THE POPULATION OF FINLESS PORPOISE
IN THE INLAND SEA OF JAPANTOSHIO KASUYA
Ocean Research Institute, University of Tokyo, TokyoAND
KAZUO KUREHA
Himeji Aquarium, Himeji, Hyogo

ABSTRACTThe observation of 1,194 finless porpoises made through 11,549 km ofsighting cruises in the Inland Sea and some ancillary observations provided
the following informations. The porpoise migrates annually to and from the
Pacific coast mainly through the two passes at the eastern Inland Sea. The
highest density (4,900 individuals) is found in April at the beginning of parturition season, and the lowest (1,600) in early winter. The ratios of solitary
adults, of solitary calves, and of cows with calf show seasonal fluctuation,
and allow the analyses of the seasonality of reproduction. Gestation last for
about 11 months. Parturition occurs between April and August with apossible peak in April and May. Most of the cows with calf born in April
and May are suspected to leave the Inland Sea in summer months. Weaning
occurs from December to June after a nursing period ranging from 6 to 15
months. Pregnancies in two contiguous years are not frequent. A 2-year
breeding cycle seems to be most common. Annual production of about
870 calves (both sexes), and gross annual reproductive rate of 17.9% are provisionally estimated for the individuals in the Inland Sea.
INTRODUCTION

On the Pacific coast of Japan, the finless porpoise, Neophocaena phocaenoides (G.
Cuvier, 1829), ranges from the west coast of Kyushu, through Inland Sea, Ise Bay,and Tokyo Bay, to the Sendai Bay (Anon., 1965; Kuroda, 1940; Mizue et al., 1965,
1968; Nakajima, 1963; Ogawa, 1950). Though the incidental catch of the species
once numerous in the Tachibana Bay in the western Kyushu (Mizue et al., 1965)
has ceased by the change of the fishing method (K. Mizue, pers. comm.), small
number of incidental catch and strandings are still common in the above range.
The confirmed northern limit of the range is at the Sendai Bay (38°20'N, 141°15'E),
but the species is considered to migrate further north (Ogawa, 1950). The species
is often trapped in set nets or sighted in the Sendai Bay in June and July, but it isabsent in winter season (T. Shimoyama, pers. comm.). The distribution of thespecies in the Sea of Japan is not confirmed.
The Inland Sea is a well known, and possibly the largest habitat of the finlessSci. Rep. Whales Res. Inst.,

No. 31, 1979, 1-44

2

KASUYA AND KUREHA

porpoise in Japan. The species is legally protected since 1930 as a natural monument. However the protection covers only the porpoise in a 1.5 km radius witha center at the southern tip (34°18.3'N, 132°57.l'E) of Awashima Island near
Takehara City. The reason of the protection is described in Kaburagi (1932).
Namely the angling fishermen of Tadanoumi Town near Awashima used to use
the feeding finless porpoise as an indicator of a kind of fish, Chrysophrys major Temminck and Schlegel, which is believed to feed on small fish Ammodytes personatus
Girard as the finless porpoise supposedly does. This fishery, operated in winterseason, ceased about 10 years ago by the disappearance of Ammodytes in the area (S.
Shiromoto, Manager of Tadanoumi Fishermens Cooperative Union, pers. comm.).
In recent years the pollution of the Inland Sea has progressed, and the increased frequency of red tide and gradual change of the fish fauna is indicated(Hoshino, 1972). However the Inland Sea is still a very productive ground offisheries and aquiculture. The fishery production, excluding aquiculture, in 1977
was 181,902 tons of fish and 102,385 tons of invertebrates and algae (Chugoku
Shikoku Noseikyoku, 1978). Though a law was established in 1973 to regurate
the amount of the pollutant discharged in the Inland Sea and the regulation was
intensified in recent years, there is no indication of improvement of the situation(Anon., 1978).
Since the catch of the finless porpoise is not practically regulated in Japan,
the possibly small population of this coastal species might be damaged if there
occurs a fishery for the finless porpoise in response to the increase of the demandof live specimens for aquariums. Furthermore the population will not be freefrom the influence of the pollution progressing in the region. The present study
was intended to analyse the distribution, abundance, seasonal movement, andreproduction of the finless porpoise in the Inland Sea, and to provide the basic
biological data necessary for the conservation of the species.
MATERIALS AND METHOD

