SC/F16/JR26

Feeding habits of sperm whales (Physeter macrocephalus)
in the western North Pacific in spring and summer
TATSUYA ISODA¹, TSUTOMU TAMURA¹, KENJI KONISHI¹, HIROSHI OHIZUMI² AND TSUNEMI KUBODERA³¹ Institute of Cetacean Research, Tokyo, Japan² School of Marine Science and Technology, Tokai University, Shizuoka, Japan³ National Museum of Nature and Science, Tsukuba, Japan
Contact e-mail: isoda@cetacean.jp
ABSTRACTThe stomach contents of 56 sperm whales (Physeter macrocephalus) sampled in the western North Pacific by the Second Phaseof the Japanese Whale Research Program under Special Permit in the western North Pacific (JARPNII) from May to Septemberof the years 2000 to 2013, were examined. A total of 49 undigested and half-digested prey items were found, including 28
species of cephalopods and six species of fish. The Index of Relative Importance (IRI) showed that Belonella borealis andHistioteuthis spp. were the dominant prey in the Subarctic Region, while B. borealis and Galiteuthis phyllura were the dominant
prey in the Transitional Domain. B. borealis and Taningia danae were the dominant prey in the Northern part of the Transition
Zone, while T. danae and Histioteuthis spp. were the dominant prey in the Southern part of the Transition Zone. In the Kuroshio
Zone, T. danae and Octopoteuthis spp. were the dominant preys. The composition of prey items changed in relation totransitional change between north and south. Canonical Correspondence Analysis (CCA) indicated that environmental andbiological factors significantly contributed to the prey composition of sperm whales. Our study demonstrated that sperm whales
moved along waters with different oceanographic conditions, feeding on a variety of prey species. Larger whales tend to feed
at offshore waters. This flexibility and different size distribution in sperm whale seems to be important to maintain large bodysize and large abundance in the western North Pacific. The commercially important Neon flying squid O. bartrami was not an
important prey of sperm whales in spring and summer.
KEYWORDS: SPERM WHALE; FOOD/PREY; SQUID; NORTH PACIFIC; SCIENTIFIC PERMITSINTRODUCTION
The sperm whale (Physeter macrocephalus) is the largest species among odontocete with remarkable sexual
dimorphism that males attain 18.3m and females attain 12.5m as maximum length. Sperm whale ranges
throughout all deep oceans of the world from the equator to the edges of the polar pack ice (Rice, 1989),
however mature males migrate at higher latitudes, while females and younger males generally occurring at
south of 40-50°N in the Northern Hemisphere, so to speak sexual geographical segregation (Ohsumi, 1966;
Rice, 1989). Sperm whales dive to mesopelagic waters (Aoki et al., 2007, Amano and Yoshioka, 2003), andthe most important food items are meso- and bathypelagic squids (Berzin, 1972, Kawakami, 1980, Clarke,
1996). For these reason, sperm whales play an important role in the ecosystem at deeper layer because of its
high abundance.
In the western North Pacific subarctic and subtropical fronts converge, and this confluence leads to a Transition
Region (Kawai, 1972), where oceanographic conditions are complex and of high productivity. This region isimportant feeding area for cetaceans (Tamura et al., 1998, Tamura and Fujise, 2002, Ohizumi et al., 2003,
Murase et al., 2007, Konishi et al., 2009, Watanabe et al., 2012).
There are few diet studies of sperm whale in the western North Pacific that only report whales feed almost on
squids (Mizue, 1951, Omura, 1950), and Histioteuthis dolfleini, Ommastrephes bartrami, Octopoteuthis sp.,Moroteuthis robusta are important prey species during autumn and winter (Kawakami, 1976, Okutani et al.,
1976, Okutani and Satake, 1978). However, studies on sperm whale feeding habits are extremely limited.
Distribution patterns of mesopelagic fishes and squids, which are prey species for sperm whale, are related towater masses (Brodeur and Yamamura, 2005, Jefferts, 1988, Watanabe, 2006). However, the information on
this relationship is still limited.
The purposes of this study were to (1) to describe the diet of sperm whales, and (2) examines the sperm whales
feeding habits, in the western North Pacific, based on samples and data collected by the JARPNII since 2000

