Technical Reports of the Institute of Cetacean Research (2017)

pp. 44–57

Technical Report (not peer reviewed)

Overview of stomach content analyses for sei, Brydeʼs andcommon minke whales under the oﬀshore component of JARPNII,
and temporal changes in feeding habits
Kenji Konishi*, Tatsuya Isoda and Tsutomu Tamura
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Contact e-mail: konishi@cetacean.jp

ABSTRACTThis study presents an overview of the stomach content analyses for sei, Brydeʼs and common minke whales
oﬀ the Paciﬁc coast of Japan based on data and samples collected by the oﬀshore component of JARPNII during 2000–2016. The three species were highly dependent on small pelagic ﬁsh, in addition to planktonic crustaceans. The prey species composition in sei whales drastically changed from Japanese anchovy in the early
2000s to Japanese sardine in 2014 to 2016, while copepods (Neocalanus spp.) steadily occurred throughout
the years in oﬀshore waters. Brydeʼs whale had a simple prey composition involving mainly Japanese anchovy,
but a lesser amount of this prey species was observed during the last three years. Prey composition in common minke whales in oﬀshore waters showed that Japanese anchovy and Paciﬁc saury are the main prey species, while in the vicinity of northern Japan, Japanese anchovy and walleye pollock were the dominant preyspecies. These three whale species showed diversities in their feeding habits reﬂecting changes in prey species
populations and availability through the years.

INTRODUCTION
The Japanese Whale Research Program in the western
North Paciﬁc, Phase II (JARPNII) started in 2000 with theprimary purpose to study the interactions between ﬁsheries and cetaceans through ecosystem modeling of the
Paciﬁc side of Japan, an area well known as a large ﬁsheries ground (GOJ, 2002; 2004). The goal of JARPNII wasto assist in the formulation of eﬀective ecosystem-based
ﬁsheries management in this research area.
This paper focuses on the study of the feeding ecologyof three baleen whale species, sei whale (Balaenoptera
borealis), Brydeʼs whale (B.edeni) and common minke
whale (B. acutorostrata) based on surveys under the oﬀshore component of JARPNII (whales sampled by the pelagic research vessels) . The baleen whales in oﬀshore waters are highly dependent on abundant pelagic ﬁshes andzooplankton which are important components of the food
web in the subarctic region of the western North Paciﬁc.
Eggs and larvae of pelagic ﬁsh, such as Japanese anchovy Engraulis japonicus and Japanese sardine Sardinops
melanostictus are transported by the Kuroshio Current
to oﬀshore waters (Itoh et al., 2009; 2011; Okunishi
et al., 2011), and these species are important prey items
for baleen whales, in addition to crustaceans such as krill.
44

In fact, the Japanese anchovy was found in the stomachof sei, Brydeʼs and common minke whales sampled in theearly half of the JARPNII (Konishi et al., 2009), in addition to mackerel (genus Scomber). Acoustic and trawlingsurveys during JARPNII (Murase et al., 2012) showed thatJapanese anchovy was distributed widely in the survey
area between 2004 and 2007. Because these pelagic ﬁsh
species are also commercially important, there are manystudies on the catch history (Yatsu et al., 2005; Yonezaki
et al., 2015), optimal environment (Takasuka et al., 2007)
and transportation to oﬀshore areas (Itoh and Kimura,2007; Itoh et al., 2009; 2011). These studies suggested
synchronized exchange of favorable environmental conditions between Japanese sardine and Japanese anchovy
caused by climate change, which can be deﬁned by Paciﬁc
Decadal Oscillation (PDO) (Mantua and Hare, 2002).
In the early 2000s, when sampling of sei and Brydeʼswhales started in the JARPNII, the sardine population had
already collapsed and the anchovy catch had increased(Yatsu et al., 2005; Takasuka et al., 2008; Itoh et al., 2009).
Since PDO ﬂuctuations occur in scale from 15–25 years
and 50–70 years (Mantua and Hare, 2002), the continuous sampling under the JARPNII for more than a decade isuseful to see changes in the feeding habits of sei, Brydeʼsand common minke whales.

Overview of stomach content analyses for sei, Brydeʼs and common minke

The main purpose of this study was to present an
overview of the studies of feeding ecology of sei, Brydeʼsand common minke whales based on stomach content
analyses, and to examine decadal changes in the feeding
habits of these three species.

