. Zenitani, R., Honda, K. and Kato, H. 2006. Yearly trend of trace element
accumulation in liver of Antarctic minke whale, Balaenoptera bonaerensis. Paper SC/D06/J28 presented to
the JARPA Review Meeting, December 2006.
Zenitani, R. and Kato, H. 2006. Temporal trend of age at sexual maturity of Antarctic minke whales based ontransition phase in earplugs obtained under JARPA surveys from 1987/88 to 2004/05. Paper SC/D06/J26
presented to the JARPA Review Meeting, December 2006.

8

35000

Blue
Fin
Sei
Humpback
Minke

30000

Catches (whales)

25000

20000

15000

10000

5000

0
1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2001

Calender year
Fig. 1. Catch history of large sized baleen whales in the Antarctic since 1904.

4,000,000

Minke

3,500,000

Right
Sperm

Catch (tons)

3,000,000

Sei

2,500,000

HumpbackFin

2,000,000

Blue
1,500,000
1,000,000
500,000

1904
1 9 /05
06
1 9 /0708
1 9 /0910
1 9 /1112
1 9 /1314
1 9 /1516
1 9 /1718
1 9 /1920
1 9 /2122
1 9 /2324
1 9 /25
26
1 9 /2728
1 9 /2930
1 9 /3132
1 9 /33
34
1 9 /3536
1 9 /3738
1 9 /3940
1 9 /4142
1 9 /43
44
1 9 /4546
1 9 /47
48
1 9 /4950
1 9 /51
52
1 9 /5354
1 9 /55
56
1 9 /57
58
1 9 /5960
1 9 /6162
1 9 /63
64
1 9 /65
66
1 9 /67
68
1 9 /6970
1 9 /71
72
1 9 /7374
1 9 /75
76
1 9 /7778
1 9 /7980
1 9 /8182
1 9 /83
84
1 9 /85
86
1 9 /87
88
1 9 /8990
1 9 /91
92
1 9 /93
94
1 9 /95
96
1 9 /9798
2 0 /9900
2 0 /01
02
2 0 /03
04
/05

0

Year

Fig. 2. Total biomass of harvested large sized baleen whales in the Antarctic since 1904.

Age at sexual maturity(year)

15

10

5

0
1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

Year

Fig. 3. Trend of age at sexual maturity of Southern fin whales by cohort (Lockyer, 1982)

9

1980

1985

1990

1995

2000

Age at sexual maturity(year)

25
20
15
10
5
0
1900

1905

1910

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

Year

Fig. 4. Trend of age at sexual maturity of Antarctic minke whales by cohort (Kato, 1987)
16
Mean age of sexual maturity

14

Male

12
10
8
6
4
2
0
1930

1935

1940

1945

1950

1955

1960
1965
Cohort

1970

1975

1980

1985

1990

1995

16
Mean age of sexual maturity

14

Female

12
10
8
6
4
2
0
1930

1935

1940

1945

1950

1955

1960
1965
Cohort

1970

1975

1980

1985

1990

1995

Fig. 5. Trend of age at sexual maturity of Antarctic minke whales (I-stock) by cohort (Zenitani and Kato, 2006)

Pregnancy rate (%)

100
90

Blue

80

Fin
Humpback

70
60
50
40
30
20
10
2000

1995

1990

1985

1980

1975

1970

1965

1960

1955

1950

1945

1940

1935

1930

1925

1920

1915

1910

1905

1900

0

Year

Fig. 6. Yearly changes of apparent pregnancy rate of blue, fin and humpback whales in the Antarctic (data fromLockyer (1982) and BIWS).

10

Fig. 7. Yearly changes in growth curve of Antarctic minke whales using samples from commercial whaling (Kato,
1987).

Body length (m)

9.0

8.0
1940s
1950s

7.0

1960s
1970s

6.0

1980s
1990s
2000s

5.0
5

10

15

20

25

30 35
Age

40

45

50

55

60

65

10.0

Body length (m)

9.0
8.0
1940s
1950s

7.0

1960s
1970s

6.0

1980s
1990s
2000s

5.0
5

10

15

20

25

30 35
Age

40

45

50

55

60

65

Fig. 8. Comparison of growth curve of body length in each cohort for Antarctic minke whales (I-stock). Upper indicates
male, and lower female, respectively (Bando et al., 2006).
11

Recruitment for I-stock "Reference-case"
25000

Recruitment

20000
15000
10000
5000
0
1930

1940

1950

1960

1970
Year

1980

1990

2000

1990

2000

Recruitment for P-stock "Reference-case"
25000

Recruitment

20000
15000
10000
5000
0
1930

1940

1950

1960

1970
Year

1980

Hg (μ g / g , dr y wt . )Fig. 9. Yearly changes in recruitment for I –stock and P-stock of Antarctic minke whale derived from VPA-analysis.
(Mori et al., 2006)

Ag e (ye ar )Fig. 10. Relation between age and hepatic mercury concentrations (μg/g) in Antarctic minke whales using samples
from commercial whaling in 1980/81 season (Honda et al., 1987)

12

Fig. 11. Relation between age and mercury load (mg) in the body of Antarctic minke whales, and accumulation curve
obtained from the simulation of accumulation model (Honda, 1984).