Description of the Inland Sea and area division
The present study covers the Inland Sea proper. It is an area of about
14,300 km 2 of water with about 3,000 islands scattered in it, and is connected toopen sea or other bay by four narrow passes.
The Kanmon Pass is situated at the northwest and opens to the Sea ofJapan.
It is the narrowest of the four passes, with the minimum width of 0.6 km, depthof 19 m, and maximum current of 8.2 knots.
The Hayasui Pass at the southwest entrance opens to the Bungo Channel
which is connected to the Pacific. It is the widest of the four passes, 11.5 km
wide and 186 m deep. The maximum current is 6 knots.
The Naruto Pass opening to the Kii Channel at the southeast corner of theInland Sea has the maximum current of 10.6 knots. The minimum width is 1.3 km,
and the maximum depth at the place is 65 m.
The Akashi Pass connects to the Osaka Bay, which is another small inland
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

Sea of Japan..

3

Honshu0(")(")

Pacific Ocean

Kyushu

131°

132°

133°

134°

135°E

Fig. 1. Geography of the Inland Sea ofJapan. Numeral indicates the area number
used in this study. The boundary between the strata is not indicated.

water opening at the southern part to the Kii Channel. It has the minimum widthof 3.7 km and the maximum depth of 104 m. The maximum current is 6 knots.
As shown in Figs 7 and 11, the depth of the Inland Sea is less than 40 m inmost of regions. The mean depth is 31 m. The depth is larger in the western
open area north of the Hayasui Pass. The depth of about 98 m, the maximum
in the Inland Sea, is recorded in this region.
The water temperature recorded in the present study was between 6.0°C in
March and 28.0°C in September. The seasonal change in the surface watertemperature is more drastic than the open waters. Because of the inflow of external water from the wide Hayasui Pass and the larger water depth in the westernregion, the western open area is more oceanic. Namely the water temperature
in winter is higher at the western part than at the eastern region, and reversed insummer. The difference of the surface water temperature between the two regions
is 3°C to 4°C in both summer and winter seasons.
As the possible result of the oceanic environment, there were often observedsome oceanic delphinids in the open water of the western Inland Sea (Figs 7
and 9).
As mentioned in the later section, the finless porpoise is distributed near thecoast. Though it is not certain if it is related to the water depth or to the distancefrom the shore, the areas were divided in the present study based on the distancefrom the coast and on the group of islands. The entire research area was, at firststep, divided into three strata. The first is the stratum of 0 to 1 nautical mile off
the coast. This stratum was divided into five areas of 1 to 5, considering the
distribution of the islands. The second stratum corresponds to the waters 1 to
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

4

KASUYA AND KUREHA

3 miles off the coast. This stratum was divided into four areas (areas 11 to 14)
by the way mentioned above. Then there remain three independent waterswhich are more than 3 miles apart from the coast. This is the third stratum anddivided into three areas of 21 to 23 (Fig. 1).

