NOT TO BE CITED WITHOUT PRIOR REFERENCE TO THE AUTHORS【 JA/J05/JR 8 】

Feeding habits and prey consumption of Antarctic minke
whales, Balaenoptera bonaerensis in JARPA research area
TSUTOMU TAMURA AND KENJI KONISHI
The Institute of Cetacean Research, 4-18, Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan.
KEYWORDS: ANTARCTIC MINKE WHALE; ANTARCTIC KRILL; ANTARCTIC; MONITORING;
ENERGETICS; FOOD/PREY; SCIENTIFIC PERMITS

ABSTRACTThe purpose of this study is to understand the feeding habits of Antarctic minke whale Balaenoptera bonaerensis
in JARPA research area of Antarctic. All 6,338 samples were taken by JARPA (the Japanese Whale Research
Program under Special Permit in the Antarctic) from 1987/88 to 2003/04 survey years. This study showed that
Antarctic krill Euphausia superba was the most important prey species for the Antarctic minke whales over thesurvey period. In coastal area (swallow area) such as Ross Sea and Prydz Bay, E. crystarollophias was also
important prey species for the Antarctic minke whales. Amphipods and fish were minor prey, which were often
observed together with abundant krill in the stomach contents. The analyses of prey digestion showed that
Antarctic minke whales tended to feed on prey in the early morning and late evening. Prey intake had decreased
gradually from early morning to daytime and then increased at late evening. Daily prey consumption by Antarctic
minke whale was estimated using two methods, direct method from diurnal changes of stomach contents mass andindirectly method from energy requirement. The results of daily consumption estimate were similar between thetwo methods ranged from 3.6 to 5.3 % of body weight (immature male: 107-142 kg, immature female: 141-201 kg,
mature male: 245-292 kg, mature female: 300-366 kg). From 1999/00 to 2002/03 seasons, the annual consumptionof Antarctic krill were calculated as 1.3 and 5.2 million tonnes, equivalent to 4 and 26 % of the krill biomass in
Area IV and V, respectively. These results indicate Antarctic minke whales are the dominant top-predator species
in Area IV and V.

INTRODUCTION
The abundance of Antarctic minke whales (Balaenoptera bonaerensis) in the Antarctic (south of 60°S) has been
estimated to be as high as 760,396 animals during the austral summer (IWC, 1991). Several researchers haveexamined the stomach contents of Antarctic minke whales, and showed Antarctic krill (Euphausia superba) is themost important prey species (Kawamura 1980, Bushuev 1986, Ichii and Kato, 1991). In coastal (shallow) areasuch as Ross Sea and Prydz Bay, they fed mainly on E. crystarollophias and some fishes (Bushuev 1986, Tamura
1998).
Some studies have estimated the prey consumption of Antarctic minke whales on the basis of energyrequirements calculations (Hinga, 1979; Lockyer, 1981). Antarctic krill, which is the main prey species ofAntarctic minke whales, is the key species in the Antarctic marine ecosystem. Seals, birds, fishes and squids aswell as baleen whales consume Antarctic krill (Laws 1977). Armstrong and Siegfried (1991) estimated that
Antarctic minke whales were reached to consume 95 % of the total consumption of Antarctic krill consumed bywhales in the Antarctic. Thus, the Antarctic minke whale is considered one of the key species and plays animportant role during the austral summer in the Antarctic Ecosystem.
In recent year, it was closed up the global climate change such as global warming and an increase in radiationof ultraviolet light due to destroy of ozone layer. Atkinson et al. (2004) analyzed the krill biomass around1

Antarctic, and reported their density had declined since the 1970s. Especially near the Antarctic Peninsula, theirbiomass sharply decreased. On the other hand, salps appear to have increased in the Antarctic. These changes have
had profound effects within the Antarctic ecosystem.
Data such as stomach contents, sexual maturity, body mass, abundance estimates of Antarctic minke whale andkrill biomass estimates from the Japanese Whale Research Program under Special Permit in the Antarctic(JARPA) provided us to understand the feeding ecology of Antarctic minke whales. The four main objectives of
the JARPA are (1) elucidation of the stock structure of Antarctic minke whales to improve the stock management,(2) estimation of biological parameters of the Antarctic minke whales, (3) elucidation of the role of whales in the
Antarctic marine ecosystem through the study of whale feeding ecology and (4) elucidation of the effect ofenvironmental changes on cetaceans. To achieve the study objectives, sighting survey for cetaceans, biologicalresearch has been conducted from the beginning of JARPA since the 1987/88 season.
In this paper, we investigated the feeding habits (prey species, distribution of prey, diurnal feeding pattern,
stomach contents mass and their prey consumption) of Antarctic minke whales in the Antarctic based on dataobtained from JARPA. And, we estimated the feeding impact on krill resources by Antarctic minke whales in
JARPA research area during 1999/00 and 2002/03 seasons.

