Technical Reports of the Ins�tute of Cetacean Research (2020)

pp. 1–11

Technical Report (not peer reviewed)

What do we know about whales and ecosystem in the Indo-Paciﬁcregion of the Antarc�c? Part 2: summary of ecological studies
Tsutomu Tamura*, Koji Matsuoka, Genta Yasunaga and Luis A. Pastene
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Contact e-mail: tamura@cetacean.jp

ABSTRACTThe Ins�tute of Cetacean Research conducted whale research under special scien�ﬁc permit in the Antarc�cstar�ng from the austral summer season 1987/88. The research was conducted systema�cally under diﬀerent
research programs such as JARPA and JARPAII, and more recently, under NEWREP-A. These research programs
employed both lethal and non-lethal methods. NEWREP-A ceased a�er the 2018/19 austral summer season asa consequence of Japanʼs decision to withdraw from the Interna�onal Conven�on for the Regula�on of Whaling. Japanʼs whale research con�nues in the Antarc�c, using non-lethal methods only. This paper summarizes
the most relevant ecological outputs from Japanʼs whale research under special scien�ﬁc permit in the IndoPaciﬁc region of the Antarc�c.

INTRODUCTION
Japan conducted systema�c research on whales and theAntarc�c ecosystem for more than 30 years. The ﬁrst
research program was the Japanese Whale Research
Program under Special Permit in the Antarc�c (JARPA),
which was followed by JARPAII and subsequently by the
New Scien�ﬁc Whale Research Program in the Antarc�c
Ocean (NEWREP-A). The Ins�tute of Cetacean Research(ICR) was the ins�tu�on in charge of designing and implemen�ng those research programs. Tamura et al. (2017)
have provided details on the objec�ves, sampling andanaly�cal methodology of the three research programs.
Several interna�onal review workshops (e.g., IWC, 2015)
discussed and evaluated the large amount of data andresults from these research programs.
As a consequence of Japanʼs change in whaling policy,
the NEWREP-A ceased on 30 June 2019, the date of Japanʼs withdrawal from the Interna�onal Conven�on for
the Regula�on of Whaling (ICRW). From the 2019/20 austral summer season, Japan started whale research in the
Antarc�c using non-lethal methods. The new research
program is called the Japanese Abundance and Stockstructure Surveys in the Antarc�c program (JASS-A) (seeIsoda et al., this issue).
At this point, it was considered important to summarize the knowledge on whales and the Antarc�c ecosystem accumulated so far by Japanʼs whale research in
the Antarc�c. The objec�ve of this paper is to summarize

the most relevant ecological outputs from Japanʼs whale
research under special scien�ﬁc permit in the Indo-Paciﬁcregion of the Antarc�c.

SURVEYS, DATA AND SAMPLES
Surveys were conducted in the Indo-Paciﬁc region of the
Antarc�c, which correspond to the Interna�onal Whaling Commission (IWC) Management Areas III, IV, V andVI (Figure 1). Survey and sampling methodologies of
the Japanese whale research programs in the Antarc�cwere described in Pastene et al. (2014) and Tamura
et al. (2017). A list of data and samples collected by thesewhale research programs in the Antarc�c is available in
IWC (2015).

MAIN RESEARCH OUTPUTS ON WHALE ECOLOGY
Abundance and abundance trends of baleen whales
JARPA and JARPAII conducted vessel-based sigh�ng surveys under the Line Transect Method with the aim ofes�ma�ng abundance and abundance trends of large
whales in the Indo-Paciﬁc sector of the Antarc�c. Detailsof the methodology used are available in Tamura et al.
(2017) and Hakamada and Matsuoka (2017). The la�erauthors summarized the informa�on on abundance andabundance trend of Antarc�c minke whales, which is notrepeated here. Figure 2 shows pictures of the relevantbaleen whale species.
Baleen whale species other than the Antarc�c minke
whale were depleted by unregulated commercial whaling1Technical Reports of the Ins�tute of Cetacean Research (2020)

Figure 1.

Figure 2.