100
80
60
40
01/0202/03 97/9898/99 94/9595/96 88/8989/90

20

84/8585/86

Survey year group80/81- 0
81/82

1-5

6-15

16-25

Hg concentration (ng/g wet wt)

120

0
26-

Age group

Fig. 12. Comparison of age trends of hepatic Hg concentrations (ng/g) of Antarctic minke whales during five survey
year groups (1980/81+1981/82, 1984/85+1985/86, 1988/89+1989/90, 1994/95+1995/96, 1997/98+1998/99,
2001/02+2002/03).
120

1-5
6-15
16-25
26-

H g c o n c e n tratio n s ( n g/ g)

100

80

60

40

20

0
80/8181/82

84/8585/86

88/8989/90

94/9595/96

97/9898/99

01/0202/03

S u rve y ye ar g ro u p

Fig. 13. Yearly changes in hepatic Hg concentrations (ng/g) of minke whales from four age groups (1-5, 6-15, 16-25, 26
or more).

13

6.0

5.5

BT/BL(*100)

5.0

4.5

4.0
1970

1975

1980

1985
Year

1990

1995

2000

Fig. 14. Yearly changes in average fattyness index of blubber thickness in February (closed circle indicates males,
open circle females. (Ohsumi et al., 1997)

6.0

Mean blubber thickness

5.5

5.0

y = -0.1117x + 4.5923
2
R = 0.6016
4.5

4.0

3.5

3.0
0

1
1987/88

2
3
4
5
6
7
8
9
1999/00
2003/04
1989/90
1993/94
1995/96
1997/98
2001/02
1991/92

10

Survey year

Fig. 15. Yearly changes in average blubber thickness of pregnant females in February (Konishi and Tamura, 2005).

Area V

Area IV140

140
y = -1.5013x + 3076.9
2
R = 0.2132

120

Male

Male

100

kg

kg

100

y = -1.1814x + 2433.4
2
R = 0.1087

120

80

80

60

60

40
1988

1990

1992

1994

1996 1998
Year

2000

2002

40
1988

2004

1990

1992

1994

1996

1998

2000

2002

2004

Year

140

140
y = -3.3535x + 6782.4
R2 = 0.3655

120

FemaleFemale

100
kg

kg

100

y = -3.48x + 7032.4
R2 = 0.7046

120

80

80

60

60

40
1988

1990

1992

1994

1996

1998

2000

2002

40
1988

2004

Year

1990

1992

1994

1996

1998

2000

2002

2004

Year

Fig. 16. Yearly changes in stomach contents (kg) of mature Antarctic minke whales in Area IV and V (Tamura andKonishi, 2006). Data used was from individuals collected from the area south of 63 degree S in January andFebruary. The content weight was the first and second stomachs combined.
14

20,000

Humpback whale
Area IV

Humpback whale
Area V

2004/05

2002/03

2000/01

1998/99

1990/91

2003/04

2001/02

1997/98

1999/2000

0
1995/960
1993/94

5,000

1991/92

10,0001996/97

10,0001994/95

20,0001992/93

Abundance estimation

15,00030,0001989/90

Abundance estimation

40,00015,000

Fin wh ale
Indian Ocean stock(South of 6 0S, 35E- 130E)
Abundance estimation

10,0005,000

0

Fin whale
Pacific ocean stock(Sou th of 60 S, 130E-145 W)
10,0005,000

2004/05

2002/03

2000/01

1996/97

2003/04

2001/02

1999/2000

1997/98

1995/960
1998/99

Abundance estimation

15,000

Seasons

SeasonsFig. 17. Yearly changes in abundance estimates for humpback whales in Areas IV and V and fin whales in Areas
IIIE+IV (35E-130E) and Areas V+VIW (130E-145W). Upper figure shows humpback whales, lower figure shows fin
whale (Matsuoka et al., 2006)

1,600,000
1,400,000

Area IVBlue
Fin
Humpback
A. Minke

Biomass [ton]1,200,000
1,000,000
800,000
600,000
400,000
200,0000
1989/90

1991/92

1993/94

1995/96

1997/98

1999/00

2001/02

2003/04

SeasonsFig. 18. Biomass of blue, fin, humpback and Antarctic minke whales in Antarctic Area IV (70E-130E) using data from
1989/90 to 2003/04 JARPA (Matsuoka et al., 2006).

15