MATERIALS AND METHODS
Study area
The JARPNII research area has a unique environment
under the eﬀect of both the cold Oyashio Current andthe warm Kuroshio Current and this transition region covers most of this research area (see Favorite et al., 1976).
High productivity is an important factor related to spring
blooming in the lower trophic level (Liu et al., 2004). Copepods (Neocalanus spp.) are the dominant zooplankton
in the Oyashio region during spring to summer in the surface layer, which depend on phytoplankton (see Kobari
and Ikeda, 1999; Tsuda et al., 2001).
The occurrence of subarctic gyres near the Kuroshio
Current is also important to marine mammals (Springer
et al., 1999). Basic oceanic features of oceanic fronts,
Kuroshio-current and eddies in July are illustrated as an

example (Figure 1). To examine positions of oceanic fronts,
Argo data were used for salinity and temperature proﬁles(http://www.argo.ucsd.edu, http://argo.jcommops.org). To
draw the Kuroshio-current and eddies, sea surface heightdata were obtained from the AVISO webpage (http://www.
aviso.altimetry.fr/duacs/). Another topographic feature associated with prey distribution in this area is the Emperor
Seamounts and the Shatsky Rise which cause upwellingand changing current stream (Figure 2). The northward
branch of the Kuroshio Extension Front near the Shatsky
Rise is located around 160°E (Mizuno and White, 1983).
Whale sampling
Data and samples used in this study were obtained by the
JARPNII oﬀshore component in the period 2002–2016
for sei whales; 2000–2016 for Brydeʼs whales; and2000–2013 for common minke whales. Sample sizes of
the whales examined are shown in Table 1. Details of thesurvey procedure under JARPNII are available in Bandoet al. (2016) and Tamura et al. (2016). During the sampling survey, information on catch date and location foreach whale sampled as well surface temperature where
the whales were ﬁrst sighted, was recorded.
Prey information
Prey information was obtained by examining stomach
content of the whales sampled. Most of the stomachs
were occupied by a single prey species. The methodology
for stomach content analysis was described in previous

Figure 1.

Geographical locations of oceanic fronts at western
North Paciﬁc in July during 2001–2013. Original datafrom Argo ﬂoat (JAMSTEC). Upper left: Subarctic
Front: 4°C isotherm at 100 m depth (Argo datafrom JAMSTEC). Upper right: Subarctic boundary.
Salinity of 34 psu at near surface (Argo data from
JAMSTEC). Bottom left: Kuroshio extension northern branch. Bottom right: Kuroshio extension fromsea surface height (AVISO absolute dynamic topography derived from sea surface height measured
by several satellites, AVISO, France, http://www.
aviso.altimetry.fr); estimated current eddies area
also drawn. Detail of oceanographic features in the
JARPNII area during 2000 to 2013 is well describedin Okazaki et al. (2016). Deﬁnition of boundary followed description in Kida et al. (2015).

Figure 2.

The locations of major geographic features at the
JARPNII research area with isobath to 4000 m depth.
The contours are from the GEBCO bathymetric atlas(Amante and Eakins, 2009). Survey Areas are shownwith thick black line. Shatsky Rise and Emperor
Seamounts are also drawn by 3000–4000 m isobathin depth in the eastern part of the research area at
155°E–160°E and around 170°E, respectively.
45

Technical Reports of the Institute of Cetacean Research (2017)
Table 1
Number of sei, Brydeʼs and common minke whales caught under the JARPNII, by area, month and year.
Area 7
Sei
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016

May

Minke
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013

46

Jul.

1

4

Aug.

Sep.

May

Jun.

Jul.

3

16
2
3
19
2
24
1
9
5
31

16
28
6
9
19
6
11
3

6

10
7
6

8
10
16

May

Jun.

Jul.

Aug.

4

12
1
2

4
4

16
11

10
1

Area 9
Sep.

Oct.

May

Jun.

Jul.

11
9
41
19
23
35
38
18
26
21

32
12
36
17
6
16
15
13
29
11
45

3

5
22
18
13
11

3
4

Bryde's May
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016

Jun.

Area 8

Jun.

Jul.

6

33

11

1

19

7

3

36
5
1
26

Aug.

Sep.

24

19

13

4

7

Sep.

Oct.

11
20
9

49

12

46

May

Jun.

23

14
13
8
6

26
3
16
9

27
5
3
13
21

4
14
1
10

22

4

Jul.

Aug.

Sep.

6

18

May

Jun.