Research period and data source
The field observation started in April 1976 and finished in October 1978.
Kureha made the observations between Himeji and Ieshima Islands andthose between Himeji and Fukuda, which routes are shown by dotted lines in Fig.
11. He had 24 expeditions in that part. Each expedition covered only a daywith more than one trip on each route.
Kasuya had 10 expeditions, 10 to 15 days each, to observe most of the partof the Inland Sea which are not cruised by Kureha.
Kasuya's 9th expedition, 6 to 15 March 1978, was for the observation of the
movement of the porpoise at four passes. The lOth expedition, 15 April to 2 May
1978, also includes cruises outside of the Inland Sea. Kureha had four expeditions to the Kanmon and Aka'>hi Passes. Though the results of the observations
made outside of the Inland Sea are not included in the Appendix, they are shownin Figs 7 to 14.
The data of some of the Kureha's expeditions in the Inland Sea were combined with those of Kasuya, and used for the population estimation (see Appendix).
A six hours cruise was made on 13 April 1976 in the nearshore waters off thenortheastern Shod03him3. Island (34°3l'N, 134°10'E) on board of a small fishingvessel. Though 4 7 porpoises were encountered, these data are not used for the
population estimation, because the course was altered by the presence of porpoise.
They are used only for the analyses of the school composition.
The aerial sighting records of the finless porpoise in the Inland Sea andadjacent waters were provided by the Fisheries Aviation Co. Ltd., Kojimachi, Tokyo. The flights were to monitor the pollution by scanning the area systematically,
and covered the years from 1972 to 1978. The season was usually limitted toJune to October with a few exceptional flights in other seasons. The observation of the porpoise was made by an experienced navigator at the altitude of 450 m,
but lowered to 100 to 150 m for the precise observation. These data were used
for the limited purpose to compare the relative density between the areas or between the seasons.
Vessels
With the exception of one trip made by the research vessel Tanseimaru (230gross tons) on 12 November 1976, all the observations were made on various commercial ferry boats. They were either for passengers or for both passengers andcars. The four of the five former cases were generally small (100 to 150 grosstons), and had cruising speed of 8 to 13 knots. The height of observer's eye wasfrom 3 to 4 m. An exceptionally large passenger boat was used between Beppu
and Imabari, and between Takamatsu and Kobe. The speed was about 18
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

5

knots, and the eye height of observer was about 15 m. Other ferry boats carrying
both passengers and cars had large variety of size. However the eye height (6to 6.5 m) was almost constant, because the roof height of car deck was designed
about 4 m. The speeds were between 8.4 and 14.2 knots.
The speed composition of 28 vessels (34 trips) in the 5th expedition, May
1977, is shown in Fig. 2. The mean speed was 11.3 knots (non weighted) or 12.3
knots (weighted with cruised distance).
miles

100
80
>u

c

<II
:::J
CT
<!J

60
JJ.

~

u.. 40,o-----0

',

'

tr

20

\,

b
',

08

10

12

14

16

18

Velocity in knot
Fig. 2. Speed composition of the vessels used in this study. Closed circle and solidline indicate the frequency weighted with cruising distance, open circle and dottedline nonweighted frequency, and vertical line the average speed.

Though the course was arranged as far as possible to cover the waters evenly,
the sighting effort was scarce in the western areas 1 and 11. The sighting effort
in offshore stratum (areas 21, 22, and 23) was scanty. Since the first expedition,
12 to 23 April 1976, was exploratory, the areas were covered in the case less completely compared with the following expeditions.

lvfethod of observation
The observer situated at a position where the maximum field of vision isavailable. It was sometimes the front seat of the cabin. However, in most of thecases, it was the posterior upper deck. Both naked eyes and a binocular (8 X,
8.5°) were used alternatively. The former were used for the near side of about
500 m or less, and the latter for the far side between 400 and 1,000 m. Though
the field of observation from 270° to 360° was available by moving between port andstarboad side, the observation of the front direction was difficult at the posterior
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

6

KASUYA AND KUREHA

upper deck. The time of one scanning was about 20 seconds with binoculars andabout 10 seconds with naked eyes. Namely a set of far side and near side scanning
took about 30 seconds, if there was found neither porpoise nor symptom suggesting
the presence of the finless porpoise. The course of vessel was not altered by thepresence of porpoise or of the symptoms.
For finding the porpoise, not only the body of porpoise or wave caused bysubmerged porpoise, but also the flock of feeding sea birds or the direction of flying
sea birds (mainly sea gulls) were extremely usefull. These indications were, if
found, carefully inspected with binocular.
When the body of finless porpoise was first confirmed, the time, direction fromthe vessel (if possible), radial distance from the observer in nearest 10 m, distancefrom the nearest coast line (if possible), number of individuals in a school, internal
structure of the school (if present), the estimated growth stage of each individual, andspecial behavior of the porpoise (if observed) were recorded. The growth stage wasrecorded as adult, juvenile (intermediate), and calf. The distinction was madebased principally on the body length relative to that of full grown individuals.
The first category represents the large individuals, and their estimated length ismore than 150 or 160 cm. The last is composed of the newborn calf which shows
its typical dark colour or older paler individuals not exceeding 120 or 130 cm inbody length. Though the juvenile (intermediate) is expected to indicate theindividuals between the two length range or those between 135 and 155 cm, theaccuracy will be worse than the other two. If an adult was accompanied by a calf,
they were considered as a mother and its calf. These individuals were always
swimming in parallel, and usually stayed within the distance of 1 m, which is muchcloser than the ordinary two adults do.
The position of the vessel was estimated from the relative position of islands
or of land marks, or from the fairway buoys.
Surface water temperature was measured two or three times a day on cruising
vessel. The wind force was recorded, in Beaufort scale, during entire cruising hours.
The observation was conducted in a wind less than 3 in Beaufort scale, andin a visibility exceeding 0.5 nautical mile (926 m).