Research area of JARPA, JARPAII and NEWREP-A in the Indo-Paciﬁc region of the Antarc�c.

Baleen whale species in the Indo-Paciﬁc region of the Antarc�c: (a) Antarc�c minke whale; (b) humpback
whale; (c) ﬁn whale; (d) southern right whale; (e) Antarc�c blue whale.

in the past, and there is an interest to inves�gate the recovery of those species a�er protec�on. Fortunately, theabundance of large whale species such as humpback, ﬁn,southern right and blue whales has been increasing, albeit at diﬀerent rates over the past decades. An increasein the abundance of large baleen whales has implica�ons
for the Antarc�c ecosystem as a whole (Fujise and Pastene, 2018).
The scien�ﬁc evidences for the recovery of baleen
whale species are shown below.
Humpback whales
Abundance and abundance trend should be ideally es�mated on a biological stock basis. The IWC SC has iden�ﬁed seven breeding stocks of humpback whales in theSouthern Hemisphere, which are denominated with alphabe�c le�ers from ʻAʼ to ʻGʼ (IWC, 2011). The breeding
stocks occurring in the Indo-Paciﬁc sector of the Antarc�c
are Stock ʻCʼ (mainly in Area III), ʻDʼ (mainly in Area IV),
ʻEʼ (mainly in Area V), and ʻFʼ (mainly in Area VI) (Kanda
et al., 2014). There are some geographical overlaps be2

tween adjacent stocks in the Antarc�c.
Abundance and abundance trend es�mates basedon Japanese surveys have focused mainly on Areas IV(Breeding Stock D) and V (Breeding Stock E). In Area
IV the abundance was es�mated at 29,067 whales(CV=0.255) based on sigh�ng data collected in 2007/08;
in Area V the abundance was es�mated at 13,894 whales(CV=0.338) based on sigh�ng data collected in 2008/09(Hakamada and Matsuoka, 2014a).
Figure 3 shows the abundance trend of Breeding Stocks
D and E based on JARPA and JARPAII data. For comparison
purposes, the ﬁgures include data from the Interna�onal
Decade for Cetacean Research/Southern Ocean Whaleand Ecosystem Research (IDCR/SOWER) programs. The
ﬁgures show a clear increasing trend which is consistent
for JARPA, JARPAII and IDCR/SOWER survey data. Annual
rate of increase was es�mated at 13.6% (95% CI=8.4–
18.7%) and 14.5% (95% CI=7.6–21.5%) for Areas IV and V,
respec�vely. The rate of increase in Areas IV and V weresta�s�cally signiﬁcant (Hakamada and Matsuoka, 2014a).
The current abundance of Breeding Stock D in Area

What do we know about whales and ecosystem in the Indo-Pacific region of the Antarctic? Part 2

Figure 3.

Abundance es�mates for humpback whales in Areas IV and V (south of 60°S). Es�mates were based onsigh�ng data collected by JARPA and JARPAII between 1989/90 and 2008/09 primarily during January to
February. Es�mates from the IDCR-SOWER surveys (Branch, 2011) are shown for compara�ve purposes(ﬁlled circles). Ver�cal lines show 95% conﬁdence intervals (a�er Hakamada and Matsuoka, 2014a).

Figure 4.

Abundance trend of ﬁn whales in the Indo-Paciﬁc region of the Antarc�c, south of 60°S. Ver�cal lines show
95% conﬁdence intervals (a�er Matsuoka and Hakamada, 2014).

IV is close to that of its pre-exploita�on level (IWC HP:
h�ps://iwc.int/status).
Fin whales
There is limited informa�on on stock structure of ﬁnwhales in the Indo-Paciﬁc sector of the Antarc�c. For the
purpose of the abundance es�mates based on JARPA and
JARPAII surveys, the whole area was divided into westernarea (assuming an Indian Ocean stock in Area IIIE+IV)
and eastern area (assuming a Paciﬁc Ocean stock in Area
V+VIW). Figure 4 shows the abundance es�mates of ﬁnwhales in Areas IIIE+IV and V+VIW, plo�ed against thesurvey seasons. An increasing trend in abundance is evident for these two areas. For the western area the abundance south of 60°S was es�mated at 3,087 (CV=0.191)
in 1995/96, and 2,610 (CV=0.285) in 2007/08. For theeastern area the abundance south of 60°S was es�matedat 1,879 (CV=0.226) in 1996/97, and 14,981 (CV=0.298)
in 2008/09.
For the western area the increasing trend between
1995/96 and 2007/08 seasons was es�mated at 8.9%

