Technical Reports of the Ins�tute of Cetacean Research (2023)

pp. 8–21

Technical Report (not peer reviewed)

What do we know about whales and the ecosystem in the western
North Paciﬁc Ocean? Part 5: Summary of results on whaleʼs ecology
including feeding habitat and ecosystem modelling
Tsutomu Tamura*, Kenji Konishi, Tatsuya Isoda and Takashi Hakamada
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Contact e-mail: tamura@cetacean.jp

ABSTRACTThe Ins�tute of Cetacean Research has conducted whale research under special scien�ﬁc permit in the western North Paciﬁc since 1994. The research was conducted systema�cally under diﬀerent research programs
such as JARPN and JARPNII, and ﬁnally, under the NEWREP-NP. These research programs employed both lethal
and non-lethal methods to study diﬀerent aspects of the biology and ecology of large whales in the western
North Paciﬁc. NEWREP-NP ceased a�er the 2019 summer season following Japanʼs decision to withdraw fromthe Interna�onal Conven�on for the Regula�on of Whaling and to start commercial whaling within its Exclusive Economic Zone. This paper summarizes the most relevant ecological research outputs from the Japanesewhaling under special scien�ﬁc permit in the western North Paciﬁc.

INTRODUCTION
Japan conducted systema�c research on whales and theecosystem in the western North Paciﬁc for more than 30
years (1994–2019). The ﬁrst research program was theJapanese Whale Research Program under Special Permit
in the North Paciﬁc (JARPN: 1994–1999), which was followed by JARPNII (2000–2016) and subsequently by the
New Scien�ﬁc Whale Research Program in the North Paciﬁc (NEWREP-NP: 2017–2019). The Ins�tute of Cetacean
Research (ICR) was the ins�tu�on in charge of designingand implemen�ng those research programs. Tamura
et al. (2017) provided details on the objec�ves, sampling
and analy�cal methodology of these research programs.
Several interna�onal review workshops (e.g. IWC,
2001; 2016) discussed and evaluated the large amount ofdata and results from those research programs.
Following the change in Japanʼs whaling policy, NEWREP-NP ceased from 30 June 2019, the date of Japanʼs
withdrawal from the Interna�onal Conven�on for the
Regula�on of Whaling (ICRW). At this point, it was considered important to summarize the knowledge on whales
and the western North Paciﬁc ecosystem accumulated so
far by the Japanese whale research in the North Paciﬁc
Ocean.
The objec�ve of this paper is to summarize the most
relevant ecological research outputs from the Japanesewhaling under special scien�ﬁc permit in the western
8

North Paciﬁc.

SURVEYS, DATA AND SAMPLES
Surveys were conducted in the western North Paciﬁc, inthe sub-areas used by the Interna�onal Whaling Commission (IWC) for the management of common minke whales(Balaenoptera acutorostrata) (Figure 1). The researcharea on the Paciﬁc side of Japan (e.g. Sanriku and Kushiro)
can be considered as Japanʼs richest ﬁshing grounds andFigure 1. Sub-areas in the western North Paciﬁc used by the
IWC for management purposes of the common minke
whale. These sub-areas were used for the Japanesewhale surveys under special scien�ﬁc permit.

What do we know about whales and the ecosystem in the western North Pacific? Part 5

provided an ideal area to study the interac�on between
cetaceans and ﬁsheries. This area can be considered as a
ʻhot-spotʼ area for cetacean/ﬁsheries interac�on.
Survey and sampling methodologies of the Japanesewhale research programs in the North Paciﬁc Ocean
regarding feeding ecology research were described in
Tamura et al. (2016). A list of relevant data and samples
collected by the Japanese whale research programs in the
North Paciﬁc Ocean is available in Tamura et al. (2016).

ABUNDANCE ESTIMATES OF LARGE BALEENWHALES
Apart from its applica�on for assessment and management, abundance es�mate informa�on is highly important for evalua�ng the impact of prey consump�onby whales on the ecosystem. Abundance es�mates are
obtained by analyzing sigh�ng data collected during
dedicated sigh�ng surveys. From the results of the feeding ecology studies, prey species of whales are diﬀerent
between the early (May–June) and late (July–September)seasons. For this reason, the abundances were es�matedfor the early and late seasons. Table 1 shows the abundance es�mates for each whale species studied in thewestern North Paciﬁc. Prey consump�on of whales werees�mated for the coastal areas of Sanriku and Kushiro as
well for the oﬀshore waters of sub-areas 7, 8 and 9. In thela�er, abundance was es�mated for the early and lateseasons as explained above (Table 1). With this informa�on, individual prey consump�on can be extrapolated toobtain the amount of consump�on by the total numberof whales in the area.