Principle of population estimation
When the abbreviations are defined as follows,
D: Cruised distance, nautical miles
N: Number of counted porpoises
P: Number of porpoises present in area of S square nautical miles
R: Finding rate, ratio of porpoises counted to the porpoises present within
0.5 W miles distance from observer (both sides)
r: Apparent finding ratek: Finding rate at 0 m distance from the course
S: Dimensions of the sea, square nautical miles
W: Observed width, nautical mile
there are following relationships.
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

7SN
P= D·W·R(1)

R = r·k(2)

As mentioned in the later section, r is influenced by the weather and other oceanographical environment. And N/(D·r) is used as an population density index corrected for the seasonal change of the apparent finding rate.
ESTIMATION OF PARAMETERS

Observed width (W)Several experiments made on a straight river or on a sea surface of known
distance suggest that a surfacing finless porpoise is identified from 450 m with nakedeyes and from 900 m with binocular at the sea condition of slight breeze (Beaufort
wind scale I). All the sightings in this study, except for two cases, occurred within
1000 m. Accordingly W was assumed in this study as I nautical mile. Even if
this estimation is biased in some degree, it does not cause any biase in the estimation of population abundance (see equations (1) and (3)).
Apparent finding rate (r)The swimming of finless porpoise is usually gentle exposing only part of headand dorsal region, and the jumping clear out of water or sprashing is rare. They
are usually indifferent to the boat encountered. No bow wave riding was observed.
The response to boat is observed as (1) a deep diving or minimum alternation of
direction when the cruising courses of the two cross about 5 to 20 m ahead of theanimal and collision is anticipated, or (2) a kind of stern wave riding lasting only
few to several seconds. The latter occurs occasionally when stern wave passes overthe porpoise.
Figure 3 shows the relationship between the number of porpoises counted andthe distance from observer. Since the finless porpoise is almost indifferent to thepresence of cruising vessel, above relationship is considered to indicate the increase of overlooked individuals with that of the distance.
The frequency of finding is relatively high at the distance below 400 m, andthe points come on a straight line (Fig. 3). This is the range where the porpoises
are identified with naked eyes. If y intercept of the linear regression is shownby Y0 in number of individuals per 100 m range, and the number of total porpoises
dealt by n, there is expected the following equation.

_ /(v.o 0.5·W·l852)
100

r- n

(3)

Wind will have serious influence on the apparent finding rate. Table 1 shows
the seasonal difference of the mean wind force and the number of porpoises sighted
per one hour's observation in different weather conditions. It shows that thesighting efficiency rapidly decreases with the increase of wind force. The efficiencies at the wind scale I to 2, and at 2 to 3 are 53.3% and 15.3% of that at wind
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

8

KASUYA AND KUREHA°loJan.- Feb.
N=40

8

y:56.88-0.2125x

20
4

20

•

•

Mar.
N:165

•

20

•

•

•

•
•

•

20
>
u 20
c
0
Q.I

::J

O'"

(!)

20

1.1...

0

0

May
N=109

6

Jun.
N:108

2

Jut.- Aug.
N:77

•

•
•

7

y:32.64 -0.0843x

20
0
40
20
No.

5

•

L..

•

Apr.
N:256

10

y:30.06-0.0569x

20

Apr.
N:133

y=22.81-0.0248x

•
•

Sept.