(95% CI: −0.145%, 32.4%), while the trend in the eastern area between 1996/97 and 2008/09 was es�matedat 12.0% (95% CI: 2.6%, 21.5%). The es�mate for theeastern area was sta�s�cally signiﬁcant (Matsuoka andHakamada, 2014).
Southern right whales
During the JARPA and JARPAII surveys in Areas III–VI,
this species was mainly sighted in Area IV. In this Area,abundance es�mates (south of 60°S) ranged from 6(CV=0.761) in the 2003/04 season to 1,557 (CV=0.303) inthe 2007/08 season.
Figure 5 shows the abundance es�mates in Area IV
plo�ed against the survey seasons. The abundance trend
was es�mated at 5.9% (95% CI: −16.4%, 28.1%) between
1989/90 and 2007/08, which was not sta�s�cally signiﬁcant (Matsuoka and Hakamada, 2014).
Blue whales
There is limited informa�on on stock structure of blue
whales in the Antarc�c. Abundance of this species for the3Technical Reports of the Ins�tute of Cetacean Research (2020)

Figure 5.

Abundance es�mates of southern right whales
in Area IV (south of 60°S). Ver�cal lines show
95% conﬁdence intervals (a�er Matsuoka andHakamada, 2014).

Figure 6.

Abundance trend of blue whales in the IndoPaciﬁc region, south of 60°S. Ver�cal lines show
95% conﬁden�al intervals (a�er Matsuoka andHakamada, 2014).

Indo-Paciﬁc region of the Antarc�c (35°E–145°W), southof 60°S was 664 (CV=0.328) in 2005/06 and 2006/07
seasons. The abundance was es�mated at 1,223 whales(CV=0.345) in the 2007/08 and 2008/09 seasons.
Figure 6 shows the abundance es�mates for the whole
Indo-Paciﬁc region plo�ed against the survey seasons.
The abundance trend was es�mated at 8.2% (95% CI:
3.9%, 12.5%) between 1995/96 and 2008/09. This es�mate was not sta�s�cally signiﬁcant.
Future surveys and analyses
Dedicated sigh�ng surveys were planned for the seasons
2009/10–2013/14 under JARPAII. However, those surveys
could not be conducted due to external interferences by
an NGO (Nishiwaki et al., 2014). Subsequently, dedicatedsigh�ng surveys were conducted under the NEWREP-A
between 2015/16 and 2018/19 and data collected during these surveys are under analyses. From 2019/20
4

Figure 7.

Occupied area indices of Antarc�c minke and humpback whales in Area IV in three periods of JARPA and
JARPAII (Murase et al., 2014).

Japan started the JASS-A, which will be conducted fora tenta�ve period of eight years. The main objec�ve of
JASS-A is to es�mate the abundance of large whales in
the Indo-Paciﬁc region of the Antarc�c (Government ofJapan, 2019) (see Isoda et al., this issue). Data collectedduring NEWREP-A and JASS-A will be analyzed by ICR
scien�sts in conjunc�on with previous data in the samearea.
Geographical distribu�on of baleen whales
Substan�al increase in the abundance could have an
implica�on in the pa�ern of distribu�on of the species.
In the Indo sector of the Antarc�c (Area IV), humpback
whales have increased signiﬁcantly over the past decades, while the abundance of Antarc�c minke whales
has been rather stable. Under this scenario, we should
expect changes in the pa�ern of distribu�on of these two
species.

