SC/D06/J20
THIS PAPER CAN NOT BE CITED WITHOUT WRITTEN PERMISSION FROM THE AUTHORS

Comparison between stomach contents of Antarctic minke
whale and krill sampled by RMT net in the Ross Sea and its
adjacent waters
TSUTOMU TAMURA*, KENJI KONISHI*, SHIGETOSHI NISHIWAKI*, KENJI TAKI**, TOMONARIHAYASHI** AND MIKIO NAGANOBU*** The Institute of Cetacean Research, 4-18, Toyomi, Chuo, Tokyo 104-0055, Japan**National Research Institute of Far Seas Fisheries, 2-12-4, Fukuura, Kanazawa, Yokohama,
Kanagawa 212-0055, JapanKEYWORDS: ANTARCTIC MINKE WHALE; ANTARCTIC KRILL; ICE KRILL, NET SAMPLING,MESOSCALE SURVEY

ABSTRACTThe comparison between stomach contents of the minke whale and the net sampling using the multiple
rectangular mid-water trawl (RMT (1+8)M) were conducted in the meso-scale area. In the Ross Sea and theadjacent waters from late of December 2004 to mid of February 2005, a cooperative survey between JARPA and
R/V Kaiyo Maru was conducted. The Antarctic minke whales (Balaenoptera bonaerensis) fed mostly on
Antarctic krill (Euphausia superba) in offshore area, and ice krill (E. crystallorophias) in coastal (shallow: depth
under 1,000 m) area on continental shelf of Ross Sea. There was almost coincidence of frequency in body lengthof the krill between the stomach contents of the whales and the RMT net sampling. The size difference of the krill
consumed by the minke whale in each meso-scale area seems to depend on the size of krill distributed. It seems
that the minke whales have not prey size selectivity. In the western slope area, the stomach content weights of theminke whale were the highest, and empty stomachs were not found. The minke whale fed on the large size (BL:40–50 mm) Antarctic krill in the western slope zone. This study indicates that the continental slope in the Ross
Sea is an important feeding ground for the Antarctic minke whales. It is still a paradox that minke whales,
especially pregnant females, are abundant in the Ross Sea, in spite of low density of their prey.

INTRODUCTION
The four main objectives of the JARPA (Japanese Whale Research Program under Special Permit in the Antarctic)are (1) elucidation of the stock structure of Antarctic minke whales to improve the stock management, (2)estimation of biological parameters of the Antarctic minke whales, (3) elucidation of the role of whales in the
Antarctic marine ecosystem through the study of whale feeding ecology and (4) elucidation of the effect ofenvironmental changes on cetaceans. Many previous studies reported that the Antarctic krill (Euphausia superba)
is the most important prey species for the Antarctic minke whale (Balaenoptera bonaerensis) (Kawamura 1980,
Bushuev 1986, Ichii and Kato, 1991). Some results of food habit of the minke whale in the Antarctic werereported in the JARPA review meeting in 1997 (e.g. Ichii et al., 1997; Tamura et al., 1997). These studies were
evaluated to understand the role of whales in the Antarctic marine ecosystem through the study of whale feeding
ecology. But it was recommended to examine the distribution and abundance of prey species in the meso- scale
area in JARPA survey. In coastal (shallow) area, such as Ross Sea and Prydz Bay, they fed mainly on the ice krill
E. crystallorophias and some fishes (Bushuev 1986, Tamura 1998).
In 2004/05 season, a cooperative prey species survey was conducted concurrently with JARPA from 25 December
2004 to 27 February 2005 (65 days) in the Ross Sea and adjacent waters by R/V Kaiyo-Maru (2,630 GT) of
Fisheries Agency of Japan.
1

In this study, the body length of Antarctic krill and ice krill between the stomach contents of the minke whale andthe net sampling were compared in the meso-scale area. Based on existing the prey species and the fresh stomach
contents weight, the food habitat of the minke whale in the Ross Sea and adjacent waters was discussed.

