SC/F14/J15

Prey composition and consumption rate by Antarctic minke
whales based on JARPA and JARPAII data
TSUTOMU TAMURA AND KENJI KONISHI
The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan
Contact e-mail: tamura@cetacean.jp

ABSTRACTIn this study, the information on the feeding habits of Antarctic minke whales (Balaenoptera bonaerensis) sampled during the surveys of
the Japanese Whale Research under Special Permit in the Antarctic (JARPA and JARPAII), for the period of 1987/88–2010/11 aresummarized. Some of the analyses considered recommendations offered during the 2006 JARPA final review meeting (e.g. those related tothe duration of the feeding period, digestion rate and examination at smaller spatial scales). We compared the feeding habits of the
Antarctic minke whales during the JARPA period (1987/88–2004/05) and the JARPAII period (2005/06–2010/11). The Antarctic minke
whales fed mostly on Antarctic krill (Euphausia superba) in offshore areas, and on ice krill E. crystallorophias in coastal (shallow) areas
on the continental shelf of the Ross Sea and Prydz Bay. The whales fed mainly before 5AM suggesting that feeding activity decreases
early in the day. The daily prey consumption was estimated using two independent methods, which were from theoretical energy
requirement calculations and from diurnal changes of stomach contents’ mass. The daily prey consumptions of Antarctic minke whales per
capita during the feeding season based on these two methods were 95.1–127.0 and 182.6–250.3kg for immature and mature males, 125.8–
138.7 and 268.1–325.5kg for immature and mature females, respectively. This is equivalent to 2.65-4.02% of their body weight. The daily
prey consumption per capita decreased between the JARPA period and the JARPAII period based on the results of the method of thediurnal change in stomach contents’ mass, for all sexual classes. The seasonal prey consumptions for all Antarctic minke whales in the
total research area was 3.51-3.98million tons, and this amounted to 7.6-8.6% of the krill biomass estimated by acoustic survey in the total
research area. These results related to prey consumption are useful as input data for the development of ecosystem models.
KEYWORDS: FEEDING; ENERGETICS; FOOD/PREY; MODELLING; SCIENTIFIC PERMITS; ANTARCTIC; ANTARCTICMINKE WHALE

INTRODUCTION
The Antarctic minke whale (Balaenoptera bonaerensis), which grows up to 10m (Horwood, 1990), is the mostabundant balaenopterid species in the Southern Ocean with abundance estimated at 515,000 animals south of 60°S in
austral summer (95% CI:360,000–730,000). These estimates were based on sighting data collected between the 1992/93
and 2003/04 seasons (IWC, 2013). Like other balaenopterid species (except the Bryde’s whale B. edeni) the Antarctic
minke whale spends its breeding season at lower latitudes in austral winter and migrates to the Southern Ocean to feedin austral summer (Horwood, 1990; Kasamatsu et al., 1995). The Antarctic minke whale feeds mainly on Antarctic krill(Euphausia superba) in offshore waters (Kawamura, 1980; Bushuev, 1986; Ichii and Kato, 1991), and on ice krill (E.
crystallorophias) on the coastal shelf along such areas as the Ross Sea and Prydz Bay (Bushuev, 1986; Tamura andKonishi, 2009).
Previous studies estimated the daily prey consumption by Antarctic minke whales in the Southern Ocean on the basis ofenergy-requirement calculations (Lockyer, 1981a; Armstrong and Siegfried, 1991; Reilly et al., 2004). None of thesestudies considered the fact that whales’ conditions change with the progression of the feeding season. It is known thatbaleen whales store energy in their blubber and internal fat in the feeding season. Therefore, for the estimation of prey
consumption, it is important to assess the energy storage during the feeding season of Antarctic minke whales.
In the 2006 JARPA review, the meeting recommended additional analyses to consider factors such as: i) determinationof the duration of the feeding period; ii) examination at smaller spatial scales; iii) using multivariate analysis to examine
trends, incorporating covariates such as age, size and reproductive status of whales as well as the date and time of day.
Furthermore in 2007 the IWC/SC summarized the three issues that would need to be addressed i) the length of thefeeding season; ii) to what extent consumption rate is sensitive to digestion rate; and iii) the extent of feeding at night(IWC, 2008). The recommendation on multivariate analysis was addressed by Konishi et al. (2008), Konishi and
Butterworth (2013), Konishi and Walloe (2014a, b) and Skaug (2012). In the present study we addressed the issues of
feeding period, examination at smaller spatial scales and the effect of digestion rate.
In this paper, we summarize the results of monitoring the feeding ecology of whales, which is part of the first objectiveof JARPAII. The feeding habits and daily prey consumption by Antarctic minke whales is examined based on a large
data set obtained during the research surveys of the JARPA (1987/88-2004/05) and JARPAII (2005/06–2010/11). It is
expected that the output of this study will assist in understanding the role of whales in the ecosystem and thedevelopment of ecosystem models for management purposes (see Kitakado et al., 2014).
1

MATERIALS AND METHODS
Research area, periods and number of samples
Data used in the present study was collected during the surveys of the JARPA and JARPAII in the International
Whaling Commission (IWC) Antarctic management Areas III-East (35°-70°E), IV (70°-130°E), V (130°E-170°W
including the Ross Sea) and VI-West (170°-145°W), south of 60°S (JARPA) and 62°S (JARPAII) (Fig. 1). The
northern boundary of the Ross Sea was fixed at 70°S in Area V and VI. The surveys were conducted in the australsummer seasons (December-March) of the 1987/88-2004/05 (JARPA) and the 2005/06-2010/11 (JARPAII) seasons.
During the surveys a total of 10,042 Antarctic minke whales were sampled. Table 1 shows the number of samples
divided by Area and sex. After sampling, whales were brought to the research base vessel where the animals were
examined by a biologist onboard. All whales were sampled during daylight hours, between 06:00 and 19:00h (Shiptime).
Sighting and sampling methods
The survey track line was designed along each 10 degree longitudinal width interval in principle. The survey starting
point was randomly selected from the arrangement of the survey track line and longitude standard lines in the survey.
Sighting procedures were the same as in the previous JARPA surveys (Nishiwaki et al. 2006, 2014). The survey was
operated under optimal research conditions (when the wind speed was below 25knots in the south strata and below
20knots in the north strata, and when visibility was more than 2n.miles). SSVs advanced along parallel track lines
7n.miles apart from each other at a standard speed of 11.5knots.
Treatment of stomach contents
All balaenopterid species have four chambered stomach compartments (Hosokawa and Kamiya, 1971; Olsen et al.,1994). Stomach contents were removed from each compartments and weighed to the nearest 0.1kg. The analysis of prey
consumption in this study was based on data collected from the first compartment (forestomach) and second
compartment (fundus). To examine the daily feeding rhythms of the minke whale, the freshness of prey in theforestomach was categorized into four digestion levels:
F = fresh (prey not affected by digestion),
fff = lightly digested (prey slightly affected by digestion),
ff = moderately digested (prey moderately to highly fragmented), andf = heavily digested (unidentifiable remains or indigestible parts only).
Because of the uniformity of prey within the stomachs of almost all whales, after checking the stomach contents,
some fresh prey (200g) in the forestomach or fundus were collected and stored in 10% formalin for species
identification at the laboratory. Prey species were identified to the lowest taxonomic level possible using external
morphology (Barnard, 1932; Fischer and Hureau, 1985a, b; Baker et al., 1990).
Biological data
An estimate of the daily prey consumption requires the use of some additional biological and morphometric data. Body
length of the whales was measured to the nearest 10cm from the tip of the upper jaw to the deepest part of the fluke
notch in a straight line. Body weight was measured using large weighing machine to the nearest 50kg. For someindividuals, muscle, blubber and internal organs were weighed for calculating the energy deposited during the feeding
season. A correction factor for blood loss was not calculated in this study. Energy requirements are different fordifferent sexual maturity classes; therefore, estimations of the daily prey consumption in this study took into
consideration information on sexual maturity. Sexual maturity of Antarctic minke whales was defined in accordancewith Ohsumi and Masaki (1975) and Kato (1986). Males with a single testis weight of 400g or more were defined as
sexually mature. Females with at least one corpus luteum or albicans in their ovaries were defined as sexually mature.
Analytical procedure of the daily prey consumption
The amount of krill consumed by Antarctic minke whales was estimated using two independent methods, which werefrom theoretical energy requirement calculations (method-1) and from diurnal changes of stomach contents (Total offorestomach (1st. stomach) and fundus (2nd. stomach)) (method-2).
Method-1 Estimation of daily consumption of krill from the standard metabolism
The daily prey consumption (Dkg) in each sexual maturity class was estimated from the standard metabolic rate (SMRkJ)and energy deposit according to the following equations:Male or Immature female : Dkg =(SMRkJ + EDkJ) / EKJ(1)Mature female(2): Dkg = (SMRkJ + EDkJ+RkJ) /EKJ
2