What do we know about whales and ecosystem in the Indo-Pacific region of the Antarctic? Part 2

Changes in the spa�al and temporal distribu�on patterns of Antarc�c minke and humpback whales in Area IV
were examined for the period of JARPA and JARPAII. The
spa�al distribu�on was es�mated using Generalized Addi�ve Models (GAM) (Murase et al., 2014). Presence orabsence of whales was used as a response variable while
seaﬂoor depth, distance from shelf break and longitude
were used as explanatory variables. Three �me periods
were deﬁned: ʻEarlyʼ (1989/90, 1991/92, 1993/94); ʻMiddleʼ (1995/96, 1997/98, 1999/00) and ʻLateʼ (2001/02,
2003/04, 2005/06).
Figure 7 shows the results of the GAM analyses. In theearly period, humpback whales were mainly distributedin the northern part of the survey area between longitudes 80°E and 100°E. In the middle period, humpback
whales expanded their habitat closer to the shelf break
between the longitudinal range of 80°E and 120°E. In
the late period, humpback whales were distributed in
the en�re survey area along the shelf break. While thespa�al distribu�on of humpback whales expanded during
the period of JARPA and JARPAII, no strong change wasobserved in the distribu�on of Antarc�c minke whales.
These results indicated a possible compe��on for habitat
between humpback and Antarc�c minke whales as abundance of humpback whales increased.
The pa�ern of spa�al distribu�on for other large
whales was examined by Matsuoka and Hakamada(2018). Based on JARPA and JARPAII data, there was acommon pa�ern for several whale species to concentrate
mainly in the sector between 80°E and 110°E, south of
60°S. This could be related to krill availability, as a highdensity of euphausiids was reported between 100°E and120°E in the 1999/00 JARPA survey (Murase et al., 2002).
Studies into the pa�ern of temporal (yearly) changes inrela�on to changes in environmental factors are underway.
Feeding ecology of Antarc�c minke whale
An overview of the procedures for examining stomach
content analyses by Japanese scien�sts was presented by
Tamura and Konishi (2014). The type and amount of prey
consumed by Antarc�c minke whales in the feeding season is fundamental for understanding the impact of theconsump�on on the ecosystem. The analyses of stomach
contents in Antarc�c minke whales have beneﬁted fromuseful sugges�ons and recommenda�ons from the IWC
SC.
Antarc�c minke whales feed mainly on Antarc�c krill(Euphausia superba) in oﬀshore waters, and on ice krill (E.
crystallorophias) (Figure 8) on the coastal shelf along the

Figure 8.

Ice krill (upper) and Antarc�c krill (lower).

Ross Sea and Prydz Bay (Tamura and Konishi, 2009; 2014).
The maximum weight of stomach contents of Antarc�c minke whales sampled by JARPA and JARPAII from1987/88 to 2010/11 were 142.4 kg (2.4% of body weight)
and 156.0 kg (3.4% of body weight) for immature males
and females, respec�vely. The ﬁgures were 387.0 kg(3.8% of body weight) and 326.9 kg (3.6% of body weight)
for mature males and females, respec�vely. The average
weight and rate of stomach contents per body weight(RSC) were 33.2±28.3 kg (RSC: 0.8%) and 37.6±29.1 kg(RSC: 0.9%) for immature males and females, respec�vely and 63.5±47.1 kg (RSC: 0.9%) and 71.8±54.3 kg(RSC: 0.9%) for mature males and females, respec�vely(Tamura and Konishi, 2014).
The daily prey consump�on by the whales in each
reproduc�ve status group was es�mated using energyrequirement and energy deposi�on methods. The daily
prey consump�ons of Antarc�c minke whales per capita
during the feeding season based on these two methods
were 95.1–127.0 and 182.6–250.3 kg for immature andmature males, 125.8–138.7 and 268.1–325.5 kg for immature and mature females, respec�vely. This is equivalent to 2.65–4.02% of their body weight. The total prey
consump�on of Antarc�c minke whale per capita during
the feeding season was 8.6–10.4 and 20.6–21.9 tons for
immature and mature males, and 11.3–12.5 and 32.2–
39.1 tons for immature and mature females, respec�vely(Tamura and Konishi, 2014).
Es�ma�on of the uncertain�es (e.g., allometric rela�onships, body weight of whales, energy values of preyspecies, assimila�on eﬃciency and length of feeding
period) in several components involved in es�ma�ng theamounts and types of prey consumed by North Paciﬁc baleen whales was based on sugges�ons from the IWC SC.
5