MATERIALS AND METHODS
Survey area and periods
The main survey areas were the Ross Sea and its adjacent waters between 165E and 165W straddling thelongitude 180 south of 60S, Antarctica. Transect lines along 165E, 175E, 180, 175W and 165W were investigatedto cover the high concentrated area, which krill and whales were expected. The six sub areas of meso-scale survey
area were divided from the latitude, longitude and the water depth as below (Fig. 1).
* Western Offshore area (WO)
Between 170E and 175W, south of 60S, over 3,000 m of the water depth.
* Eastern Offshore area (EO)
Between 175W and 160W, south of 60S, over 3,000 m of the water depth.
* Western continental slope (WSL)
Between 170E and 175W, south of 68S, between 1,000 and 3,000m of the water depth.
* Eastern continental slope (ESL)
Between 175W and 160W, south of 68S, between 1,000 and 3,000m of the water depth.
* Western continental shelf (ES)
Between 170E and 175W, south of 68S, under 1,000 m of the water depth.
* Eastern continental shelf (ES)
Between 175W and 160W, south of 68S, under 1,000 m of the water depth.
In the Ross Sea and the adjacent waters during 25 December 2004 to 27 February 2005, a cooperative survey
between JARPA and R/V Kaiyo Maru was conducted. The comparison between the stomach contents of the
Antarctic minke whales and the catch of net sampling using the multiple rectangular mid-water trawl(RMT(1+8)M) were conducted in the small scale area. The station point of RMT net by R/V Kaiyo Maru and thesighting position of the minke whales sampled in each prey species was shown in Fig. 1.
Analyses of stomach contents and net sample
A total of 231 minke whales were collected in random sampling method during the cooperative survey during 25
December 2004 to 27 February 2005 (Table 1). The detail of this cruise is described by Nishiwaki et al. (2005)
and Naganobu et al. (2005). The sighting positions of the minke whales sampled were shown in Fig. 1.
The stomach contents were removed after capture on the ship's deck. The contents were first classified to major
prey groups, such as euphausiids, copepods, fish and others on board. The freshness of stomach contents was
categorized into four classes (1 = fresh, 2 = lightly digested, 3 = moderately digested, 4 = heavily digested). Then,the contents from each stomach were weighed to the nearest 0.1 kg. When undigested krill were occurred, a subsample (N=66) was removed and fixed in 10 % formalin water for later analyses.
The net samples using the multiple rectangular mid-water trawl (RMT (1+8)M) was described in Naganobu et al.
(in this meeting).
In the laboratory, prey species in the sub-samples were identified to the lowest taxonomic level as possible.
Between 50 and 100 individuals of krill from each sub samples, the body length was measured to the nearest 1
mm, from the anterior tip of the rostrum to the posterior end of the telson using Makarov and Denys (1981).