MATERIALS AND METHODS
Research area, periods, sample size and sighting position of whales sampled
A total of 549, 2,864, 2,535 and 390 Antarctic minke whales were randomly sampled in Area III-East (35°E to70°E), Areas IV (70°E to 130°E), V (130°E to 170°W) and VI-West (170°W to 145°W) of Antarctic between
1987/88 and 2003/04 seasons, respectively (Table 1).
The whales were sampled according to sampling procedures described by Nishiwaki et al (2005). Sampled whales
were immediately transported to a research base vessel, where biological measurements and sampling werecarried out. Body length was measured to the nearest 10 cm from the tip of the upper jaw to the deepest part of the
fluke notch. Body weight was measured using the special large weighing machine on the flensing deck of theresearch base vessel. The JARPA survey used ship time, which was converted into local time. As result, our study
covered from 3:00 to 21:00 hrs.
Sampling and analyses of stomach contents
Antarctic minke whales have some chambered stomach system (Hosokawa and Kamiya, 1971; Olsen et al., 1994).
Each stomach contents were weighed to the nearest 0.1 kg. The freshness of forestomach (1st. stomach) contents
was categorized into four classes (F = fresh, fff = lightly digested, ff = moderately digested, f = heavily digested).
Then, some individuals of all whales sampled, a sub-sample (300 g) of forestomach contents from each whalewith relatively fresh prey in its stomach contents was removed and fixed in 10% formalin solution water for later
analyses. In the laboratory, prey species in the sub-samples were identified to the lowest taxonomic level as
possible (Barnard 1932, Fischer and Hureau, 1985a; 1985b, Baker et al., 1990).
The daily prey consumption by Antarctic minke whales
The amount of krill consumed by Antarctic minke whales was estimated directly from information on the massesof stomach contents (Forestomach and fundus (2nd. stomach)) (method-1), and indirectly by calculating thewhale’s energy requirements (method-2).
Method-1 Estimation of daily consumption of krill from diurnal change in stomach content mass
Miura (1969) proposed a method for estimating daily prey consumption from diurnal changes in stomach content
mass (Vi) with the passage of time based on a known digestion rate in the stomach. If the proportion of preydigested during an interval is d, and the proportion of undigested prey (S) is 1-d, the amount of prey consumed(Ci) is given by the following equations:t1: C1=V1
t2: C2=V2-SV1
t3: C3=V3-SV2-S2V1
ti: Ci=Vi-SVi-1-S2Vi-2…Si-1V1kTherefore, the daily prey consumption (∑ C ) is given by:
i =1

i

2

k

∑
i =1

C i = V1

(1 − 2 S + S k )(1 − 2S + S k −1 )+‥+ V k −1 (1 − S ) +‥+ V k
+ V2
1− S
1− S

In this study, we calculated the mean stomach content mass as % of body mass (Vi) at 1 hour intervals. Assumingthat prey takes 8 hours to digest the stomach contents of whales (Tobayama, 1974, Bushuev, 1986) and that d isexponential (Elliott and Persson, 1978), we estimated S to be 0.69 and 0.75, if the proportion of undigested prey inthe stomach after 8 hours is 5 % and 10 %, respectively.
We assumed that Antarctic minke whales did not feed during 21:00 to 03:00 hrs, because E. superba disperses atnight in the late summer (Ichii, 1987).
Method-2 Estimation of daily consumption of krill from the standard metabolism
The Antarctic minke whales are thought to undertake seasonal migrations between winter breeding areas intropical or subtropical waters and summer feeding areas in the Southern Ocean.
We calculated the daily prey consumption (F) during the austral summer by different maturity stages of Antarctic
minke whale from the field metabolic rate and energy deposit according to following equations:
Immature male or female :Mature male:
Mature female:F (kg day-1)=(FMR ×1.575 + ED) / E / A
F (kg day-1)= (FMR + ED) / E / A
F (kg day-1)= (FMR + ED +R) / E / A

FMR :Field metabolic rate (kJ day-1)
ED :Energy deposit (Blubber and muscle) (kJ day-1)
E:Caloric value of E. superba (kJ kg-1)
R:Reproduction cost (kJ day-1)
A:Assimilation efficiency
We made the following additional assumptions:(1) Mean body mass (W)We calculated mean body masses of 2,900 kg and 3,800 kg for immature males and females, and 6,800 kg and
8,100 kg for mature males and females from JARPA data.
(2) Field metabolic rate (FMR)
The average FMR used in these calculations was proposed by Blix and Folkow (1995). The value of 80 kJ kg-1 per
day is based on indirect determination of oxygen consumption from studies of the respiratory rates. However,young and sexually immature animals have higher metabolic rates (Kleiber, 1975; Innes et al., 1986). We applied
this higher metabolic tare for young and sexually immature animals by multiplying with a factor AWF. This AWF
was given a definition by Markussen et al. (1992). We calculated field metabolic rate by multiplying with anaverage AWF (1.575) for immature animals.
FMR=80×W (kJ day-1) ; W is body mass (W)(3) Energy deposited during feeding season in Antarctic (ED)The total muscle, internal organs fat and blubber masses of Antarctic minke whales, which were sampled during
December and March were weighed in JARPA surveys, in order to calculate seasonal growth and fat deposition.
These depositions were converted to energy deposition by measuring the energy density of samples of muscle andblubber of some whales sampled in the early and late seasons during austral summer, by Bomb calorimeter.
(4) Caloric value of E. superba (E)Antarctic minke whales feed mainly on E. superba. The mean caloric value of E. superba is 4,473 kJ kg-1 (= 1,070
kcal kg-1). This value was calculated using the energy density of E. superba samples of JARPA surveys by Bombcalorimeter.
(5) Residence time in the Antarctic (D)The encounter rate (as a simple index of density) of Antarctic minke whales in the Antarctic increased from earlyNovember to late December and peaked in January, followed by a steady decrease through February (Kasamatsu
et al., 1996). We assumed that Antarctic minke whales spend about 100 days during the austral summer in the
Antarctic.