54

2

Jul.
22
1

19

14

3

14
11
79

18
11

11

4

14

Aug.

7
9
5

54

Sep.

Oct. Total

6
13
2

4
4

4

Aug.

Sep.

16
Aug.

7

Sep.

Oct.

May

Jun.

10
1

26
14
5

1

Jul.
23
20

3

18

11
4
12

10
1

16

47
57

Jul.

17
1
2

16
16

26

4

6
22

29

5

9

28

39
50
100
100
100
100
100
100
100
95
100
100
90
90
90

49
32

Jun.

Oct. Total

28
28

7
44

5
8
15

Sep.

23

1

May

3
27
6
23
9
17

35
13

Aug.

Aug.

3

3
10
5
3
4
1

24
3
14

16
5
5
28
60
38

29

22

12

2
1

3
3

4

1

43
50
50
50
50
50
50
50
50
50
50
50
34
28
25
25
25

Oct. Total
40
100
100
100
100
100
100
100
59
43
14
49
74
3

Overview of stomach content analyses for sei, Brydeʼs and common minke

reports (e.g. Tamura et al., 1998; Konishi et al., 2009), andit involves the steps shown in Figure 3. Prey length distributions for pelagic ﬁsh in the stomachs of the sampledwhales are shown in the Appendix.

RESULTSSei whale
Figure 4 shows the geographical position (based on the ﬁrst
sighting) of sei whales sampled including information of theprey species found in the stomachs. Whales were widelydistributed in the survey area, but mostly from east of 150°E
and south of 46°N between north of the Kuroshio extension
and just north of the Subarctic Front (see also Figure 1).
The main prey species were copepod (Neocalanusspp.), euphausiid (Euphausia spp.), Japanese anchovy,
two mackerel species (Scomber japonicus and S. aus-Figure 3.

Figure 4.

tralasicus) and Japanese sardine. Paciﬁc saury (Cololabis
saira) was found in the eastern side of the research areain every year. Most of the copepods found in the stomachs were 5th copepodite stage of Neocalanus cristatus
and N. plumchrus (also see Konishi et al., 2009). Minimalarmhook squid (Berryteuthis anonychus) was also foundmainly in far eastern areas near the Emperor Seamounts.
The locations of whales feeding on Japanese sardine was
the most eastern in the survey area, overlapping withwhales feeding on Japanese anchovy and copepods.
Prey composition in the stomach of sei whales sampledduring 2002–2016 is shown for each Area in Figure 5.
Copepod and Paciﬁc saury were dominant preys in Area
9 than in western Area 8, while Japanese anchovy andeuphausiid were found widely in both Areas 8 and 9. In
the years 2002–2012, Japanese anchovy, copepod andA schematic diagram of the steps in the analyses on stomach contents.

The distribution of sampled sei whales (based on ﬁrst sighting), and information of prey species in theirstomachs (period 2002–2016). The contours are from the GEBCO bathymetric atlas.
47

Technical Reports of the Institute of Cetacean Research (2017)

Figure 5.

Figure 6.

Prey composition in the stomach of sei whales sampled in the period 2002–2016, by Area and year.

Surface temperature in which sei whales were sampled, and prey species in their stomachs (2002–2016).

euphausiid were major components with the exceptionof years 2005 and 2008. After 2007, mackerel became
one of the major preys which coincided with a decreasing occurrence of anchovy and copepod. In the years
2014–2016, Japanese sardine was the dominant prey
while some Japanese anchovy was found only in 2016.
Stomachs with no contents (NC) were also found widely
throughout the survey years. Japanese sardine was not
the main prey species until recently.
Figure 6 shows the surface temperature in which sei
whales were found, including information on prey species in their stomachs. Surface temperature in which sei
whales were found varied according the prey species. Japanese anchovy was found in a wider range of surface temperatures. Copepods and Paciﬁc saury tend to be found atlower temperatures (c.a. <15°C) than mackerel. Althougha variation of surface temperature is observed within
years, these are not consistent among years. Length dis48

tribution of main ﬁsh prey species in the stomachs of sei
whales had diﬀerent modes among years (see Appendix).
Brydeʼs whale
Figure 7 shows the geographical position (based on theﬁrst sighting) of Brydeʼs whale sampled including information of the prey species found in the stomach. Their
distribution is mainly south and west of the distributionof sei whales sampled. They were concentrated around
145°E–150°E and 155°E–160°E, south of 41°N. Japanese
anchovy and euphausiids were found in a wide longitudinal range. Mackerels and stomiiforms (Vinciguerria nimbaria and Maurolicus muelleri) occurred oﬀshore.
Prey composition in the stomachs of Brydeʼs whales
sampled during 2000–2016 is shown for each Area in
Figure 8. Japanese anchovy, stomiiforms and euphausiid
were the dominant prey species. Mackerels were occasionally found in some years. The composition of mainOverview of stomach content analyses for sei, Brydeʼs and common minke

Figure 7.

