SC/D06/J18
THIS PAPER CAN NOT BE CITED WITHOUT WRITTEN PERMISSION FROM THE AUTHORS

Food habit and prey consumption of Antarctic minke whale
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

ABSTRACTWe analyzed the stomach contents of Antarctic minke whale (Balaenoptera bonaerensis) in the Southern Ocean.
The Antarctic minke whales fed mostly on Antarctic krill (Euphausia superba) in offshore area, and ice krill (E.
crystallorophias) in coastal (shallow) area on continental shelf such as Ross Sea and Prydz Bay. The average offresh stomach contents per capita has decreased year after year. Daily prey consumption was estimated using two
independent methods, which were from theoretical energy requirement calculations and from diurnal changes ofstomach contents mass. The results showed that estimated daily prey consumptions were similar between theabove two methods and ranged from 2.67 to 4.95 % of body weight (immature male: 84-144 kg, immature female:120-188 kg, mature male: 182-337 kg, mature female: 283-401 kg). These estimates almost corresponded with theresults of maximum weight of stomach contents. The prey consumption during feeding season was 7.5-12.9 and16.4-30.3 tons for immature and mature male, 10.8-16.9 and 33.9-48.1 tons for immature male and mature
pregnant female, respectively. Our results seems useful to assess the Antarctic minke whale’s feeding impact on
krill resources and the level of interspecific competition among other baleen whales, seals and sea birds.

INTRODUCTION
Recently, the consumption of krill by baleen whales is getting important for the ecosystem in the Southern Ocean.
Although the Antarctic krill (Euphausia superba) is preyed upon by many predators such as baleen whales, seals,
sea birds, fish and squid. The prey consumption by whales can not disregard to understand the ecosystem becauseof their large biomass (Miller and Hampton, 1989).
The Antarctic minke whale (Balaenoptera bonaerensis) is most abundant baleen whale species in the Southern
Ocean (south of 60°S) estimated to be as high as at 760,396 animals with 95 % confidence interval (510,000 –
1,140,000) in the austral summer of 1980s (IWC 1991). It breeds in austral winter at lower latitude and migrate to
the Antarctic Ocean for feeding in austral summer (Horwood 1990, Kasamatsu et al. 1995). In Southern Ocean,
the Antarctic minke whale feed mostly on Antarctic krill in offshore (e.g. Kawamura 1980, Bushuev 1986, Ichii
and Kato 1991), and ice krill (E. crystallorophias) in coastal (shallow) area on the continental shelf such as Ross
Sea and Prydz Bay (Bushuev 1986, Tamura 1998).
Some studies already estimated the daily prey consumption of the whales on the basis of energy-requirement
calculations (Hinga 1979, Lockyer 1981a, 1981b, Armstrong and Siegfried 1991, Reilly et al. 2004). However,these methods were based on estimates and some assumptions regarding basal metabolic rate, growth,
reproduction, migration and energy deposition in austral winter. So this, the estimates have some uncertain
information such as body weight of the whale. The quantitative data of stomach contents were few until now.
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,1(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 and sample size
The research area covers Areas III-East (35°E to 70°E), IV (70°E to 130°E), V (130°E to 170°W) and VI-West(170°W to 145°W) which were designated by the IWC (Fig. 1). The surveys were conducted mainly from
December to March between 1987/88 and 2004/05 seasons (Table 1). A total of 6,778 minke whales were sampled
by the JARPA between 1987/88 and 2004/05 seasons. This study used the data of 6,777 minke whales, because
one individual was lost before the landing on the flensing deck of the research base vessel (Table 1).
Research activity
The whales were randomly sampled using three sighting and sampling vessels and brought to a research basevessel, where biological measurements and sampling were carried out.
Sex, sexual maturity, body length, body weight, stomach contents mass, freshness category of stomach contents
and prey species were used in this paper. 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 was weighed using the special large weighing machine on theflensing deck of the research base vessel. All whales were sampled during daylight hours, between 03:00 and
21:00 local time.
Sampling and analyses of stomach contents
All Balaenopterid species have four chambered stomach system (Hosokawa and Kamiya 1971, Olsen et al. 1994).
Each stomach contents mass 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, See Appendix. 1). Then, sub samples (approx. 300 g) from forestomach contents with relatively fresh
prey was removed and fixed in 10% formalin solution water for later analyses. At the laboratory, prey species inthe sub samples were identified to the lowest taxonomic level as possible (Barnard 1932, Fischer and Hureau
1985a, 1985b, Baker et al. 1990).
The estimation of daily prey consumption by Antarctic minke whale
The amount of krill consumed by Antarctic minke whales was estimated using two independent methods, whichwere from theoretical energy requirements calculations (method-1) and from diurnal changes of stomach contents(Forestomach and fundus (2nd. stomach)) (method-2).
Method-1 Estimation of daily consumption of krill from the standard metabolism
We calculated the prey consumption (F) during the austral summer in each different maturity stages of Antarctic
minke whale from the standard metabolic rate (SMR) and energy deposit according to following equations:Male or Immature female : F(kg day-1)=(SMR + ED) /E / A
Mature female:F(kg day-1)=(SMR+ ED+R) /E / A