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MATERIALS AND METHODS
Research area and sampling of whales
The sampling area was comprised between the Pacific coast of Japan and 170°E, in the latitudinal range
between 35°N and 50°N (Figure 1). A total 56 sperm whales were sampled by JARPNII from May to
September during 2000-2013. The sampling of sperm whales was restricted to animals of body length < 13 m
because of logistical reasons (capacity of research base vessel) in the operation. The sampled whales weretransported to a research base vessel where biological survey was conducted. All whales were measured,weighed, and their reproductive organs were examined to determine sexual maturity.
Stomach contents analyses
The stomach contents were removed from each compartments, (i.e. forestomach, fundic, pyloric and duodenal
ampulla, see Hosokawa and Kamiya, 1971, Olsen et al., 1994), and were weighted to the nearest 0.1kg.
Stomach contents were frozen for further analysis in the laboratory. In the case when large fresh preys were
found in the stomach, their body lengths (BL): standard or total length (SL, TL) for fishes, mantle length or
dorsal mantle length (ML, DML) for cephalopods and wet body weight (BW) were measured. Buccal mass
(beaks with surrounded muscle) or head (head and arms including buccal mass) and whole undigested prey
were sampled.
At the laboratory, stomach contents were sorted into the following categories, (1) undigested: nearly intact
whole body or body with little digestion effects, include fishes when most of muscle was still attached to thebone (2) partially digested: head containing buccal masses with beaks in cephalopods and sagittal otoliths infishes, head was detached from mantle or vertebra, (3) isolated buccal mass with beaks, (4) digested: isolated
beaks and sagittal otoliths, (5) other remains and parasites. The BL and BW were measured for undigested
items. There are many beaks remained in the stomachs because this parts are hard and need long time to digest
or broken. Therefore following two categories which reflect recent feeding, were used (1) undigested items,(2) partially digested items and buccal mass with beaks in the analyses.
Cephalopods and fishes were identified to the lowest taxonomic level as possible based on the morphology of
their lower beaks and sagittal otoliths, respectively (Clarke, 1986; Kubodera and Furuhashi, 1987; Kubodera,
2005, and the beak reference collection at the National Science Museum, Tokyo), as well as on external
morphology in regards to undigested items (Nesis, 1987; Okutani, 1995, 2005; Nakabo, 2000). The rostral
length of the lower beak (LRL) of cephalopods was measured using vernier calipers to the nearest 0.1 mm andpreviously published equations (Wolff, 1982; Clarke, 1986; Jackson, 1995; Kubodera, 2005; Lu and Ickeringill,
2002; Orlov, 2007) were used to estimate DML or ML and body weight.
Restoration of prey weight
To examine total prey weight fed by sperm whale, two step calculation to restore weight from digested preyfrom hard parts remained. We made equations to restore dorsal mantle length (DML) or body weight (BW) forsome squid species. For example, to estimate DML or BW, lower rostral length of beak (LRL) of Taningia
danae were used on 34 undigested items. Existing equations of the same genus or family were adapted for theestimates of some cephalopod species for which the equations have not reported. BW and ML were thencalculated from BL or DML by equations of Orlov (2007), Lu and Ickeringill (2002), Clarke and Young (1998)
and Watanabe et al. (1999).
Oceanography
Positions of oceanographic boundary and water masses were examined to know at which water mass whale
feed on the prey species. From mixed Layer data set of Argo by JAMSTEC (Japan Agency for Marine-Earth
Science and Technology) (Hosoda et al., 2010), water temperature and salinity from 2001 to 2013 werevisualized using software Ocean Data View (Schlitzer, R., Ocean Data View, http://odv.awi.de, 2014).
Monthly mean of temperature in 2000 were obtained by Japan Meteorological Agency (JMA) and Japan
Oceanographic Data Center (JODC) (http://near-goos1.jodc.go.jp/index_j.html; accessed 26 August 2014) and
Off Tohoku Temperature Field by Tohoku National Fisheries Research Institute (TNFRI)(http://tnfri.fra.affrc.go.jp/kaiyo/temp/temp.html; accessed 27 August 2014).
Then water mass was determined using above dataset into 5 areas based on the definition by Yasuda (2003)
and Brodeur and Yamamura (2005) as follows: Subarctic Region (SA), Transitional Domain (TD), Northernpart of Transition Zone (NTZ), Southern part of Transition Zone (STZ) and Kuroshio Zone (KZ) (see Figure
1).