Where Dkg is daily prey consumption (kg day-1), SMRkJ is the standard metabolic rate (kJ day-1), EDKJ is Energy
deposition (kJ day-1), R is Reproduction cost (kJ kg-1) and EkJ is the caloric value of prey species (kJ kg-1). The details ofthese items are described as follows:
1) SMRkJ (Standard metabolic rate)
To account for energy spent on activities such as foraging, moving between food patches and migration thestandard metabolic rate (SMRkJ) was calculated using the following equation (Markussen et al., 1992):
SMRkJ=1.45×BMR×4.184 (kJ day-1)(3)

The basal metabolic rate (BMR) was calculated following the Kleiber's equation (Kleiber, 1961):
BMR=70M0.75 (kcal day-1)(4)

where M is the Antarctic minke whale body weight (kg). The figure 1.45 is the coefficient for energy spent on
activities such as foraging, moving between food patches and migration. The figure 4.184 is the coefficient value
from Kcal to KJ. The average body lengths of Antarctic minke whales were 6.5 and 8.4m for immature and mature
males and 6.7 and 8.9 m for immature and mature females, respectively.
2) EDkJ (Energy deposited during feeding season in Antarctic)
The total muscle, blubber and internal organs weight of some Antarctic minke whales were weighed to calculateseasonal growth and fat deposition. In this study, the deposition was converted to energy deposition by measuring
the energy density of samples of muscle and blubber of some whales sampled in the early and late seasons during
austral summer by bomb calorimeter (n=1 in each sexual category). The weight of others’ fat deposition (e.g.
internal organs) was estimated to deduct the weight of blubber deposition and the weight of muscle deposition
from total body weight.
3) RKJ (Reproduction cost)
The RKJ for a female Antarctic minke whale was calculated by Lockyer (1981a) to be 1.89×106kJ, assuming thatthe length at birth is 273cm (Best, 1982). We assumed that almost all mature females were pregnant, and that all
reproduction costs were during feeding season (120 days). The RKJ for a female Antarctic minke whale wascalculated to be 15.8×104kJ per day.
4) EKJ (Energy value of Euphausia superba)
Antarctic minke whales feed mainly on E. superba. The energy value is 4,473kJkg-1. In this study, this value wasmeasured by bomb calorimeter (n=1). We assumed the same value for other prey items such as E. crystallorophias.
Lockyer (1981a) estimated that Antarctic minke whales had an assimilation efficiency of 84%. We used the samevalue of assimilation efficiency for calculating the daily prey consumption. Therefore, the energy value of prey
items of whales was estimated to be 3,757kJ kg-1.
5) Feeding period (residence days in the feeding ground)
The encounter rate (as a simple index of distribution density) of Antarctic minke whales in the Antarctic increased
from early November to late December and peaked in January, followed by a steady decrease through February(Kasamatsu et al., 1996). Lockyer (1981a, b) estimated the residence days of immature animals and mature males
to be 90 days in the feeding ground, while mature females spent 120 days in the feeding ground. Antarctic minke
whales were tagged for the first time in 2013 during the survey of the Southern Ocean Research Partnership(SORP). Their movement patterns are in the process of being analysed and include a variety of movement patterns.
While some animals remained in close proximity to near-shore bays for over 120 days, other whales moved fromthe Antarctic Peninsula into both the Weddell Sea to the north and east and the Bellingshausen Sea to the south andwest (Bell, 2013). Based on the results of these studies, we also assumed that they moved southward in November
and northward in March. We also assumed that immature animals and mature males spend 90days, and mature
females spend 120days, respectively, the same as Lockyer’s (1981a, b) assumptions. The total prey consumption
during the feeding period (SDkg) was applied as follows:
Immature animals and mature males: SDkg = 90 Dkg(5)

Mature females: SDkg = 120 Dkg(6)Method-2 Estimation of daily consumption of krill from diurnal change in stomach contents mass
Miura (1969) proposed a method for estimating daily prey consumption from diurnal changes in stomach contents mass(Vi) with the passage of time based on a known digestion rate in the stomach. If the proportion of prey digested during
an interval is d, and the proportion of undigested prey (S) is 1-d, the amount of prey consumed (Ci) is given by thefollowing equations:(7-1)
t1: C1=V1(7-2)
t2: C2=V2-SV1(7-3)
t3: C3=V3-SV2-S2V1
3

ti: Ci=Vi-SVi-1-S2Vi-2…Si-1V1

(7-4)
k

Therefore, the daily prey consumption (∑ C ) is given by:
i =1

k

∑

C i = V1i =1i(1 − 2 S + S k )(1 − 2 S + S k −1 )+ V2+‥+ V k −1 (1 − S ) +‥+ V k
1− S
1− S

(7-5)