3

(6) Reproduction cost (R)The total reproductive cost for a female Antarctic minke whales was re-calculated from the analysis by Lockyer(1981a) to be 1.89×107 kJ (=0.45×107 kcal), assuming a length at birth fetus of 273 cm (Best, 1982). We
assumed that all reproduction costs of Antarctic minke whales were stored during residence time in the Antarctic(D).
(7) Assimilation efficiency (A)We assumed that Antarctic minke whales have an assimilation efficiency of 84 % (Lockyer, 1981a).
The total prey consumption by Antarctic minke whales in Area IV and V
We estimated the total prey consumption of krill consumed by different maturity stages of Antarctic minke whales
in Areas IV and V based on the abundance data of Antarctic minke whale (Hakamada et al., 2005) andcomposition of maturity stages of Antarctic minke whales sampled during JARPA surveys. Furthermore, we
compared between the prey consumption by Antarctic minke whale and the standing stock of krill in Area IV andV, and the feeding impact on standing stock of krill (the percentage of krill consumption in total krill biomass) by
Antarctic minke whales in Area IV and V were estimated. The resources of krill in Area IV and V were calculatedusing echo sounder by JARPA surveys (Murase et al., 2005).

RESULTS
Prey items
A total of ten prey species, including one amphipod and four euphausiids and five fish species were identified(Table 2). Major prey item was krill. The ratio of empty stomach has no yearly trend (Table 3). Antarctic minke
whales fed mainly on Euphausia superba (Table 4). The occurrence and distribution of amphipod and fishes
showed in Fig. 1. Amphipod was found in offshore of eastern Area IV and Area V. Fishes were found in coastal(shallow) area of Prydz Bay and Ross Sea, especially. The occurrence and distribution of krill species showed inFig. 2. Antarctic minke whales fed mainly on E. superba excluding in coastal area. In coastal (shallow) area of
Prydz Bay and Ross Sea, they fed mainly on E. crystarollophias.
The diurnal changes in feeding activity
The relationship between freshness categories and the diurnal change in the mean stomach content mass as % ofbody mass was showed in Figs. 3 and 4. These figures show the proportion of undigested category of F and fff andthe rate of the mean stomach content mass have decreased with time periods. After 19:00 hrs, F of freshness
categories and the rate of the mean stomach content mass have increased.
Daily prey consumption of Antarctic minke whales
To clear the daily prey consumption, the average of fresh stomach contents (category: F and fff) was calculated formature male and female in each survey year (Fig. 5). In area IV, Fig. 5 shows that the average of fresh stomach
contents for mature male and female has decreased significantly year after year excluding 1989/90 JARPA(Mature male: F=0.008, Mature female F=0.007). In area V, there was same trend in that of mature female(Mature male: F=0.59, Mature female F=0.03).
Method-1
These estimate rates of daily prey consumption diurnal changes in stomach content mass (Fig. 4) were 3.7 and
4.3 % of body mass.
If the proportion of undigested prey in the stomach after 8 hours is 5 %, estimates of prey consumption were
124.7 kg and 163.4 kg for immature male and female, 292.4 kg and 348.3 kg for mature male and female,respectively (Table 5).
If the proportion of undigested prey in the stomach after 8 hours is 10 %, Estimates of prey consumption were
107.3 kg and 140.6 kg for immature male and female, 251.6 kg and 299.7 kg for mature male and female,respectively (Table 5).
Method-2
FMR
The mean body length was calculated of 6.2 and 6.7 m for immature males and females, and 8.4 and 8.9 m formature males and females from JARPA data. We calculated mean body masses of 2,900 and 3,800 kg for4immature males and females, and 6,800 and 8,100 kg for mature males and females from JARPA data. Using
these body mass and the value for the energy requirement of minke whale proposed by Folkow and Blix (1995),
field metabolic rate of immature and mature males were 365,400 and 544,000 kJ day-1, respectively. And, field
metabolic rate of immature and mature females were 478,800 and 648,000 kJ day-1, respectively (Table 6).
Blubber deposition
An immature male of 6.2 m with a mid-December blubber mass of 608 kg deposits 96 kg of blubber between
mid-December (average capture date, 19 December) and mid-March (average capture date, 10 March) (Fig.6).
The energy density of blubber increased from 14,435 to 20,711 kJ kg-1 during feed residence time in the Antarctic.
