FOOD OF STENELLA CAERULEOALBANOBUYUKI MIYAZAKI
TAKAYA KUSAKAAND
MASAHAR U NISHIWAKI
Ocean Research Institute, University of Tokyo

ABSTRACT

Food contents of27 stomachs of Stenella caeruleoalba taken from two schools
were examined. In total, 5410 fishes were identified by otolith and 1,448 fishes
by facial bones. Four species from 3 genera and 3 families were identified byotolith and 31 species from 14 genera and 11 families by facial bones. Twospecies from 2 genera and 2 families were observed in 35 squids contained and4 species from 4 genera and 3 families in 1,971 shrimps. Myctophid fishes andBentheogennema borealis were dominant in number in the food components. Allspecies identified are pelagic or semipelagic. The estimated body length offishes, the mantle length of squids, and the total length of shrimps are in therange of60-300 mm, 95-190 mm, and 38-130 mm, respectively. The numberof specimens of food components with luminous organs amounted to 74% of thetotal number of all specimens identified.
INTRODUCTION

Schools of blue white dolphin, Stenella caeruleoalba are found around the coast ofOshima Island mostly from southeast to north (Tobayama, 1969) and several
thousands individuals of this animal are caught commercially in Sagami Bay
throughout autumn and early winter (Tobayama, 1969; Kasuya, 1972). Accordingly, this animal is considered to migrate into Sagami Bay in autumn and earlywinter.
The study of the food and the food habits of this population may be important
for recognizing the behavior and a cycle of ecosystem to which this animal belongs.
In the present paper, species, numbers and sizes of the food specimens in thestomach contents of 27 blue white dolphins from two schools were studied.
MATERIAL AND METHOD

In this study, contents of the first stomach were examined. The dolphins werechosen randomly from 13 and 14 individuals of schools A and B respectively. Bothschools were found in Sagami Bay (Fig. 1) and driven into Kawana harbor byfishermen. Biological examination suggests that school A is considered to be abreeding school consisted of sexually maturged animals and their calves, and school
B to be a nonbreeding school consisted of sexually immatured animals. OtherSci. Rep. Whales Res. Inst.,

No. 25, 1973, 265-275.

266

MIYAZAKI, KUSAKA AND NISHIWAKITABLE !.

BIOLOGICAL INFORMATION OF SCHOOLS A AND B,
STENELLA CAERULEOALBA.

Items
Time of found
Position of foundTime of expire
School size
No. of individuals examined
No. of stomachs collected
Range of body length
Schoolcomposition

MIMSchool A

School B

09: 00 2 Dec. 1970
34°49'N 139°24'E
13: 00 2 Dec. 1970
25625513108-250 crn

06: 30 10 Dec. 1970
34°49'N 139°25'E
09: 00 10 Dec. 1970
8877
14182-245 crn

54565986

0161645

femalemale
femalemaleM and IM indicate mature and immature respectively.

information is shown in Table 1.
The samples were taken to the laboratory after they had been freezed to -20°C.
In the laboratory, specimens were separated into three groups, fishes, squids andshrimps, then their species were identified.
As it has been formerly done (Kusaka, 1969, 1970; Kusaka and Thuc, 1972), fish
species were used to be identified mostly by facial bones mainly by the urohyals, andpartly by the otoliths. The number of specimens was counted by urohyals andotoliths. All otoliths refered in this report were sagittae. The body length of fish
specimens was estimated from the size of the urohyal. Squid species were identified
only by the half digested body and not by the beaks. The number of specimens,
however, was counted by the beaks. Shrimp species were identified by the half
digested individuals by the help of Dr. Y. Aizawa, and the number of specimens
was also counted.
RESULT

1.

The weight of stomach content

The weight of stomach contents of 26 dolphins is shown in Table 2. The
average weight of those from school A is almost similar to those from school B.

2.