Technical Reports of the Ins�tute of Cetacean Research (2020)

Similar es�ma�ons of uncertain�es are being conducted
for Antarc�c minke whales.
In Areas III east and IV in the 2007/2008 season, theabundance of Antarc�c minke whales was es�mated at
9,406 and 14,739, respec�vely. In Area V and VI west in
the 2008/2009 season, the abundance was es�mated at
108,097 and 26,364, respec�vely (Hakamada and Matsuoka, 2014b). These abundance es�mates were used forinves�ga�ng the total consump�on of krill by Antarc�cminke whales.
In Areas III east and IV the seasonal (120 days) prey
consump�on of krill by Antarc�c minke whales wases�mated at 0.17–0.19 and 0.33–0.37 million tons,
respec�vely. In Areas V and VI west, the consump�on
was es�mated at 2.51–2.88 and 0.50–0.54 million tons,
respec�vely. The seasonal prey consump�on by Antarc�cminke whales in the total research area was es�matedat 3.51–3.98 million tons, amoun�ng to 7.6–8.6% of thekrill biomass es�mated by acous�c survey in the researcharea (Tamura and Konishi, 2014).
Energe�cs of Antarc�c minke whale
Whales generally accumulate energy as lipid in the blubber during the summer feeding period at high la�tudes,
and they spend the energy in migra�on and reproduc�onin low la�tude waters. The proxy of fat reserves in blubber have been used as an indica�on of body condi�on inwhale studies (e.g., Lockyer et al., 1985; 1986). The measurements of blubber thickness posi�vely correlate withlipid content in the whole body fat and have proven to bea dependable proxy for energy storage in whales (Lockyer
et al. 1985).
For the 18 years of JARPA period (1987/88–2004/05),
the annual trend in energy storage in the Antarc�c minke
whales was examined using blubber thickness (Figure 9)at two lateral measurement points, in addi�on to total

Figure 10.

6

fat weight in the whale body and girth measured at two
speciﬁed posi�ons.
Blubber thickness measurements were available for
4,689 whales; fat weight was available for 740 whales;
and half girth measurements were available for 4,681
animals. Regression analysis was carried out on blubber
thickness in 4,689 whales. The explanatory variables
were age, body weight, fetus length and total fat weight.
A large number of linear mixed-eﬀects sta�s�cal models
were inves�gated for each of the dependent variables,
and the Bayesian Informa�on Criterion (BIC) was used to
select the best model. All models examined had ʻyearʼ as
a possible explanatory variable. This regression analyses
clearly showed that blubber thickness had been decreasing in this period. The decrease per year in the JARPA
period was es�mated at approximately 0.02 cm for midlateral blubber thickness (Figure 10).
Similar analyses and results were found for fat weight,
which decreased 17 kg in the 18-year period (Figure 10).
Furthermore, the runs using ʻhalf girthʼ as another dependent variable also gave similar results. The total magnitude of the decline over these 18 years was 4% for girth

Figure 9.

Measurement of blubber thickness.

Temporal trends in body condi�on indicators of Antarc�c minke whales in the feeding season (a: blubber thickness; b: fatweight; c: half girth) for the Antarc�c minke whale in the feeding season (Konishi et al., 2008).