SMR :Standard metabolic rate (kJ day-1)
ED :Energy deposition (muscle, internal organs fat and blubber masses) (kJ day-1)
E :Caloric value of prey (E. superba) (kJ kg-1)
R :Reproduction cost (kJ day-1)
A :Assimilation efficiency

We made the following additional assumptions:2(1) Mean body length and mass during feeding season (W)We calculated mean body lengths of 6.2 m and 6.7 m for immature males and females, and 8.4 m and 8.9 m formature males and females from the data of JARPA surveys. The body mass values were obtained by use ofweighing machine which was able to measure body mass of an Antarctic minke whale directly. All Balaenopterid
species become fat by storing large amount of fat inside their body in feeding season, and become slim conversely
by consuming the stored fat in breeding season. The body length – mass relationship for Antarctic minke whales,
which were caught in December and March showed in Fig. 2. Immature and mature male of 6.2 m and 8.4 m were
estimated to have an increase in body mass of 305 kg and 703 kg, respectively. A similar calculation was made for
immature and mature female of 6.7 m and 8.9 m, and an increase in body mass of 308 kg and 595 kg wereobtained, respectively. We also calculated mean body masses during feeding season 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 the data of JARPA
surveys.
(2) Standard metabolic rate (SMR)

We calculated the basal metabolic rate (M) according to Kleiber's equation (Kleiber 1961):
M=70W0.75 (kcal day-1)
where W is the Antarctic minke whale body mass during feeding season (kg).
To account for energy spent on activities such as foraging, moving between food patches and migration, we
calculated the standard metabolic rate (SMR) using the following equation (Markussen et al. 1992):
SMR=1.45×M×4.184 (kJ day-1)(3) Energy deposited during feeding season in Antarctic (ED)The total muscle and blubber masses of Antarctic minke whales were weighed in JARPA surveys, in order tocalculate seasonal growth and fat deposition. These depositions were 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.
Blubber mass (tons) as a function of the body length (m) in Antarctic minke whales, which were caught inDecember and March showed in Fig. 3. Immature and mature male of 6.2 m and 8.4 m were estimated to have an
increase in blubber mass of 105 kg and 271 kg, respectively. A similar calculation was made for immature andmature female of 6.7 m and 8.9 m, and an increase in blubber mass of 120 kg and 214 kg were obtained,
respectively. There was a significant increase in the energy density of blubber, from 14,435 kJ kg -1 to 20,711 kJ
kg -1 (wet mass) from December to March in feeding season.
Muscle mass (tons) as a function of the body length (m) in Antarctic minke whales, which were caught inDecember and March showed in Fig. 4. Immature and mature male of 6.2 m and 8.4 m were estimated to have an
increase in muscle mass of 242 kg and 448 kg, respectively. A similar calculation was made for immature andmature female of 6.7 m and 8.9 m, and an increase in muscle mass of 189 kg and 271 kg were obtained,
respectively. The energy density of muscle increased from 5,858 kJ kg -1 to 6,234 kJ kg -1 (wet mass) from
December to March in feeding season.
The mass of internal organs fat deposition was estimated to deduct the blubber deposition and growth and/or
deposition of muscle from total body mass. The energy density of internal organs fat is assumed as same as
blubber’s value.
(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) Feeding season (F)Many baleen whale generally known to migrate between the feeding ground in high latitudinal waters in summer
and the breeding ground in low latitudinal waters in winter. The encounter rate (as a simple index of distribution
density) of Antarctic minke whales in the Antarctic as feeding ground increased from early November to late
December and peak in January, followed by a steady decrease through February (Kasamatsu et al. 1996). There isa segregation pattern of Antarctic minke whales in the Antarctic. The proportion of males tends to decrease withlatitude; maturity rate of males are related to the school sizes and mature males tend to make larger schools.
Females, especially mature females, tend to be distributed in southern part of the research area (Kato 1982,3