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Data analysis
The composition of each prey items was calculated as percent by number (%N), percent by weight (%W), andpercent by frequency of occurrence (%F). %N is the total number of a single prey item/the total number of all
prey items × 100; %W is the total wet weight of a single prey item/the total wet weight of all prey items ×100; %F is the total number of stomachs including a single prey item/the total number of stomachs examined(excluding heavy damaged stomach by harpoon or no undigested and partially digested prey items) × 100. The
Index of Relative Importance IRI (Pinkas et al. 1971) was calculated as IRI = (%N + %W) × %F. The IRI
expressed as a percent basis was also calculated.
Canonical Correspondence Analysis (CCA), which is categorized as one of the habitat models (Redfern et al.,2006), and is a powerful tool that can identify features within diet compositions and habitat use, together withbiological and environmental factors (Guisan and Zimmermann, 2000, Redfern et al., 2006). CCA of number
and weight data for the most important prey items (frequency >5% in 49 whales and whales occurring in >10%of all prey types) was conducted after ln(x+1) transformation to examine diet composition in relation toenvironmental variables (latitude, longitude, sampled date, depth of sampled site) and biological variables(body length, sex, sexual maturity), using the ‘vegan’ package (ver.2.3-0, Oksanen et al., 2015) in R
(http://www. r-project.org). According to the preliminary CCA, collinear environmental variables with highvariance inflation factors (VIF > 20) were eliminated from further analyses. The variable excluded was bodyweight, which was correlated positively to body length. Each environmental and biological factors was tested
by 1,000 permutations and considered significant at the 5% level.
Distribution of sperm whales
This study used sighting data collected from JARPNII from 2000-2013. Density Index by 0.5 degree mesh
(number of whales found per n.mile) of sperm whales distribution in the research area was calculated by month.

RESULTS
Whales examined
A total of 56 sperm whales were examined. Biological data of sperm whales in this study were summarized byoceanographic features (Table 1). Body length ranged from 7.4 to 13.7m (average 10.1m) and body weight
ranged from 4.1 to 32.7t (average 15.5t). The sample of sperm whales was composed of eight immature females,
seven immature males, 32 mature females, one mature male and eight males in puberty. In the case of threewhales (TD: one whale, STZ: two whales) the stomachs were largely damaged by the harpoon. In the case offour whales (STZ: two whales, KZ: two whales) undigested, partially digested and buccal mass with beaks
items were not found in the stomachs. Those seven whales were excluded from the analyses. Although thesample size is small and sampling was restricted to sperm whales with body length of 13m or smaller, thesamples obtained were widely distributed in the western North Pacific.
Diet composition
A total of 49 types of prey items were found, including 28 species of cephalopods and 6 species of fish (Table2). Indeces of Relative Importance (IRI) for prey items of sperm whales in water masses are shown in Figure
2.
Subarctic Region (SA)Belonella borealis was the most important prey item by number (26.4%), weight (24.8%) and frequency ofoccurrence (100%), followed by Histioteuthis spp. (30.5%, 14.5% and 100.0%, respectively). Weight of Onikia(Onikia) robusta was the highest (27.8%), however its number (1.4%) and frequency of occurrence (50.0%)
were lower than in B. borealis and Histioteuthis spp.. The %IRI was in the following order: B. borealis (30.9%),
Histioteuthis spp. (27.2%), O. (Onikia) robusta (8.8%), Gonatopsis aff. makko (7.5%), Gonatus spp. (7.5%),
Histioteuthis dofleini (7.3%), Galiteuthis phyllura (5.9%) and Chiroteuthis calyx (1.9%).
Transitional Domain (TD)B. borealis was the most important prey item by number (36.6%), weight (27.9%) and frequency of occurrence(100%), followed by G. phyllura (25.7%, 8.4% and 85.7%, respectively). Weight of O. (Onikia) robusta(26.9%) was almost the same as in B. borealis, but its number (2.1%) and frequency of occurrence (28.6%)
were lower. The %IRI was in the following order: B. borealis (47.4%), G. phyllura (21.4%), Histioteuthis spp.