Fish

In 27 stomachs of the dolphins 1,448 fishes found, were identified by facialbones and 31 species from 14 genera and 11 families were detected (Table 3).
Among these fishes, 1,234 fishes of 13 species were found in both schools, 210 fishesof 15 species, were found only in school B and 4 fishes of 3 species, were found onlyin school A (Table 3).
Myctophid fishes are dominant in number amounting to 63.9% of the totalnumber.
Myctophidae spp., Poryipnus spinosus, Gonostomatidae sp. and Chauliodontidae
spp. have luminous organs.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

FOOD OF STENELLA CAERULEOALBA

139°

267

140°

Fig. 1. Surface isothermal line around Sagami Bay in Dec. 1970 (Japanese Maritime
Safety Agency, 1970), with the position of finding of the schools A and B. Broken
line indicates 200 m contour line of the depth. K and F indicate Kawana andFu to.

The ranges of estimated body length of fish species are shown in Fig. 3.
By the otoliths 5,410 fishes were identified and represented 4 species belong
to 3 genera and 3 families. These four species are Diaphus elucens, Polyipnus spinosus,Diaphus coeruleus and Argentina semifasciata.
The average number of fishes in the stomachs counted by the number ofotoliths is higher than that counted by the number of urohyals (Table 2, Fig. 2).
This difference in number may indicate the fact that otoliths remain in the firststomach longer than urohyals. Possibly, the process of digestion is more proceededin the stomachs from school A than in those from school B, because the ratio of thenumber of urohyals to that of otoliths is lower in the stomachs from school A.
3. SquidThirty five squids found in 19 stomachs were identified by the half digested
specimens and represented 2 species from 2 genera and 2 families (Table 4).
The number of individuals and the mantle length frequency of these two
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

268

MIYAZAKI, KUSAKA AND NISHIWAKITABLE 2. THE CONTENT OF FIRST STOMACHS OF STENELLA CAERULEOALBA.

SchoolSerial
Number

Weight ofStomachcontent (g)A

2345212930313233343536
Total
Ave.
S.D.

1500

B

1150
660
1380
885
1245
440
410
1310
500
965
1285
11730
978
392

Fish

Squid
~

No.
Otoliths/2

No.
UrohyalsNo.
H.D.I.

No.
Beaks

116
124
178
105
133
209
265
135
283
135
309
129
49
2170
167

57
39
35
23
35
12
11
13
12
23
9
19
27
315
24
14

10

47
31
37
31
42
42
29
35
8
47
46
38
13
456
35
1377

2095
235
151010
149
16285
175
171000308
181465
304
19
1595
117
20
1650
302
22910
172
23
1135
189
24
935
172
25
1095
199
26
1110
371
27
1140
192
28790
355
Total
16215
3240
Ave.
1158
231
S.D.
434
81
H.D.I. : indicates half digested individuals.

1899055
813025140975451
98
100
75
48
1133
81
44

8

1931430

139
8975
128
272794
108
98
43156
12170
174
1349
96
50

No.
H.D.I.
233
31
42
3
22

2
1
12

1
2
13

ShrimpNo.
H.D.I.
154
120
85
173
58
189
21
6
138693
106
140
1244
96
60
67
34
25
20
208
167
48
9
1462
17
4
36
16727
52
61

species are shown in Fig. 4.
Todarodes pacificus is found in both schools. Symplectoteuthis luminosa is foundonly in school B.
The number of beaks is higher in school B than in school A (Table 2, Fig. 2).
4. Shrimp
In 27 stomachs 1,971 shrimps found were identified by the half digested shrimps.
Four species from 4 genera and 3 families were observed (Table 5). All individuals
except one belong to 3 species. Only individual of 1 species is from school B.
Bentheogennema borealis is dominant in number which amounts to 85.6% of theSci. Rep. Whales Res. Inst.,
No. 25, 1973.

269

FOOD OF STENELLA CAERULEOALBA.

300--.....