The distribution of sampled Brydeʼs whales (based on ﬁrst sighting), and information of prey species intheir stomachs (period 2000–2016). The contours are from the GEBCO bathymetric atlas.

Figure 8.

Prey composition in the stomach of Brydeʼs whales sampled in the period 2000–2016, by Area and year.

prey species is highly variable among years, however
there was no obvious variation among Areas and decadalchange in the prey composition. However, it should be
noted that lower occurrence of anchovy and high occurrence of ʻNCʼ stomachs were observed in the last two
years (2015–2016). Japanese sardine was not a main preyspecies and was just found occasionally.
Figure 9 shows the surface temperature in which
Brydeʼs whales were found, including information on preyspecies in their stomachs. Brydeʼs whales fed on prey inwarmer surface temperature areas compared to sei andcommon minke whales in JARPNII. No obvious variationof surface temperature among the prey species was observed. Length distribution of pelagic ﬁsh prey species
showed variation of mode among years (see Appendix).

Common minke whale
Figure 10 shows the geographical position (based on theﬁrst sighting) of common minke whales sampled including information of the prey species found in the stomach.
Figure 11 shows details of the coastal area in the westernside of the research area.
Paciﬁc saury is the key prey species in oﬀshore waters and common minke whales occurred mainly northcompared to the sei whales sampled. Japanese anchovy
was found widely through longitudinal sectors, and also
was intensively fed on by common minke whales in the
coastal area (Figure 11). Minimal armhook squid and Paciﬁc
pomfret (Brama japonica) were found in the far northeastern regions near and above the Emperor Seamounts (Figure 10). In coastal waters, walleye pollock (Theragra chalcogramma), which occurs at bottom or midwater depth, wascommonly found above shelf edge and slope oﬀ eastern49

Technical Reports of the Institute of Cetacean Research (2017)

Figure 9.

Surface temperature in which Brydeʼs whales were sampled, and prey species in their stomachs(2000–2016).

Figure 10.

The distribution of sampled common minke whales (based on ﬁrst sighting), and information of prey species in their stomachs (period 2000–2013). The contours are from the GEBCO bathymetric atlas.

Hokkaido (Figure 11). Japanese anchovy, Paciﬁc saury andeuphausiids were also common prey species in this area.
The Japanese ﬂying squid (Todarodes paciﬁcus) was also
found just on the continental slope but only in early years of
JARPNII (Figures 10 and 11). Feeding on Japanese anchovyand euphausiid by common minke whales was also foundabove the continental shelf oﬀ Hachinohe (Figure 11).
Prey composition in common minke whales diﬀers among
years, but not to the extent as in the case of the sei whale.
Recent transition of pelagic ﬁsh species was not found probably due to the absence of common minke whale samples
50

during 2014–2016 (see Table 1 and Figure 12).
Surface temperature varied in the range of 10°C–20°C,
and the range was small in the oﬀshore area (Figure 13).
Length distribution of Japanese anchovy, mackerel andPaciﬁc saury in the stomach of common minke whales
diﬀers within and among years (see Appendix).

DISCUSSION
This study showed a general overview of stomach content analyses and decadal changes in feeding habits forsei, Brydeʼs and common minke whales in the westernOverview of stomach content analyses for sei, Brydeʼs and common minke

Figure 11.

Ampliﬁed plots of Figure 10 to show details of the situation in areas near to the coast of the Paciﬁc sideof Japan and northern Honshu and Hokkaido.

Figure 12.

Prey composition in the stomachs of common minke whales sampled in the period 2000–2013, by Areaand year.