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SC/F16/JR26(10.3%), O. (Onikia) robusta (6.1%), Taningia danae (3.7%), Gonatopsis borealis (3.6%), C. calyx (1.6%) and
G. aff. makko (1.4%).
Northern part of Transition Zone (NTZ)
The most important species were B. borealis in number (35.9%) and T. danae in weight (51.5%). However,number of T. danae was very low (5.2%). The frequency of occurrence in Histioteuthis spp., G. phyllura andG. borealis were 82.4%, 88.2% and 76.5%, respectively, higher than B. borealis (58.8%) and T. danae(47.1%). The %IRI was in the following order: B. borealis (30.1%), T. danae (22.8%), Histioteuthis spp.
(13.8%), G. phyllura (11.6%), G. borealis (7.3%), H. dofleini (3.5%), Gonatus berryi (3.2%) and Gonatus spp.
(3.1%).
Southern part of Transition Zone (STZ)
The most important species were Histioteuthis spp. in number and frequency of occurrence (37.2% and 88.2%,
respectively) and T. danae in weight and frequency of occurrence (58.6% and 64.7%, respectively), while theweight of Histioteuthis spp. and number of T. danae were was low (9.7% and 8.6%, respectively). The %IRI
was in the following order: T. danae (36.6%), Histioteuthis spp. (34.8%), H. dofleini (7.6%), O. (Onikia)
robusta (5.5%), Ancistrocheirus lesueurii (5.0%), G. phyllura (2.0%), Megalocranchis sp. (1.6%) and B.
borealis (1.4%).
Kuroshio Zone (KZ)
The common species in number were Octopoteuthis spp. (15.9%), followed by Gonatus spp. (14.2%) andHistioteuthis spp. (14.2%). The common species in weight were T. danae (32.1%), followed by Octopoteuthis
spp. (15.7%). The most common species in frequency of occurrence were B. borealis, H. dofleini and Gonatus
spp. (75.0%, 75.0% and 75.0%, respectively) and Histioteuthis spp. (75.0%). The %IRI was in the following
order: T. danae (19.7%), Octopoteuthis spp. (15.9%), Gonatus spp. (14.2%), A. lesueurii (10.7%), B. borealis(10.2%) and Histioteuthis spp. (9.7%). Trachipterus spp. as a fish prey was ranked 3.2%, and this differed fromother water masses.
Prey compositions by environmental and biological factors
The CCA analyses for correlation between prey items of weight and environmental factors (Longitude, Latitude,
Date, Sex, Depth, Maturity and Body length) had eigenvalues of 0.200 and 0.093, explaining 41.1% and 19.1%of the species-environment variance (Figure 3). Within above seven variables, “latitude” and sampled “date”
were significant at p<0.001 and P<0.05, respectively. Positive scores of Axis 1(longitudinal axis (a) in Figure3) was explained by higher latitude and later day. “Longitude”, “maturity” and “body length” were alsosignificant values at p<0.01, p<0.01 and p<0.01, respectively. On the second axis 2 represents lager whale andmaturity.
From the plots of each whales, such as TD6 or NTZ1 etc., whales sampled at SA and TD had positive scoreson Axis 1, while whales sampled in STZ and KZ had negative scores on Axis 1 except STZ2. Whales sampled
in NTZ scores were plotted at positive and negative on the Axis 1. This result indicated sperm whales shift tonorthward at later days, large and mature sperm whales distribute offshore, and contrarily small and immature
sperm whales distribute more inshore area.
The prey items could be separated into three groups along Axis 1 in Figure 3b. The first group (e.g. G. madokai,
G. middendorffi, G. aff. makko, O. borealijaponica) appeared to have positive scores (>0.5) on Axis 1. The
second group (e.g. Architeuthis dux, C. akimushkini, Megalocranchia sp., Octopoteuthis spp., D. discus,
Trachipterus spp.) appear to have negative scores (<-0.5) on Axis 1. The third group with close to neutralscores (>-0.5, <0.5), appeared between first and second group. In these prey items, O. sicula, C. calyx, B.
borealis, G. borealis, G. phyllura, G. berryi and Gonatus spp. plotted positive scores on Axis 1, A. lesueurii,
T. danae, O. (Onykia) robusta, O. (Onykia) loennbergii, O. deletron and C. imperator plotted negative scoreson Axis 1. Genus Histioteuthis plotted almost neutral scores on Axis 1. This result indicated squids composition
strongly affect by latitude. G. madokai and O. (Onykia) loennbergii plotted have largest positive score andmost negative score on Axis 2, respectively. G. madokai distributed at most North and offshore area and O.
(Onykia) loennbergii is distributed inshore.
Distribution patterns of sperm whales
Density index based on sighting survey data suggested that the sperm whales were widely distributed in thewhole research area. However, sperm whales east of 150°E moved northward in July and August, while highdensity remained in northern Japan west of 150°E.