200 '"

0:'"

UJea~::::>z 100-j -0

A I B
I
UROHYAL OTOL I TH
F I S H
AB!IABSQUID-AI

BSHRIMPFig. 2. Number of individuals eaten by Stenellacaeruleoalba in schools A and B. Vertical line, range; box, range of a standard deviation; horizontal line in box,average.

total number of shrimps.
The ranges of the total length of B. borealis and Pasiphaea sp. are 38-68 mm and110-130 mm, respectively.
The number of individuals found in school A is almost similar to that in school B(Table 2, Fig. 2).
DISCUSSIONThe number of fish specimens is 59% of the total number of all specimens. It isconsidered that Stenella caeruleoalba feeds mainly on fish. Among fish species,
Myctophids is the most dominant in number. The results are similar to thoseSci. Rep. Whales Res. Inst.,
No. 25, 1973.

270

MIYAZAKI, KUSAKA AND NISHIWAKITABLE 3.

SPECIES AND NUMBERS OF FISHES IN
School A

Serial number -->Species of fishes !
Myctophidae
Myctophum orientate
Diaphus elucens
Diaphus coeruleus
Lampanyctus jordani
Diaphus sp. A
Diaphus sp. B
Nemichthyidae
Nemichthys scolopaceusEmmelichthyidae
Erythrocles schlegeli
Erythrocles sp.
Chauliodontidae
Chauliodus sloani
Chauliodus sp.
Paralepididae
Lestidium sp. A
Lestidium sp. B
Lestidium sp. c
Lestidium sp. D
Lestidium sp. E
Lestidium sp. F
Lestidium sp. G
Lestidium sp. H
Sternoptychidae
Polyipnus spinosus
Argyropelecus hemigymnus
Argentinidae
Argentina semifasciata
Argentina sp.
Acinaceidae
Acinacea sp. A
Acinacea sp. B
Acinacea sp. c
Acinacea sp. D
Acinacea sp. E
Lutjanidae
Luljanus sp.
Priacanthidae
Priacanthus sp.
Gonostomatidae
Gonostoma sp.
Total species number
Total individual number

234521292631209194936652376312230313233343536Total

39456137
4234091594

46128841233526293857

639

935

42383551241121331252339619627315

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

271

FOOD OF STENELLA CAERULEOALBATHE STOMACHS OF STENELLA CAERULEOALBA.
School B

Total

151617181984
33675922527440

1461847943696202223

967
430
21060

330
221415561228423

34254562425

262728Total

31231151
52173
52335

23267609
23803267746
2780
42

720

521

6150

190

23117

677

22189
21

2

5

93113

732710118

1446243

1919
2

6

15

92
1212
3
22

3

6

6

222221133

1448

142

2

322

117189

1390

1155

981

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

830

7251314089711541151

9986100775548272

MIYAZAKI, KUSAKA AND NISHIWAKITABLE 4.

SPECIES AND NUMBERS OF SQUIDS IN
School A

Serial number ->Species of squids l234Todarodes po,cificus
Symplectoteuthis luminosa
Unidentified species
Total

233474931343740

5292130334331313231

TABLE 5.

3293342434245

3435358847493536

346464851Total
33

1314456
478

SPECIES AND NUMBERS OF SHRIMPS IN
School A

Serial number ->2345212930313233343536Total

147
6116

157
1550
8

168
19216
55103

65
2174
14
597
72

136
4470
1321111
116
17120

85

173

58

189

21

61386

93

106

140

1244

Species of shrimps l

Bentheogennema borealis
Pasiphaea sp.
Acanthephyra sp.
Aristeinae sp.
Total

154

190

Nemichthys scolopaceus

0I

I

500

1000
15

Argentina semifasciata

89

Chauliodus sloani
117

Erythrocles schlegelif-----0---;I~

Diaphus elucens

BO

Lampanyctus jordanir-----<0>------t~z0

Diaphus coeruleus
Priacanthus sp.

~

Myctophum orientate~

Polyipnus spinosus~Lutjanus sp.

