SC/J09/JR9Prey consumption and feeding habits of common minke
whales in coastal areas off Sanriku and Kushiro
TSUTOMU TAMURA1), KENJI KONISHI1), MUTSUO GOTO1), TAKEHARU BANDO1), TOSHIYA KISHIRO2), HIDEYOSHIYOSHIDA2), RYOSUKE OKAMOTO3) AND HIDEHIRO KATO3)
1) The Institute of Cetacean Research, 4-5, Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan.
2) National Research Institute of Far Seas Fisheries, 5-7-1, Shizuoka, 424-8633, Japan.
3) Tokyo University of Marine Science and Technology, Faculty of Marine Science, 4-5-7, Konan, Minato-ku, Tokyo,108-8477, Japan
Contact e-mail: tamura@cetacean.jp

ABSTRACTThe stomach contents of common minke whales Balaenoptera acutorostrata sampled off Sanriku
from April to May and Kushiro region from September to October in 2002-2007 JARPN II wereanalyzed. In Sanriku region, the dominant prey species consisted of one krill (Euphausia pacifica)
and two fishes (Japanese sand lance Ammodytes personatus and Japanese anchovy Engraulisjaponicus). On the other hand, in the Kushiro region, the dominant prey species consisted of one
krill (E. pacifica), three fishes (Japanese anchovy, Pacific saury Cololabis saira and walleye
pollock Theragra chalcogramma) and one squid (Japanese flying squid Todarodes pacificus). All
these prey species are targeted by local fisheries. In Sanriku region, the yearly compositions ofJapanese sand lance, Japanese anchovy and krill in wet weight were 58.8–84.2 %, 0.0–39.5 % and
0.1–37.9 %, respectively. In Kushiro region, the yearly compositions of Pacific saury, walleye
pollock, Japanese flying squid and Japanese anchovy in wet weight were 1.2–40.6 %, 3.6–71.5 %,0.1–33.8 % and 9.5–60.6 %, respectively. The estimated daily prey consumption of immature male,
immature female, mature male and mature female were 78-118kg, 73-114kg, 107-224kg and 133270kg, respectively. The total prey consumption in the Sanriku region of Japanese sand lance,
Japanese anchovy and Krill by common minke whales was estimated as 1,616 and 683 tons, 194
and 150 tons, 109 and 1 tons per year in 2005 and 2006 seasons, respectively. The consumption ofsand lance by minke whales was equivalent to 18.7 and 12.3 % of the 2005 and 2006 fisheries catch,
respectively. Distribution of common minke whale in Sendai Bay overlapped Japanese sand lance
fisheries ground. In Kushiro region, the total prey consumption of Pacific saury, walleye pollock
and Japanese flying squid and Japanese anchovy by common minke whales was estimated as 39–
1,075 tons, 95–2,322 tons 3-1,753 tons and 308–1,422 tons per year, respectively. The consumptionof Pacific saury, walleye pollock and Japanese flying squid by minke whales were equivalent to
0.1-1.8 %, 0.1-3.6 % and 0.1-117.1 % of fisheries catch, respectively.
KEYWORDS: COMMON MINKE WHALE; SANRIKU; KUSHIRO; NORTH PACIFIC;FISHERIES INTERACTION, SCIENTIFIC PERMITINTRODUCTION
The common minke whale Balaenoptera acutorostrata is widely distributed in the world. In thewestern North Pacific, two stocks have been recognized: one in the Sea of Japan - Yellow Sea East China Sea (J stock) and the another in the Sea of Okhotsk – West Pacific (O stock) (IWC,
1983). The abundance of common minke whales was estimated to be 19,209 animals with 95 %1