In this study, we calculated the mean stomach contents (forestomach and fundus stomach) mass as % of body mass (Vi)at 1 hour intervals based on the stomach contents mass (kg) and body mass (kg). Nordøy et al. (1995) showed that krill
were digested by bacterial fermentation, and that this digestion process was very rapid. Assuming that it takes 4 hours
for prey to be digested in the stomach of Antarctic minke whales (Bushuev, 1986) and that d is exponential (Elliott andPersson, 1978), we estimated S to be 0.82, if the proportion of undigested prey in the stomach after 4 hours is 45%(Appendix 1). We estimated the daily prey consumption of krill from diurnal change in stomach contents’ mass inresearch areas excluding the Ross Sea of JARPA and JARPAII periods. We eliminated the data with less than 10
samples in each hourly interval.
Estimation of seasonal prey consumption in Areas III east, IV, V and VI west
The seasonal prey consumption for all Antarctic minke whales in the research area was estimated using information onabundance and residence days in the feeding ground. The information on abundance of Antarctic minke whales was
described in Hakamada and Matsuoka (2014). The abundance of Antarctic minke whales without taking model error
into account was applied in this study. The seasonal prey consumption of Antarctic minke whales in each area wasapplied using the results of Method-1 and Method-2 in the JARPAII period.
We estimated the seasonal prey consumption for all Antarctic minke whales in the research area from 2007/2008 to
2008/09 seasons. Furthermore, we also compared seasonal prey consumption of Antarctic minke whales with krill
biomass in each sub area of the Antarctic from 2007/2008 to 2008/09 seasons. The krill biomass in Areas III east, IV, V
and VI west was estimated by acoustic survey (Wada and Tamura, 2014).
RESULTS
Prey species composition
A total of ten prey species, one amphipod (Parathemisto gaudichaudi), four euphausiids (Euphausia superba, E.
crystallorophias, E. frigida, Thysanoessa macrura) and five fishes (Pleragramma antarcticum, Notolepis coatsi,
Electona antarctica, Chinodraco sp.and Notothenis sp.), were identified from the stomachs of the Antarctic minke
whales (Table 2). The Antarctic krill was the dominant prey species, 66–100% of the weight composition of the whale
stomachs examined in each area (Table 3, Figs. 2a, b), followed by ice krill, two euphausiids (E. frigida, T. macrura),
one amphipod (P. gaudichaudi) and one fish species (P. antarcticum). The frequency of occurrence of ice krill in theRoss Sea decreased between the JARPA period and JARPAII period (Table 3).
Diurnal changes in feeding activity
The composition of freshness categories and the diurnal change in the mean of the ratio of stomach contents weight tobody weight, expressed as a percentage (RSC), is shown in Figs. 3 and 4. These figures show that the proportion of
fresh and lightly digested categories and the RSC gradually decreased from early morning to afternoon. After 19:00 h,
the fresh categories and the weight of the mean stomach contents showed a slight increase in the survey area north of
70ºS. In the Ross Sea, there was no trend for the proportion of fresh and lightly digested categories and the RSC.
Stomach contents weight and RSC
The average and maximum weight and the ratio of stomach contents weight to body weight, expressed as a percentage(RSC) of fresh or lightly digested stomach contents (freshness category F and fff) by different reproductive classes areshown in Table 4. During the JARPA seasons, the average weight and RSC were 36.6±28.5kg (RSC:1.0%) and
43.6±31.8kg (RSC:1.1%) for immature males and females, respectively and 75.5±50.3kg (RSC:1.1%) and 77.1±55.0kg(RSC:1.0%) for mature males and females, respectively. The maximum weight and RSC were 130.8kg (RSC:3.1%) and
156.0kg (RSC:3.4%) for immature males and females, respectively and 343.8kg (RSC:4.2%) and 326.9kg (RSC:3.6%)
for mature males and females, respectively. While, during the JARPAII seasons, the average weight and RSC were33.2±28.3kg (RSC:0.8%) and 37.6±29.1kg (RSC:0.9%) for immature males and females, respectively and 63.5±47.1kg(RSC:0.9%) and 71.8±54.3kg (RSC:0.9%) for mature males and females, respectively. The maximum weight and RSC
were 142.4kg (RSC:2.4%) and 136.9kg (RSC:3.0%) for immature males and females, respectively and 387.0kg(RSC:3.8%) and 301.6kg (RSC:4.0%) for mature males and females, respectively. The average weight and RSC
decreased between the JARPA period and the JARPAII period for all sexual classes.

4Per capita daily and seasonal prey consumption by sex and maturity
Method-1 Estimation of daily consumption of krill from the standard metabolism
Body weight of whales
We calculated the average body length and weight during the JARPA and the JARPAII. The average body lengths were
6.5±0.9 (Average±S.D) and 8.4±0.4m for immature and mature males, and 6.7±1.0 and 8.9±0.4m for immature andmature females, respectively. The mean body weight was 3,500±1,400 and 6,900±1,000kg for immature and mature
males, and 3,800±1,600 and 8,100±1,200kg for immature and mature females, respectively. SMRkJ of immature andmature males were 193×103 and 322×103kJ, respectively. SMRkJ of immature and mature females were 206×103 and363×103kJ, respectively (Table 5).
Energy deposited during feeding season
Fig. 5 shows the relationship between blubber weight (t) and body length (m), classified by sex and maturity class.
Immature and mature males had an increase in blubber energy contents per day of 79,866kJ and 162,664kJ, respectively.
Immature and mature females had an increase in blubber energy contents per day of 144,620kJ and 303,619kJ,
respectively (Table 5). Fig. 6 shows the relationship between muscle weight (t) and body length (m), by sex andmaturity class. Immature and mature males had an increase in muscle energy contents per day of 29,353kJ and 50,245kJ,
respectively.
Immature and mature females had an increase in muscle energy contents per day of 20 088kJ and 31,175kJ, respectively(Table 5). The weight of the fat deposition of other parts (e.g. internal organs) was estimated to deduct the weight ofblubber deposition and the weight of muscle deposition from the total body weight (Figs. 5, 6 and 7). Immature andmature males had an increase in the fat energy contents of other parts per day of 54,693kJ and 151,704kJ, respectively.
Immature and mature females had an increase in muscle energy contents per day of 150,950kJ and 368,105kJ,
respectively (Table 5).
There was an increase in the energy density of blubber of males from 14,435 to 20,711kJ kg-1 (wet weight) and offemales from 16,443 to 28,075kJ kg-1 (wet weight) between December and March. There was also an increase in theenergy density of muscle in males from 5,858 to 6,234kJ kg-1 (wet weight) and in females from 5,941 to 6,192kJ kg-1
(wet weight) between December and March (Table 6). These results were obtained on the basis of the JARPA and
JARPAII data sets combined (amount of data of the JARPAII alone was small for this analyses).
Daily and seasonal prey consumption
The calculated daily energy requirements during feeding season were 425×103 and 817×103kJ for immature and mature
males, and 620×103and 1,456×103kJ for immature and mature females, respectively (Table 7).
When the mean prey energy value of 4,473kJ kg-1 and the assimilation efficiency of 84 % were considered, the daily
prey consumption during the feeding season was 95.1 and 182.6kg for immature and mature males, and 138.7 and325.5kg for immature and mature females, respectively. These values were equivalent to 2.70 and 2.65% of bodyweight for immature and mature males, and 3.65 and 4.02% of body weight for immature and mature females,
respectively (Table 7). The total prey consumption of Antarctic minke whale per capita during the feeding season was
8.6 and 21.9tons for immature and mature males, and 12.5 and 39.1tons for immature and mature females, respectively(Table 7).
Method-2 Estimation of daily consumption of krill from diurnal change in stomach contents mass
During the JARPA period, estimated rates of daily prey consumption were 3.63% of the body mass of Antarctic minke
whales. The daily prey consumption during the feeding season was 127.0 and 250.3kg for immature and mature males,
and 137.9 and 293.9kg for immature and mature females, respectively. The total prey consumption of Antarctic minke
whale per capita during the feeding season was 11.4 and 22.5tons for immature and mature males, and 12.4 and35.3tons for immature and mature females, respectively (Table 8).
During the JARPAII period, estimated rates of daily prey consumption were 3.31% of the body mass of Antarctic minke
whales. The daily prey consumption during the feeding season was 115.9 and 228.4kg for immature and mature males,
and 135.8 and 268.1kg for immature and mature females, respectively. The total prey consumption of Antarctic minke
whale per capita during the feeding season was 10.4 and 20.6tons for immature and mature males, and 11.3 and
32.2tons for immature and mature females, respectively (Table 8).
Seasonal prey consumption for all Antarctic minke whales in the research area
In Areas III east and IV in the 2007/2008 season, the abundance was estimated to be 9,406 and 14,739, respectively. In
Area V and VI west in the 2008/2009 season, the abundance was estimated to be 108,097 and 26,364, respectively(Table 9). In Area III east and IV in the 2007/2008 season, the krill biomass was estimated to be 6.6million tons and12.5million tons, respectively. In Area V and VI west in the 2008/2009 season, the biomass was estimated to be
24.0million tons and 3.4million tons, respectively (Table 9).
5