DISTRIBUTION OF LARGE WHALES
Analyses of seasonal and spa�al distribu�on of common
minke, sei (B. borealis) and Brydeʼs (B. edeni) whalesin the sub-areas of Figure 1 using Generalized Addi�ve
Models (GAM) indicated that all species shi�ed their distribu�on toward the north as the season progressed fromspring to summer. However, the extent of the shi� was
diﬀerent among whale species. While spa�al segrega�onoccurred among the three baleen whale species, someoverlaps occurred. Given this, the extent of direct interac�on among whale species could be minimal althoughindirect interac�on could occur as they share the same
prey species (Figure 2) (Murase et al., 2016a).

OVERVIEW OF OCEANOGRAPHY, PREY SPECIESDISTRIBUTION AND BIOMASS AND PREY PREFERENCE STUDIES
Oceanography
Oceanographic surveys are important in understanding
the pa�ern of distribu�on of prey species of whales. The
northern part of the survey area is under the inﬂuenceof the Oyashio (a subarc�c western boundary current
with cold, low-salinity water) whereas the southern partis under the inﬂuence of the Kuroshio and its extension(the subtropical western boundary current with warm,
high-salinity water). The area between the Oyashio andthe Kuroshio is called the Kuroshio–Oyashio or subarc�csubtropical transi�on (interferen�al) zone (Figure 3).
Oceanographic condi�ons in the research area were
examined using FRA-ROMs data. This is an ocean forecast
system developed by Fisheries Research Agency (FRA)
based on Regional Ocean Modeling System (ROMS). Annual mean PDO index from 1900 to 2015 was calculatedusing monthly data available from “h�p://research.jisao.
washington.edu/pdo/” [accessed on 6 October 2015].
Nega�ve values of annual mean PDO index were dominant in the period from 2000 to 2013 (Figure 4). It can beconsidered that JARPNII surveys from 2000 to 2013 wereconducted in the nega�ve phase of PDO index.
Prey distribu�on and prey preference
Prey distribu�on and prey preferences of common minke,
Brydeʼs and sei whales at meso-scale were es�matedusing data from the coopera�ve surveys of cetacean sampling and prey of cetaceans (using echosounder and several trawl nets). The surveys were conducted as a part ofthe oﬀshore component of JARPNII in the western North
Paciﬁc from 2002 to 2007 (Figure 5).
For example, in the post-stra�ﬁed block 1 in 2007, prey
distribu�on, sigh�ng posi�ons and stomach contents ofsampled common minke, Brydeʼs and sei whale, watertemperature at 100 m and 200 m are shown in Figure 6.
All blocks were examined for prey preference of whales.
The standardized form of Manlyʼs selec�on index called
Manlyʼs α, also known as Chessonʼs index, was used fores�ma�ng prey preference. Table 2 showed the average
Manlyʼs α of three baleen whale species in the JARPNII
oﬀshore component survey area in summer seasons from2002 to 2007. As a result, common minke whales showed
preference for Japanese anchovy and Paciﬁc saury while
they avoided krill. Brydeʼs whales showed preference
for Japanese anchovy while they also avoided krill. Sei
whales showed preference for copepods and Japanese9Technical Reports of the Ins�tute of Cetacean Research (2023)
Table 1Abundance es�mates for several large baleen whale species based on dedicated sigh�ng surveys in coastal and oﬀshore waters (fromTamura et al., 2019).
Area: Coastal Sanriku
Species: Common minke whale