confidence interval (10,069 – 36,645) in the Sea of Okhotsk and 5,841 animals with 95 %confidence interval (2,835 – 12,032) in the Northwest Pacific during August and September in 1989
and 1990 (IWC, 1992). In the western North Pacific, common minke whales are opportunistic
feeders consuming a broad of prey with flexible feeding habits. According to previous reports, they
consume several prey species such as pelagic schooling fish and zooplankton (Kasamatsu and Hata,
1985; Kasamatsu and Tanaka, 1992; Tamura et al., 1998, Tamura and Fujise, 2002a).
The results of the Japanese Whale Research Program under Special Permit in the Western North
Pacific (JARPN) and JARPN II feasibility study showed that common minke whales fed on various
prey species such as Japanese anchovy Engraulis japonicus, Pacific saury Cololabis saira, walleye
pollock Theragra chalcogramma and Japanese flying squid Todarodes pacificus, and the main preyspecies changed seasonally and geographically. For example, they feed on Japanese anchovy in
May/June and Pacific saury in July/August (Tamura and Fujise, 2000a, 2002b). The estimated prey
consumption by common minke whales was comparable to that of the commercial fisheries(Tamura and Fujise, 2000b, 2002c), indicating the interaction between common minke whales andfisheries may occur in the coastal area.
However, the Nisshin-Maru and large sighting/sampling vessels can not be operated in the nearshore area because of various restrictions and obstacles. Furthermore, these vessels can not joinsurvey in late autumn and early spring for operational reason. In order to cover the geographical andseasonal gaps of JARPN and JARPN II feasibility study, sampling of common minke whales in the
coastal area using small type whaling catcher boats was planed in 2002 (Government of Japan,
2002). Off Sanriku region, the coastal component of JARPN II was conducted in April and May.
On the other hand, in Kushiro region, the coastal component of JARPN II was conducted in
September and October. In this document, the abundance of common minke whales and theconsumption of targeted fisheries species by common minke whales were calculated using someassumption off Sanriku and Kushiro regions. Then, the prey consumptions by common minke
whales and fisheries catches were compared.

MATERIALS AND METHODS
Research area, year, season and sample size
Sanriku region
The sampling area covers within the 30 n.miles (maximum 50 n.miles) from the Ayukawa port
(Fig.1). The researches were conducted in April and May from 2003 to 2007. The sample size forthe minke whale in the Sanriku component started 50 animals in 2003. After 2004, the sample sizechanged to 60 animals to be taken in every spring (April and May). These surveys were described indetail by Kishiro et al. (2009).The actual sampling number of whales between 2003 and 2007 isshown in Table 1.
Kushiro region
The study area was covered north of 41N and longitude from 143.15E (Cape Erimo) to 146E. The
sampling area covers within the 30 n.miles (maximum 50 n.miles) from the Kushiro port (Fig.1).
The researches were conducted in September and October from 2002 to 2007. The sample size forthe minke whale in the Kushiro component started 50 animals in 2003. After 2004, the sample sizechanged to 60 animals to be taken in every autumn (September and October). These surveys were
described in detail by Kishiro et al. (2009).The actual sampling number of whales between 2002
and 2007 is shown in Table 1.

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Sampling of stomach contents of minke whales
Baleen whales have four chambered stomach system (Hosokawa and Kamiya, 1971; Olsen et al.,1994). The stomach contents remain in the forestomach (1st. stomach) and fundus (2nd. stomach).
Therefore, this study was based on contents from forestomach and fundus.
The stomach contents were removed at the research land station. Then, contents were weighed to
the nearest 0.1 kg. A sub-sample (1-5 kg) of stomach contents was removed and frozen and/or fixedwith 10 % formalin water for later analyses. The stomach contents were transferred to a system
consisting of three sieves (20 mm, 5 mm and 1 mm), which were applied in the Norwegianscientific research to filter off liquid from the rest of the material (Haug et al. 1995). The subsample (3-4 kg) included all undigested fish skulls, free otoliths and squid beaks, which were kept
frozen for later analyses in the laboratory.
Data analyses
Prey species identification and restoring stomach contents weight
In the laboratory prey species in the sub-samples were identified to the lowest taxonomic level as
possible. Undigested preys were identified using morphological characteristic of copepods(Brodskii, 1950), euphausiacea (Baker et al., 1990), squids (Kubodera and Furuhashi, 1987) andfish (Masuda et al., 1988; Chihara et al., 1997). The otoliths and jaw plate were used to identify thefish and squid with advanced stage of digestion (Morrow, 1979; Ohe, 1984; Kubodera andFuruhashi, 1987; Arai, 1993).
When undigested fish and squid were found, fork length, mantle length and the weights were
measured to the nearest 1 mm and 1 g, respectively. This data were used for restoring their stomach
contents with advanced stage of digestion.
The total number of each fish and squid species in the sub-sample were calculated by adding to
the number of undigested fish or squid, undigested skulls and half the total number of free otoliths.
The total weight of each prey species in the sub-sample was estimated by multiplying the average
weight of fresh specimens by the number of individuals. The total number and weight of each preyspecies in the stomach contents were estimated by using the figures obtained from the sub-sample
and the total weight of stomach contents. The total weight of each zooplankton was estimated byusing an assimilation efficiency of 84 % (Lockyer, 1981).
Prey composition in each year
In order to simplify the comparison of feeding indices, prey species were divided into the following
prey groups: krill (Euphausia pacifica), Japanese anchovy, Japanese sand lance, Pacific saury,walleye pollock, Japanese pomfret (Brama japonica), Salmonids, Japanese flying squid and otherfishes.
The relative prey composition (%) in weight of each prey species (RW) in each month was
calculated as follows:
RW i = (Wi / Wall) × 100
W i = the weight of contents containing prey group i
Wall = the total weight of contents analyzed.
Estimation of daily and seasonal prey consumption in each whale species
The daily consumption of each prey species (D) by different maturity stages of minke whale were
calculated from the following equations (Sigurjónsson and Víkingsson, 1997):
3