2

RESULTS
Prey species
The minke whales fed mainly on E. superba from the continental slope to offshore, but they changed the prey toE. crystallorophias above the continental shelf of the Ross Sea (shallow area). The stomach contents of somewhales were other fishes, Amphipods and salps, but those were less abundant (Table 2).
Food habits of the minke whales in some meso-scale areas
The body length composition of Antarctic krill and ice krill consumed by the minke whales and sampled by RMT
net were shown in Fig. 2 in meso-scale areas. The prey composition of the minke whales in each small area wasshown in Fig. 3. The fresh stomach contents weight of the minke whales was shown in Fig. 4. The distribution of
the stomach contents weight of the minke whales was shown in Fig. 5. The empty ratio of the stomach contents ofthe minke whale in each meso-scale area was shown in Fig. 6.
Western Offshore area (WO)
The minke whale fed only on the Antarctic krill. The Antarctic krill with a mode at body length of 20-30 mm were
dominant in the stomach contents of the minke whale and the RMT net samples. The body length composition of
Antarctic krill consumed by the minke whale coincided with that of the RMT net samples. The average undigested
stomach content was 62.4 kg. The empty ratio of the stomach contents of the minke whale was 10.0 %.
Eastern Offshore area (EO)
The minke whale fed only on the Antarctic krill. The Antarctic krill with a mode at body length of 15-20 mm were
dominant in the stomach contents of the minke whale. The krill samples caught by the RMT net were few. The
average undigested stomach content was 54.9 kg. The empty ratio of the stomach contents of the minke whale was
8.3 %.
Western continental slope area (WSL)
The minke whale fed only on the Antarctic krill. The Antarctic krill with a mode at body length of 40-50 mm were
dominant in the stomach contents of the minke whale and the RMT net samples. The average undigested stomach
content was the largest in six meso-scale areas, 94.7 kg. The empty ratio of the stomach contents of the minke
whale was the smallest in six meso-scale areas, 0.0 %.
Eastern continental slope area (ESL)
The minke whale fed only on the Antarctic krill. The Antarctic krill with a mode at body length of 40-50 mm were
dominant in the stomach contents of the minke whale. The krill samples caught by the RMT net were few. The
average undigested stomach content was the smallest in six meso-scale areas, 23.5 kg. The empty ratio of thestomach contents of the minke whale was 15.4 %.
Western continental area (WS)The prey composition of Antarctic krill and ice krill in the stomach of the minke whales were 44 % and 56 %,respectively. The Antarctic krill with a mode at body length of 40-50 mm were dominant in the stomach contentsof the minke whale. The Antarctic krill samples caught by the RMT net were few. The ice krill with a mode atbody length of 15-35 mm were dominant in the stomach contents of the minke whale, whereas the ice krill with amode at 10-15 mm in the RMT net samples. The average undigested stomach content was 43.6 kg. The empty
ratio of the stomach contents of the minke whale was the largest in six meso-scale areas, 21.6 %.
Eastern continental area (ES)The prey composition of Antarctic krill and ice krill in the stomach of the minke whales were 15 % and 85 %,respectively. The Antarctic krill with a mode at body length of 40-50 mm were dominant in the stomach contentsof the minke whale. The Antarctic krill samples caught by the RMT net were few. The ice krill with bimodal atbody length of 10-15 mm and 20-35 mm were dominant in the stomach contents of the minke whale and the RMT
net samples. The average undigested stomach content was 49.2 kg. The empty ratio of the stomach contents of theminke whale was the largest in six meso-scale areas, 13.3 %.