Area: Coastal Kushiro
Species: Common minke whale

PeriodNumbers

CV

95% CI LL

95% CI ULPeriodNumbers

CV

95% CI LL

95% CI UL

2005
2006
2012

401
216
124

0.321
0.407
0.385

217
101
121

741
466
521

2002
2003
2004
2005
2006
2007
2012

551
888
338
290
221
130
433

0.350
0.406
0.352
0.350
0.351
0.553
0.542

283
413
173
149
113
47
160

1,073
1,908
660
564
431
358
1,171

Area: Oﬀshore sub area 7
Species: Common minke whale

Area: Oﬀshore sub area 8
Species: Common minke whale

PeriodNumbers

CV

95% CI LL

95% CI ULPeriodNumbers

CV

95% CI LL

95% CI UL

Early
2000–2007
2008–2014

4,969
269

0.934
0.951

1,052
56

23,457
1,297

Early
2000–2007
2008–2014

769
755

0.636
0.738

245
207

2,411
2,747

Late
2000–2007
2008–2014

665
—

0.667
—

203

2,182

Late
2000–2007
2008–2014

226
—

0.746
—

61

832

95% CI ULSpecies: Bryde's whale
PeriodSpecies: Bryde's whale
Numbers

CV

Early
2000–2007
2008–2016

804
2,595

1.593
0.445

Late
2000–2007
2008–2016

3,090
3,394

0.456
0.486

95% CI LL

95% CI ULPeriodNumbers

CV

95% CI LL

89
1,128

7,280
5,967

Early
2000–2007
2008–2016

535
—

1.296
—

76

3,742

1,318
1,376

7,245
8,369

Late
2000–2007
2008–2016

2,918
2,733

0.466
0.467

1,224
1,145

6,958
6,526

Species: Sei whale
PeriodSpecies: Sei whale
Numbers

CV

95% CI ULPeriodNumbers

CV

95% CI LL

95% CI UL

253
77

1,768
1,729

Early
2002–2007
2008–2016

2,341
614

0.334
0.683

1,237
182

4,431
2,064

1.148
1.130

40
10

1,452
353

Late
2002–2007
2008–2016

1,400
908

0.541
0.635

518
290

3,780
2,840

Numbers

CV

95% CI LL

95% CI UL

Early
2000–2007
2008–2014

1,600
2,605

0.577
0.701

560
754

4,574
9,000

Late
2000–2007
2008–2014

2,085
3,080

0.618
0.677

684
924

6,362
10,266

Early
2002–2007
2008–2016

668
364

0.529
0.938

Late
2002–2007
2008–2016

241
60

95% CI LL

Area: Oﬀshore sub area 9
Species: Common minke whale
PeriodSpecies: Brydeʼs whale
PeriodNumbers

CV

95% CI LL

95% CI UL

Early
2000–2007
2008–2016

338
363

0.732
0.441

93
159

1,220
828

Late
2000–2007
2008–2016

3,790
7,179

0.582
0.358

1,315
3,636

10,92014,173

Numbers

CV

95% CI LL

95% CI UL

Early
2002–2007
2008–2016

4,735
3,756

0.371
0.182

2,340
2,636

9,579
5,353

Late
2002–2007
2008–2016

3,765
4,119

0.352
0.444

1,928
1,793

7,352
9,460

Species: Sei whale
Period10

What do we know about whales and the ecosystem in the western North Pacific? Part 5

Figure 2.

Number of sighted schools of common minke (a), sei (b) and Brydeʼs (c) whales in 1×1 longitude and la�tude grids from May to September. Total numbers from 2002 to 2013 are shown (from Murase et al., 2016a).

anchovy while they avoided krill and Paciﬁc saury.

Figure 3.

Schema�c map of oceanographic structure in thesurvey area (from Okazaki et al., 2016).

Overview of Prey Biomass Studies
In Japan, ﬁsh abundance and biomass for species such
as Japanese anchovy, Japanese sardine, mackerels andwalleye pollock have basically been es�mated by cohort
analysis. Es�ma�on of the biomass of prey species using
a quan�ta�ve echosounder in JARPNII were also used.
In oﬀshore waters, basin-scale distribu�on pa�ern andbiomass es�ma�on of Japanese anchovy, which was oneof the main prey species, were examined using a quan�ta�ve echosounder between 2004 and 2007. Taking
account of the spa�al coverage of the survey each year,
the most reliable biomass es�mate of Japanese anchovy
11

Technical Reports of the Ins�tute of Cetacean Research (2023)

for this region was 3.4 million tons (CV= 0.22) (Murase
et al., 2012). As an example, Figure 7 shows the distribu�on of Japanese anchovy in 2006 using a quan�ta�veechosounder.
In coastal waters oﬀ Sanriku, the prey surveys were
included in the coastal component of JARPNII. The survey
area for prey species was divided into ten blocks (A–J)
based on bo�om depth (20, 40, 100 and 200 m) andprefectural boundary (between Miyagi and Fukushima
prefecture) (Figure 8). The biomass of sand lance andJapanese anchovy were examined using a quan�ta�veechosounder between 2005 and 2009. The biomasses�ma�ons of sand lance were between 2,827 tons
and 28,340 tons. The biomass es�ma�ons of Japanese
anchovy were between 0.20 and 9,060 tons, respec�vely(Table 3) (Murase et al., 2009b; Wada et al., 2016).