D = 206.25M0.783 ; F = D/E
D : Daily prey consumption (kcal day-1)
M: Mean body weight of whales (kg)F : Daily prey consumption (kg day-1)
E : Caloric value of prey species (kcal kg-1)
The following figures and assumptions were used for this method.
A: Mean body weight (M)In Sanriku region, the mean body weight of 2,080 kg and 2,120 kg for immature male and female ofminke whale were calculated, respectively. For mature male and female of minke whale were 4,060
kg and 5,330 kg, respectively. In Kushiro region, the mean body weight of 2,130 kg and 1,980 kg
for immature male and female of minke whale were calculated, respectively. For mature male andfemale of minke whale were 4,830 kg and 6,140 kg, respectively. These weights were obtained
from JARPN II survey data.
B: Caloric value of prey species (E)Stomach contents analyses show large variations in the diet of baleen whales in the western North
Pacific (Kasamatsu and Tanaka, 1992; Tamura et al., 1998). In the North Atlantic, the energy
contents of the prey species varies from 900 kcal kg-1 when feeding on Parathemisto spp. to ashigh as 3,000 kcal kg-1 when feeding on herring (Markussen et al., 1992). In this study, the meancaloric value of copepods, krill, Japanese anchovy, Pacific saury, walleye pollock and Japanese
flying squid were calculated using bomb caloric meter (Table 2).
C: Residence time in the western North Pacific (D)It was assumed that the minke whales spend about 150 days in the feeding areas in the western
North Pacific. These assumptions for estimating the feeding days were used. Lockyer (1981)
indicated that around 83% of the annual energy intake in southern Hemisphere balaenopterids isingested during the summer season, corresponding to approximately ten times higher feeding rates
during feeding season of summer than non-feeding season of winter.
Based on this assumption, the average daily prey consumption during feeding season (SF), andduring non-feeding season (NF) were made for the baleen whales by the following equations:
SF = 2.020 F
NF = 0.289 F
The residence time of the common minke whale off Sanriku and Kushiro region was assumed to be
60 days, respectively
D: The composition of maturity stages of whales
The composition of maturity stages of whales was shown in Table 3. Sexually mature male ofcommon minke whales were defined by testis weight (larger side) of more than 290g. Female had at4least one corpus luteum or albicans in their ovaries was determined as sexually mature (Kishiro etal., 2009; Yoshida et al., 2009).
E: The yearly number of whales distributed by each sexual maturity stage and area
The number of whales distributed in each area and year was described by Hakamada et al. (2009).
In this study, the number of the minke whales distributed off Sanriku during the survey period wasused only that of coastal strata. The yearly number of whales distributed in each sexual maturity
stage and area is estimated in Table 4.

RESULTS
Diversity and composition of prey species
Sanriku region
Three prey species consisting of 1 krill and 2 fish (Japanese sand lance and Japanese anchovy) wereidentified in stomachs of common minke whales caught off Sanriku region in 2003 - 2007 JARPNII.
Japanese sand lance, Japanese anchovy and krill were dominant prey species and composed 58.8–
81.9 %, 0.0–39.5 % and 0.1–37.9 % in wet weight (%), respectively (Table 5). Most minke whales(74 %) had fed upon one single prey species. Animal of 25.6 % had fed upon two species in thestomach (Table 6).
Kushiro region
The dominant prey species consisting of 1 krill (Euphausia pacifica), 3 fishes (Japanese anchovy,
Pacific saury, and walleye pollock) and 1 squid (Japanese flying squid) were identified in common
minke whales caught off Kushiro region in 2002 - 2007 JARPNII. Japanese anchovy, Pacific saury,walleye pollock and Japanese flying squid were dominant prey species and composed 9.5–60.6 %,1.2–40.6 %, 3.6–71.5 % and 0.1-33.8 % in wet weight (%), respectively (Table 5). Most minke
whales (67 %) had fed upon one single prey species. Animal of 27 % had fed upon two species andonly 6.1% had more than two prey species in the stomach (Table 6).
The size distribution of three main prey consumed by common minke whales
Japanese sand lance
The size distributions of Japanese sand lance in the stomach of common minke whales are shown in
Fig. 2-1. Minke whale feed on matured sand lance, the fork length ranged from 103 to 294 mm witha single mode at 130 mm.
Pacific saury
The size distributions of Pacific saury in the stomach of common minke whales are shown in Fig. 22. The fork length ranged from 127 to 342 mm with a bimodal mode at 150 mm and 250-270 mm.
Walleye pollock
The size distributions of walleye pollock in the stomach of common minke whales are shown in Fig.
2-3. The fork length ranged from 177 to 517 mm with a bimodal mode at 250 mm and 400 mm.