Thus, it can be calculated that 70 781 KJ day-1 was deposited as blubber during residence time in the Antarctic(100 days). If a similar calculation is made for mature male of 8.4 m, a value of 164,064 kJ day-1 was obtained(Table 6).
An immature female of 6.7 m with blubber mass of 791 kg in mid-December deposits 103 kg of blubber
between mid-December (average capture date, 19 December) and mid-March (average capture date, 8 March)(Fig.6). The energy density of blubber increased from 16,443 to 28,075 kJ kg-1. Thus, it can be calculated that
164,064 kJ day-1 was deposited as blubber during residence time in the Antarctic (100days). If a similarcalculation is made for mature female of 8.9 m, a value of 326,204 kJ day –1 was obtained (Table 6).
Growth and/or deposition of muscle
An immature male of 6.2 m with muscle mass of 1,484 kg in mid-December deposits 194 kg of muscle between
mid-December (average capture date, 19 December) and mid-March (average capture date, 10 March) (Fig.7).
The energy density of muscle increased from 5,858 to 6,234 kJ kg-1 during feed residence time in the Antarctic.
Thus, it can be calculated that 21,553 KJ day-1 was deposited as muscle during residence time in the Antarctic(100 days). If a similar calculation is made for mature male of 8.4 m, a value of 43,046 kJ day-1 was obtained(Table 6).
An immature female of 6.7 m with muscle mass of 1,973 kg in mid-December deposits 100 kg of muscle
between mid-December (average capture date, 19 December) and mid-March (average capture date, 8 March)(Fig.7). The energy density of muscle increased from 5,941 to 6,192 kJ kg-1. Thus, it can be calculated that 13,930
kJ day-1 was deposited as muscle during residence time in the Antarctic (100days). If a similar calculation is madefor mature female of 8.9 m, a value of 37,102 kJ day-1 was obtained (Table 6).
Internal organs fat deposition
We estimated the mass of internal organs fat deposition to deduct the blubber deposition and growth and/or
deposition of muscle from total body mass. Total body mass shows in Fig. 8. The energy density of internal organs
fat assumed as same as blubber’s value.
An immature male of 6.2 m can be calculated that 75,955 kJ day-1 was deposited as internal organs fat duringresidence time in the Antarctic (100 days). If a similar calculation is made for mature male of 8.4 m, a value of
168,901 kJ day-1 was obtained (Table 6).
An immature female of 6.7 m can be calculated that 112,529 kJ day-1 was deposited as internal organs fat
during residence time in the Antarctic (100days). If a similar calculation is made for mature female of 8.9 m, avalue of 173,280 kJ day-1 was obtained (Table 6).
Daily prey consumption during residence time in the Antarctic
We calculated the daily prey consumption during residence time in the Antarctic of 100 days. The field metabolic
rate, blubber deposition, growth and/or deposition of muscle and internal organs fat rate were assumed to obtainthe same deposition day by day during feed residence time in the Antarctic.
These estimate rates of daily prey consumption using method-2 were 4.9 and 5.3 % of body weight for
immature male and female, 3.6 and 4.5 % for mature male and female, respectively. Estimates were 142.0 and
201.3 kg for immature male and female, 244.9 and 365.6 kg for mature male and female, respectively (Table 6).
Seasonal prey consumption of Antarctic minke whales in Area IV and V of the Antarctic
We estimated the total prey consumption of krill consumed by Antarctic minke whales in Area IV and V based on
the abundance of whales, the average of daily prey consumption using method-1 and 2, and the composition of
maturity stages of Antarctic minke whales sampled during JARPA. These average estimate rates of daily prey
consumption were 4.3 and 4.4 % of body weight for immature male and female, 3.9 and 4.2 % for mature maleand female, respectively. Estimates were 124.7 and 168.4 kg for immature male and female, 263.0 and 337.9 kg
for mature male and female, respectively.
In Area IV, total prey consumptions of krill by Antarctic minke whales of 1999/00 and 2001/02 season were
estimated to be 1.3 and 1.9 million tonnes, respectively. On the other hand, in Area V, total prey consumptions ofkrill by Antarctic minke whales of 2000/01 and 2002/03 season were estimated to be 4.8 and 5.2 million tonnes,
5respectively (Appendix 1, Table 7).
The estimations of feeding impact on krill resources by Antarctic minke whales in Area IV and V were ranged
from 4 to 5 % of krill standing stock, and from 25 to 26 %, respectively. The average estimations of feeding
impact on krill resources by Antarctic minke whales in Area IV and V were 4 and 25 % of krill standing stock a
year, respectively (Table 7).