FEEDING ECOLOGY OF LARGE BALEEN WHALES

Figure 4.

Annual mean of Paciﬁc Decadal Oscilla�on (PDO)
index from 1900 to 2015. Monthly PDO data
available from “h�p://research.jisao.washington.
edu/pdo/” (accessed on 6 October 2015) are used
to calculate annual mean. Climate regime shi� indicated in several published papers are also shown inthe ﬁgure (see Okazaki et al., 2016).

Figure 5.

12

Sampling and treatment of stomach contents
Baleen whales have a four chambered stomach system.
The stomach contents remain in the forestomach (ﬁrststomach) and fundus (second stomach). For the analyses,
and a�er capture, the stomach contents were removed
from each compartment and weighed to the nearest
0.1 kg on the shipʼs ﬂensing deck.
The analysis of prey consump�on was based on datacollected from the forestomach and fundus. A subsample (1–5 kg) of stomach contents was removed andfrozen and/or ﬁxed with 10% formalin water for later
analyses. The stomach contents were transferred toa system consis�ng of three sieves (20 mm, 5 mm and1 mm), which were applied in the Norwegian scien�ﬁcresearch to ﬁlter oﬀ liquid from the rest of the material(Haug et al., 1995). In the laboratory, prey species inthe sub-samples were iden�ﬁed to the lowest possible

Pre-deﬁned survey blocks for the coopera�ve whale and prey surveys in JARPNII oﬀshore component from2002 to 2007. Each color represents boundary of surveyed blocks. These blocks were post-stra�ﬁed basedon observed oceanographic condi�ons. Zigzag lines within each block represent planned track lines of preysurveys (from Murase et al., 2009a).

What do we know about whales and the ecosystem in the western North Pacific? Part 5

Figure 6.

Maps in block 1 in 2007: Distribu�on pa�erns of krill (a), Japanese anchovy (b), copepods (Neocalanus spp.
(Copepodite stage 5)) (c) and Paciﬁc saury (d). Sigh�ng eﬀort and sigh�ng posi�ons of common minke,
Brydeʼs and sei whales (e). Sampled posi�ons and stomach contents of common minke (f) and sei (g)whales. Water temperature at 100 m (h) and 200 m (i) water depth. Encircled areas by red and blue lines
are the post-stra�ﬁed area, E–N and E–S, respec�vely. Light blue and orange lines in maps (a)–(g) represent
4°C and 10°C isotherm at 100 m water depth, respec�vely (from Murase et al., 2009a).

Table 2Es�mated average values of Manlyʼs α of common minke, Brydeʼs and sei whales α in the JARPNII oﬀshore component survey area insummer from 2002 to 2007 using the log-likelihood func�on based on a mul�nomial distribu�on (from Murase et al., 2009a).
SpeciesCommon minke whale
Bryde's whale
Sei whale

Copepods

Krill

Japanese anchovy

Paciﬁc saury

Manlyʼs αSE

Manlyʼs αSE

Manlyʼs αSE

Manlyʼs α

SE

—
—
0.41

—
—
0.10

0.05
0.05
0.13

0.03
0.04
0.04

0.36
0.95
0.25

0.19
0.04
0.10

0.59
—
0.20

0.17
—
0.08

taxonomic level. The total weight of each prey species inthe stomach contents were es�mated by using the values
obtained from the sub-sample and the total weight ofstomach contents (see details in Tamura et al., 2019).
Data analyses
An es�mate of the daily prey consump�on by whales
requires the use of some addi�onal biological and morphometric data. For example, body length of the whales
was measured to the nearest 1 cm from the �p of theupper jaw to the deepest part of the ﬂuke notch in astraight line. Body weight was measured to the nearest
50 kg using large weighing machine. Furthermore, energy
requirements are diﬀerent for sexual maturity classes,

and therefore, es�ma�ons of the daily prey consump�ontook into considera�on informa�on on sexual maturity.
Sexual maturity of each whale was deﬁned by either tes�s weight or examina�on of ovaries.
The daily amount of prey consump�on consumed ises�mated using theore�cal energy requirement formulae. The total seasonal prey consump�on by whales wases�mated using the informa�on on abundance in Table
1, sexual maturity composi�on, daily prey consump�onand a seasonal feeding period of 150 days. The uncertain�es associated with the relevant parameters weretreated by Monte Carlo simula�ons (see details in Tamura
et al., 2019).