5Japanese flying squid
The size distributions of Japanese neon flying squid in the stomach of common minke whales areshown in Fig. 2-4. The fork length ranged from 127 to 296 mm with a single mode at 210 mm.
Daily and seasonal prey consumption by whales
Sanriku region
The estimated daily prey consumption weights during feeding period off Sanriku region were 93113 kg and 94-114 kg for immature male and female, and 156-190 kg and 193-236 kg for mature
male and female, respectively (Table 7).
The total prey consumption in the Sanriku region of Japanese sand lance, Japanese anchovy andKrill by common minke whales was estimated as 1,616 and 683 tons, 194 and 150 tons, 109 and 1
tons per year in 2005 and 2006 seasons, respectively (Table 8).
Kushiro region
The estimated daily prey consumption weights during feeding period off Kushiro region were 78118 kg and 73-111 kg for immature male and female, and 107-224 kg and 133-270 kg for mature
male and female, respectively (Table 7).
The total prey consumption of Pacific saury, walleye pollock and Japanese flying squid andJapanese anchovy by common minke whales was estimated as 39–1,075 tons, 95–2,322 tons 31,753 tons and 308–1,422 tons per year, respectively (Table 8).
The feeding impact of fisheries resources
Sanriku region
Catch data of important commercial fish were provided from the Miyagi Prefecture Fisheries
Technology Institute (2008). The catches of Japanese sand lance around the Sendai Bay fromFebruary to May in 2005 and 2006 seasons were 8,623 tons and 5,552 tons, respectively. The
consumption of sand lance by minke whales was equivalent to 18.7 and 12.3 % of the 2005 and2006 fisheries catch (Table 9).
Kushiro region
Catch data of important commercial fish were provided from the Hokkaido Government (2008).
This data was the catch of the Kushiro blanch. The fisheries catches of Pacific saury, walleye
pollock and Japanese flying squid in 2002-2006 were 48,403-61,895 tons, 52,524-75,041 tons and1,497-5,042 tons per year, respectively. The consumption of Pacific saury, walleye pollock andJapanese flying squid by minke whales were equivalent to 0.1-1.8 %, 0.1-3.6 % and 0.1-117.1 % offisheries catch, respectively (Table 9).