0100

200300ESTIMATEDBODY LENGTH(MM)

Fig. 3. Range and average (open circle) of the estimated body length of fishes
eaten by Stenella caeruleoalba in schools A and B. Number indicates thenumber of individuals.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

273

FOOD OF STENELLA CAERULEOALBATHE STOMACHS OF STENELLA CAERULEOALBA.
School B

15139
139

89
90

16

1775
75

2128
130

20::

I

1827
28

1927
28

22

2094
95

1108llO

232443
4498
98

156
157

26121
121

27707128Total29413491362174
176-Iw

co:E255;:Jz510MANTLE

15LENGTH20(CM )Fig. 4. Mantle length frequency of squids in the stomachs of Stenella caeruleoalba.
Top: Symplectoteuthis luminosa.
Bottom: Todarodes pacificus

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

274

MIYAZAKI, KUSAKA AND NISHIWAKI

formerly studied on Stenella longirostris and Stenella grajfmani (Fitch and Brownell,1968). Gonostomatidae spp. is commonly eaten by the above 3 Stenella species.
Bathylagidae sp., Bregmacerotidae sp., Centrolophidae sp., Paralepididae sp. andExocoetidae sp. have formerly been found in S. longirostris or S. grajfmani (Fitch andBrownell, 1968). These species offish inhabit in the adjacent waters of Japan, butthey are not found from S. caeruleoalba in this study. The fish species which arefound in S. caeruleoalba but neither in S. longirostris nor in S. grajfmani, are 24 species
belong to 9 genera and 9 families. Especially, Chaulidus sloani, Nemichthys scolopaceusand Erythrocles schlegeli are found abundantly from S. caeruleoalba.
The range of estimated body length of fishes from S. caeruleoalba is 60-300 mm.
Nemichthys scolopaceus which is very slender (B. L. 350-1,000 mm), is an exception.
The result is similar to that formerly studied on S. longirostris and grajfmani.
Fish species of Diaphus elucens, Nemichthys scolopaceus and Erythrocles schlegeli, andshrimp species of Bentheogennema borealis and Pasiphaea sp. are found abundantly inmost of the stomachs of the dolphins studied this time.
Fish species of Myctophidae spp., Polyipnus spinosus, Gonostomatidae sp. andChauliodontidae spp. and squid species of Symplectoteuthis luminosa have luminous
organs. The number of specimens of these species amounts to 74% of the total
number of specimens identified in the present study.
ACKNOWLEDGMENTS

We are indebted to Dr. Y. Aizawa of the Ocean Research Institute, for his kind
help in identification of shrimp, to Mr. T. Tobayama of the Kamogawa Seaworld
for presenting us his specimens of otoliths to study, and to Mr. N. Oguro of theOyster Research Institute, for helping us to collect the specimens. We also thankto the following persons for their kind advices: Dr. T. Kasuya and Dr. K. Numachi
of the Ocean Research Institute, and Dr. W. H. Dawbin of the University of Sydney.

Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

FOOD OF STENELLA CAERULEOALBA275

REFERENCES
FITCH, J.E. and R. L. BROWNELL, 1968. Fish otoliths in cetacean stomachs and their importance in interpreting feed habits. J. Fish. Res. Bd. Canada 25, (12): 2561-2574.
JAPANESE MARITIME SAFETY AGENCY, 1970. State of the Adjacent Seas of Nippon. Vol. 4 Tokyo.
KAsUYA, T., 1972. Growth and reproduction of Stenella caeruleoalba based on the age determination bymeans of dentinal growth layers. Sci. Rep. Whales Res. Inst., 24: 57-79.
KusAKA, T., 1969. Research on facial membrane bones of fish-I Regarding feature of urohyal on 100species. Lamer (Bulletin de la Societefranco-japonaise'd oceanographie), 7 (2): 126-143.
KusAKA, T., 1970. Research on facial membrane bones offish-II Regarding feature of urohyal on 220 species.
Ibid., 8 (3): 149-170.
KusAKA, T. and N. T. THuc, 1972. Regarding features of urohyal, parasphenoid, hyomandibular andpelvic bone oftheJapanese lanternfishes (Family Myctophidae, Teleostei). Ibid., 10 (4): 145-155.
ToBAYAMA, T., 1969. School size and it3 fluctuation in the catch of Stenella caeruleoalba in Sagami Bay.
Geiken Tsushin, 217: 109-119. (in Japanese).

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.