North Paciﬁc in terms of rather qualitative information based on data collected by JARPNII in the period
2000–2016. The Japanese anchovy was an important
prey for the three whale species across the entire survey
area, and it was also important in the coastal area forcommon minke whales. The results showed a remarkable
shift in prey species in the case of the sei whales late in
the JARPNII period (2015–2016), i.e. a limited occurrenceof Japanese anchovy and higher incidence of Japanesesardine as main prey in the last three years (2014–2016).
A similar decrease of Japanese anchovy as prey species ofBrydeʼs whales also supported the prey shift.
There is no doubt that prey composition in the baleen
whales reﬂected a pelagic ﬁsh shift from Japanese anchovy
to Japanese sardine and mackerel in the western North
Paciﬁc. Mechanisms of these decadal scale shifts of pe-

lagic ﬁsh composition in the western North Paciﬁc wereinﬂuenced by large-scale SST variability by the Aleutian
Low (Miller et al., 2004; Sasaki et al., 2012). The responses
to the SST in terms of growth rate in sardine, saury andanchovy diﬀer. For example, the patterns of spawning temperature clearly show ʻwarmʼ and ʻeurythermalʼ Japanese
anchovy and ʻcoolʼ and ʻstenothermalʼ Japanese sardine in
the western North Paciﬁc (e.g. Takasuka et al., 2007; 2008;
Oozeki et al., 2009; Watanabe, 2009; Itoh et al., 2011).
Locations where whales were found in JARPNII elucidated the site-speciﬁc feeding behaviors of the whales.
Sei whales occurred where both pelagic ﬁsh and copepod
were available which covers the oﬀshore research area
to mainly feed on copepod and small pelagic ﬁsh. Brydeʼswhales occurred from the near coastal area in sub-area
7 to around the Shatsky Rise in sub-area 9, where both
51

Technical Reports of the Institute of Cetacean Research (2017)

Figure 13.

Surface temperature in which common minke whales were sampled, and prey species in their stomachs(2000–2013).

pelagic ﬁsh from the Kuroshio Current and euphausiid
are both common. They possibly can feed on euphausiids
even if pelagic ﬁsh is not available. Common minke whales
showed unique feeding habits with occurrences at higher
latitude to ca. 48°N and high dependency on Paciﬁc sauryin the oﬀshore area and prey related to the continental
shelf in coastal areas. They feed on minimal armhook
squid near the Emperor Seamounts where the mature
minimal armhook squid occurs in summer (Konishi andTamura, 2007). Minke whales also feed on larger prey,such as walleye pollock, Paciﬁc pomfret and salmonids.
This study highlighted the fact that feeding ecology studies of sei, Brydeʼs and common minke whales in the western North Paciﬁc are beneﬁted by long-term systematicsurveys, which allow decadal-level variability be studied.

ACKNOWLEDGEMENTS
We would like to thank all researchers and crews involvedin the JARPNII surveys, who supported feeding habits
studies on board of Nisshin-Maru ﬂeet. Thanks are also
due to the members of the Institute of Cetacean Researchfor useful suggestions and helping to conduct stomach
contents treatment. We ﬁnally thank the Fisheries Agency of Japan for supporting the JARPNII program.

REFERENCES
Amante, C. and Eakins, B.W. 2009. ETOPO1 1 Arc-Minute
Global Relief Model: Procedures, Data Sources and Analysis.
52

NOAA Technical Memorandum NESDIS NGDC-24. National
Geophysical Data Center, NOAA.
Bando, T., Yasunaga, G., Tamura, T., Matsuoka, K., Murase, H.,
Kishiro, T. and Miyashita, T. 2016. Methodology and survey
procedures under the JARPNII -oﬀshore component- during
2008 to 2014 with special emphasis on whale sampling procedures. Paper SC/F16/JR4 presented to the JARPNII special
permit expert panel review workshop, Tokyo, February 2016
(unpublished). 14 p.
Favorite, F., Dodimead, A. J. and Nasu, K. 1976. Oceanography ofthe subarctic Paciﬁc region, 1960–71. Int. North Paciﬁc Fish.
Comm. Bull. 33: 1–187.
Government of Japan. 2002. Research plan for cetacean studies
in the western North Paciﬁc under special permit (JARPNII).
Paper SC/54/O2 presented to the IWC Scientiﬁc Committee,
May 2002 (unpublished). 115 pp.
Government of Japan. 2004. Revised research plan for cetacean
studies in the western North Paciﬁc under special permit(JARPNII). Paper SC/56/O1 presented to the IWC Scientiﬁc
Committee, May 2004 (unpublished). 14 pp.
Itoh, S. and Kimura, S. 2007. Transport and survival of larvaeof pelagic ﬁshes in Kuroshio system region estimated with
Lagrangian drifters. Fish Sci. 73: 1259–1308.
Itoh, S., Yasuda, I., Nishikawa, H., Sasaki, H. and Sasai, Y. 2009.
Transport and environmental temperature variability of eggs
and larvae of the Japanese anchovy (Engraulis japonicus) andJapanese sardine (Sardinops melanostictus). Fish. Oceanogr.
18: 118–133.
Itoh, S., Saruwatari, T., Nishikawa, H., Yasuda, I., Komatsu, K.,
Tsuda, A. and Shimizu, M. 2011. Environmental variability andOverview of stomach content analyses for sei, Brydeʼs and common minke