In Areas III east and IV in the 2007/2008 season, seasonal prey consumption of krill for all Antarctic minke whales in
the research area was estimated to be 0.17-0.19and 0.33-0.37million tons, respectively. On the other hand, in Areas V
and VI west in the 2008/2009 season, seasonal prey consumption of krill by Antarctic minke whales was estimated tobe between 2.51-2.88 and 0.50-0.54million tons, respectively (Table 9).
The seasonal prey consumption for all Antarctic minke whales in the total research area was 3.51-3.98million tons,
amounting to 7.6-8.6% of the krill biomass estimated by acoustic survey in the total research area (Table 9).

DISCUSSION
Diversity of prey species
The main prey species of Antarctic minke whales during austral summer were two krill species (Antarctic krill and ice
krill). Consumption of these species depended on the distributional difference of the krill species. The Antarctic minke
whales fed mostly on Antarctic krill in the offshore area, and ice krill in the coastal (shallow) area on the continental
shelf along such areas as the Ross Sea and Prydz Bay. Ice krill is a dominant euphausiid on the continental shelf(<1,000m), the occurrence of Antarctic krill increases close to the continental shelf break and further off the shelf(Thomas and Green, 1988). It is strongly suggested that Antarctic minke whales feed on local predominant prey species.
The frequency of occurrence of ice krill in the stomachs of Antarctic minke whales sampled in the Ross Sea changed
between the JARPA period and the JARPAII period. Regional differences of the prey species of minke whales mightreflect changes in the distribution of these prey species in the research area.
The diurnal feeding rhythm
Our results suggest that Antarctic minke whales have a diurnal feeding rhythm, with a primary peak early in themorning. This coincided with results of previous reports (Ohsumi, 1979; Bushuev, 1986). Other studies on common
minke whales (B. acutrostrata) in the Northern Hemisphere have shown a tendency for a diurnal feeding activity (Hauget al., 1997; Lindstrøm et al., 1998). In the eastern North Atlantic and western North Pacific, they do not feed at night(Folkow and Blix, 1993; Haug et al., 1997; Tamura, 1998). Our results showed that Antarctic minke whales fed on prey
easily and may reduce their feeding earlier in the day due to sufficient food intake. If they feed on prey fully at one
feeding time, they can satisfy their daily energy-requirement.
Whether or not the minke whales feed on prey at night needs to be confirmed using methodology such as the depth datalogger system in the future.
Daily prey consumption of Antarctic minke whales
Following a recommendation from the IWC SC the estimations of prey consumption in this study was carried out at
smaller spatial scales e.g. by management Areas in contrast with the previous study where the estimations were madefor the whole research area.
Previous estimates of daily prey consumption rates using respiratory allometry of male and female Antarctic minke
whales during the austral summer were 6.7 and 6.2% of body weight, respectively (Armstrong and Siegfried, 1991).
These estimates may be overestimates because those values would require a maximum of two feeding times per day forthe daily energy requirement. However, the results of this study indicated a range of maximum weight for the stomach
contents from 2.6 to 4.0% of their body weight. Furthermore, our study detected only one peak of the diurnal feedingrhythm. In this study estimates of the daily prey consumption rate (RSC) ranged from 2.7 to 4.0% of their body weight.
These values were similar to the estimates by Lockyer (1981b), Bushuev (1986) and Mori and Butterworth (2004).
Using the modelling approach, Mori and Butterworth (2004) indicate that the daily prey consumption rate of Antarctic
minke whales ranged from 3.0 to 5.0% of their body weight. The estimates from our energy requirement calculations
almost corresponded with the results of maximum weight of the stomach contents in the field data. Therefore, theseresults can be used with confidence as the estimation of daily prey consumption by Antarctic minke whales. In the 2006
JARPA review, we estimated daily prey consumption ranged from 2.67 to 4.95% of the body weight, while weestimated daily prey consumption ranged from 2.65 to 4.02% of the body weight in this study. We obtained the actual
data in this study by applying the actual digestion rate (see Appendix 1) for method 2 in the daily prey consumption
estimation. Tamura and Konishi (2006) assumed the digestion rate based on previous published reports. They assumed
that the proportion of undigested prey in the stomach after 4 hours was between 20% and 30%. The previous IWC SC
recommendation on digestion rate was addressed in this study (see Appendix 1). The proportion of undigested krill inthe stomach after 4 hours was 45%. This value was similar to those in Sekiguchi (1994). We applied this digestion rate
for method 2 in this study.
The average weight of stomach contents and RSC decreased between the JARPA period and the JARPAII period for all
sexual classes. Furthermore, the daily prey consumption based on method 2 decreased from 3.63% to 3.31% between
the JARPA period and the JARPAII period. Regression analyses clearly showed that blubber thickness, girth, fat weightand stomach contents weight have been decreasing for nearly 2 decades (Konishi and Walloe, 2014a, b). Our results