3DISCUSSION
Prey selectivity and size selectivity
It was confirmed that the Antarctic minke whales fed mostly on the Antarctic krill in the offshore area (WO andEO) and the continental slope area (WSL and ESL), and the ice krill in the continental shelf area (WS and ES).
The stomach contents of some whales have also shown the occurrence of less abundant other prey such as fishes,
Amphipods and salps, but those were less abundant. Generally the baleen whales are grouped into two types on
the feeding behavior, swallowing and skimming (Nemoto, 1959). They feed on swarming zooplankton such as the
Antarctic krill and the ice krill, indicating an ability of the minke whales to pursue single prey species
aggregations. The other prey such as less abundant other krill species, fishes, Amphipods and salps were assumed
to be eaten by chance.
According to the krill composition of RMT net sampling data in the offshore area, the Antarctic krill was mostdominant species, whereas Thysanoessa macrura was dominated secondary and E. triacantha was thirdly
dominated species (Naganobu et al, in this meeting). T. macrura has been reported to be an important prey species
for other baleen whales such as fin and humpback whales in the area ranged from 100 W to 130 W. However, theminke whales did not feed on T. macrura in this study. As E. triacantha does not swarm in the adult stages(Baker, 1959), it is assumed that it does not comprise a suitable prey for the minke whales. The difference of krill
composition between stomach contents of the minke whale and RMT net samples in the offshore area suggeststhat the minke whales seems to feed selectively on E. superba.
In the continental shelf area, the ice krill is dominant krill species, while the occurrence of Antarctic krill increases
close to the continental shelf break and further off the shelf (Thomas and Green, 1988). According to RMT net
sampling data in the continental slope area, the ice krill was most dominant species. The ice krill is important prey
for the minke whales in the Ross Sea. RMT net sample have also shown the occurrence of less abundant
euphausiids such as E. superba. In this concurrent prey and whale survey, it was confirmed that the prey speciesof the minke whales during austral summer fed mainly on two krill species depending on the distribution of eachspecies. It is suggested that the minke whale in the Ross Sea and the adjacent waters has been feeding on mostabundant prey species, the Antarctic krill and the ice krill.
Ruud (1932) reported that the large size of the Antarctic krill consumed by the fin whale, while small ones wereconsumed by blue whale. The body length composition of Antarctic krill and ice krill consumed by the minke
whales and sampled by RMT net were almost coincided. The body length of krill ingested by the minke whales
ranged from 9 to 56 mm. These results were coincided with the previous report (Mackintosh, 1974, Kawamura
and Kikuno, 1980, Tamura, 1998). Ichii and Kato (1991) noted that the larger Antarctic krill (BL: 40-50 mm)
were more important prey for the minke whale than smaller ones (BL: 15-30 mm). According to the theoretical
growth curve for the Antarctic krill (Ikeda, 1985), body length between 40 and 50 mm are matured krill, 3 or 4
years old, while 15-30 mm krill are juvenile stage, one years old. Our results suggested that the smaller Antarctic
krill was consumed by the minke whale in the offshore area, whereas the larger Antarctic krill consumed by theminke whale in the continental slope area and the continental shelf area. In this concurrent prey and whale survey,
the size difference of the krill consumed by the minke whale in each meso-scale areas seems to be depended on
the size of krill distributed. It seems that the minke whales have not size selectivity. However, the density of theminke whales expressed as number seen per 100 n miles in the continental slope area and the continental shelfarea were higher than one in the offshore area (Naganobu et al, in this meeting). This result seems to lead that theminke whale were concentrated in the aggregation of the larger size Antarctic krill.
The suitable feeding ground for the Antarctic minke whales
In the western continental slope area, the stomach contents weight of the minke whale was the largest, the empty
ratio was the smallest in six meso-scale areas. Generally, in the continental slope area, the large matured Antarctic
krill distributed and spawned (Siegel, 1988). Our results suggested that it was important for the feeding ground of
the Antarctic minke whales in this area. However, the other baleen whales such as fin whales and humpback
whales mainly distributed in the western offshore area (Naganobu et al, in this meeting). In the western offshorearea, it was topographically complex. The water depth is ranged from under 1,000 m to over 3,000 m. The
biomass of the krill was higher than other meso-scall areas (Naganobu et al, in this meeting). In this 2004/2005
JARPA, the segregation was observed among the Antarctic minke whales and other baleen whales such as fin
whales and humpback whales (Naganobu et al, in this meeting). It seems that fin and humpback whales fed
mainly on the smaller Antarctic krill or other krill species such as T. macrura (Nemoto and Nasu, 1958).

4

The Ross Sea
The Ross Sea (the continental shelf area, WS and ES in this study) is a wide and deep embayment of thecontinental shelf, its average depth is 500 m (Hatherton, 1990). Ichii et al. (1998) noted that although a large
number of minke whales, especially pregnant female were distributed in the Ross Sea, their stomach contents
were low. The Ross Sea area was characterized by a low food supply throughout the austral summer season.
Because the summer was short, it could not sustain a high biomass of zooplankton (Hempel, 1985). Our results
lead the same situation. The empty ratio of the stomach contents of the minke whale in the western continental
shelf (WS) was the highest in the six meso-scale areas, and the stomach contents weight was significantly low.
However, the pregnant female with high energy requirements was mainly distributed in the Ross Sea in
2004/2005 season (Nishiwaki et al., 2005). In this area, only blue whale and the minke whales were distributed(Naganobu et al., in this meeting). The predator avoidance hypothesis can not be understand, because the killer
whales, a potential predator on the minke whales, are also relatively abundant in the Ross Sea (Kasamatsu et al.,
1990; Naganobu et al., in this meeting). One of the reasons for this phenomenon, pregnant females can reduce theeffects of unfavorable weather such as heavy wind and swell. However it is still a paradox that minke whales,
especially pregnant female are abundant in the Ross Sea, in spite of low density of their prey.
In the future works
In recent years, abundance of large baleen whales in the Antarctic was increased (Matsuoka et al., 2005). Further
study on the interaction among the baleen whales such as the Antarctic minke, blue, fin and humpback whales will
be needed for modelling study and long-term monitoring research, which clarify the interaction of major predatorsand their prey in the Antarctic.