Horwood 1990). Lockyer (1981a, b) estimated the feeding season that immature animals and mature male spend
90days, mature female spend 120 days, respectively. We assumed that they moved southward in austral summer
and northward in austral winter at the same time. We also assumed that immature animals and mature male spend
90days, mature female spend 120 days, respectively.
(6) Reproduction cost (R)The total reproductive cost for a female Antarctic minke whales was calculated by Lockyer (1981a) to be 1.89
×107 kJ (= 0.45 × 107 kcal), assuming that the length at birth is 273 cm (Best 1982). We assumed that almost
mature female were pregnant, and all reproduction cost took during feeding season (120 days).
(7) Assimilation efficiency (A)We assumed that Antarctic minke whales have an assimilation efficiency of 84 % (Lockyer, 1981a).

Method-2 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

k

∑C =V
i

1

i =1

i

(1 − 2S + 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 (forestomach and fundus stomach) mass as % of body mass(Vi) at 1 hour intervals based on the stomach content mass (kg) and body mass (kg). Nordøy et al. (1993) showedthat krill were digested by bacterial fermentation, and that this digestion process was very rapid. Assuming that it
takes 4 hours that prey is digested in the stomach of Antarctic minke whales (Bushuev 1986) and that d isexponential (Elliott and Persson 1978), we estimated S to be 0.67 and 0.74, if the proportion of undigested prey inthe stomach after 4 hours is 20 % and 30 %, respectively.

RESULTS
Prey items
A total of ten prey species, including one amphipod, four euphausiids and five fishes were identified in thestomachs of Antarctic minke whales (Table 2). Euphausia superba and were the dominant prey species, occurringin 85-100 % of the stomach examined in each area (Table 3, Fig. 5), followed by E. crystallorophias, E. frigida,
Thysanoessa macrura, an amphipod Parathemisto gaudichaudi and one fish species Pleragramma antarcticum. In
offshore area, E. superba was the most dominant prey species, follwed by T. macrura. In inshore area such as
Ross Sea in Area V, E. crystallorophias was the most dominant prey species.
The diurnal changes in feeding activity
The composition of freshness categories and the diurnal change in the mean stomach content mass as % of bodymass of Antarctic minke whale was showed in Figs. 6 and 7. These figures show that the proportion of undigested
category of F (fresh) and fff (lightly digested) and the rate of the mean stomach content mass have gradually
decreased with time periods. After 19:00 hrs, F of freshness categories and the rate of the mean stomach content
mass showed a slight increase.

4

Stomach contents weight
The mean and maximum weight of stomach contents were shown in table. 4. The mean weight of undigested
stomach contents (freshness category F and fff) were 30.9 ± 23.5 kg (1.0 % of body weight) and 43.0 ± 31.5 kg(1.0 % of body weight) for immature male and female, respectively and 74.2 ± 50.1 kg (1.1 % of body weight)
and 76.3 ± 54.6 kg (1.0 % of body weight) for mature male and female, respectively.
The maximum weight of stomach contents (category F and fff) were 125.7 kg (3.1 % of body weight) and 156.0
kg (3.4 % of body weight) for immature male and female, respectively and 343.8 kg (4.2 % of body weight) and
321.2 kg (3.6 % of body weight) for mature male and female, respectively.
The trend of stomach contents
To clear the daily prey consumption, the average of undigested stomach contents (category: F and fff) was
calculated for mature male and female in each survey year (Fig. 8). In area IV, Fig. 8 shows that the average of
undigested stomach contents for mature male and female has decreased year after year (Mature male: F=0.25,
Mature female F=0.11). In area V, there was same trend. Especially, the trend of decrease for mature female wassignificant (Mature male: F=0.59, Mature female F=0.009).
Daily prey consumption of Antarctic minke whales
Method-1 Energy-requirements calculations
Standard metabolic rate (SMR)
The mean body lengths of Antarctic minke whales were 6.2 and 6.7 m for immature males and females and 8.4
and 8.9 m for mature males and females, respectively in JARPA surveys. The mean body masses during feeding
season were 2,900 and 3,800 kg for immature males and females, and 6,800 and 8,100 kg for mature males andfemales in JARPA surveys.
Standard metabolic rate per day of immature and mature males were 16.8×104 and 31.8×104 kJ, respectively. And,
standard metabolic rate per year of immature and mature females were 20.6×104 and 36.3×104 kJ, respectively(Table 5).
Energy deposition during feeding season in the Southern Ocean
We estimated the energy deposition as blubber deposition, growth and/or deposition of muscle and internalorgan’s fat deposition during feeding season.
Deposited energy intakes as blubber during feeding season of immature and mature males were 7.0×104 and16.3×104 kJ per day, respectively. And, deposited energy intakes as blubber during feeding season of immatureand mature females were 14.5×104 and 30.2×104 kJ per day, respectively (Table 5).
Deposited energy intakes as muscle during feeding season of immature and mature males were 2.5×104 and5.0×104 kJ per day, respectively. And, deposited energy intakes as muscle during feeding season of immature andmature females were 2.0×104 and 3.3×104 kJ per day, respectively (Table 5).
Deposited energy intakes as fat (internal organ’s fat) during feeding season of immature and mature males were
5.3×104 and 15.2×104 kJ per day, respectively. And, deposited energy intakes as fat during feeding season of
immature and mature females were 8.1×104 and 20.7×104 kJ per day, respectively (Table 5).