6indicate an increasing shortage of food for the Antarctic minke whales per capita during the JARPA and the JARPAII
period.
As the next step an assessment of geographical, seasonal and yearly changes in the energy requirements of Antarctic
minke whales should be investigated. The output from these analyses will be important for the development of
ecosystem models.
Uncertainties in the prey consumption estimates
Some uncertainties in the prey consumption estimates were discussed in some IWC/SC meetings (e.g. Tamura et al.,2009) and by Leaper and Lavigne (2007). The important parameters used for estimating prey consumption in this study
are the energy contents of prey, muscle and blubber of whales themselves. However, in this study, these values were
calculated on the basis of very few samples. To account for differences within the season a sufficient number ofsamples should be examined in the future.
Regarding the duration of the feeding period, we assumed 120days for mature females. Baleen whales are generally
known to migrate between feeding grounds in high latitudinal waters in summer and the breeding grounds in low
latitudinal waters in winter. This issue had some progress recently. Antarctic minke whales were tagged for the firsttime in 2013 by the Southern Ocean Research Partnership (SORP) surveys. Their movement patterns are in the processof being analyzed but include a variety of movement patterns. While some animals remained in close proximity to nearshore bays for over 120days, other whales moved from the Antarctic Peninsula into both the Weddell Sea to the northand east and the Bellingshausen Sea to the south and west (Bell, 2013). It might be possible in the future to provide
more information on residence time using satellite tagging.
Prey consumption as an input parameter for ecosystem modelling
At present there is little information about the consumption by other krill predators such as seabirds and pinnipeds inour study region for comparison with our results. Furthermore, krill biomass above 150m depth was used in this study(Wada and Tamura, 2014). It is a limitation for the echo sounder system. The value of krill biomass seems to be anunderestimate. If Antarctic minke whales can feed on prey deeper than 150m of depth, these values for the rates areoverestimates. The foraging diving depth of Antarctic minke whales has not been reported so we need information on
the foraging diving depth of Antarctic minke whales in the future.
Many parameters for application in the multi-species ecosystem modeling should be improved in the future (Kitakado etal., 2014). Improving estimates of the daily and seasonal consumption by Antarctic minke whales is also important. Our
results are useful to apply as the input data for the daily consumption by Antarctic minke whales for ecosystem-based
management.
As the next step, the assessment of geographical, monthly and yearly changes of the energy requirements of minke
whales is needed. This is needed for the comparison of krill resources and other krill predators’ distribution andconsumption.
ACKNOWLEDGMENTS
The stomach contents examined in this study were collected by many researchers and crews. We would like to thank thecaptains, crews and researchers who were involved in the JARPA and JARPAII research cruises for their efforts. We
appreciate very much the helpful analysis of the digestion experiment on krill by Chihiro Kobayashi. This work was apart of her master's thesis. Our sincere thanks also go out to Hiroshi Hatanaka and Luis A. Pastene of the Institute of
Cetacean Research (ICR) for their valuable suggestions and useful comments on this paper.

REFERENCES
Armstrong, A.J. and Siegfried, W.R. 1991. Consumption of Antarctic krill by minke whales. Antarctic Science, 3:13-8.
Baker, A.de C., Boden, B.P. and Brinton, E. 1990. A practical guide to the euphausiids of the world. Natural History Museum Publications London.
96pp.
Barnard, K.H. 1932. Amphipoda. Discovery Rep., 5:1-326.
Bell, E.M. 2013. Report of the Southern Ocean Research Partnership (SORP) conference and workshops, 31 May – 2 June 2013. Paper SC/65a/SH25
presented to the 65a IWC Scientific Committee, June 2013 (unpublished). 53pp. [Available from the Office of this Journal]
Best, P.B. 1982. Seasonal abundance, feeding, reproduction, age and growth in minke whale off Durban (with incidental observations from theAntarctic). Rep. int. Whal. Commn, 32:759-86.
Bushuev, S.G. 1986. Feeding of minke whales, Balaenoptera acutorostrata, in the Antarctic. Rep. int. Whal. Commn, 36:241-5.
Elliott, J.M., Persson, L. 1978. The estimation of daily rates of food consumption for fish. J. Animal Ecol. 47:977-91.
Fischer, W. and Hureau, J.C. (eds). 1985a. FAO species identification sheets for fishery purposes. Southern Ocean (Fishing areas 48, 58 and 88)(CCAMLA Convention Area). Prepared and published with the support of the Comission for the Conservation of Antarctic Marine Living Resources.
Rome, FAO., Vol. 1:1-232.

7

Fischer, W. and Hureau, J.C. (eds). 1985b. FAO species identification sheets for fishery purposes. Southern Ocean (Fishing areas 48, 58 and 88)(CCAMLA Convention Area). Prepared and published with the support of the Comission for the Conservation of Antarctic Marine Living Resources.
Rome, FAO., Vol. 2:233-470.
Folkow, L.P. and Blix, A.S. 1993. Daily changes in surfacing rates of minke whales (Balaenoptera acutorostrata) in Norwegian waters. Rep. int.
Whal. Commn, 43:311-4.
Hakamada, H. and Matsuoka, K. 2014. Estimates of abundance and abundance trend of the Antarctic minke whale in Areas IIIE-VIW, south of 60ºS,
based on JARPA and JARPAII sighting data (1989/90-2008/09). SC/F14/J3 (this meeting).
Haug, T., Nilssen, K.T., Lindstrom, U. and Skaug, H.J. 1997. On the variation in size and composition of minke whale (Balaenoptera acutorostrata)
forestomach contents. J. Northwest Atl. Fish. Sci. 22:105-14.
Horwood, J. 1990. Biology and exploitation of the minke whale. CRC Press, Inc., Boca Ration Florida. 238pp.
Hosokawa, H. and Kamiya, T. 1971. Some observations on the cetacean stomachs, with special considerations on the feeding habits of whales. Sci.
Rep. Whales Res. Inst., 23:91-101.
Ichii, T. and Kato, H. 1991. Food and daily food consumption of southern minke whales in the Antarctic. Polar Biol., 11:479-87.
International Whaling Commission. 2008. Report of the Intersessional Workshop to Review Data and Results from Special Permit Research on Minke
Whales in the Antarctic, Tokyo, 4-8 December 2006. J. Cetacean Res. Manage. (Suppl.) 10: 411-45.
International Whaling Commission. 2013. Report of the Scientific Committee. Annex G. Report of the Sub-Committee on In-depth Assessments. J.
Cetacean Res. Manage. (Suppl.) 14:195-213.
Jackson, S., Duffy, D.C. and Jenkins, J.F.G. 1987. Gastric digestion in marine vertebrate predators: in vitro standards. Funct. Ecol. 1:287-81.
Kasamatsu, F., Nishiwaki, S. and Ishikawa, H. 1995. Breeding areas and southbound migrations of southern minke whales Balaenoptera
acutorostrata. Mar. Ecol. Prog. Ser., 119:1-10.
Kasamatsu, F., Joyce, G.G., Ensor, P. and Mermoz, J. 1996. Current occurrence of baleen whales in Antarctic waters. Rep. int. Whal. Commn, 46:293304.
Kato, H. 1986. Study on changes in biological parameters and population dynamics of southern minke whales. Doctoral Thesis submitted to the
Hokkaido University. 145pp. (in Japanese).
Kawamura, A. 1980. A review of food of Balaenopterid whales. Sci. Rep. Whales Res. Inst., 32:155-97.
Kitakado, T., Murase, H., Tamura, T. and Yonezaki, S. 2014. Ecosystem modelling for species in Area IV in the Antarctic Ocean using JARPA and
JARPAII data and its implication to management of cetacean species. Paper SC/F14/J26 presented to the JARPAII Review Meeting, Tokyo,
February 2014 (unpublished). **pp.
Kleiber, M. 1961. The fire of life. J. Wiley and Sons Inc., New York and London. 454pp.
Konishi, K., Tamura, T., Zenitani, R., Bando, T., Kato, H. and Walløe, L. 2008. Decline in energy storage in the Antarctic minke whale(Balaenoptera bonaerensis) in the Southern Ocean. Polar Biol. DOI 10.1007/s00300-008-0491-3.
Konishi, K. and Butterworth, D.S. 2013. Further investigation of whether correlations amongst data are invalidating the conclusion of a statisticallysignificant trend in Antarctic minke body condition over time. Paper SC/65a/EM04 presented to the IWC Scientific Committee, Jun 2013
(unpublished). 3pp. [Available from the Office of this Journal].
Konishi, K. and Walløe, L. 2014a. Time trends in the energy storage in the Antarctic minke whales during the JARPA and JARPAII research periods.
Paper SC/F14/J13 (this meeting)Konishi, K.and Walløe, L. 2014b. Time trends in the stomach content weight in the Antarctic minke whales during the JARPA and JARPAII research
periods. Paper SC/F14/J14 (this meeting).
Leaper, R. and Lavigne, D. 2007. How much do large whale eat? J. Cetacean Res. Manege. 9(3):179-88.
Lindstrøm U, Fujise, Y. Haug, T. and Tamura, T. 1998. Feeding habits of western North Pacific minke whales, Balaenoptera acutorostrata, as
observed in July-September 1996. Rep. int. Whal. Commn, 48:463-9.
Lockyer, C. 1981a. Estimation of the energy costs of growth, maintenance and reproduction in the female minke whale, (Balaenoptera acutorostrata),
from the southern hemisphere. Rep. int. Whal. Commn, 31:337-43.
Lockyer, C. 1981b. Growth and energy budgets of large baleen whales from the Southern Hemisphere. FAO Fish. Ser. [Mammals in the Seas] 3:397487.
Markussen, N.H., Ryg, M. and Lydersen, C. 1992. Food consumption of the NE Atlantic minke whale (Balaenoptera acutorostrata) population
estimated with a simulation model. ICES J mar Sci., 49:317-23.
Miura, T. 1969. Research methods of the productivity of limnological life. Koudansya. Tokyo. 505pp. (in Japanese).
Mori, M. and Butterworth, D.S. 2004. Consideration of multispecies interactions in the Antarctic: A preliminary model of the minke whale-Blue
whale- Krill interaction. Afr. J mar Sci. 26:245-59.
Nishiwaki, S., Ishikawa, H. and Fujise, Y. 2006. Review of general methodology and survey procedure under the JARPA. Paper SC/D06/J2 presented
to the Intercessional Workshop to Review Data and Results from Special Permit Research on Minke Whales in the Antarctic, Tokyo, December
2006 (unpublished). 47pp.
Nishiwaki, S., Ishikawa, H., Goto, M., Tamura, T. and Matsuoka, K. 2014. Review of general methodology and survey procedure under the JARPA II.
Paper SC/F14/J2 presented to the JARPAII Review Meeting, Tokyo, February 2014 (unpublished). 15pp.
Nordøy, E.S., Folkow, L.P., Mårtensson, P.E. and Blix, A.S. 1995. Food requirements of Northeast Atlantic minke whales. pp. 307-17. In: Blix, A.S.,
Walløe, L. and Ulltang, Ø. (eds.) Whales, seals, fish and man. Elsevier. [Developments in Marine Biology] 4:720 pp.
Ohsumi, S. and Masaki, Y. 1975. Biological parameters of the Antarctic minke whale at the virginal population level. J. Fish. Res. Board Can.
32(7):995-1004.