6

DISCUSSION
Sanriku region
Some sand lance species in the world have specific habit, summer aestivation (Robards et al, 1999).
They hide themselves in near shore substrates every summer, when water temperature is high. In
Sendai Bay, they hide during August and December, at mainly rough sand sediment in shallow
water (< 50 m depth) (Kobayashi et al. 1991). So, Japanese sand lance as prey of common minke
whale off Sanriku region is presumably available only from February to June through a year.
The dominant prey species of common minke whales sampled off Sanriku region in April and May
were Japanese sand lance and followed Japanese anchovy and krill Euphausia pacifica. This result
was similar to that of previous report (Kasamatsu and Tanaka, 1992). They analysed the yearlychange of prey species of common minke whale off Sanriku during 1948 to 1987. Commercial
whaling had been made from January to September with peaks from April to June. After 1980, thepeak of catch was observed in April. The dominant prey species were krill, Japanese sand lance andiwashi (Japanese sardine and/or Japanese anchovy). They pointed out that the yearly change ofJapanese sardine in stomach contents were similar to the yearly trend of fisheries catch of Japanesesardine in this area.
The observed maximum stomach contents weight was 102.6 kg (2.0 % of body weight). Our daily
estimated prey consumption was from 120 kg to 244 kg (from 3.8 % to 4.8 % of body weight).
Common minke whale should take on prey at several times due to meet a demand for their energy
requirement in a day. Based on diurnal change in feeding activity of common minke whale in thewestern North Pacific, Tamura and Fujise (2000c) pointed out that common minke whales feed on
prey at several times throughout the day at the surface. Our results supported their consideration.
The seasonal consumption of common minke whales distributed off Sanriku during April and May(60 days) was 834-1,919 tons. The total consumption of Japanese sand lance estimated 683-1,616
tons. Based on results of the sand lance consumption by common minke whales and the degree ofoverlap between fisheries ground of Japanese sand lance and sighting position of common minke
whales, it is conceivable that the possibility with direct interaction between common minke whale
and Japanese sand lance fisheries occurs. The fisheries season of Japanese sand lance is fromFebruary to May, and common minke whales also feed on Japanese sand lance in the later half ofthe season. Furthermore, sighting positions of common minke whales were overlapped fisheries
ground of Japanese sand lance. The catch quota and season of Japanese sand lance off the Sanriku
region (around the Sendai Bay) is regulated by the fisheries conference in order to protect theresources of Japanese sand lance and price control. However common minke whales feed onJapanese sand lance about one third of catch. Therefore, consumption by common minke whales
should be taken into account for fishery management of Japanese sand lance off Sanriku region.
The ecosystem model (e.g. Okamura et al., 2009) will make clear the interaction between minke
whales and sand lance.
Furthermore, some fishermen indicate the fishing operation have interfered by common minke
whales. Some minke whales attack and feed on the school of sand lance when fishermen attracted
fishes around boat, causing dispersion of the schools of Japanese sand lance.
Kushiro region
Kasamatsu and Tanaka (1992) analysed the yearly change of prey species of common minke whale
off Kushiro region during 1948 to 1987. Commercial whaling was made from April to October withpeaks from July to September. After 1982, two peaks were observed in July and September. The
dominant prey species were krill, Japanese sand lance, chub mackerel, iwashi (Japanese sardine
and/or Japanese anchovy), walleye pollock, Pacific saury and Japanese flying squid. They pointed
out that the yearly change of Japanese sardine in the stomach contents were similar to the yearly
trend of abundance of Japanese sardine in this area. In the results of JARPN II, the dominant prey7

species of common minke whales sampled off Kushiro region from September to October were krill,
Japanese anchovy, Pacific saury, walleye pollock and Japanese flying squid. This result was similar
to the previous report.
The maximum stomach contents weight was 154.3 kg (2.6 % of body weight). Our daily estimatedprey consumption was from 73 kg to 270 kg (from 3.8 % to 4.8 % of body weight). Common minke
whale should take on prey at several times due to meet a demand for their energy requirement in aday. Based on diurnal change in feeding activity of common minke whale in the western North
Pacific, Tamura and Fujise (2000c) pointed out that common minke whales feed on prey at several
times throughout the day at the surface. Our results supported their consideration.
The total consumption of common minke whales distributed off Kushiro during September andOctober (60 days) was approximately 745–5,190 tons. The prey consumption of economicallyimportant Pacific saury, walleye pollock and Japanese common squid by common minke whales
were calculated as 39–1,075 tons, 95–2,322 tons and 3–1,753 tons, respectively.
Based on results of the Pacific saury consumption by common minke whales and the degree ofoverlap between fisheries ground of Pacific saury and sighting position of common minke whales, it
is conceivable that the possibility with direct interaction between common minke whale and Pacificsaury fisheries occurs. The fisheries season of Pacific saury is from August to October, andcommon minke whales also feed on Pacific saury in the same season. Tamura and Fujise (2002c)
noted that most of the common minke whales sightings in sub-area 7W occurred close to fishinggrounds of Pacific saury. This observation suggested the direct interaction between common minke
whales and Pacific saury fishery from summer to autumn in the western North Pacific. Therefore,
consumption by common minke whales should be taken into account for fishery management ofPacific saury off Kushiro region. Furthermore, some fishermen indicate the fishing operation haveinterfered by common minke whales. Some minke whales attack and feed on the school of Pacificsaury when fishermen attracted fishes around boat, causing dispersion of the schools of Pacificsaury.

ACKNOWLEDGEMENTS
We would like to thank all captains, crews and researchers, who were involved in coastal
component of JARPNII surveys. Our sincere thank to Dr. H. Hatanaka and Dr. Luis A. Pastene of
the Institute of Cetacean Research (ICR) for their valuable suggestions and useful comments on thispaper. Catch data of sand lance ware provided from Dr. H. Nagashima of the Miyagi Prefecture
Fisheries Research and Dr. S. Izumi of the Development Centre and Fukushima Prefecture Fisheries
Research Centre. We would like to thanks them for their cooperation.