ACKNOWLEDGMENTS
The stomach contents examined in this study were collected by many researchers and crews. We also thank thecaptains, crews and researchers who were involved in the JARPA research cruises for their efforts. Our sincere
thank to Dr. Hiroshi Hatanaka, Dr. Luis A. Pastene of the Institute of Cetacean Research (ICR) for their valuablesuggestions and useful comments on this paper.

REFERENCES
Baker, A.C. 1959. The distribution and life-history of E. triacantha Holt and Tattersall. Discovery Rep 29: 309340.
Bushuev, S.G. 1986. Feeding of minke whales, Balaenoptera acutorostrata, in the Antarctic. Rep. int. Whal.
Commn 36:241-245.
Hatherton, T. 1990. Antarctica - the Ross Sea region-. Wellington. 287p.
Hempel, G. 1985. Antarctic marine food webs. In: Siegfried WR, Condy PR, Laws, RM (eds) Antarctic nutrient
cycles and food webs. Springer-Verlag, Berlin, p 266-270.
Ichii, T. and Kato, H. 1991. Food and daily food consumption of southern minke whales in the Antarctic. Polar
Biol., 11:479-487.
Ichii, T., Tamura, T., Fujise, Y., Nishiwaki, S. and Matsuoka, K. 1997. Interannual changes in body fat condition,
stomach contents mass and distribution of minke whales in Areas IV and V. IWC Scientific Committee
working paper SC/M97/16, 19p. (unpublished).
Ichii, T., Sinohara, N., Fujise, Y., Nishiwaki, S. and Matsuoka, K. 1998. Interannual changes in body fat conditionindex of minke whales in the Antarctic. Mar. Ecol. Prog. Ser. 175:1-12.
Ikeda, T. 1985. Life history of Antarctic krill Euphausia superba: a new look from an experimental approach. Bull
Mar. Sci.37: 599-608.
Kasamatsu, F. and Joyce, GG. 1995. Current status of Odontocetes in the Antarctic. Antactic Science 7 (4): 365379..
Kawamura A. 1980. A review of food of Balaenopterid whales. Sci Rep Whales Res Inst 32:155-197.
Kawamura, A. and Kikuno, S. 1980. The body length composition of Euphausia superba consumed by the
Antarctic minke whales. Geiken Tsuusin (in Japanese). 334: 23-34.
Mackintosh, N.A., 1974. Sizes of krill eaten by whales in the Antarctic. Discovery Rep., 36: 157-178.
Makarov, R.R. and Denys, C.J. 1981. Stages of sexual maturity of Euphausia superba Dana. Biomass Handbook
11: 1-13.
Matsuoka, K., Hakamada, T., Kiwada, K., Murase, H. And Nishiwaki, S. 2005. Abundance increase of large
baleen whales in the Antarctic based on the sighting survey during Japanese Whale Research Program
5