What do we know about whales and ecosystem in the Indo-Pacific region of the Antarctic? Part 2

measurements (Figure 10).
Similar analyses were conducted for stomach contents
weight (sieved contents of the forestomach). Regression
analyses using the weight of the stomach contents as thedependent variable, and explanatory variables such as
year, date, local �me, la�tude, sex and body length, wereconducted. A linear mixed-eﬀects analysis showed a 31%(95% CI=12.6–45.3%) decrease in the weight of stomach
contents over the 20 years since 1990/1991 (Konishi
et al., 2014).
The trend in stomach content was consistent withthat of the blubber thickness (Konishi and Walløe, 2015).
These results suggested that the food availability for Antarc�c minke whales may have declined in recent decades.
Monitoring of environmental pollutants
Pollutant analyses by Japanese scien�sts started under
the JARPA program for the objec�ve of ʻElucida�on of theeﬀect of environmental changes on cetaceansʼ and con�nued under the JARPAII program. The objec�ve involved
the elucida�on of the pa�ern of pollutant accumula�on
and the eﬀects of pollutants on cetaceans. Diﬀerent
kinds of pollutants were monitored, which included traceelements and organochlorine compounds (OCs). Traceelements included the toxic ones Hg, Cd, Pb and Ni (nonessen�al elements), and Cu, Zn, Fe and Mn (essen�al elements). Toxic elements induce adverse eﬀects in animals
and humans, and are more persistent than the essen�alelements. Essen�al elements are important for survival
and health of animals and humans.

Figure 11.

Details of the analy�cal procedures for pollutants were
given in Appendix 4 of Government of Japan (2005).
Regarding OCs, the levels of PCB and DDT in ﬁn andAntarc�c minke whales in the Antarc�c Ocean could be
the lowest among whale species in the world (Figure 11)(Yasunaga et al., 2006). The results during the JARPA/
JARPAII period suggested that levels of HCHs in the Antarc�c Ocean have varied from decreasing slightly to being
steady in the mid-1990s. HCB levels in large whales would
be aﬀected by trophic levels of its preys rather than byspa�al diﬀerences.
Regarding trace elements, the hepa�c Hg levels of Antarc�c minke whales of all age groups in Area IV decreased
signiﬁcantly over the research years, whereas that of
15–26 years old whales in Area V increased signiﬁcantly,
possibly indica�ng that food availability of Antarc�cminke whales in the 2000s may have diﬀered from thosein the 1980s and 1990s (Yasunaga et al., 2014).
Oceanography
Informa�on on oceanographic structure and its dynamics are important in interpre�ng changes in the Antarc�cecosystem. Changes in oceanographic condi�ons aﬀect
krill distribu�on and biomass and, in turn, the abundanceand distribu�on of whales. Changes in oceanographic
condi�ons might indicate an eﬀect of climate change. Details of the oceanographic survey can be found in Wada
(2019).
Watanabe et al. (2014) analyzed oceanographic observa�on data obtained by JARPA and JARPAII to clarify

PCB and DDT levels in the blubber of baleen whales (Yasunaga et al., 2006).
7

Technical Reports of the Ins�tute of Cetacean Research (2020)

physical oceanographic condi�ons in the JARPA/JARPAII
research area as a basis for understanding the habitat environment of whales. About 2,500 proﬁles were obtained
by XBT, XCTD and CTD observa�ons from 1990 to 2009.
Based on this data set, the averaged feature of the oceanographic structure in the research area for two decades
was described. In the area east of the Kerguelen Plateau,
the posi�on of the Southern Boundary (SB) changed on a
decadal �mescale. The SB is indicated by the 0°C contour
on 27.6σ 0. The southward shi� of the SB in the region wasobserved in the early 2000s, and the northward shi� wasobserved in the later 2000s (Figure 12).
Unlike the Antarc�c Peninsula region, the JARPA and
JARPAII temperature data showed no sta�s�cally signiﬁcant warming in the JARPA area for the two decades.
Inves�ga�on of the oceanographic condi�ons in the
Indo-Paciﬁc region of the Antarc�c is one of the secondary objec�ves of JASS-A. Data will be analyzed in conjunc�on with the large data sets produced by JARPA/JARPAII
and NEWREP-A in the Indo-Paciﬁc region of the Antarc�c.

Figure 12.

Temperature on the 27.6σ 0 isopycnal surface
for the Area IV (a) and Area V (b) (Watanabe
et al., 2014).

Figure 13.