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Pacific minke whale Paper SC/F2KJ24 presented to the JARPN review meeting, February 2000
(unpublished). 18pp.
Tamura, T. and Fujise, Y. 2000c. Diurnal change in feeding activity in the western North Pacificminke whale. Paper SC/F2KJ23 presented to the JARPN review meeting, February 2000
(unpublished). 16pp.
Tamura, T and Fujise, Y.2002a. Geographical and seasonal changes of prey species of minke whalein the Northwestern Pacific. ICES Journal of Marine Science. 59:516-528.
Tamura, T. and Fujise, Y. 2002b. Food habit of common minke whales based on JARPN II.
Apendix 4, pp 47-63. In: Government of Japan (Fujise, Y., Kawahara, S., Pastene, L.A. andHatanaka, H. Eds.) Report of 2000 and 2001 feasibility study of the Japanese Whale Research
Program under Special Permit in the western North Pacific-Phase II (JARPN II). Paper SC/54/O17
submitted to the 54th IWC Scientific Committee Meeting (Available from the IWC Secretariat).

10

Tamura, T and Fujise, Y. 2002c. Daily and seasonal prey consumption by common minke whale
and Bryde’s whale in the western North Pacific. Appendix 4. pp 85-96. In: Government of Japan(Fujise, Y., Kawahara, S., Pastene, L.A. and Hatanaka, H. eds.), Report of 2000 and 2001
feasibility study of the Japanese Whale Research Program under Special Permit in the western
North Pacific-Phase II (JARPN II). Paper SC/54/O17 submitted to the 54th IWC ScientificCommittee Meeting (Available from the IWC Secretariat).
Yoshida, H., Kishiro, T., Goto, M., Bando, T., Tamura, T., Konishi, K., Okamoto, R. and Kato, H.
Relationship between body size, maturity, and feeding habit of common minke whales off Sanriku
in spring season, from 2003-2007 whale sampling surveys under the JARPN II coastal component
off Sanriku. Paper SC/J09/JR12 presented to the JARPN II Review Workshop, Tokyo, January
2009 (unpublished) 20pp.

11

Table 1. Sample size of common minke whale off Sanriku and Kushiro regions.
Year
Sanriku
Kushiro

2002
50

2003
50
-

2004
59

2005
60
60

2006
60
35

2007
57
50

Table 2. Results of caloric value of dominant prey species
SpeciesSize

Copepoda (Neocalanus cristatus )Krill （Eupahusia pacifica ）Sand lance
Japanese anchovy
Small
Large
Pacific saury
Small
Large
Walleye pollock
Japanese flying squid
Deep-sea squid

BodylengthBody
weightEnergyKcal/kg
920
850
1,840

86 mm
125 mm

7g
18 g

1,320
1,530

158 mm
16 g
300 mm
145 g
192 mm
66 g
430 mm
624 g
206 mm200 g
6,700 mm 6,930 g

1,260
3,140
1,490
1,480
1,580
650

Table 3. Sexual maturity composition (%) of common minke whales off Sanriku and Kushiro
regions.
(IM: Immature male; MM: Mature male; IF: Immature female; MF: Mature female)

Sanriku
IM
MM
IF
MF
N

2003
24.5
16.3
40.8
18.4
50

2005
25.0
13.3
38.3
23.3
60

2006
23.3
20.0
51.7
5.0
60

2007
19.6
16.1
51.8
12.5
57

Kushiro
Year
IM
MM
IF
MF
N

12

2002
32.0
32.0
22.0
14.0
50

2004
25.4
54.2
16.9
3.4
59

2005
25.4
49.2
25.4
0.0
60

2006
36.4
33.3
24.2
6.1
35

2007
35.4
29.2
35.4
0.0
50

Table 4. Results of numbers of whales distributed in Sanriku and Kushiro regions(Ref. Hakamada et al., 2009; Table 3)(IM: Immature male; MM: Mature male; IF: Immature female; MF: Mature female)

Sanriku
Year Sex maturity
2005
IM
MM
IF
MF
Total
2006
IM
MM
IF
MF
Total

Number
62
33
95
58
247
29
25
64
6
123

KushiroYear Sex maturity
2002
IM
MM
IF
MF
Total
2004
IM
MM
IF
MF
Total
2005
IM
MM
IF
MF
Total
2006
IM
MM
IF
MF
Total
2007
IM
MM
IF
MF
Total

Number
192
192
132
84
601
94
200
62
12
368
80
155
80
0
316
88
80
58
15
241
50
41
50
0
142

Table 5. Diet composition (RW: %) in the stomach contents of common minke whales off Sanriku
and Kushiro regions
Sanriku
NumberSpecies
Krill
Anchovy
Sand lance