•
3

N:57
Nov.- Dec.
N=34

306.9 porpoises/ 100m range
y=30.6.9-0.592x

Total

200

•
00

200
400
Distance from••

N,,981•600
800
observer in•mFig. 3. Relationship between the distance from the observer and the number ofthe porpoises sighted. Numeral indicates the expedition number. Data ofKasuya
and Kureha included.

0 to 1. As shown in Fig. 4, it can be said for any of 9 expeditions that the sighting
efficiency was higher in the weather of lower wind force.
The r calculated for each expedition shows a seasonal fluctuation (Table 1).
The relationship between the mean wind force and r is shown by a linear regression.
However, as shown in Fig. 5, the 2nd (July to August) and 3rd (November toDecember) expeditions give extremely low apparent finding rates. Though theprecise observation of density of sea bird was not recorded, it is worth to note thatthe extreme scarcity of sea bird in the 2nd expedition was noticed and recorded on
several pages of the field book. This may perhaps have a effect to lower theSci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

.....

9

Wind scale:J5.......

..c
,_
(!J
a.

4

··O··

Ill

3

-

2

0

c:n
.£
..c
c:n

0-1
1- 2
2- 3

7

3

(/)

M

F

J

A

0- - -------- - - --- - - -o-- --------_______ .o------

0

J

M

J

A

s

0

N

D

Month
Fig. 4. Relationship between the wind force and the number of individuals sighted
per one hour of observation. Upper limit of each wind range excluded. Numeralby the circle indicates the expedition number .
.5

. .
5

1
Apr.

-:::-

May

2 .4
6•June~.

10•Apr.
li•Mar.

01

c

-g .3

.

7
Sept.

2

Jul.-Aug.

c
Cll

~ .2

a.
a.

<(

.
3

.
B

Jan.-F~ .

Nov.-Oec .

. 1'---'-~-'---'~-'--~~~~-'---'~-'--~~~~-'---'
.6
.8
1
1.2
1.4
1. 6

Mean wind force

Fig. 5. Relationship between mean wind force and the apparent finding rate (r).
Numeral indicates the expedition number.

apparent finding rate.
Though it is not possible to explain the low r value of the 3rd expedition,
it is concluded that the apparent finding rate r calculated by the above method
reflect the wind force and probably some other oceanographical conditions. So
it is unnecessary for r to have further wind force correction. The visibility will notneed to be corrected because the observation was made only when the visibility exceeds the observable distance (W/2). There might be personal difference of the rvalue. However it was confirmed in the previous cooperative works that oursighting ability is not significantly different.
Though it is more reasonable to use perpendicular distance measured fromthe position of porpoise to the course of the vessel instead of the radial distance between porpoise and observer (Seber, 1973; Doi, 1974), it was not used in the present
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

KASUYA AND KUREHA

10

study mainly from the absence of adequate data. Where the porpoise is densely
distributed, the recording of both finding direction and the distance was often impossible for single observer without increasing the overlooked individuals. Only
the radial distance at the first sighting was recorded in such a case. When the
direction of finding is group into nearest 45° angle, they are distributed as follows.
Number of individuals
22
28
601
27
7
685

Direction

oo

45°

goo

135°.
180°
Total

Percent
3.2
4.1
87.7
4.0
1.0
100.0

The finding on stern (180°) or bow (0°) direction is only a few percent of the total,and most of the sightings occurred on the side direction or between 67.5° and 112.5°.
This tendency will be more exagerated in the dense area where angle was notrecorded. Though the present calculation will slightly overestimate the r value,
the above analysis of the finding direction suggests that the bias will not be solarge compared with the uncertainty of the estimation of k value mentioned below.
TABLE 1.

EFFECT OF WIND ON SIGHTING OF FINLESS PORPOISE

no.

date

8 27/I-10/II
4 2/III-15/III
l l 2/IV-23/IV
10 15/IV-30/IV
5 8/V-19/V
6 14/VI-25/VI
2 22/VII-4/VIII
7 15/IX-28/IX
3 12/XI-21/XII
Total
Total, no./hr
Total, no./hr rate

Wind force 2lSightingsll

Expeditions
no.

hrs.