(JARPA). Global Environment Research. 9 (2): 105-115.
Naganobu, M., Taki, K. and Hayashi, T. 2005. Preliminary report of the Japanese R/V Kaiyo Maru survey in theRoss Sea and Adjacent Waters, Antarctica in 2004/2005. IWC Scientific Committee working paper
SC/57/O16, 8p. (unpublished).
Naganobu, M., Nishiwaki, S., Yasuma, H., Matsukura, R., Takao, Y., Taki, K., Hayashi, T., Watanobe, Y., Yabuki,
T., Yoda, Y., Noiri, Y., Kuga, M., Yoshikawa, K., Kokubun, N., Murase, H., Matsuoka, K. and Ito, K.
Interactions between oceanography, krill and baleen whales in the Ross Sea and Adjacent waters: An
overview of Kaiyo Maru - JARPA joint survey in 2004/05. (SC/D06/J23 in this meeting)
Nemoto, T and Nasu, K. 1958. Thysanoessa macrura as food of baleen whales in the Antarctic. Sci Rep Whales
Res Inst 13:193-199.
Nemoto, T. 1959. Food of baleen whales with reference to whale movements. Sci. Rep. Whales Res. Inst. 14:149290.
Nishiwaki, S., Toyyama, D., Goto, M., Mogoe, T., Isoda, T., Tsunekawa, M., Yoshimura, K., Kasai, H., Teraoka, T.,
Koyanagi, T., Ito, S., Kitajima, A., Ogihara, M., Hasegawa, A. and Fujihira, T. 2005. Cruise report of theJapanese Whale Research Program under Special Permit in the Antarctic (JARPA) Area V and Western Partof Area VI in 2004/2005. IWC Scientific Committee working paper SC/57/O5, 22p. (unpublished).
Ruud, J.T. 1932. On the biology of southern euphausiidae. Hvalrad Skr. 2: 1-105.
Siegel, V. 1988. A consept of seasonal variation of krill (Euphausia superba) distribution and abundance west of
the Antarctic peninsula. pp.219-230. In: D. Sahrhage (ed.), Antarctic Ocean and Resources Variability.
Springer-Verlag. Berlin Heidelberg.
Tamura, T., Ichii, T. and Fujise, Y. 1997. Consumption of krill by minke whales in Areas IV and V of the Antarctic.
IWC Scientific Committee working paper SC/M97/17, 9p. (unpublished).
Tamura, T. 1998. The study of feeding ecology of minke whales in the Northwest Pacific and the Antarctic. D.C.
Thesis. Hokkaido University. 125pp [in Japanese].
Thomas, P.G. and Green, K. 1988. Distribution of Euphausia crystallorophias within Prydz Bay and its
importance to the inshore marine ecosystem. Polar Biol. 8:327-331.

6

Table 1. Sample size used in this study

Male
Female
Total

WO
35
19
54

WSL
11
17
28

WS
14
77
91

EO
1
13
14

ESL
0
13
13

ES
2
29
31

Total
63
168
231

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

species
Main prey
Krill

Euphausia superba
E. crystallorophias

Miner prey
Amphipoda Parathemisto gaudichaudi
Salps
Unidentified
PiscesPleuragramma antarcticum
Notolepis coatsi
Electona antarctica
Chionodraco sp.
Notothenis sp.

7

Prey of minke whale

161°03′E

155°24′W

オキアミ計測ポイント

170°E

E.superba

180°

170°W

160°W

58°29′S

58°29′S

3000m
E.crystallorophias

60°S

60°S
3000m

WO
62°S

62°S

1000m

64°S

64°S

3000m

3000m

3000m

66°S

66°S
3000m

EO
1000m

1000m

68°S

68°S
3000m

3000m
1000m

WSL

70°S

70°S

3000m
1000m

72°S

72°S
1000m

74°S

74°S

ESL
1000m

76°S

3000m

ES

78°S

76°S

78°S

WS
1000m

79°02′S

79°02′S
170°E

180°

170°W

161°03′E

160°W
155°24′W

Fig. 1. The station point of RMT net by R/V Kaiyo Maru and the sighting position of the minke whales
sampled in each prey species. Shade area is shown in the continental slope (■: the station
point of RMT, ●: Euphausia superba, ▲: Euphausia crystallorophias).