8

Krill survey
Krill is a key prey species in the Antarc�c ecosystem, suppor�ng diﬀerent species of baleen whales, pinnipeds,
birds and ﬁsh. For this reason, the ICR has been conducting krill surveys alongside the whale sigh�ng surveys.
Sigh�ng of whales and krill surveys were carried out
concurrently in JARPAII and NEWREP-A. Details of the krill
survey can be found in Wada (2019).
Wada and Tamura (2014) presented results of krill biomass es�ma�ons based on the data from a quan�ta�veecho sounder (EK500; Simrad, Norway). Es�ma�ons weremade based on data obtained in Area IV in the 2007/08
JARPAII survey and in Area V in the 2008/09 JARPAII survey. The biomass es�mates obtained in Area IV was 12.5
million tons, and that in Area V was 24.0 million tons.
These es�ma�ons were useful to evaluate the impact of
the krill consump�on by three baleen whale species.
Regarding krill demography, informa�on on length frequency distribu�on and maturity stage of Antarc�c krill
are being obtained using samples from stomachs of Antarc�c minke whales taken in JARPA, JARPAII and NEWREPA (1989/90–2017/18). Figure 13 shows an example ofoutputs of such analyses.
Marine debris
In recent years marine debris has been recorded in the
sub-Antarc�c and Antarc�c islands. Marine debris causes
nega�ve eﬀects on whales through inges�on and by entanglement. JARPA, JARPAII and NEWREP-A conductedsystema�c monitoring of marine debris in whales andtheir environment in the Antarc�c. Details of the resultsof marine debris during JARPA/JARPAII can be found in
Isoda et al. (2018).
The density index (DI: number of marine debris per 100
nau�cal miles) of marine debris in the Antarc�c is lower
by two orders of magnitude in comparison to the North
Paciﬁc Ocean and its adjacent waters. Thus, the observa-

Length frequency distribu�on (le�) and maturity stage (right) of Antarc�c krill sampled from stomach
contents of Antarc�c minke whales in 2008/09 in the sector 130°E and 140°E.

What do we know about whales and ecosystem in the Indo-Pacific region of the Antarctic? Part 2

Figure 14.

Food web in the Antarc�c modeled in Mori and Bu�erworth (2006) and Moosa (2017).

�ons proved that the Antarc�c waters have a very low
density of marine debris on the sea surface. The level ofimpact of entanglements on Antarc�c minke whales was
low in comparison with other oceanic basins. Given the
low indices, the eﬀect of marine debris on whales in the
Antarc�c was expected to be limited at the present �me(Isoda et al., 2018).
Modelling work
An overview of the ICR work on ecosystem modelling in
the Antarc�c was presented by Hakamada and Tamura(2018). The ecological background for the modelling exercise was provided by Fujise and Pastene (2018).
Mori and Bu�erworth (2006) constructed a mul�species modelling in the Antarc�c Ocean using baleen
whales and seals as predators and krill as prey (Figure 14).
One of the main objec�ves of their modelling exercise
was to determine whether predator-prey interac�ons
alone can broadly explain observed popula�on trends
without the need for recourse to environmental change
hypotheses. Preliminary results indicated that this is likely
to be the case.
New ecosystem modelling studies are underway(Moosa, 2017).

CONCLUSIONSJapanʼs whale research programs under special permit
have provided important informa�on on the ecology of
Antarc�c minke whales and other baleen whale species
in the Indo-Paciﬁc region of the Antarc�c. The long �meseries of data produced by the research programs havebeen fundamental to the study and understanding ofabundance trends of several large whale species, thechanges in distribu�on of Antarc�c minke and humpback
whales, and the changes in nutri�onal condi�ons of the
Antarc�c minke whales. The research programs haveproduced new informa�on in helping to understand theoceanographic structure of the Indo-Paciﬁc region of the
Antarc�c.
Also, studies on the distribu�on, abundance and demography of the krill have commenced. Further, these

programs have provided informa�on on the level ofpollutant and marine debris in the Antarc�c, which fortunately are at low levels. Ecosystem models are being
developed to understand the predator-prey interac�on.

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