growth histories of larval Japanese sardine (Sardinops melanostictus) and Japanese anchovy (Engraulis japonicus) near
the frontal area of the Kuroshio. Fish. Oceanogr. 20: 114–124.
Kida, S., Mitsudera, H., Aoki, S., Guo, X., Ito, S., Kobashi, F.,
Komori, N., Kubokawa, A., Miyama, T., Morie, R., Nakamura,H., Nakamura, T., Nakano, H., Nishigaki, H., Nonaka, M., Sasaki,
H., Sasaki, Y.N., Suga, T., Sugimonot, S., Taguchi, B., Takaya, K.,
Tozuka, T., Tsujino, H. and Usui, N. 2015. Oceanic fronts andjets around Japan: a review. J. Oceanogr. 71 (5): 469–497.
Kobari, T. and Ikeda, T. 1999. Vertical distribution, population
structure and life cycle of Neocalanus cristatus (Crustacea:
Copepoda) in the Oyashio region, with notes on its regionalvariations. Mar. Biol. 134: 683–696.
Konishi, K. and Tamura, T. 2007. Occurrence of theminimal armhook squids Berryteuthis anonychus(Cephalopoda:Gonatidae) in the stomachs of common minke
whales Balaenoptera acutorostrata in the western North
Paciﬁc. Fish Sci. 73: 1208–1210.
Konishi, K., Tamura, T., Isoda, T., Okamoto, R., Hakamada, T.,
Kiwada, H. and Matsuoka, K. 2009. Feeding Strategies andPrey Consumption of Three Baleen Whale Species within the
Kuroshio-Current Extension. J. Northw. Atl. Fish. Sci 42: 27–40.
Liu, H., Suzuki, K. and Saito, H. 2004. Community structure anddynamics of phytoplankton in the western subarctic Paciﬁc
Ocean: A synthesis. J. Oceanogr. 60: 119–137.
Mantua, N.J. and Hare, S.R. 2002. The Paciﬁc decadal oscillation.
J. Oceanogr. 58: 35–44.
Miller, A., Chai, F., Chiba, S., Moisan, J.R. and Neilson, D.J. 2004.
Decadal-scale climate and ecosystem interactions in the
North Paciﬁc Ocean. J. Oceanogr. 60: 163–188.
Mizuno, K. and White, W.B. 1983. Annual and interannual variability in the Kuroshio Current system. J. Phys. Oceanogr. 13:
1847–1867.
Murase, H., Kawabata, A., Kubota, H., Nakagami, M., Amakasu,
K., Abe, K., Miyashita, K. and Oozeki, Y. 2012. Basin-scale
distribution pattern and biomass estimation of Japanese anchovy Engraulis japonicus in the western North Paciﬁc. Fish
Sci. 78: 761–773.
Okazaki, M., Masujima, M., Murase, H. and Morinaga, K. 2016.
Oceanographic conditions in the JARPNII survey area from2000 to 2013 using FRA-ROMS data. Paper SC/F16/JR5 presented to the JARPNII special permit expert panel review
workshop, Tokyo, February 2016 (unpublished). 25 pp.
Okunishi, T., Ambe, D., Ito, S., Kameda, T., Setou, T., Komatsu, K.,
Kawabata, A., Takasuka, A. and Kubota, H. 2011. A Numerical
Modeling Study of Japanese Sardine (Sardinops melanostictus)
Migrations in the Western North Paciﬁc. pp. 51–56. In: K. Omori,
X. Guo, N. Yoshie, N. Fujii, I. C. Handoh, A. Isobe and S. Tanabe(Ed.) Marine Environmental Modeling & Analysis TERRAPUB.
Oozeki, Y., Takasuka, A., Okamura, H., Kubota, H. and Kimura,
R. 2009. Patchiness structure and mortality of paciﬁc saury
Cololabis saira larvae in the northwestern paciﬁc. Fish.
Oceanogr. 18: 328–345.