Daily prey consumption during feeding season
The daily prey consumptions during feeding season were 37.5×104 and 81.3×104 kJ for immature and mature
male, 53.8×104 and 126.5×104 kJ for immature and mature female, respectively (Table 5).
When the mean energy value of prey (E. superba) was 4,473 kJ kg-1 (= 1,070 kcal kg-1), the daily prey
consumptions during feeding season were 83.7 and 181.7 kg for immature and mature male, 120.2 and 282.9 kg
for immature and mature female, respectively (Table 5).

Method-2 Diurnal changes of stomach content mass
Estimated rates of daily prey consumption were 4.36 and 4.95 % of body mass of Antarctic minke whales. The
estimated prey consumption weights were 126.4-143.6 kg and 165.7-188.1 kg for immature male and female,respectively and 296.5-336.6 kg and 353.2-401.1 kg for mature male and female, respectively (Table 6).
Prey consumption during feeding season and annual consumption
We estimated the prey consumption during feeding season based on methods 1 and 2.

5Based on method 1, the prey consumption were 7.5 and 16.4 tons for immature and mature male, 10.8 and 33.9
tons for immature and mature female, respectively (Table 7). Based on method 2, the total prey consumption were11.4-12.9 and 26.7-30.3 tons for immature and mature male, 14.9-16.9 and 42.4-48.1 tons for immature andmature female, respectively (Table 7).
We also estimated the annual prey consumption based on methods 1 and 2. Based on method 1, we calculated theannual prey consumption using SMR, reproduction cost, energy value of prey and assimilation efficiency. Basedon method 2, we assumed that Antarctic minke whales spend about 90 days and 120 days in the feeding areas in
the feeding ground (Lockyer 1981a, 1981b). Lockyer (1981b) reported that the daily food consumption of theminke whale in winter was equivalent to 10 % of that in the summer. We adopted these assumptions forcalculating annual prey consumption. Based on method 1, the prey consumption were 19.4 and 36.8 tons for
immature and mature male, 23.8 and 40.0 tons for immature and mature female, respectively (Table 7). Based on
method 2, the total prey consumption were 14.9-16.9 and 34.8-39.6 tons for immature and mature male, 19.5-22.1
and 51.0-57.9 tons for immature and mature female, respectively. The prey consumption during feeding season
based on methods 1 and 2 accounted for 64-86 % and 77-83 % of annual prey consumption, respectively (Table
7).
Feeding impact on krill resources by Antarctic minke whales in Area IV and V of the Antarctic
In Area IV, total prey consumptions of krill by Antarctic minke whales of 1999/00 and 2001/02 season were
estimated to be 1.19 and 1.33 million tons, respectively. On the other hand, in Area V, total prey consumptions ofkrill by Antarctic minke whales of 2000/01, 2002/03 and 2004/05 season were estimated to be between 4.48, 5.73
and 2.97 million tons, respectively (Appendix 2, Table 8). The estimations of feeding impact on krill resources by
Antarctic minke whales in Area IV and V were 4 %, and from 22 to 25 % of krill standing stock, respectively(Table 8).
DISCUSSION
Prey items
The Antarctic minke whales fed mostly on Antarctic krill (Euphausia superba) in offshore area, and ice krill (E.
crystallorophias) in coastal (shallow) area on continental shelf such as Ross Sea and Prydz Bay. It is strongly
suggested that Antarctic minke whale has been feeding on most abundant prey species among target species. E.
crystallorophias is 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).
The diurnal changes in feeding activity
Our results suggested that Antarctic minke whales seem to have a diurnal feeding rhythm, with a primary peak inthe early morning. This coincided with previous reports (Ohsumi 1979, Bushuev 1986). Other studies in common
minke whales (B. acutrostrata) in Northern Hemisphere have shown 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 preyat night (Folkow and Blix 1993, Haug et al. 1997, Tamura 1998).
Our result showed that Antarctic minke whales fed on the prey easily and might be ceased to feed at earlier timein the day due to the satisfaction with feeding. If they feed on prey fully at once, they can be satisfied with dailyenergy-requirement for whales.
Daily prey consumption of Antarctic minke whales
Using method 1, the daily prey consumption was little to that using method 2. However, the estimate based on
method 1 may be negatively biased to some extent depending on the residence time in the Antarctic. In the case ofthat immature animals and mature male spend 90days in the feeding ground, the prey consumption during feeding
season was estimated to be 16.3-31.6 tons and accounted for 56-63% of annual prey consumption. It was clearedthat they needed to extend the stay period to fill their demand energy requirement. In the case of method 1, we
estimated the daily prey consumption using energy deposition during feeding season in Antarctic. This energy
deposition during feeding season was based on one assumption that they moved southward in austral summer andnorthward in austral winter at the same time. If their migration were multiform pattern, our body length – mass
relationship for Antarctic minke whales in December and March had negatively biased to some extent.
Using method 2, the daily prey consumption would underestimate the actual prey consumption, because no
information is available from 21:00 to 03:00 hrs. Thus, the daily consumption rate was estimated to be at least