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DISCUSSION
Sperm whales in the western North Pacific off Pacific coast of Japan fed upon a variety of mesopelagic squids
throughout the whole study area. Prey items in the Subarctic Region and Transitional Domain were mainlycomposed by subarctic and subarctic-transitional squids. Contrarily, prey items in the Kuroshio Zone andSouthern part of Transition Zone were mainly composed of subtropical and subtropical-transitional squids.
Prey items in the northern part of the Transition Zone were composed of squids that mixed in Subarctic Region
to Kuroshio Zone. The composition of prey items changed in relation to transitional change between north andsouth in the study area and B. borealis, genus Histioteuthis and T. danae were the most important prey species
with high abundance.
Kuroshio Zone had unique prey composition, having a small number of prey types and IRI values of each preytypes (not more than 20%). The Kuroshio Zone had prey squids at lower density and important prey squids
like B. borealis and T. danae did not occur at water masses in the north of Kuroshio Extension Front. In the
Townsend’s American (Yankee) whaling charts which Mizroch and Rice (2013) showed, sperm whales were
not distributed in the Kuroshio Current System and high density was observed on both side of Kuroshio Current
System. Uda (1954) stated that whale school does not occur in the easterly rapid flowing Zone of warm current.
Accordingly the whaling grounds are poorly found in the westerly drift wind current area (a branch of
Kuroshio) in the North Pacific Ocean and Kuroshio itself. Low density of sperm whales in the Kuroshio Zone
may reflect feeding environment as well as oceanographic factor.
Sperm whales have a general shift northward during the northern summer (Rice, 1989). East of northern Japan
area whaling ground by Yankee whalers namely Cast of Japan Ground (Mizroch and Rice, 2013) and costal
whaling (Kasuya and Miyashita, 1988) occurred. In this study, results of the CCA and distribution of sperm
whales suggested similar patterns northward movement and high density area off northern Japan at west of
150°E. High density areas of the northern part of research area and east of 150°E probably corresponds to the
Subarctic Region and west of Northern/Southern part of the Transition Zone, respectively. Mizroch and Rice(2013) concluded by analyzing whaling data and movement data of whales marked with Discovery marks thatsperm whales appear to be nomadic, most likely traveling in response to the geographical and temporalvariations in the abundance of medium- and large-sized pelagic squids, their primary food. We confirmed thatsperm whales feed there. Feeding environment of Subarctic Region and west of Northern/Southern part of theTransition Zone may represent favourable situation for sperm whales.
Distribution depth in the daytime of most important prey, B. borealis, H. dofleini and T. danae is 500-700m,
500-700m, and 600-900m, respectively (Watanabe et al., 2006, Kubodera et al., 2007). B. borealis and H.
dofleini is non-diel vertical migration squids (Watanabe et al., 2006). Therefore it is suggested that the main
feeding depth of sperm whales is around 500-700m, in the western North Pacific east of Japan. Important preyspecies in autumn and winter for sperm whales in the east coast of Japan were H. dolfleini, O. bartrami,
Octopoteuthis sp., Moroteuthis robusta (Kawakami, 1976, Okutani et al., 1976, Okutani and Satake, 1978).
These squids were identified in the present study, in particular H. dolfleini and O. robusta were identified asimportant preys in this study. According to the result of Tamura et al. (2009) and the present study, O. bartrami
was not important prey of sperm whales in spring and summer. O. bartrami in nearby Subarctic Front mainly
distributed 0–40m depths during the night and 200–350m depths during the day in summer (Nakamura, 1995,
Tanaka, 1999). Important prey squids of sperm whales distributed deeper than O. bartrami. O. bartrami was
not an important prey for sperm whales from spring to summer probably because of differences between
feeding depth of sperm whale and distribution depth of O. bartrami.
In 2000 to 2013 JARPNII, the large male sperm whales (Body length > 13m) could not obtain for technicalreason. To understand more precisely the feeding habits of sperm whales, more samples, especially mature
males are needed. However, food habit and consumption by sperm whale were used as input data for Ecopath& Ecosym type model to understand the role of sperm whale in the marine ecosystem (Mori et al., 2009,
Murase et al., 2016: SC/F16/JR28).
In conclusion, our study suggest that the distribution and movement of sperm whales throughout Kuroshio to
Subarctic Zone west of 170°E seems to reflect the abundance of mesopelagic squids in spring and summer, inparticular B. borealis, genus Histioteuthis and T. danae. Larger whale likely feed at offshore waters which also
be a factor of prey composition. This flexibility and different size distribution in sperm whale seems to beimportant to maintain large size of the body and high abundance in the North Pacific.

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ACKNOWLEDGEMENTS
We thank the captains, crewmembers, cruise leaders and researchers on board of the research vessels in
JARPNII for their contributions in collecting the samples and data used in this study. We appreciate very muchthe help in sorting and analyses by the graduate students of the School of Marine Science and Technology ofTokai University. Our sincere thanks to Dr. Luis A. Pastene of the ICR for their valuable suggestions and usefulcomments on this paper.
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SC/F16/JR26

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8

SC/F16/JR26
Table 1. Biological data and stomach contents weight of sperm whales sampled from 2000 to 2013 in the western North Pacific. Sexual maturity of male was assigned based onsummed weight of both testes as immature <1.2kg, puberty >1.2kg (Rice, 1989), sexually mature >4.85kg (Gambell, 1972). Sexual maturity of female was determined by the presenceof at least one corpus luteum or corpus albicans in the ovaries and/or pregnancy. Stomach contents weight was the total net weight of forestomach and fundic compartment.
Subarctic Region (SA)
FemaleM ale