0-1

1-2

2-3

mean

36
155
251
256
109
101
76
57
51
1092

29.86
53.93
49.57
55.43
50.57
47.05
49.63
51.64
57.00
444.68

0.167
0.530
0.920
0.618
0.827
0.515
0.915
0.350
0.519
0.613
3.174
I

0.420
0.381
0.080
0.195
0.128
0.380
0.085
0.551
0.243
0.267
1.693
0.533

0.413
0.089
0
0.187
0.045
0.105
0
0.099
0.238
0.120
0.486
0.153

I. 746
1.059
0.580
1.069
0. 718
1.090
0.585
1.249
1.219
1.007
2.456
0.774

lJ Only data obtained by T. K. included.
limit inclusive, Beaufort scale.

2lApparent
finding
rate (r)
0.190
0.345
0.473
0.356
0.498
0.378
0.280

o.:m
0.165
0.345

Shown by the ratio of length of time, wind range lower

Estimation of k and R
For the estimation of the population size the true rate of finding at zero distance need to be estimated. Since the mean speed of the vessels is about 12.3
knots, an entire observation field of 1 nautical mile is cruised within 4.9 minutes,
and more efficient observation field of about 900 m within 2.4 minutes. On theother hand the surfacing interval of the finless porpoise ranges form 4 to 80 seconds
with an average of about 40 seconds (T. Kataoka, unpublished data). Then theSci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

11

number of surfacings expected for one porpoise in an observation field is from 73
to 3. 7 occasions with an average of 11, and that in the efficient observation field
is from 36 to 1.8 with an average of 3.6. These figures will be doubled for a schoolof average size (l.97 individuals/school). On the other hand one complete scanning, near side and far side, was made at most once every 30 seconds, and certainly less when porpoise was sighted. This means that one observer can scan
the near side and far side ranges only less than five occasions. Then it will besuggested that t~e finding rate at zero distance (k) must be below l.
In the present study k was estimated from the relationship between the numberof sightings and number of observers on one vessel. This experiment was madein 9th expedition on both sides of the Naruto Pass. The season corresponds to thatwhen the porpoise is most abundant. The weather was calm. The other observer
was Mr T. Hiwatari, a graduate student with one week experience of whale
watching. The sighting was recorded by Kasuya in two categories. The first is
the porpoises found by Kasuya or Kasuya and Hiwatari. The second represents
the porpoise which might have been overlooked if Hiwatari had not been there.
There was 73 individuals in the first category and 37 in the second category. When
X indicates the probability of one surfacing not encountered with a visual angleof one observer, the probability of a surfacing not encountered with the visual
angle of any of n observers is shown by xn (Doi, 1974). Accordingly when p indicates the number of finless porpoises present on the course of a vessel, there willbe the following equations,l-k=p-73p(l-k)2 = p-(73+37)p

and k is calculated as
k = 0.493

which is rounded to 0.50.
When a school of porpoise is sighted, the scanning has to be stopped in orderto have its detailed observation. This means that the presence of a porpoise may
obstacle the finding of another school, and that the estimation of k is inversely
correlated with the density of porpoise. Because the density of the porpoise aroundthe Naruto Pass, where k value was estimated, was extremely high as indicated in
the latter section (Table 2 and Appendix I), true k in calm seasons (expeditions
I, 2, and 5) can be 0.5 or larger. However, since k is suspected to be inversely
correlated with the wind, the value for other expeditions will perhaps close to 0.5
or lower.
Though the finding rate R is calculated by

R = k·r
various uncertainties of the estimation of k and r have to be remembered.
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

12

KASUYA AND KUREHA

5000
3000
1000

v\

100
>u
c
(!)

::J
CJ"'

?

80

(!)
I...

u....

60

'
'

40
'

20
\
~ ...

0

0

5

10
15
20
No. of individuals

Fig. 6. Frequency distribution of number of sightings in each 1 nautical mile
section of the cruise (closed circle and solid line), and the Poisson distribution
with the same mean and same sample size (open circle and dotted line).