DISCUSSION
Prey items
The Antarctic minke whales in the Antarctic during austral summer from 1987/88 to 2003/04 seasons were
stenophagous. We confirmed that they fed mainly on Antarctic krill Euphausia superba in offshore. Prey species
varied geographically. In coastal area (swallow area) such as Ross Sea and Prydz Bay, they fed mainly on E.
crystarollophias and some fishes. The results were coincided with previous reports (e.g. Bushuev 1986). E.
crystarollophia distribute in coastal/ swallow area (Thomas and Green 1988, Hosie 1991).
In Northern Hemisphere, prey switching of minke whales B. acutorostrata has been observed in some regions(the Barents Sea in the North Atlantic (Haug et al. 2002); the western North Pacific (Tamura and Fujise 2002)). In
Antarctic, Antarctic krill and salps (mainly Salpa thompsoni) are major zooplankton (Pakhomov et al. 2002).
In recent years, it has reported that krill densities have decreased, and salps densities appear to have increasedin the Southern Ocean (Loeb et al. 1997; Atkinson et al. 2004). However, there was no evidence the preyswitching of Antarctic minke whale from krill to salps in the Antarctic. This result shows that salps are not fit toeat for Antarctic minke whales.
The diurnal changes in feeding activity
Our results suggested that Antarctic minke whales seem to have a bimodal durnal feeding rhythm, with a primary
peak in the early morning and a secondary one in the late evening. Our results were coincided with previous
reports (Ohsumi 1979, Bushuev 1986). Unfortunately, no information is available from 21:00 hours to 03:00 hours.
Although, they might not feed on prey during night due to E. superba disperses at night in the austral summer(Ichii 1987). Other studies of minke whales in Northern Hemisphere have shown tendency for a diurnal feeding
activity (Haug et al. 1997, Lindstrom et al. 1998). In feeding areas of abundant and stable prey, Antarctic minke
whales are not hungry and might ceased to feed at earlier time in the day due to be satisfied with feeding. It takes
8 hours to digest the stomach contents of whales (Tobayama 1974, Bushuev 1986). After digestion of prey, theymight feed on prey again.
The average mass of fresh stomach contents for mature male and female has decreased significantly year after
year in Area IV excluding 1989/90 season. In area V, there was same trend in that of mature female. We did not
identify that krill densities have decreased, and salps densities appear to have increased in our survey area. Thisphenomenon may show that the krill availability has been decreased year after year.
Daily prey consumption of Antarctic minke whales
Using method 1, the daily prey consumption rates were calculated to be 3.7 and 4.3 % of body weight if the
proportion of undigested prey after 8 hours was 5 and 10 %, respectively. If feeding also occurred at night, these
rates would underestimate the actual prey consumption rates. Thus, the daily consumption rate was estimated to
be at least 3.7 %.
The estimated prey consumption rates using method-2 were 4.9 and 5.3 % of body weight for immature males
and females, respectively, and 3.6 and 4.5 % for mature males and females, respectively. All estimates of daily
prey consumption rate obtained from the two methods ranged from 4 to 5%. These values were similar toestimates by Lockyer (1981b) and Bushuev (1986).
Armstrong and Siegfried (1991) estimated the mean daily prey consumption rates from respiratory allometry
methods of male and female minke whales during the austral summer to be 6.7 and 6.2 %, respectively. Since
JARPA data indicate that the maximum stomach contents mass (Forestomach and fundus) was 343.8 kg and 4.2 %,Armstrong and Siegfried's prey consumption rates may be overestimates.
Reilly et al. (2004) considered the question of energy budget studies of baleen whales in the Antarctic. They
estimated the prey consumption of Antarctic minke whale from Tamura et al. (1997). Tamura et al. (1997)
compared the daily prey consumption using three methods. One method was a direct approach based on diurnalchange in stomach contents mass, the others were energetic-based approaches. The average of three estimates
ranged from 3.4 % to 3.8 % of body weight. Our present study was improved from these previous methods of
Tamura et al. (1997). The present authors regard the present estimates to be more reliable. These estimates could
be used with confidence for the estimation of total prey consumption of Antarctic minke whales.
6Consumption of krill during austral summer by Antarctic minke whales in Areas IV and V
In the Antarctic, large baleen whale species were depleted rapidly in the 20th century. Laws (1977) suggested that
before the 1970’s, blue whale and humpback whale were the most harvested and were reduced to about 3 and 5 %of their estimated initial biomasses. This rapidly decreasing of baleen whales provided the annual surplus of krill
as much as 150 million tonnes. This surplus became available for other krill predators, such as Antarctic minke
whale, crabeater seals (Lobodon carcinophagus), Antarctic fur seals (Arctocephalus gazella), some penguins andsea birds.
Some researchers estimated the total prey consumption of baleen whales using energy budget models in the
Antarctic. Armstrong and Siegfried (1991) indicated that the Antarctic minke whales consume 95 % of the total
biomass of krill that is consumed by baleen whales in the Antarctic. This prey consumption of Antarctic minke
whale was equal to be 35.5 million tonnes using 760,396 of the estimated population. Tamura (2003) showed thatthe annual crustacean consumption by Antarctic minke whales was 42-64 million tonnes, and that this amounted
to 40-54 % of total annual crustacean consumption by cetaceans in the Southern Hemisphere.
We estimated the total prey consumption of krill consumed by Antarctic minke whales in Area IV and V basedon the abundance, the average of daily prey consumption using direct method and energy requirement method,
and the composition of maturity stages of Antarctic minke whales sampled during JARPA.
In Area IV, total prey consumption of krill by Antarctic minke whales of 1999/00 and 2001/02 seasons were
estimated to be 1.3 and 1.9 million tonnes, respectively. In Area V, total prey consumption of krill by Antarctic
minke whales of 2000/01 and 2002/03 seasons were estimated to be 4.8 and 5.2 million tonnes, respectively. The
average estimations of feeding impact on krill resources by Antarctic minke whales in Area IV and V were 4 and
25 % of krill biomass, respectively.
Tamura et al. (1997) estimated the prey consumption of krill by Antarctic minke whales around the Ross Sea in
the Antarctic to be an order of magnitude greater than the estimated consumption by Adelie penguins (Phgoscelis
adeliae) and crabeater seals.
Reilly et al. (2004) estimated the prey consumption and energy transfer of baleen whales in the South Atlantic
sector of the Antarctic (about 30W – 70W). The estimations of feeding impact on krill resources by baleen whales
were ranged from 4 to 6 %. They estimated that the prey consumption of baleen whales in this region wasapproximately 1.6 million tonnes, possibly up to as much as 2.7 million tonnes in the Antarctic. However, theabundance of Antarctic minke whale was only 18,000 animals in their study.
Mori and Butterworth (2004) tried to build up the Multi-species type ecosystem modeling in the Antarctic. They
treated Antarctic minke whale, blue whale (B. musculus) and Antarctic krill. Antarctic minke whales and blue
whales feed mainly on Antarctic krill, their distributions are similar, near the ice edge in the Antarctic. They noted
two interesting features of the dynamics of these species using simple ecosystem model. First, a decrease of krill
biomass from the 1970s to the 1990s due to the rapid increasing abundance of Antarctic minke whales. Second, arecovery of blue whales despite the impact of Antarctic minke whales on krill resources and its resultant decrease
the abundance of Antarctic minke whale. Finally, their model’s result showed that the Antarctic minke whale
population decreases gradually, on the other hand, blue whale population increases gradually, both populations
returning to their original population level.
Results in this study suggest that Antarctic minke whales play an important role within current ecosystem of the
Antarctic during austral summer. Some results of JARPA suggest there are some changes of krill availability of
Antarctic minke whale in recent years (Konishi and Tamura, 2005, Bando et al., 2005, Zenitani and Kato, 2005),
the pursuit of the cause and future prediction of baleen whale stock dynamics are important in future. At the sametime, the ecosystem is changing due to the change of krill availability to them. These data collected during JARPA
surveys of scientific whaling were needed to understand the ecosystem of Antarctic, and should be collected
continuously to follow the future ecosystem change. We should conduct comparative research on the seasonal,
local and annual distribution and abundance of cetaceans and their prey and the monitoring of their feeding habits.
Further studies on these modeling and long-term monitoring researches would clarify the interaction of major
predator such as baleen whales (Antarctic minke, fin, humpback, blue whale) and krill in the Antarctic.