Sasaki, Y.N., Minobe, S. and Schneider, N. 2012. Decadal responseof the Kuroshio Extension jet to Rossby waves: observationand thin-jet theory. J. Physical Oceanogr. 43: 442–456.
Springer, A., Piatt, J., Shuntov, V., Van Vliet, G., Vladimirov, V.,
Kuzin, A. and Perlov, A. 1999. Marine birds and mammals of
the Paciﬁc Subarctic Gyres. Prog. Oceanogr. 43: 443–487.
Takasuka, A., Oozeki, Y. and Aoki, I. 2007. Optimal growth temperature hypothesis: why do anchovy ﬂourish and sardine
collapse or vice versa under the same ocean regime? Can. J.
Fish. Aquat. Sci. 64 : 786–776.
Takasuka, A., Oozeki, Y., Kubota, H. and Lluch-Cota, S.E. 2008.
Contrasting spawning temperature optima: Why are anchovyand sardine regime shifts synchronous across the North
Paciﬁc? Prog. Oceanogr. 77: 225–232.
Tamura, T., Fujise, Y. and Shimazaki, K. 1998. Diet of minke whales
Balaenoptera acutorostrata in the northwestern part of theNorth Paciﬁc in summer, 1994 and 1995. Fish Sci. 64: 71–76.
Tamura, T., Konishi, K. and Isoda, T. 2016. Updated estimation of
prey consumption by common minke, Brydeʼs and sei whalesin the western North Paciﬁc. Paper SC/F16/JR15 presented
to the JARPNII special permit expert panel review workshop,
Tokyo, February 2016 (unpublished). 58 pp.
Tsuda, A., Saito, H. and Kasai, H. 2001. Geographical Variationof Body Size of Neocalanus cristatus, N. plumchrus and N.
ﬂemingeri in the Subarctic Paciﬁc and its Marginal Seas:
Implications for the Origin. J. Oceanogr. 57: 341–352.
Watanabe, Y. 2009. Recruitment variability of small pelagic ﬁshpopulations in the Kuroshio-Oyashio transition region of theWestern North Paciﬁc. J. Northw. Atl. Fish. Sci. 41: 197–204.
Yatsu, A., Watanabe, T., Ishida, M., Sugisaki, H. and Jacobson,
L.D. 2005. Environmental eﬀects on recruitment and productivity of Japanese sardine Sardinops melanostictus andchub mackerel Scomber japonicus with recommendations for
management. Fish. Oceanogr. 14: 263–278.
Yonezaki, S., Kiyota, M. and Okamura, H. 2015. Long-term ecosystem change in the western North Paciﬁc inferred fromcommercial ﬁsheries and top predator diet. Deep-Sea Res. II
113: 91–101.

Appendix
Length distribution of main pelagic ﬁsh in the stomachs of sei, Brydeʼs and common minke whales during
JARPNII period (2000–2016)
Length distributions of pelagic ﬁshes in the stomach ofsei, Brydeʼs and common minke whales are shown in Figs.
A1–A4. Mackerels include both Scomber japonicus andS. australasicus because these species were sometimes
found mingled in half digested stomach contents. The
length distributions diﬀer among years and whale species, suggesting that prey length, as also deﬁned as age
class, reﬂects the relative abundance and availability inthe feeding area for the baleen whales.
53Technical Reports of the Institute of Cetacean Research (2017)

Figure A1. Length distribution of Japanese anchovy in the stomach of sei, Brydeʼs and common minke whales during
JARPNII (2000–2016).

54

Overview of stomach content analyses for sei, Brydeʼs and common minke

Figure A2.

Fork length distribution of mackerels (including Scomber japonicus and S. australasicus) in the stomach of sei, Brydeʼsand common minke whales during JARPNII (2000–2016).

55

Technical Reports of the Institute of Cetacean Research (2017)

Figure A3. Length distribution of Japanese sardine in the stomach of sei, Brydeʼs and common minke whales during
JARPNII (2000–2016).

56

Overview of stomach content analyses for sei, Brydeʼs and common minke

Figure A4.

Knob length distribution of Paciﬁc saury in the stomach of sei, and common minke whales during JARPNII(2000–2016).

57