4.4 % of body weight of whales. However, the estimates based on two independent methods were coincidence6well each other. These estimates based on methods 1 and 2 were supported by the maximum weight of stomach
contents and the diurnal feeding rhythm obtained in the field data.
Estimates of the daily prey consumption rate obtained from the above two methods ranged from 2.67 to 4.95 %.
These values were similar to estimates by Lockyer (1981b) and Bushuev (1986). Our results were reasonableestimates even from the point of energy requirement and field stomach contents data. The estimates of this study
almost corresponded with the results of maximum weight of stomach contents, could be used with confidence forthe estimation of daily prey consumption by Antarctic minke whales.
The estimates daily prey consumption rates using respiratory allometry of male and female Antarctic minke
whales during the austral summer is to be 6.7 and 6.2 %, respectively (Armstrong and Siegfried 1991). But theseestimates may be overestimates, because, it needs to be a maximum of two feeding times per day for daily energy
requirement. However, the results of maximum weight of stomach contents were ranged from 3.1 to 4.2 % of theirbody mass. And, there was only one peak of the diurnal feeding rhythm, it was difficult to feed on prey over 6 %of their body mass in a day.
Mori and Butterworth (2004) built up the Multi-species (Antarctic minke whale, blue whale (B. musculus) andAntarctic krill) type ecosystem modeling in the Antarctic. Antarctic minke whales and blue whales both feed
mainly on Antarctic krill near the ice edge in the Antarctic. 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. They assumed the daily prey consumption rate (% of bodymass) by Antarctic minke whales were ranged from 0.6 or 2.85 or 5.1 %. And, they assumed that the body weightof Antarctic minke whales was 7 tons, the feeding days was 90 days. They indicate that the daily prey
consumption rate of Antarctic minke whale was ranged from 3.0 to 5.0 % of body mass using their model. It
seems plausible based on our results. It might be useful for analyzing of ecosystem modeling in the Southern
Ocean.
Consumption of Antarctic minke whales on krill during austral summer by in Areas IV and V
Some studies proposed the annual prey consumption of Antarctic minke whales using energy requirement models
in the Antarctic. Armstrong and Siegfried (1991) estimated that an ‘average-sized’ male and female of Antarctic
minke whale consume 37.2 tons, 56.2 tons during feeding season, respectively. They indicated that the Antarctic
minke whales consume 95 % of krill biomass that is consumed by baleen whales in the Antarctic equal to 35.5
million tons, if the estimated population of Antarctic minke whales was applied 760,396 animals. However, theirannual prey consumption was more than 2.9-4.0 and 3.3-5.2 times the range of 9.2-12.8 tons and 10.9-16.9 tons
for immature male and female animals by this study. The result of consumption by Antarctic minke whales seems
overestimate.
In the Southern Ocean, large baleen whale species were depleted drastically in the 20th century. Laws (1977)
suggested that before the 1970’s, blue whale and humpback whale were the most harvested and were reduced toabout 3 and 5 % of their initial biomasses. This rapid decreasing of large baleen whale species provided the annual
surplus of krill as much as 150 million tones (Laws 1977). This surplus became available for other krill predators,
such as Antarctic minke whale, crabeater seal (Lobodon carcinophagus), Antarctic fur seal (Arctocephalus
gazella), some penguins and sea birds.
Mori and Butterworth (2004) indicated that trend of abundance of Antarctic minke whale had been declined after
1980’s using multispecies interaction model among Antarctic minke whale, blue whale and krill in the Southern
Oceans. The causes of abundance of Antarctic minke whale decreasing seem to be over carrying capacity of
Antarctic minke whales, competition among Antarctic minke whales, some baleen whales such as blue, fin (B.
physalus) and humpback whales (Megaptera novaeangliae) and some predators such as seals and sea birds, ordecreasing of krill biomass due to environment changes. It was reported that abundances of humpback whales
increased 11-12 % per year in the some region of Southern Oceans (Bannister, 1994, IWC, 2000). And, it wasreported that Antarctic krill biomass in the south western Atlantic reduced by 80% from the level in 1970’s due tothe rise in seawater temperature (Atkinson et al. 2004). Kato (1987) indicated that the growth rate of Antarctic
minke whales increased from 1955 to 1970 possibly resulted from prey availability as potential competitive
baleen whales such as blue whales being depleted. If the carrying capacity level of Antarctic minke whale isdecreasing, the growth rate of Antarctic minke whales will increase, and the age at maturity will decrease. It mustmonitor the biological parameters such as the growth rate, the age at maturity and the body condition such as
blubber thickness of whales for longtime.
Unfortunately, the information of abundance and biological parameters of cetaceans, seals and sea birds werelimited in the Southern Oceans. It will be necessary to monitor abundance and biological parameters of cetaceans
and other organisms in the Antarctic to evaluate the role of Antarctic minke whales in the Antarctic marine
ecosystem in the future.