8

Ohsumi, S. 1979. Feeding habits of the minke whale in the Antarctic. Rep. int. Whal. Commn, 29:473-6.
Olsen, M.A., Nordøy, E.S., Blix, A.S. and Mathiesen, S.D. 1994. Functional anatomy of the gastrointestinal system of North eastern Atlantic minke
whales (Balaenoptera acutorostrata). J Zool, Lond., 234:55-74.
Reilly, S., Hedley, S., Borberg, J., Hewitt, R., Thiele, D., Watkins, J. and Naganobu, M. 2004. Biomass and energy transfer to baleen whales in theSouth Atlantic sector of the Southern Ocean. Deep-Sea Research II., 51A:1397-409.
Sekiguchi, K. 1994. Studies of feeding habits and dietary analytical methods for smaller odontocete species along the Southern African Coast.
Doctoral Thesis submitted to the Pretoria University. 258pp.
Skaug, H.J. 2012. Report of the Scientific Committee. Annex K1. Report of the working Group to Address Multi-Species and Ecosystem Modelling
Approaches. Appendix 2. Results of mixed-effects regression analyses of blubber thickness in Antarctic minke whales from data collected under
JARPA. J. Ceatacean Res. Manage (Suppl.) 13:262.
Tamura, T. 1998. The study of feeding ecology of minke whales in the Northwest Pacific and the Antarctic. Doctoral Thesis submitted to the
Hokkaido University. 125pp. (in Japanese).
Tamura, T. and Konishi, K. 2006. Food habit and prey consumption of Antarctic minke whale Balaenoptera bonaerensis in JARPA research area.
Paper SC/D06/J18 presented to the Intercessional Workshop to Review Data and Results from Special Permit Research on Minke Whales in the
Antarctic, Tokyo, December 2006 (unpublished). 22pp.
Tamura, T. and Konishi, K. 2009. Feeding habits and prey consumption of Antarctic minke whale (Balaenoptera bonaerensis) in the Southern Ocean.
J. Northw. Atl. Fish. Sci., 42:13–25.
Tamura, T., Konishi, K., Isoda, T., Okamoto, R., Bando, T. and Hakamada, T. 2009. Some examinations of uncertainties in the prey consumption
estimates of common minke, sei and Bryde’s whales in the western North Pacific. Paper SC/61/JR2 presented to the IWC Scientific Committee,
June 2009 (unpublished). 24pp. [Available from the Office of this Journal].
Thomas P.G. and Green, K. 1988. Distribution of Euphausia crystallorophias within Prydz Bay and its importance to the inshore marine ecosystem.
Polar Biol., 8:27-331.
Wada, A. and Tamura, T. 2014. Estimation of krill biomass based on JARPAII acoustic surveys. Paper SC/F14/J21 (this meeting).

9

Table 1
Sample size of Antarctic minke whales used in this study
Area

Area III-East

Area IV

Area V

Area VI-West

Total

Sex

Male Female

Male Female

Male Female

Male Female

Male Female

638

1,856 1,645

1,863 2,110595

4,952 4,582

Number517

Table 2Prey species found in the stomachs of Antarctic minke whales sampled in this study.
Species
Major prey
Amphipods Parathemisto gaudichaudi
Krill

Euphausia superba
E. crystallorophias
E. frigida
Thysanoessa macrura

FishPleuragramma antarcticum

Minor prey
Fish

Notolepis coatsi
Electona antarctica
Chionodraco sp.
Notothenis sp.