Transitional Domain (TD)FemaleNorthern part of Transition Zone (NTZ)

M ale

FemaleSouthern part of Transition Zone (STZ)

M ale

FemaleKuroshio Zone (KZ)

M ale

Female

Total
M ale

M aturePuberty

Immature

M atureM atureImmature

M atureImmature

Puberty

Immature

M atureImmature

Puberty

Immature

M atureImmature

Puberty

Number of whales

1

3

3

4

1

2

10

2

3

2

14

4

1

1

3

1

1

56

Average body length (m) ± S.D.

12.7

11.8 ± 0.56

8.6 ± 1.08

10.5 ± 0.61

13.7

8.5 ± 0.35

10.6 ± 0.50

8.6 ± 0.21

10.7 ± 1.87

8.8 ± 0.57

10.3 ± 0.86

9.3 ± 0.67

10.9

8.3

9.9 ± 0.25

7.9

10.2

10.1 ± 1.27-

(11.3 - 12.4)(7.4 - 9.4)

(9.9 - 11.3)-(8.2 - 8.7)

(9.8 - 11.5)(8.4 - 8.7)

(9.2 - 12.8)(8.4 - 9.2)

(8.9 - 11.6)(8.8 - 10.3)--(9.7 - 10.2)--(7.4 - 13.7)

24.9

22.9 ± 4.10

9.0 ± 4.31

17.6 ± 4.28

32.7

8.0 ± 0.64

17.0 ± 4.34

9.3 ± 0.14

19.0 ± 9.91

9.5 ± 1.98

16.5 ± 3.74

11.4 ± 1.85

17.0

7.5

13.6 ± 2.32

6.3

14.4

15.5 ± 5.97-

(19.7 - 27.5)(4.1 - 12.2)(13.5 - 23.5)-(7.5 - 8.4)

(13.0 - 26.2)(9.2 - 9.4)

(12.4 - 30.4)(8.1 - 10.9)(10.2 - 22.0)(10.2 - 14.1)--(11.8 - 16.2)--(4.1 - 32.7)b55.4±28.5

c

54

16

21.6±17.7

4.1

6.7

51.4±46.2(38.5-88.3)--(3.6-39.0)--(2.2-179.1)(Body length range)
Average body weight (t) ± S.D.
(Body weight range)
Average stomach contents weight (kg) ± S.D.
(Stomach contents weight range)
a

a

32.4

98.3±54.4

28.9

19.1±21.2

179.1

41.1±3.867.5±58.1

56.8±48.8

40.7±17.1

49.6±57.0

50.5±44.0-(41.1-149.4)-(2.7-50.3)-(38.4-43.8)(9.0-168.7)(22.3-91.3)(22.1-55.8)(9.3-89.9)(2.2-148.3)

Two whales was excluded, for stomach was broken by harpoon and no stomach content weight data, respectively; b and c One whale was excluded, for stomach was broken by harpoon.

9SC/F16/JR26
Table 2. Prey items compositions in the stomach contents from sperm whales sampled in the western North Pacific from 2000 to 2013.

%N

Subarctic Region (SA)
n=4
%W
%F

%IRI

Transitional Domain (TD)
n=7
%N
%W
%F
%IRI

Northern part of Transition Zone (NTZ)
n=17
%N
%W
%F
%IRI

Southern part of Transition Zone (STZ)
n=17
%N
%W
%F
%IRI

%N

Kuroshio Zone (KZ)
n=4
%W
%F

%IRI

Cephalopods
Ancistrocheiridae
Enoploteuthidae
Onychoteuthidae

Gonatidae

Octopoteuthidae

Cycloteuthidae

Histioteuthidae

Lepidoteuthidae
Architeuthidae
Ommastrephidae
Chiroteuthidae

Mastigoteuthidae
Cranchiidae

Alloposidae

Ancistrocheirus lesueurii
Enoploteuthis chuni
Onychoteuthis borealijaponica
Onykia (Onykia) robusta
Onykia (Onykia) loennbergii
Gonatus berryi
Gonatus middendorffi
Gonatus madokai
Gonatopsis aff. makko
Gonatopsis borealis
Berryteuthis magister
Gonatus spp.
Gonatopsis sp.
Gonatidae sp.
Octopoteuthis sicula
Octopoteuthis deletron
Taningia danae
Octopoteuthis spp.
Cycloteuthis akimushkini
Discoteuthis discus
Cycloteuthidae sp.
Histioteuthis dofleini
Histioteuthis corona inermis
Histioteuthis spp.
Pholidoteuthis boschmai
Architeuthis dux
Ommastrephes bartramii
Chiroteuthis imperator
Chiroteuthis calyx
Asperoteuthis acanthoderma
Mastigoteuthis sp.
Liocranchia reinhardti
Belonella borealis
Galiteuthis phyllura
Taonius sp.
Galiteuthis sp.
Megalocranchia sp.
Cranchiinae spp.
Haliphron atrantica
Unidentified cephalopods