13

Technical Reports of the Ins�tute of Cetacean Research (2023)
Table 4Prey species of common minke, Brydeʼs and sei whales in thewestern North Paciﬁc during May and September in the years
1994–2022.
Prey species/Whale species

Figure 7.

Figure 8.

Distribu�on pa�erns of Japanese anchovy in 2006.
Bars Rela�ve densi�es of anchovy. Thin black lines
Surveyed track lines. Seasonal composite surface
seawater temperature (SST) data in the summer,
derived from the Moderate Resolu�on Imaging
Spectroradiometer (MODIS) aboard the satellite,
Aqua, are also shown (from Murase et al., 2012).

Ten blocks (A–J) surveyed for whalesʼ prey species inSanriku since 2005 (from Wada et al., 2016).

Table 3
Biomasses of sand lance and Japanese anchovy in B, C, E and F
blocks (surveyed in 2005 and 2006) and B, C blocks (surveyed in2008 and 2009). See Figure 8 for surveyed blocks (from Wadaet al., 2016).

14

Year

Sandlance (tons)

Japanese anchovy (tons)

2005
2006
2008
2009

7,610
28,340
9,310
2,827

1,320
9,060
0.2
0.6

Main prey species
Copepoda
Neocalanus cristatus
N. plumchrus
Krill
Euphausia paciﬁca
E. similis
E. gibboides
Thysanoessa gregaria
T. inermis
T. inspinata
T. longipes
Nematoscelis diﬃcilis
PiscesJapanese anchovy
Japanese sardine
Paciﬁc saury
Chub mackerel
Spo�ed mackerel
Walleye pollocke
Japanese pomfret
Pink salmon
Chum salmon
Atka mackerel
Sand lance
Vinciguerria nimbaria
Auxis rochei
SquidsJapanese common squid
Minimal armhook squid
Minor prey species
PiscesParalepis atlantica
Arothron ﬁrmamentum
Decapterus russelli
Diaphus theta
Tarletonbeania taylori
Starry toado
Nemichthys scolopaceus
Lestidiops jayakari
SquidsJapanese common squid

Common
minke

Sei

✔

✔
✔

✔

✔
✔

✔
✔
✔
✔

✔

Brydeʼs

✔
✔
✔
✔

✔
✔
✔
✔
✔

✔
✔
✔
✔
✔

✔

✔
✔

✔
✔
✔
✔
✔
✔
✔
✔
✔
✔

✔

✔
✔
✔
✔
✔
✔
✔
✔
✔

What do we know about whales and the ecosystem in the western North Pacific? Part 5

Summary of results for three baleen whale species
Prey species in stomach
Common minke whales (1994–2022)
A total of eighteen preys, including one species of copepod, ﬁve species of krill, ten species of ﬁshes and two
species of squids were iden�ﬁed in 3,036 stomachs ofcommon minke whales (Table 4).
Sei whales (2002–2022)
A total of eleven preys, including two species of copepods, three species of krill, ﬁve species of ﬁshes and one
species squid were iden�ﬁed in 1,722 stomachs of sei
whales (Table 4).
Brydeʼs whales (2000–2022)
A total of eighteen preys, including ﬁve species of krill,
twelve species of ﬁshes and one species squid were iden-

�ﬁed in 1,478 stomachs of Brydeʼs whales (Table 4).
Geographical and yearly changes of main prey species in
the oﬀshore area
Common minke whales (1994–2019)
Prey composi�on in the stomach of common minke
whales is shown for each season (early [May–June] andlate [July–September]), sub-area and year in Figure 9.
The composi�on of main prey species is highly variable
between years.
In sub-area 7, Japanese anchovy has been an important
prey in both seasons since 1994. A�er 2017, Japanesesardine and mackerels have become important preys.
In sub-area 8, krill and Japanese anchovy have been
important preys since 1994. A�er 2017, Japanese sardine
has been an important prey in the early season. In lateseason Paciﬁc saury has been an important prey since

Figure 9.

Prey composi�on in the stomach of common minke whales by season, sub-area and year, in the period
1994–2019 (par�ally from Konishi et al., 2017).

Figure 10.