ACKNOWLEDGMENTS
We thank Dr. Hidehiro Kato, Dr. Yoshihiro Fujise, Mr. Kazuo Yamamura, late Dr. Fujio Kasamatsu, Mr.
Shigetoshi Nishiwaki and Mr. Hajime Ishikawa, research leaders of these cruises for giving us the opportunity tocarry out this study. The stomach contents examined in this study were collected by many researchers and crews.
We also thank the captains, crews and researchers who were involved in the JARPA research cruises for theirefforts. We thank Mrs. Ryoko Zenitani, Mr. Takeharu Bando and Dr. Yoshihiro Fujise for providing us maturity
data of Antarctic minke whales sampled. We thank Mrs. Ikuyo Kouda for her helpful analyzing of the stomach
contents. Our sincere thank to Dr. Hiroshi Hatanaka, Dr. Luis A. Pastene of the Institute of Cetacean Research
7

(ICR) and Dr. Hidehiro Kato, Dr. Taro Ichii of the National Research Institute of Far Seas Fisheries for theirvaluable suggestions and useful comments on this paper.

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8

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Table 1. Areas, years of surveys and sample size used in this study
Area III-East
1995/9669
41
110

1997/9874
36
110

1999/00
63
46
109

2001/0254
56
110

2003/04
62
48
110

Male
FemaleTotal

1987/88
153
119
272

1989/90
184
142
326

1991/92
165
123
288

1993/94
200
130
330

1995/96
204
126
330

Male
FemaleTotal

1997/99
205
123
328

1999/00
170
160
330

2001/02
147
183
330

2003/04
138
192
330

Total
1,566
1,298
2,864

Male
FemaleTotal

1988/8985
151
236

1990/91
164
159
323

1992/93
167
160
327

1994/95
200
130
330

1996/97
132
198
330

Male
FemaleTotal

1998/99
207
122
329

2000/01
186
144
330

2002/03
168
162
330

Total
1,309
1,226
2,535

1998/9940
20
60

2000/01
72
38
110

2002/03
67
43
110

Male
FemaleTotal
Area IV

Area V

Area VI-West
Male
FemaleTotal

1996/97
74
36
110

10

Total
253
137
390

Total
322
227
549

Table 2. Prey species found in the stomachs of Antarctic minke whales sampled by the JARPA
species
Main prey
Amphipoda
Krill

PiscesParathemisto gaudichaudi
Euphausia superba
E. crystallorophias
E. frigida
Thysanoessa macrura
Pleuragramma antarcticum

Miner prey
Pisces
Notolepis coatsi
Electona antarctica
Chionodraco sp.
Notothenis sp.

Table 3. Composition of main prey found in the stomachs of Antarctic minke whales sampled
by JARPA surveys
Area III-East
Year
Number1995/96 1997/98 1999/00 2001/02 2003/04
110
110
109
110
110

(Main prey)
Krill
Ampipods
Fish
%
Krill
Ampipods
Fish

66
0
0

71
0
0

75
0
0

90
0
0

86
0
0

100.0
0
0

100.0
0
0

100.0
0
0

100.0
0
0

100.0
0
0

Empty
%
Broken

28
29.8
16

36
33.6
3

18
19.4
16

11
10.9
9

12
12.2
12

Area IV
Year
Number1987/88 1989/90 1991/92 1993/94 1995/96 1997/98 1999/00 2001/02 2003/04
272
326
288
330
330
328
330
330
330

(Main prey)
Krill
Ampipods
Fish
%
Krill
Ampipods
Fish

210
0
0

171
0
0

208
0
0

253
0
0

173
0
0

206
0
0

206
0
0

244
1
0

186
1
0

100.0
0
0

100.0
0
0

100.0
0
0

100.0
0
0

100.0
0
0

100.0
0
0

100.0
0
0

99.6
0.4
0

99.5
0.5
0

Empty
%
Broken

49
18.9
13

134
43.9
21

66
24.1
14

65
20.4
12

136
44.0
21

103
33.3
19

89
30.2
35

66
21.2
19

123
39.7
20

11

Table 3. Continued
Area VI-WestYear
Number

1996/97 1998/99 2000/01 2002/03
110
60
110
110

(Main prey)
Krill
Ampipods
Fish
%
Krill
Ampipods
Fish

65
0
0

28
0
0

76
0
0

46
0
0

100.0
0
0

100.0
0
0

100.0
0
0

100.0
0
0

Empty
%
Broken

37
36.3
8

26
48.1
6

23
23.2
11

58
55.8
6

Area VYear
Number1988/89 1990/91 1992/93 1994/95 1996/97 1998/99 2000/01 2002/03
236
323
327
330
330
329
330
330