7

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(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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Ichii, T. and Kato, H. 1991. Food and daily food consumption of southern minke whales in the Antarctic. Polar
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8

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transition phase in earplugs. (JA/J05/PJR7 in this meeting)9

10

Table 1. Areas, years of surveys and sample size used in this study
Area
Season1987/88
1988/89
1989/90
1990/91
1991/92
1992/93
1993/94
1994/95
1995/96
1996/97
1997/98
1998/99
1999/2000
2000/01
2001/02
2002/03
2003/04
2004/05
Total

Area III-East
Male Female

Area IV
Male Female
153
184
165

130

203

126

74

36

205

123

54
62
322

56
48
227

147
138
1,565

153
85
184
164
165
167
200
200
272
206
279
247
233
258
201
235
200
177
3,626

85

151

164

159

167

160

200

130

132

198

74

36

207

122

40

20

186

144

72

38

168

162

67

43

110
1,419

220
1,446

67
320

43
180

123

200

170

Total
Male Female

142

41

46

Area VI-WestMale Female

119

69

63

Area V
Male Female

160
183
192
1,298

Table 2. Prey species found in the stomachs of Antarctic minke whales sampled
by the JARPA surveys.

species
Main prey
Amphipoda
Krill

Parathemisto gaudichaudi
Euphausia superba

PiscesE. crystallorophias
E. frigida
Thysanoessa macrura
Pleuragramma antarcticum

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

11

119
151
142
159
123
160
130
130
167
234
159
142
206
182
239
205
240
263
3,151

Table 3. Occurrence (%) of main prey species found in the stomachs of
Antarctic minke whales sampled by JARPA surveys
SpeciesKrill
Euphausia superba
E. crystallorophias
E. frigida
Thysanoessa macrura
Ampipods Parathemisto gaudichaudi
FishPleuragramma antarcticum

Area III-E
100.0
99.5
0.1
0.4
0.0
0.0
0.0

Area IV
99.9
95.2
2.7
0.0
2.1
0.1
0.0

Area V
99.7
85.4
11.5
0.2
2.9
0.1
0.2

Area VI-W
100.0
93.0
0.0
0.0
6.8
0.0
0.0

Table 4. Stomach contents weight of Antarctic minke whales
Sex

Male

Maturity

NumberImmature

MatureFemale Immature

MatureContents weight (All)

NumberAverage

S.D.