Prey composi�on in the stomach of sei whales by season, sub-area and year, in the period 2002–2022(par�ally from Konishi et al., 2017).
15

Technical Reports of the Ins�tute of Cetacean Research (2023)

1994. A�er 2017, Japanese sardine has become an important prey.
In sub-area 9, Japanese anchovy and krill have been
important preys since 1994. A�er 2017, mackerels havebecome important preys in the early season. In late season, Paciﬁc saury has been an important prey since 1994.
A�er 2017, Paciﬁc saury and mackerels have become
important preys.
Sei whales (2002–2022)
Prey composi�on in the stomach of sei whales is shownfor each season, sub-area and year in Figure 10. The composi�on of main prey species is highly variable among
years.
In sub-area 7, krill and Japanese anchovy have been
important preys since 2003. A�er 2016, Japanese sardine
has become an important prey in the early season. In thelate season, krill and Japanese anchovy have been important preys since 2003. A�er 2019, Japanese sardine andkrill have become important preys.
In sub-area 8, krill, copepod, Japanese anchovy and16mackerels have been important preys since 2002 in bothseasons. A�er 2017, Japanese sardine has become an
important prey.
In sub-area 9, copepod has been an important preysince 2002 in both seasons. A�er 2015, Japanese sardine
and mackerels have become important preys.
Brydeʼs whales (2000–2022)
Prey composi�on in the stomach of Brydeʼs whales isshown for each season, sub-area and year in Figure 11.
In sub-area 7, krill and Japanese anchovy have been
important preys since 2000. A�er 2020, Japanese sardine
has become an important prey in the early season. In thelate season, krill and Japanese anchovy have been important preys since 2000.
In sub-areas 8 and 9, krill and Japanese anchovy
have been important preys since 2002 in both seasons.
Occasionally, high propor�ons of lantern ﬁshes wereobserved. A�er 2016, Japanese sardine has also been
observed as the main prey.

Figure 11.

Prey composi�on in the stomach of Brydeʼs whales, by season, sub-area and year, in the period 2000–
2022 (par�ally from Konishi et al., 2017).

Figure 12.

Yearly change of dominant prey species of common minke whales in Sanriku (A) and Kushiro (B), in the
period 2002–2022 (par�ally from Tamura et al., 2016).

What do we know about whales and the ecosystem in the western North Pacific? Part 5

Geographical and yearly changes of main prey species ofcommon minke whales in the coastal areas (2002–2022)
Sanriku
Figure 12 shows the yearly changes in prey composi�on based on data from commercial whaling and somescien�ﬁc surveys in Sanriku. A�er 2003, sand lance has
been the dominant prey species. Since 2016, the dominant prey species switched from sand lance to Japanesesardine.
KushiroLong term informa�on of prey composi�on is available
from past commercial whaling (Kasamatsu and Tanaka, 1992). Figure 12 shows the yearly changes in preycomposi�on based on data from commercial whaling andsome scien�ﬁc surveys in Kushiro. Un�l 1976, the dominant prey species of common minke whales was the chubmackerel. The dominant prey species switched from chubmackerel to Japanese sardine in 1977, from Japanesesardine to Paciﬁc saury or Japanese anchovy in 1996, andfrom Paciﬁc saury or Japanese anchovy to Japanese sardine and mackerels in 2012.
Daily and seasonal prey consumption by whales
Oﬀshore area
The es�mated daily prey consump�on by sex and repro-

duc�ve status is shown in Table 5 for the three species ofbaleen whales.
Es�mated prey consump�on (thousand tons) per year
over 150 days, from May to September, in two periods(2000–2007 and 2008–2016) by three baleen whale species is shown in Table 6. See details of this calcula�on in
Tamura et al. (2019). The consump�on per year of Japanese anchovy by three baleen whale species in the two
periods (2000–2007 and 2008–2016) were 754 thousand
tons and 565 thousand ton, respec�vely. The consump�on per year of mackerels by three baleen whale species
in the same two periods was 25 thousand tons and 74
thousand tons, respec�vely. The consump�on per yearof Paciﬁc saury by common minke and sei whales in thesame two periods was 38 thousand tons and 35 thousand
tons, respec�vely. Recently, Japanese sardine has been
the dominant prey species for three baleen whale species. The consump�on per year of Japanese sardine by
three baleen whale species in the 2008–2016 period was
54 thousand tons.
Coastal areas
For Sanriku, prey consump�on per year during midMarch to mid-June (90 days) by common minke whales isshown in Table 7. For Kushiro, seasonal prey consump�on
per year during September-October (60 days) by common

Table 5Es�mates of daily prey consump�on (kg) by three baleen whale species in the oﬀshore area, by sex and reproduc�ve status (fromTamura et al., 2019).
Male