2003
N=50
Broken12
Empty
0 （0.0%）N W%
kg±S.D
13 37.9
45.13± 40.93
29 62.1
33.20± 44.76

2005
N=60
Broken10
Empty
0 （0.0%）N W%
kg±S.D
15 5.752.39±34.95
26 10.1
31.12±28.78
48 84.2
32.42±32.72

N
1
7
1

2006
N=60
Broken15
Empty
1 （1.7%）
W%
kg±S.D
0.1
1.24
18.0
11.67±17.44
81.9
24.46±27.17

2007
N=57
Broken17
Empty
0 （0.0%）N W%
kg±S.D
1
1.7
13.01
39.5
13.40±18.80
2 58.812.08±19.15

Kushiro2002
N=50
Broken3
Empty
0 （0.0%）Species
N W%
kg±S.DKrill
4 10.942.42±38.61
Anchovy
31 19.0
9.56±9.32
Saury
20 16.6
12.96±26.30
Walleye pollock 12 19.7
25.58±22.57
Japanese flying squid 833.8
65.90±50.12
Pacific pomfret Salmonids
Other fish20.1
0.44±0.15
Number2004
N=59
Broken1
Empty
0 （0.0%）N W%
kg±S.D1
1.9
26.89
43 53.7
17.80±15.18
23 40.6
25.13±27.29
4
3.6
12.89±15.61
1
0.1
1.58
1
0.2
2.25
-

2005
2006
N=60
N=35
Broken5
Broken
1
Empty
Empty
0 （0.0%）0 （0.0%）N W%
kg±S.DN W%
kg±S.D17 13.3
0.5
3.32
22.95±17.34 1
30 9.5
6 60.69.31±8.56
12.13±14.34
5
1.2
6
7.6
7.10±9.82
15.67±6.02
20 71.5 104.61±220.83 7 25.4
22.56±48.80
3
4.5
5.9
36.42
43.59±71.49 2
-

13

2007
N=50
Broken13
Empty
0 （0.0%）N W%
kg±S.D5
2.9
9.26±7.01
20 46.2
36.92±51.43
9 13.824.46±41.74
15 25.0
26.58±28.04
2 12.196.48±135.31
1
0.1
1.24
0
-

Table 6. Prey composition of common minke whales sampled in JARPN II.

Sanriku
Number ofprey species
1Japanese sand lance
Krill
Japanese anchovy

Prey species
N
109
10
9
128
18
2
19
5
44
172

%
63.4
5.8
5.2
74.4
10.5
1.2
11.0
2.9
25.6
100.0

Number ofPrey species
prey species
N
1
Japanese anchovy99
Walleye pollock
21
Pacific saury
19
Krill
9
Japanese neon flying squid
6
Total
154
2
Japanese anchovy+Pacific saury
13
Japanese anchovy+Walleye pollock
4
Japanese anchovy+Japanese neon flying squid
2Japanese anchovy+Salmonidae
1
Walleye pollock+Japanese anchovy
9
Walleye pollock+Pacific saury2
Walleye pollock+Krill
2
Walleye pollock+Japanese neon flying squid
1
Pacific saury+Japanese anchovy
10
Pacific saury+Japanese neon flying squid
1
Krill+Walleye pollock
6
Krill+Japanese anchovy
5
Krill+Pacific saury
2
Krill+Japanese neon flying squid
1Japanese neon flying squid+Japanese anchovy
3
Total
62
3
Japanese anchovy+Pacific saury+Walleye pollock
1
Japanese anchovy+Pacific saury+Japanese neon flying squid 1
Walleye pollock+Japanese anchovy+Pacific saury
5Walleye pollock+Krill+Pacific saury
1Walleye pollock+Pacific saury+Other squid
1
Pacific saury+Walleye pollock+Japanese anchovy2
Pacific saury+Walleye pollock+Japanese pomfret
1
Krill+Japanese anchovy+Walleye pollock
1
Krill+Pacific saury+Walleye pollock
1
Total
14
No. whales Observed
230

%
43.0
9.1
8.3
3.9
2.6
67.0
5.7
1.7
0.9
0.4
3.9
0.9
0.9
0.4
4.3
0.4
2.6
2.2
0.9
0.4
1.3
27.0
0.4
0.4
2.2
0.4
0.4
0.9
0.4
0.4
0.4
6.1
100.0

Total
Japanese sand lance+Japanese anchovy
Japanese sand lance+Krill
Japanese anchovy+Japanese sand lance
Krill+Japanese sand lance
Total
No. whales Observed
2

Kushiro14

Table 7. The daily consumption (kg) n each year and area of common minke whales.
(IM: Immature male; MM: Mature male; IF: Immature female; MF: Mature female)
Sanriku
2003