10

310

Table 3
Occurrence (% by weight composition) of main prey species found in the stomachs of Antarctic minke whales sampled
by the JARPA and JARPAII surveys.
Area III-E

Species

Area IV

Area V< 70S

Area VI-W Area V and VI-W
< 70S

≧70S
(Ross Sea)

JARPA （1987/88-2004/05）

N=314

N=926

N=633

N=232

N=324

Krill

Euphausia superba

99.4

94.5

95.0

93.5

66.9

E. crystallorophias

0.2

2.6

0.9

0.0

29.5

E. frigida

0.5

0.0

0.2

0.0

0.0

Thysanoessa macrura

0.0

2.7

3.8

6.5

2.3

Amphipods Parathemisto gaudichaudi

0.0

0.2

0.2

0.0

0.0

Fish

0.0

0.0

0.0

0.0

1.3

JARPA II （2005/06-2010/11）

N=45

N=72

N=85

N=44

N=86

Krill

Euphausia superba

100.0

89.0

92.6

93.2

96.7

E. crystallorophias

0.0

6.9

3.8

0.0

3.1

E. frigida

0.0

0.0

0.0

0.0

0.0

Thysanoessa macrura

Pleuragramma antarcticum

0.0

4.0

3.7

6.8

0.1

Amphipods Parathemisto gaudichaudi

0.0

0.0

0.0

0.0

0.0

Fish

0.0

0.0

0.0

0.0

0.0

Pleuragramma antarcticum

Table 4
The average and maximum weight of fresh or lightly digested stomach contents (freshness category F and fff) and RSC(the ratio of stomach contents weight to body weight, expressed as a percentage) of Antarctic minke whales sampled by
the JARPA and JARPAII surveys.
Sex

Maturity

Weight (Categories F and ｆｆｆ)

NumberAverage (kg)S.D.

Maximum (kg)JARPA （1987/88-2004/05）
Male

Immature

250

36.6

28.5

(RSC: 0.98%)
Mature

1,161

75.5

(RSC: 3.14%)
50.3(RSC: 1.07%)
FemaleImmature

325

43.6

780

77.1

343.8
(RSC: 4.21%)

31.8(RSC: 1.08%)
Mature

130.8

156.0
(RSC: 3.40%)

55.0(RSC: 0.95%)

326.9(RSC: 3.60%)

JARPA II （2005/06-2010/11）
Male

Immature

131

33.2

28.3

(RSC: 0.82%)
Mature566

63.5(RSC: 2.39%)
47.1(RSC: 0.92%)
FemaleImmature

182

Mature513

37.6(RSC: 0.90%)

11

387.0
(RSC: 3.76%)

29.1(RSC: 0.86%)
71.8

142.4

136.9
(RSC: 3.04%)

54.3

301.6
(RSC: 4.02%)

Table 5-1

Required energy contents (KJ d ) of Antarctic minke whales
Sex

Male

Maturity

Body

Body

lengthweight(m)(kg)

Immature

6.5

3,500

Mature8.4

Female Immature
MatureSMR

Blubber

MuscleFat

Reproduction(KJ/day) deposition deposition deposition(KJ/day)(KJ/day)(KJ/day)

193,245

79,86629,35354,693

6,900

321,510

162,664

50,245

151,704

6.7

3,800

205,540

144,620

20,088150,950

8.9

8,100

362,595

303,619

31,175368,105

cost(KJ/day)

157,500

Table 6
-1

Energy value of blubber and muscle (KJ kg ) of Antarctic minke whales

Blubber (KJ/kg)

Sex

Muscle (KJ/kg)

December

March

December

March

Male

14,43520,711

5,858

6,234

Female16,44328,075

5,941

6,192

Table 7The daily and seasonal prey consumption for all Antarctic minke whales in the research area using Method-1
Sex

Male

Maturity

Body

Body

lengthweight(m)(kg)(KJ/day)

Immature

6.5

3,500

425,188

95.1

2.72

8.6

Mature8.4

6,900

816,813

182.6

2.65

16.4

6.7

3,800

620,473

138.7

3.65

12.5

8.9

8,100

1,455,945

325.5

4.02

39.1

Female Immature
MatureDaily prey consumption

Seasonal
consumption

12(kg/day) (% of B.W.)(tons)

Table 8
The daily and seasonal prey consumption for all Antarctic minke whales in the research area using Method-2
Sex

Male

Maturity Body weight

JARPA period

Seasonal

JARPA II period

Seasonal

(kg)

(kg)

(%)

consumption (tons)

(kg)

(%)

consumption (tons)

Immature

3,500

127.0

3.63

11.4

115.9

3.31

10.4

Mature

6,900

250.3

3.63

22.5

228.4

3.31

20.6

3,800

137.9

3.63

12.4

125.8

3.31

11.3

8,100

293.9

3.63

35.3

268.1

3.31

32.2

Female Immature
MatureTable 9Seasonal prey consumption and comparison with krill biomass in Areas IV and V (Hakamada and Matsuoka, 2014;
Wada and Tamura, 2014).
Method-1
Stratum

Year

Abundance Prey consumption Krill biomass(inds.)(A: million tons) (B: million tons)

III East

2007/08

9,406

0.19

6.6

2.8

IV

2007/08

14,739

0.37

12.5

3.0

V

2008/09108,097

2.88

24.0

12.0

VI WestTotal

2008/0926,364
158,606

0.54
3.98

3.4
46.5

15.8
8.6

Ratio A/B(％）

Method-2
JARPA II period
Abundance Prey consumption Krill biomass(inds.)(A: million tons) (B: million tons)

Ratio A/B(％）

Stratum

Year

III East

2007/08

9,406

0.17

6.6

2.6

IV

2007/08

14,739

0.33

12.5

2.6

V

2008/09108,097

2.51

24.0

10.5

VI WestTotal

2008/0926,364
158,606

0.50
3.51

3.4
46.5

14.6
7.6

13

Area III
East

Area IV

Area V

Area VI
West

Ross Sea(Areas V+VI)

Fig.1.

Research area in the Antarctic● Euphausia superba○ Euphausia crystallorophias◇ Euphausia frigida◆ All Thysanoessa spp. (include Thysanoessa macrura , T. vicina ??)△ Mingle (Euphausia superba +E. crystallorophias )▲ Mingle (Euphausia superba +All Thysanoessa spp.)▼ Mingle (Euphausia superba +the other species*)
× Euphausia spp. (E . spp. /E. superba ? /E.crystallorophias ?/E.vallentini ?/E. frigida ?)□ Amphipods■ FishFig.2(A). Sampling position of Antarctic minke whales and their dominant prey species in Areas III-East and IV. Lineshows water depth contour of 1,000m.

14

● Euphausia superba○ Euphausia crystallorophias◇ Euphausia frigida◆ All Thysanoessa spp. (include Thysanoessa macrura , T. vicina ??)△ Mingle (Euphausia superba +E. crystallorophias )▲ Mingle (Euphausia superba +All Thysanoessa spp.)▼ Mingle (Euphausia superba +the other species*)
× Euphausia spp. (E . spp. /E. superba ? /E.crystallorophias ?/E.vallentini ?/E. frigida ?)□ Amphipods■ FishFig.2(B). Sampling position of Antarctic minke whales and their dominant prey species in Areas V and VI-West. Lineshows water depth contour of 1,000m.