SpeciesCommon minke whale
Bryde's whale
Sei whale

FemaleImmature

MatureImmature

Mature73–187
380–578
265–665

118–304
51–839341–878

69–179369–563294–727

140–359
619–943
405–1,021

Table 6Es�mates of prey consump�on (thousand tons) per year by common minke, Brydeʼs and sei whales in the oﬀshore area in two diﬀerent periods (from Tamura et al., 2019).
PeriodPrey species

2000–2007

Japanese anchovy
Paciﬁc saury
Mackerels
Japanese sardine
Other
Total

Consump�on(thousand tons)
754
38
25
0
349
1,166

Period2008–2016

Prey species
Japanese anchovy
Paciﬁc saury
Mackerels
Japanese sardine
Other
Total

Consump�on(thousand tons)
565
35
74
54
593
1,321
17

Technical Reports of the Ins�tute of Cetacean Research (2023)
Table 7Es�mates of prey consump�on (tons) by common minke whales in coastal areas of the western North Paciﬁc based on data collected
between 2002 and 2012 (from Tamura et al., 2019).
Year

Sanriku
Krill

KushiroSandlance Anchovy

Total

Krill

Anchovy Sardine

Saury Mackerels Pollock

Squid

Total

2002
2003
2004
2005
2006
2007
2012

—
—
—
1,533
758
—
356

—
—
—
2,338
1,033
—
472

—
—
—
606
363
—
269

—
—
—
4,477
2,154
—
1,097

453
—
41
241
8
27
217

733
—
1,171
170
907
292
2

0
—
0
0
0
0
669

635
—
878
20
118
125
0

0
—
0
0
0
0
178

815
—
76
1,562
378
227
902

1394
—
0
101
92
111
92

4,030
—
2,166
2,094
1,503
782
2,060

Average

882

1,281

413

2,576

165

546

112

296

30

660

298

2,106

Table 8Prey consump�on (tons) by common minke whales and ﬁsheries catch of sand lance in Sanriku in the period 2002 and 2012.
Fisheries catch data were obtained from Sta�s�cal Survey on
Marine Fishery Produc�on (h�ps://www.maﬀ.go.jp/j/tokei/
kouhyou/kaimen_gyosei/).
Year

Prey consump�on(tons)

Fisheries catch(tons)

Ra�o
(%)

2002
2003
2004
2005
2006
2007
2012

—
—
—
2,338
1,033
—
472

—
—
—
8,679
5,250
—
479

—
—
—
26.9
19.7
—
98.5

Average

1,281

4,803

26.7

minke whales is shown in the same table.
Amount of prey consumed by common minke whales incomparison with catch by ﬁsheries
The es�mated consump�on of sand lance by common
minke whales and ﬁsheries catch of sand lance in Sanriku
is shown in Table 8.
The es�mated consump�on of Paciﬁc saury andwalleye pollock by common minke whales and ﬁsheries
catch of those species in Kushiro is shown in Table 9. The
prey consump�on of Paciﬁc saury and walleye pollock
by common minke whales in Kushiro were calculated as
0–878 tons and 76–1,562 tons. Consump�on of them bycommon minke whales in Kushiro waters corresponded
to approximately 0–3% of the ﬁsheries catch of theseresources (Table 9).
To further evaluate the interac�on between whale and18

ﬁsheries, long-term informa�on of prey composi�on ofwhales, accurate abundance of prey species and eachwhale, and accurate resident period of each whale areneeded.

PROGRESS IN MODELLING WORKThis sec�on presents an overview of the objec�ves andprogress made in the research on ecosystem modelling in
the western North Paciﬁc. Whale abundance, prey composi�on and prey consump�on of whales have been used
as input data to the models. Those values were obtained
as described above.
Oﬀshore area
Mori et al. (2009) developed the EwE in the western
North Paciﬁc (north of 35°N and west of 170°E), where
JARPNII surveys were conducted. The model consistsof 31 species/groups ranging from detritus to whales(Table 10). Input data required for the model were biomass, produc�on, prey consump�on, diet composi�onand total ﬁshery catch of each predator in the target area.
When produc�on is not available, total mortality wasused in the Ecopath instead of produc�on per biomass.
Once the mass-balance model was constructed, possible eﬀect by ﬁsheries of the species in the model were
simulated by using Ecosim under the harves�ng scenarios
examined.
The work by Mori et al. (2009) was updated in the studies by Murase et al. (2016b) and Watari et al. (2019). They
have focused on the interac�ons between forage ﬁsh andtheir predators including target species of JARPNII (common minke, sei, Brydeʼs and sperm whales). They haveupdated the input data to the models by considering thedata available in the period 1994–2013 and made several
technical adjustments following recommenda�ons from