(Main prey)
Krill
Ampipods
Fish
%
Krill
Ampipods
Fish

159
0
0

230
1
3

214
0
0

243
1
0

193
0
0

213
0
0

256
1
1

227
0
0

100.0
0
0

98.3
0.4
1.3

100.0
0
0

99.6
0.4
0

100.0
0
0

100.0
0
0

99.2
0.4
0.4

100.0
0
0

Empty
%
Broken

67
29.6
10

75
24.3
14

85
28.4
28

75
23.5
11

113
36.9
24

91
29.9
25

57
18.1
15

86
27.5
17

12

Table 4. Wet weight composition (%) of krill found in the stomachs of Antarctic minke whales
sampled by JARPA surveys
Area III-East
Year
Species / Number
Krill
Euphausia superba
E. crystallorophias
E. frigida
Thysanoessa macrura

1995/96 1997/98 1999/00 2001/02 2003/04
63
80
107
28
35
100.0

97.5
0.6
1.9

100.0

100.0

100.0

Area IVYear
Species / Number

1987/88 1989/90 1991/92 1993/94 1995/96 1997/98 1999/00 2001/02 2003/04
55
45
164
138
182
180
96
75

Krill
Euphausia superba
E. crystallorophias
E. frigida
Thysanoessa macrura

98.0
1.8

97.8
2.2

97.6
0.6
0.01
1.8

0.2

87.7
8.8

96.0

96.1

90.7
8.3

97.5

3.5

4.0

3.9

0.9

2.5

Area VYear
Species / Number
Krill
Euphausia superba
E. crystallorophias
E. frigida
Thysanoessa macrura

1988/89 1990/91 1992/93 1994/95 1996/97 1998/99 2000/01 2002/03
69
33
142
162
163
139
95
71
88.2
7.5
1.4
2.9

86.0
10.7

81.8
16.5

88.9
3.1

85.1
10.4

97.1
0.7

69.2
27.6

3.3

1.7

8.0

4.5

2.2

3.2

Area VI-WestYear
Species / Number
Krill
Euphausia superba
E. crystallorophias
E. frigida
Thysanoessa macrura

1996/97 1998/99 2000/01 2002/03
80
40
56
23
94.4

98.8

89.3

82.6

5.6

1.3

10.7

17.4

13

97.3
2.7

Table 5. Daily prey consumption of Antarctic minke whales using method-1
Sex

Maturity Body weight
(kg)
Male
Immature
2,900
Mature6,800
Female Immature
3,800
Mature8,100

Method-1
(%)
(kg)
3.7
124.7
3.7
292.4
3.7
163.4
3.7
348.3

(kg)
107.3
251.6
140.6
299.7

(%)
4.3
4.3
4.3
4.3

Table 6. Daily prey consumption of Antarctic minke whales using method-2
Sex

Maturity

Body

Body

FMR

Immature
MatureFemale Immature
Maturelength
(m)
6.2
8.4
6.7
8.9

weight
(kg)
2,900
6,800
3,800
8,100

(KJ/day) deposition deposition deposition(KJ/day) (KJ/day) (KJ/day)
365,400 70,781
21,55375,955544,000 164,064
43,046
168,901
478,800 151,158
13,930112,529
648,000 326,204
37,102
173,280

Male

Blubber

MuscleFat

Reproduction
cost(KJ/day)

189,000

Daily prey consumption(KJ/day)
635,345
1,095,252
900,497
1,635,221(kg/day)
142.0
244.9
201.3
365.6

(%)
4.9
3.6
5.3
4.5

Table 7. Abundance and prey consumption of Antarctic minke whales and feeding impact on
Antarctic krill resources estimating by JARPA data in Area IV and V between
1998/99 JARPA and 2003/04 JARPA
StratumYear(inds.)

Prey consumption（million ton）

Krill biomass（million ton）

Feeding impact(％）

AbundanceIV

1999/00
2001/0244,572
61,463

1.3
1.9

36.4
38.1

3.7
4.9

V

2000/01
2002/03

148,509
163,593

4.8
5.2

18.7
21.0

25.8
24.8

14

Area III-East

Area III-East

Area IV

Fig.1-a.

Distribution of fish and amphipods consumed by Antarctic minke whales in
Area III-East and IV (● and 〇 : Fish, ▲ and △ : Amphipods)

15

Area V

Area VI-West

Fig.1-b.

Distribution of fish and amphipods consumed by Antarctic minke whales in
Area V and VI-West (● and 〇 : Fish, ▲ and △ : Amphipods)

16

Area IIIArea IV

Fig.2-a.

Distribution of krill consumed by Antarctic minke whales in Area III-East and IV(●: Euphausia. superba, 〇: E. crystarollophias, △: Thysanoessa spp.,□: E. S. + others, ×: E. spp.)

17

Area VI-West

Fig.2-b.

Area V

Distribution of krill consumed by Antarctic minke whales in Area V and VI-West(●: Euphausia. superba, 〇: E. crystarollophias, △: Thysanoessa spp.,□ : E. S. + others, ×: E. spp.)

18

100
75

%

50
25
0
3

5

7

9

11

13

15

17

19

21

Ho u rFig. 3.

Relationships between freashness categories for prey and time periods in Antarctic(F: fresh, fff: lightly digested, ff: moderately digested, f: heavily digested,

1 .2
1 .0

%

0 .8
0 .6
0 .4
0 .2
0

5

10

15

20

Ho u rFig. 4.

Change in the mean mass ± S.E. of stomach content with time.
Weight expressed as percentage of Antarctic minke whale body mass.

19:Empty)Area IV
*Mature male*Mature female

140.0

140.0
y = -3.2868x + 6646.1
R2 = 0.7873

120.0

y = -5.9346x + 11942
R2 = 0.7913

120.0

100.0
kg

kg

100.0

80.0

80.0

60.0

60.0

40.0
1990

1992

1994

1996

1998

2000

2002

40.0
1990

2004

1992

1994

1996

Year

1998

2000

2002

2004

Year

Area V*Mature male*Mature female
140.0

120.0

120.0

100.0

100.0

y = -3.6764x + 7424.1
R2 = 0.6431

kg

kg

140.0

80.0

80.0

60.0

60.0

40.0
1988

1990

1992

1994

1996

1998

2000

2002

40.0
1988

2004

Year

Fig. 5.