15North of 70°S
JARPA periods (1987/88-2004/05) N=4,901

JARPAII periods (2005/06-2010/11) N=2,380
100
Frequency (%)

Frequency (%)

100
75
50
25

5

7

9

11

13

15

17

50
25
0
21

0
3

75

19

3

5

7

9

13

15

17

19

21

19

21

Hour

Hour

Ross Sea area (South of 70°S)
JARPA periods (1987/88-2004/05) N=647

JARPAII periods (2005/06-2010/11) N=612

100

100
Frequency (%)

Frequency (%)

11

75
50
25
0
3

5

7

9

11

13

15

17

19

75
50
25
0
21

3

5

Hour

(F

: fresh, fff: lightly digested, ff

7

9

11

13

15

17

Hour

: moderately digested, f: heavily digested, 0: empty)Fig 3. Composition of prey freshness categories throughout the day in Antarctic minke whales in North of 70°S and in
the Ross Sea area (South of 70°S) in the JARPA and JARPAII period.

16

JARPAII periods (2005/06-2010/11) N=1,071

1.4
1.2
1.0
0.8
0.6
0.4
0.2
0

5

10

15

20

Ratio of stomach contents to whale
body weight (%)

Ratio of stomach contents to whale
body weight (%)

North of 70°S
JARPA periods (1987/88-2004/05) N=4,693

1.4
1.2
1.0
0.8
0.6
0.4
0.2
0

5

10

Hour

1.4
1.2
1.0
0.8
0.6
0.4
0.2
5

10

20

JARPAII periods (2005/06-2010/11) N=363

15

20

Ratio of stomach contents to whale
body weight (%)

Ratio of stomach contents to whale
body weight (%)

Ross Sea area (South of 70°S)
JARPA periods (1987/88-2004/05) N=628

0

15
Hour

Hour

1.4
1.2
1.0
0.8
0.6
0.4
0.2
0

5

10

15

20

Hour

Fig.4. Change in the ratio of stomach contents to whale body weight (RSC) throughout the day in North of 70°S andin the Ross Sea area (South of 70°S) in the JARPA and JARPAII period. Error bars are ± 1 S.E.

17

Immature male

Immature female
2.5○December, Wm = 0.0068L

2.0● March, Wm = 0.0057L

2.42032.611

2, N= 43, r = 0.86
Blubber mass (tons)

Blubber mass (tons)

2.5

2, N=12, r = 0.91

1.5
1.0
0.5

○December, Wb = 0.0096L

2.0● March, Wb = 0.0072L2, n=67, r = 0.902

, n=20, r = 0.93

1.5
1.0
0.5
0.0

0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

4.00

11.0

5.00

6.00

7.00

8.00

9.00

10.00

11.00

9.0

10.0

11.0

Body length (m)Body length (m)Mature male

Mature female

2.5

2.5
Blubber mass (tonnes)

Blubber mass (tons)

2.25882.49262.0
1.5
1.0○December, Wb = 0.0082L

0.5● March, Wb = 0.0092L

2.35482.39412, n=138, r = 0.61

2.0
1.5
1.0

2.339

2

7.0

8.0

, n=48, r = 0.51
○December, Wb = 0.0094L
2.47832, n=42, r = 0.52
● March, Wb = 0.0079L

0.5

2, n=53, r = 0.57

0.0

0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

4.0

11.0

5.0

6.0

Body length (m)Body length (m)Fig. 5. The blubber weight (Wb, t) as a function of body length (L, m) for Antarctic minke whales sampled in December
and March.

Immature male

Immature female

6.0

6.0
● March, Wb = 0.0032L

3.35793.41162, N=43, R = 0.87

, N=12, R = 0.98

4.0

2.0

0.0

● March, Wm = 0.0081L

4.0

2.87722, n=67, r = 0.962

, n=20, r = 0.95

2.0

0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

4.00

5.00

6.00

Body length (m)

7.00

8.00

9.00

10.00

11.00

9.0

10.0

11.0

Body length (m)Mature male

Mature female

6.0

6.0
Muscle mass (tonnes)

Muscle mass (tons)

3.0361○December, Wm = 0.0054L

2

Muscle mass (tons)

Muscle mass (tons)○December, Wb = 0.003L

4.0

2.0
○December, Wm = 0.0067L● March, Wm = 0.0202L

2.94472.48232, n=138, r = 0.71

4.0

2.0
○December, Wm = 0.0177L

2● March, Wm = 0.0136L, n=53, r = 0.59

0.0

2.47

2.61822, n=48, r = 0.572

, n=42, r = 0.55

0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

4.0

Body length (m)

5.0

6.0

7.0

8.0

Body length (m)Fig. 6. The muscle weight (Wm, t)as a function of body length (L, m) for Antarctic minke whales sampled in December
and March.

18

Immature male

Immature female

12.0● March W T = 0.0181L

2.76482.8131

8.0

2, N=43, r = 0.932

, N=12, r = 0.93

Body mass (tons)

Body mass (tons)○ December W T = 0.0178L
8.0

4.0

4.0

○December, WT = 0.0164L● March, WT = 0.0221L

0.02, n=67, r = 0.95
2, n= 20,r = 0.95

0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

4.00

5.00

6.00

Body length (m)

7.00

8.00

9.00

10.00

11.00

10.0

11.0

Body length (m)Mature male

Mature female
12.0
Body mass (tonnes)

12.0

Body mass (tons)

2.81782.70548.0

4.0○December, W T = 0.026L● March, W T = 0.0531L

2.60162.31362, N=138, r = 0.67

8.0

4.0
○December, W T = 0.0314L

2● March, W T = 0.0562L, N=53, r = 0.63

2.51992.28612, n=48, r = 0.622

, n=42, r = 0.45

0.0

0.0
4.0

5.0

6.0

7.0

8.0

9.0

10.0

4.0

11.0

Body length (m)

5.0

6.0

7.0

8.0

9.0

Body length (m)Fig. 7. Total body weight (WT, t) as a function of body length (L, m) for Antarctic minke whales sampled in December
and March.

19

Appendix 1. The digestion experiment of krill using an artificial solution
This experiment addressed the recommendation on digestion rate by the IWC SC in 2007. The purpose of thisexperiment was to estimate the appropriate digestion rate of Antarctic minke whales.
For this experiment, the set-up and procedure followed that of Jackson et al (1987). The digestive solution was made up
of 10% HCL, 10% Na2CO3 and the digestive enzyme from fundus of Antarctic minke whales same as 1.0% pepsin.
The temperature of the solution in the container was maintained at 37 oC. The digestive solution was adjusted to ph 2.3(Sekiguchi, 1994). The pH value was maintained by the occasional addition of 10% HCL.
The digestive solution (500ml) filled the beakers. The beakers were set in the water bath which were agitated (in arocking motion) 30-40times per minute and maintained the solution at 37 oC. Krill (50g) was put in a small bag of glass
fiber with a mesh size of 0.5 x 0.5mm and placed in the solution.
Every hour, the bag was lifted from the solution. All excess solution wiped off by paper towel, and then weighed to thenearest 0.1g. The physical appearance of the sample was recorded at the same time.
The result is shown in figure 1. The proportion of undigested krill in the stomach after 4 hours is 45 %. This value wassimilar to those in Sekiguchi (1994). We applied this value for estimating daily prey consumption of Antarctic minke
whales based on method 2 in this study.

Remaining weight (%)

100.0

75.0

50.0

25.0

0.0
0

3

6

9

12

15

18

Time (h)Fig. 1 The rate of digestion of Euphausia superba in an artificial solution, expressed as a percentage of their original
weight remaining at hourly intervals.

20