What do we know about whales and the ecosystem in the western North Pacific? Part 5
Table 9Prey consump�on (tons) by common minke whales and ﬁsheries catch of Paciﬁc saury and walleye pollock in Kushiro in the period
2002 and 2012. Fisheries catch data were obtained from Sta�s�cal Survey on Marine Fishery Produc�on (h�ps://www.maﬀ.go.jp/j/tokei/kouhyou/kaimen_gyosei/).
Prey species: Paciﬁc saury

Prey species: Walleys pollock

Year

Prey consump�on(tons)

Fisheries catch(tons)Ra�o (%)

Year

Prey consump�on(tons)

Fisheries catch(tons)Ra�o (%)

2002
2004
2005
2006
2007
2012

635
878
20
118
125
0

55,594
48,40358,52861,89569,62949,550

1.1
1.8
0.0
0.2
0.2
0.0

2002
2004
2005
2006
2007
2012

815
76
1,562
378
227
902

52,52465,18654,62856,582
51,08859,061

1.6
0.1
2.9
0.7
0.4
1.5

Average296

57,267

0.6

Average

660

56,512

1.2

Table 10
List of the species/groups used in the EwE model and Trophic Level (TL) es�mated by Ecopath (from Mori et al., 2009).
Species/Group

TL

Species/Group

TL

Species/GroupTL

Minke whale
Bryde's whale
Sei whale
Other baleen whales
Sperm whale
Baird's beaked whale
Short-ﬁnned pilot whale
Ziphidae
Other toothed whales
Northern fur seal
Marine birds

3.99
3.83
3.73
3.23
4.17
4.15
4.40
4.24
4.46
4.08
4.24

Albacore
Sword ﬁsh
Skipjack tuna
Blue shark
Samon shark
Lantern ﬁsh
Neon ﬂying squid
Large surface squid
Small surface squid
Mid-deep water sea squid
Mackerels

4.08
4.81
3.97
4.27
4.35
3.06
4.12
3.41
3.01
3.11
3.30

Paciﬁc ponfretSardineAnchovy (<8 cm)
Anchovy (>8 cm)
Paciﬁc saury
Phytoplankton
Euphausiids
Copepods eaten by whales
Other Copopods
Detritus

4.20
2.30
3.04
3.04
3.12
1.00
2.18
2.00
2.00
1.00

the IWC Scien�ﬁc Commi�ee. They have iden�ﬁed several poten�al future data and tasks required to progress
the development of ecosystem modelling in the western
North Paciﬁc.
Coastal areas
Okamura et al. (2009) examined the eﬀects of preda�on of common minke whales on sand lance stock oﬀ
Sanriku in order to inves�gate the eﬀect of preda�on by
the common minke whales in terms of MSY of sand lance
popula�on. Bayesian delay-diﬀerence model was used
to develop an ecosystem model. By using new data, Kitakado et al. (2016) updated the model work by Okamura
et al. (2009). The preda�on by the common minke whales
accounts for a certain propor�on of the current adult biomass of the sand lance popula�on, although the level ofpropor�on is sensi�ve to the model assump�on.
The results are s�ll preliminary because further valida-�on of consump�on of sand lance by predator species
and further modelling process for linking sand lance andseveral predators through simultaneous es�ma�on of
popula�ons dynamics are needed. Progress in the workon the MRM is presented in a diﬀerent paper to thismee�ng (Kawano et al., 2019).

CONCLUSIONSThe Japanese whale research programs under special
permit provided important informa�on on the ecology ofseveral baleen whale species in the western North Paciﬁc.
Such informa�on is key for the elucida�on of the role ofwhales in the ecosystem. There is a need to further evaluate the interac�on between prey consump�on by whales
and commercial ﬁsheries, either directly or indirectly,
using simula�on models for speciﬁc geographical regions.
The commercial whaling within Japanʼs Exclusive Economic Zone commenced in 2019. It is important to collect19

Technical Reports of the Ins�tute of Cetacean Research (2023)

addi�onal informa�on on the feeding ecology of baleen
whales from this source.

ACKNOWLEDGEMENTS
We thank Luis A. Pastene for his assistance in preparing
this document and the Editorial Team of TEREP-ICR for
editorial work.

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