0.7
1.4
1.0
0.2
0.2
4.1
0.3
0.8
8.1
0.7
0.7
0.2
0.5
11.2
30.5
0.2
5.1
26.4
6.9
0.3
-

1.1
27.8
0.4
<0.1
0.2
8.3
0.3
1.0
8.4
0.4
0.3
2.2
0.2
5.0
14.5
<0.1
1.2
24.8
2.9
<0.1
-

50.0
50.0
75.0
25.0
25.0
100.0
25.0
25.0
75.0
25.0
50.0
25.0
50.0
75.0
100.0
25.0
50.0
100.0
100.0
25.0
-

0.5
8.8
0.6
<0.1
<0.1
7.5
<0.1
0.3
7.5
0.2
0.3
0.4
0.2
7.3
27.2
<0.1
1.9
30.9
5.9
<0.1
-

0.4
2.1
1.9
0.4
1.2
3.5
1.4
0.2
0.7
0.9
0.2
3.7
17.3
3.2
36.6
25.7
0.2
0.2
-

0.1
26.9
0.6
0.3
3.1
3.3
1.6
<0.1
0.5
8.0
<0.1
1.3
7.2
0.6
27.9
8.4
0.4
0.1
-

28.6
28.6
57.1
28.6
42.9
71.4
57.1
14.3
28.6
57.1
14.3
14.3
57.1
57.1
100.0
85.7
14.3
14.3
-

0.1
6.1
1.1
0.1
1.4
3.6
1.3
<0.1
0.2
3.7
<0.1
0.5
10.3
1.6
47.4
21.4
<0.1
<0.1
-

0.7
0.6
0.2
6.1
0.3
0.4
0.5
7.0
<0.1
3.9
0.4
0.2
1.5
5.2
0.1
<0.1
<0.1
4.9
14.5
<0.1
0.2
5.0
35.9
11.9
-

0.5
0.3
3.6
1.1
<0.1
0.2
1.0
4.2
<0.1
0.9
<0.1
<0.1
0.8
51.5
<0.1
<0.1
<0.1
2.0
5.2
0.2
<0.1
0.9
23.9
3.4
-

29.4
41.2
11.8
52.9
17.6
11.8
17.6
76.5
5.9
76.5
11.8
17.6
35.3
47.1
11.8
5.9
5.9
58.8
82.4
5.9
17.6
47.1
58.8
88.2
-

0.3
0.3
0.4
3.2
<0.1
<0.1
0.2
7.3
<0.1
3.1
<0.1
<0.1
0.7
22.8
<0.1
<0.1
<0.1
3.5
13.8
<0.1
<0.1
2.3
30.1
11.6
-

8.3
0.1
0.3
1.5
1.4
1.0
0.1
0.1
2.4
1.3
0.4
1.5
8.6
2.6
1.4
0.5
12.5
0.3
37.2
0.6
0.9
1.0
0.1
3.0
5.9
1.1
0.4
3.9
0.4
0.1
0.3

4.4
<0.1
<0.1
10.7
0.3
0.2
<0.1
0.1
1.0
0.5
<0.1
0.4
58.6
0.7
0.8
<0.1
2.9
<0.1
9.7
5.4
<0.1
0.1
<0.1
0.9
0.8
0.1
0.1
0.6
<0.1
<0.1
NA

47.1
5.9
5.9
52.9
17.6
29.4
5.9
5.9
17.6
47.1
5.9
29.4
64.7
35.3
17.6
17.6
58.8
5.9
88.2
23.5
23.5
23.5
5.9
41.2
35.3
5.9
11.8
41.2
5.9
5.9
5.9

5.0
<0.1
<0.1
5.5
0.3
0.3
<0.1
<0.1
0.5
0.7
<0.1
0.5
36.6
1.0
0.3
<0.1
7.6
<0.1
34.8
1.2
0.2
0.2
<0.1
1.4
2.0
<0.1
<0.1
1.6
<0.1
<0.1
NA