8

・ Western offshore (WO) : 175E－175W
Euphausia superba
Stomach contents（N=3）

RMT net sample

30.0

30.0

04/05・WO
N =300E.superba

20.0

04/05・WO
E.superba

%

%

20.0

10.0

10.0

0.0

0.0
10 15 20 25 30 35 40 45 50 55 60

10 15 20 25 30 35 40 45 50 55 60mmmm

・ Eastern offshore (EO) : 175W－160W
Euphausia superba
Stomach contents（N=1）

RMT net sample
100.0

30.0
04/05・EO・105
N =100E.superba

75.0

%

%

20.0

04/05・EO
E.superba

50.0

10.0
25.0

0.0

0.0

10 15 20 25 30 35 40 45 50 55 60

10 15 20 25 30 35 40 45 50 55 60

mm

mm

・ Western continental slope (WSL) : 175E－175W
Euphausia superba
Stomach contents（N=5）

RMT net sample
30.0

30.0

20.0

%

%

20.0

04/05・WSL
E.superba

04/05・WSL
N =500E.superba

10.0

10.0

0.0

0.0

Fig. 2.

10 15 20 25 30 35 40 45 50 55 60

10 15 20 25 30 35 40 45 50 55 60

mm

mm

The body length of Antarctic krill and ice krill consumed by the minke whales and sampled by
RMT net.

9

・ Eastern continental slope (ESL) : 175W－160W
Euphausia superba
Stomach contents（N=5）

RMT net sample
30.0

30.0

04/05・ESL
E.superba

04/05・ESL
N = 471
E.superba

20.0

%

%

20.0

10.0

10.0

0.0

0.0
10 15 20 25 30 35 40 45 50 55 60

10 15 20 25 30 35 40 45 50 55 60

mm

mm

・ Western continental shelf (WS) : 175E－175W
Euphausia superba
Stomach contents（N=3）

RMT net sample
30.0

30.0

04/05・WS
E.superba

04/05・WS
N =251E.superba

20.0

%

%

20.0

10.0

10.0

0.0

0.0
10 15 20 25 30 35 40 45 50 55 60

10 15 20 25 30 35 40 45 50 55 60

mm

mm

Euphausia crystallorophias
Stomach contents（N=4）

RMT net sample

30.0

60.0
04/05・WS
N =400E.crystarollophias

40.0
%

%

20.0

04/05・WS
E.crystarollophias

10.0

20.0

0.0

0.0
5

10

15

20

25

30

35

40

45

5

mm

Fig. 2.

10

15

20

25
mm

Continued.

10

30

35

40

45

・ Eastern continental shelf (ES) : 175W－160W
Euphausia superba
Stomach contents（N=1）

RMT net sample
100.0

30.0

04/05・ES
E.superba

04/05・198（ES)N =69
E.superba

75.0

%

%

20.0

50.0

10.0

25.0
0.0

0.0
10 15 20 25 30 35 40 45 50 55 60

10 15 20 25 30 35 40 45 50 55 60

mm

mm

Euphausia crystallorophias
Stomach contents（N=7）

RMT net sample

30.0

30.0
04/05・ES
E.crystarollophias

04/05・ES
N =700E.crystarollophias

20.0
%

%

20.0

10.0

10.0

0.0

0.0
5

10

15

20

25

30

35

40

45

5

mm

Fig. 2.

10

15

20

25
mm

Continued.

11

30

35

40

45

100%

Frequency (%)

80%

60%

40%

20%

0%
Shelf

Slope

Offshore

Shelf

West

Offshore

East
EC

Fig. 3.

Slope

ES

The prey composition of the minke whales in each meso-scale area.

（EC: Euphausia crystallorophias, ES: Euphausia superba）

Stomach contents (kg)

150.0

100.0

50.0

0.0
Shelf

Slope

Offshore

Shelf

West

Slope

Offshore

East
Avg.

Fig. 4.

The undigested stomach contents weight of the minke whales

12Fig. 5.

The distribution of the stomach contents weight of the minke whales

25.0

Frequency (%)

20.0

15.0

10.0

5.0

0.0
Shelf

Slope

Offshore

Shelf

West

Slope

Offshore

East
Empty

Fig. 6.

The empty ratio of the stomach contents of the minke whale in each meso-scale area.

13