Maximum

18.1

20.4

125.7

(0.6%)(0.6%)(3.1%)

50.0

47.6

343.8

(0.7%)(0.7%)(4.2%)

25.4

28.1

156.0

(0.7%)(0.7%)(4.2%)

49.5

50.8

321.2

(0.6%)(0.6%)(3.6%)

535

2,532

978

1,895

182

1,180

321

756

Contents weight (F+fff)
Average

S.D.

Maximum

30.9

23.5

125.7

(1.0%)(0.7%)(3.1%)

74.2

50.1

343.8

(1.1%)(0.7%)(4.2%)

43.0

31.5

156.0

(1.0%)(0.7%)(3.4%)

76.3

54.6

321.2

(1.0%)(0.7%)(3.6%)

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

Male

Maturity

Immature
MatureFemale ImmaturePregnant

Body
length
(m)
6.2
8.4
6.7
8.9

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

SMR
(KJ/day)
167,825
318,009205,540
362,595

Blubber
deposition(KJ/day)
69,610162,664
144,620
302,215

Muscledeposition(KJ/day)
24,69850,24520,08833,265

12

Fat
Reproduction
Daily prey consumption
deposition
cost
during feeding season(KJ/day)(KJ/day)(KJ/day)(kg/day) (%)
52,535
374,605
83.7
2.89
151,704
812,645181.7
2.67
81,306
537,562120.2
3.16
207,344
157,500
1,265,379
282.9
3.49

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

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

S =0.74
(kg)
126.4
296.5
165.7
353.2

S =0.67
(%)
4.36
4.36
4.36
4.36

(kg)
143.6
336.6
188.1
401.0

(%)
4.95
4.95
4.95
4.95

Table 7. The prey consumption of Antarctic minke whales during feeding season
Sex

Male
FemaleMaturity

Immature
MatureImmature
MaturePrey consumption
during feeding season
Method-1 Method-2
(t)
(t)
7.5
11.4 - 12.9
16.4
26.7 - 30.3
10.8
14.9 - 16.9
33.9
42.4 - 48.1

Annual prey consumption
Method-1
(t)
(%)
19.4
64.3
36.8
64.3
23.8
64.3
40.0
85.8

Method-2(t)(%)
14.9 - 16.9 76.6
34.8 - 39.6 76.6
19.5 - 22.1 76.6
51.0 - 57.9 83.0

Table 8. 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
1999/2000 JARPA and 2002/03 JARPA (Ref. Murase et al. in this meeting)
StratumYear(inds.)

Prey consumption（million ton）

Krill biomass（million ton）

Feeding impact(％）

AbundanceIV

1999/00
2001/0244,931
48,960

1.19
1.33

34.2
34.1

3.5
3.9

V

2000/01
2002/03

164,789
201,883

4.48
5.73

20.7
22.6

21.6
25.4

13

Area III
(east)

Area IV

Area V

Area VI
west

Ross Sea(Area V)

Fig.1.

Research area in the Antarctic14

B o d y m a s s (t o n n e s )*Immature male*Mature male

12.0

12.0

8.0

8.0

4.0

4.0

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

7.0

B o d y m a s s (t o n n e s )Body length (m)

8.0

9.0

10.0

11.0

Body length (m)*Immature female*Mature female

12.0

12.0

8.0

8.0

4.0

4.0

0.0

0.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

4.0

Body length (m)Fig. 2.

5.0

6.0

7.0

8.0

9.0

10.0

11.0

Body length (m)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.
Immature male (December 〇, n=170; March ●, n=72):(December: y=0.0178x2.7648, r2=0.93; March: y=0.0181x2.8131, r2=0.93)
Mature male(December 〇, n=709; March ●, n=404):(December: y=0.0260x2.6016, r2=0.67; March: y=0.0531x2.3136, r2=0.63)
Immature female (December 〇, n=276; March ●, n=109):(December: y=0.0164x2.8178, r2=0.95; March: y=0.0221x2.7054, r2=0.95)
Mature female(December 〇, n=243; March ●, n=260):(December: y=0.0317x2.5161, r2=0.63; March: y=0.0570x2.2815, r2=0.44)

15

B l u b b e r m a s s (t o n n e s )*Immature male*Mature male

2.5

2.5

2.0

2.0

1.5

1.5

1.0

1.0

0.5

0.5

0.0

0.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

4.0

5.0

6.0

Body length (m)

8.0

9.0

10.0

11.0

9.0

10.0

11.0

Body length (m)*Immature female*Mature female

2.5

2.5

2.0

2.0

1.5

1.5

1.0

1.0

0.5

0.5

B l u b b e r m a s s (t o n n e s )

7.0

0.0

0.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

4.0

Body length (m)Fig. 3.