MonthMaturity stage

2005

2006

2007

IM

MM

IF

MF

IM

MM

IF

MF

IM

MM

IF

MF

IM

MM

IF

MF

43

72

43

89

5

9

5

11

0.1

0.2

0.1

0.2

2

3

2

3

Prey / Consumption (kg)

Krill
Anchovy

0

0

0

0

10

16

10

20

17

28

17

35

38

65

39

80

Sand lance

70

118

71

146

79

134

81

166

76

128

77

158

57

96

58

119

Total

113

190

114

236

94

159

96

197

93

156

94

193

97

164

99

203

MF

IM

MM

IF

MF

Kushiro2002

Month
Maturity stage

2004
IM

MM

2006

2005
IF

IM

MM

2007

IM

MM

IF

MF

IF

MF

IM

MM

IF

MF

Krill

11

20

10

24

1

3

1

3

16

30

15

36

1

1

0

1

3

3

2

4

Anchovy

18

35

17

42

42

79

39

95

11

21

11

26

61

115

57

139

45

49

26

62

Prey / Consumption (kg)

Saury

16

31

15

37

31

60

30

72

1

3

1

3

8

14

7

17

13

15

8

18

Walleye pollock

19

36

18

44

3

5

3

6

84

160

80

193

25

48

24

58

24

27

14

33

Japanese flying squid

33

62

31

75

0

0

0

0

5

10

5

12

6

11

6

14

12

13

7

16

Pacific pomfret

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0.1

0.1

0.1

0.1
0

Salmonids

0

0

0

0

0.2

0.3

0.1

0.4

0

0

0

0

0

0

0

0

0

0

0

Other fish

0.1

0.2

0.1

0.2

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

97

184

92

223

78

147

73

178

118

224

111

270

100

190

95

229

97

107

57

133

Table 8. The prey consumption (tons) by common minke whales off Sanriku and Kushiro regions
Sanriku
Year

2005

2006

Krill

109

1

Anchovy

194

150

Sand lance

1,616

683

Total

1,919

834

Year

2002

2004

2005

2006

2007

Krill

565

50

432

10

22

Anchovy

985

1,422

308

1,217

344

Saury

861

1,075

39

153

103

Walleye pollock 1,021

95

2,322

510

186

Japanese flying squid

1,753

3

146

118

90

Pacific pomfret

0

0

0

0

1

Salmonids

0

5

0

0

0

Other fish

5

0

0

0

0

KushiroTotal

5,190 2,650 3,247 2,008

15

745

Table 9. Commercial fish catches and estimated consumption by minke whales of the Japanesesand lance, Pacific saury, walleye pollock and Japanese flying squid(Ref. Miyagi Prefecture Fisheries Technology Institute, 2008; Hokkaido government,
2008)
Sanriku

KushiroSand lance

Pacific saury

Year
2003
2004
2005
2006

Fisheries
catch
6,659
7,016
8,623
5,552

Consunption
by whales
1,616
683

%

Year

18.7
12.3

2002
2003
2004
2005
2006

Fisheries
catch
55,59459,984
48,40358,527
61,895

Consunption
by whales
861
1,075
39
153
103

%
1.5
1.8
0.1
0.3
0.2

Walleye pollock
Year
2002
2003
2004
2005
2006

Fisheries
catch
52,52475,041
65,18654,62856,582

Consunption
by whales
1,021
95
2,322
510
186

%
1.9
0.1
3.6
0.9
0.3

Japanese flying squid
Year
2002
2003
2004
2005
2006

16

Fisheries
catch
1,497
3,751
3,721
5,042
2,311

Consunption
by whales
1,753
3
146
118
90

%
117.1
0.1
3.9
2.3
3.9

1) Sanriku

2) Kushiro

Fig1. Research area off Sanriku and Kushiro regions

600
N=1,656

N

400

200

0
50

100

150

200

250

300

mm

Fig 2-1. The distribution of Japanese sand lance size in the stomach contents of minke whales inSanrilu region
15
N=53

12

N

9
6
3
0
100

150

200

250

300

350

400

mm

Fig 2-2. The distribution of Pacific saury size in the stomach contents of minke whales in Kushiro
region
17

30
N=233

N

20

10

0
150

200

250

300

350

400

450

500

550

mm

Fig 2-3. The distribution of walleye pollock size in the stomach contents of minke whales inKushiro region

150
N=392

N

100

50

0
100

150

200

250

300

350

400

mm

Fig 2-4. The distribution of Japanese flying squid size in the stomach contents of minke whales inKushiro region

18