1990

1992

1994

1996

1998

2000

2002

2004

Year

Yearly changes in the mean mass of stomach content. Data used in 63-67oS andJanuary and February.

20

*MaleBlubber mass (tonnes)

2.5
2.0
1.5
1.0
0.5
0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

9.0

10.0

11.0

Body length (m)*FemaleBlubber mass (tonnes)

2.5
2.0
1.5
1.0
0.5
0.0
4.0

5.0

6.0

7.0

8.0

Body length (m)Fig. 6.

The blubber mass (tonnes) as a function of body length (m) in Antarctic minke whale,
which were sampled in December and March. The equations describing the linear
regressions were as following. Male: (December 〇 , n=156: y=0.29x-1.19, r2=0.84;
March ●, n=71: y=0.37x-1.59, r2=0.87), Female: (December 〇, n=94: y=0.33x-1.42,
r2=0.91; March ●, n=66: y=0.42x-1.92, r2=0.87).

21

*MaleMuscle mass (tonnes)

6.0

4.0

2.0

0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

9.0

10.0

11.0

Body length (m)*FemaleMuscle mass (tonnes)

6.0

4.0

2.0

0.0
4.0

5.0

6.0

7.0

8.0

Body length (m)Fig. 7.

The muscle mass (tonnes) as a function of body length (m) in Antarctic minke whales,
which were sampled in December and March. The equations describing the linear
regressions were as following. Male: (December 〇, n=156: y=0.97x-4.53, r2=0.87;
March ●, n=71: y=1.04x-4.77, r2=0.89), Female: (December 〇, n=94: y=0.89x-3.99,
r2=0.93; March ●, n=66: y=0.99x-4.56, r2=0.89).

22

*MaleBody mass (tonnes)

12.0

8.0

4.0

0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

9.0

10.0

11.0

Body length (m)*FemaleBody mass (tonnes)

16.0
12.0
8.0
4.0
0.0
4.0

5.0

6.0

7.0

8.0

Body length (m)Fig. 8.

Total body mass (tonnes) as a function of body length (m) in Antarctic minke whales,
which were sampled in December and March. The equations describing the linear
regressions were as following. Male: (December 〇, n=816: y=1.68x-7.49, r2=0.89;
March ●, n=473: y=1.87x-8.33, r2=0.89), Female: (December 〇, n=503: y=1.77x8.05, r2=0.94; March ●, n=375: y=1.90x-8.60, r2=0.89).

23

24

East

East

West

StratumMF

83,734

2000/01

2002/03

MM

IF

MF

6.0

48.0 10.0 36.0

17.1 50.7 13.6 18.6

IM
5,024

3,267

IM

5,335
4,073
3,062

1,456

IM
2,589
8,118
5,308
4,228

40,192

9,665
8,373

2,586

Abundance (inds.)
MMIF

12,293
9,998
7,289

7,606

Abundance (inds.)
MM
IF

0.32
0.23

0.39

0.24

0.11
0.09

0.16

0.05

0.37
0.44

0.41

0.18

0.85
0.80

1.05

0.50

30,144 2,900 6,800 3,800 8,100 124.7 263.0 168.4 337.9

0.20
0.16

0.08

1.53
0.91

1.27

0.21
0.22

0.17

2.32
1.18

1.22

4.26
2.48

2.73

Body weight （kg）
Daily prey consumption （kg）Annual consumption in Antarctic（million ｔon）
IM MM
IF
MF
IM MM
IF
MF
IM
MM
IF
MF
Total
2,900 6,800 3,800 8,100 124.7 263.0 168.4 337.9 0.05
0.30
0.05
0.14
0.55

0.06
0.05

9,011 2,900 6,800 3,800 8,100 124.7 263.0 168.4 337.9
10,934 2,900 6,800 3,800 8,100 124.7 263.0 168.4 337.9

MF
3,539

0.08

Daily prey consumption （kg）Annual consumption in Antarctic（million ｔon）
IM MM
IF
MF
IM
MM
IF
MF
Total
0.02

Body weight （kg）
MM
IF
MF

2,900 6,800 3,800 8,100 124.7 263.0 168.4 337.9

4,531

IM

10,205 2,900 6,800 3,800 8,100 124.7 263.0 168.4 337.9

MF

129,452 10.5 37.4 7.9 44.2 13,627 48,374 10,220 57,231 2,900 6,800 3,800 8,100 124.7 263.0 168.4 337.9
79,859 13.5 36.1 13.9 36.5 10,764 28,819 11,111 29,166 2,900 6,800 3,800 8,100 124.7 263.0 168.4 337.9(inds.)
19,057

2000/01
2002/03IF

47.0 16.0 28.0

MM

14.8 34.2 22.6 28.4
14.3 35.2 18.7 31.7
12.0 28.6 16.6 42.9

9.0

IM

Abundance Sexual maturity （％）

2001/02
1999/00
2001/02

Year

35,95028,39025,513

1999/00

West* Area V(inds.)
16,182Abundance Sexual maturity （％）

Year

Stratum* Area IV

Appendix 1. Total prey consumption and the estimations of feeding impact on krill resources by Antarctic minke whales in Area IV and V between 1999/00 and 2002/03.