11.5
14.2
3.5
7.1
15.9
1.8
2.7
5.3
14.2
1.8
0.9
0.9
0.9
8.8
4.4
1.8
2.7

9.8
4.7
3.2
32.1
15.7
2.1
2.1
3.5
5.1
2.4
0.2
0.9
<0.1
4.7
1.6
0.6
NA

50.0
75.0
25.0
50.0
50.0
50.0
25.0
75.0
50.0
25.0
25.0
25.0
25.0
75.0
25.0
50.0
25.0

10.7
14.2
1.7
19.7
15.9
2.0
1.2
6.7
9.7
1.1
0.3
0.5
0.2
10.2
1.5
1.2
NA

Nannobrachium regale
Laemonema longipes
Moridae spp.
Coryphaenoides pectoralis
Himantolophus groenlandicus
Diretmoides parini
Trachipterus spp.
Icosteus aenigmaticus
Unidentified fish
Total
Number of prey items

0.2
0.3
0.2
100
591

0.2
0.9
NA
100
590

25.0
25.0
25.0

<0.1
0.2
NA
100

0.2
100
565

9.7
100
565

14.3
-

1.0
100

<0.1
0.1
100
1626

<0.1
0.2
100
1626

5.9
5.9
-

<0.1
<0.1
100

0.1
0.1
0.1
0.4
100
793

<0.1
<0.1
<0.1
1.5
100
791

5.9
5.9
5.9
11.8
-

<0.1
<0.1
<0.1
0.2
100

1.8
100
113

11.1
100
110

25.0
-

3.2
100

FishesMyctophidae
Moridae
Macrouridae
Himantolophidae
Diretmidae
Trachipteridae
Icosteidae

10SC/F16/JR26

Figure 1. Sampling positions of sperm whales from 2000 to 2013 and schematic illustration of front and water mass structures in western North Pacific. Schematic illustration of front
and water mass structures was determined according to Yasuda (2003) and Brodeur and Yamamura (2005) as follows. Subarctic Region (SA); north of the Oyashio Front(OyF) which is defined as a 5°C isotherm at 100 m depth at west of approximately 155°E and the Subarctic Front (SAF) is defined as the 4°C isotherm at 100 m depth at eastof approximately 155°E. Transitional Domain (TD); area of between of the Oyashio Front/the Subarctic Front and the Subarctic Boundary (SAB), which is defined as a nearsurface salinity front (salinity of 34 psu). SAF (OyF) and SAB separate east of 150°E, this area between SAF (OyF) and SAB is referred to as the Transition Domain.
Northern part of Transition Zone (NTZ); area of between the Subarctic Boundary and 6°C isotherm at 300m, which is index of the Kuroshio Bifurcation Front (KBF): thenorthward branch form the Kuroshio Extension Front near the Shatsky Rise located around 160°E (Mizuno and White 1983), however in this study, south of 6°C isotherm
at 300m in the Transition Zone was assume to strong influence area from the Kuroshio. Southern part of Transition Zone (STZ); area of between 6°C isotherm at 300m andthe Kuroshio Extension Front (KEF). Kuroshio Zone (KZ); south of the Kuroshio Extension Front which is defined as a 14°C isotherm at 200m depth.

11SC/F16/JR26

Figure 2. Percentage composition of eight major prey items found in stomachs of sperm whales in five water masses. The eachrectangle indicates an Index of Relative Importance for each food item.
(a) SA: Subarctic Region, (b) TD: Transitional Domain, (c) NTZ: Northern part of Transition Zone, (d) STZ: Southern part ofTransition Zone, (e) KZ: Kuroshio Zone; n is the number of whales.

12SC/F16/JR19

(a)

(b)

Figure 3. Canonical correspondence analysis ordination biplots, showing important prey items of sperm whales
sampled in the western North Pacific, relation to the environmental and the variables (body length, sex, sexual
maturity, latitude, longitude, sampled date, depth of sampled sites). (a) Bioplot of sperm whales (sampling sites)
and the environmental and the biological variables. (b) Bioplot of important prey items and the environmental andthe biological variables. Superscripts on environmental and biological factors represents p-values (*** <0.001, **<0.01, * <0.05). The length and direction of arrow represents the strength and direction of the effect of the variableson the ordination. Codes for whales are the same as in Table 1. Species are identified by epithets formed frominitial letters in genus and species names, see Table 2. Weight of prey species are used this analysis.

Figure 4. Density Index of sperm whales by 0.5 degree mesh (number of whales found per n.mile) based onsighting surveys under the JARPNII from 2000 to 2013. Red symbols indicate sighting position of sperm whales.

13