5.0

6.0

7.0

8.0

Body length (m)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.
Immature male (December 〇, n=30; March ●, n=14):(December: y=0.0068x2.4203, r2=0.86; March: y=0.0057x2.611, r2=0.91)
Mature male(December 〇, n=135; March ●, n=59):(December: y=0.0082x2.3548, r2=0.61; March: y=0.0092x2.3491, r2=0.57)
Immature female (December 〇, n=54; March ●, n=23):(December: y=0.0096x2.2588, r2=0.90; March: y=0.0072x2.4926, r2=0.93)
Mature female(December 〇, n=47; March ●, n=43):(December: y=0.0094x2.3390, r2=0.51; March: y=0.0078x2.4831, r2=0.51)

16

M u s c l e m a s s (t o n n e s )*Immature male*Mature male

6.0

6.0

4.0

4.0

2.0

2.0

0.0

0.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

4.0

5.0

6.0

7.0

*Mature female

6.0

6.0

4.0

4.0

2.0

2.0

0.0

0.0

M u s c l e m a s s (t o n n e s )*Immature female

5.0

6.0

7.0

8.0

9.0

10.0

4.0

11.0

10.0

11.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

Body length (m)Body length (m)Fig. 4.

9.0

Body length (m)Body length (m)

4.0

8.0

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.
Immature male (December 〇, n=30; March ●, n=14):(December: y=0.0030x3.3579, r2=0.87; March: y=0.0032x3.4116, r2=0.98)
Mature male(December 〇, n=135; March ●, n=59):(December: y=0.0067x2.9447, r2=0.71; March: y=0.0202x2.4823, r2=0.59)
Immature female (December 〇, n=54; March ●, n=23):(December: y=0.0054x3.0361, r2=0.96; March: y=0.0081x2.8772, r2=0.95)
Mature female(December 〇, n=47; March ●, n=43):(December: y=0.0177x2.4700, r2=0.57; March: y=0.0121x2.6746, r2=0.55)

17

Area III
III-East

Area IV

Fig.5-a.

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

18

Area VI

Fig.5-b.

Area V

Distribution of krill consumed by Antarctic minke whales in Areas V and VI-West.

(●:Euphausia. superba, 〇:E. crystallorophias,:Thysanoessa spp., □:E. S. + others, ×: E. spp.)

19

Frequency (%)

100
75
50
25
0
3

5

7

9

11

13

15

17

19

21

Ho u rFig. 6.

Composition of between freashness categories for prey and time periods in Antarctic(F : fresh, fff : lightly digested, ff : moderately digested,f : heavily digested, 0 : empty)

Percentage of body mass (%)

1.4
1.2
1.0
0.8
0.6
0.4
0.2
0

5

10

15

20

Hour

Fig. 7.

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

20

Area IV
*Mature male*Mature female
140.0

120.0

120.0

100.0

100.0
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

1990

1992

1994

1996

Year

1998

2000

2002

2004

Year

Area V*Mature female

140.0

140.0

120.0

120.0

100.0

100.0

y = -3.48x + 7032.4
2
R = 0.7046

kg

kg*Mature male

80 .0

80.0

60 .0

60.0

40.0
1988

1990

1992

1994

1996

1998

2000

2002

40.0
1988

2004

Year

Fig. 8.

1990

1992

1994

1996

1998

2000

2002

2004

Year

Yearly trend of the mean mass of undigested stomach content.
(Data was from individuals collected from an area south of 63 degrees in January
and February.)

21

Appendix. 1. Classification of freshness of forestomach (1st. stomach) contents.

Code
F

Class
FreashDescription
Prey not affected by digestion

fff

Lightly digested

Prey slightly affected by digestion

ff

Moderately digested

Prey moderattory to highly fragmentedfHeavily digested

Unidentifiable remains or indigestible parts only

22

Appendix 2. Total prey consumption and the estimations by Antarctic minke whales in Area
IV and V between 1999/2000 and 2004/05.
(Ref. Hakamada et al., in this meeting)23