Confidence range
One of the most important factors causing error in the estimation of population size will be the biase of sighting effort. Since the present study was made on
board of commercial regular service vessels, most of the observations were madein the nearshore waters. It was to decrease the effect of this bais that the analysesof the data were often made by each stratum or area.
The other problem is the simple error of the estimation of density index. The
distribution of the porpoise is not random even in an area or in a stratum, but as
mentioned in the later section more porpoise are apt to aggregate in a small area.
When the course of a vessel is divided into contiguous 1 nautical mile sections andnumber of the finless porpoises encountered in each section is compiled into a frequency distribution, all the individuals in each expedition were found in the sections
from 3.0% to 11.5% of the total number of sections. This feature is shown in Fig.
6, where the data of 9 expeditions used for the calculation of the population arecompiled. Though this frequency distribution seems to follows the Poisson distribuSci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

13

tion, it is significantly different from the Poisson distribution of the same meanvalue (0.203 individuals/mile).
The standard error and the 90% confidence range of the mean number ofsightings per observation of one nautical mile was calculated from these frequency
distributions, and used to estimate the 90% confidence range of the population ineach stratum. The variance of the sum of population estimates of three strata
was calculated as the sum of the variances of the mean population estimate of eachstrata, and then the confidence range of total population was calculated.
RESULT

Geographical and seasonal variation of density
The actual positions of sightings and the course of the vessels are shown in
Figs 7-16. In the Inland Sea, the finless porpoise is frequently distributed near
the coast, especially off the pointed rocky shore or near narrow passes between
the islands. The current of these places is usually moderate. Though the actual
density of porpoise may change seasonally, the density in most of these locations isin any seasons higher than that in surrounding waters. There are other kind ofwaters which is occupied only in spring months by large number of individuals
but almost vacant in other seasons. Typical example of these locations are southernpart of the Hiroshima Bay (34°N, 132°30'E), between Setoda and lnokuchi(34°17.0'N, 133°03.5'E), and around Nakajima (33°58'N, 132°33'E).
In case of aerial sighting records used in this study, the position of sighting
will be less accurate and the porpoises in the nearshore area seems to have been
overlooked. However the absence of the species in the deeper part of the Inland
Sea is clearly indicated in Figs 15 and 16.
If the distribution of the finless porpoise is analysed in relation to the distance from the coast line, it becomes clear that 82.4% of the individuals were observed within one nautical mile from the coast, 15.5% between 1 and 2 miles,
1.5% between 2 and 3 miles, and 0.6% in waters more than 3 miles from the coast.
This general tendency is true even when the bias of the effort is corrected (Fig.
17). The number of individuals sighted per 10 nautical miles of observation is
2 .5 7 individuals in the nearshore stratum (0-1 mile from the coast, areas 1 to 5 ),1.19 in the intermediate stratum (1-3 miles, areas 11 to 14), and only 0.24 in theoffshore stratum (more than 3 miles off coast, areas 21 to 23). Namely the relative
density of the porpoise in the three strata is 1: 0.46: 0.09. However it must be
noted that these figures are strongly influenced by the distribution of the porpoisein the season of highest population density.
The relative density of finless porpoise in the intermediate stratum expressedby the ratio to the density in the nearshore stratum is shown in Fig. 18. It gradually
increases from the minimum in November to the following September when thedensity apparently exceeds that of nearshore stratum. This is an indiciation thatthe porpoise leaves the coastal stratum and the animals are going to be evenly
distributed in summer low density season. The decrease of relative density ofSci. Rep. Whales Res. Inst.,
No. 31, 1979

~.:~

~~

..i....:""

""'~

~~

~

~

~

0

..,..,z

I

I

!~

J.I

;,">:

R"

I

·····...........

~/I

I

f

/

Fig. 7. Observation routes and number of sightings of the finless porpoise (circle),a school of Delphinus (D), and a school of Grampus (G). March to May. Small
closed cicle indicates one individual, large closed circle 5, and open circle 10.
Numerals in the circle indicates number of cruises, dotted line the 40 m contourof water depth.

-------~--;-------~\--7f~ ~132°E
Mar. Apr. May

~

g;

~

~

;;

c

cr.i

;.>-

\i'l

"""

-

:9•

u

S'

~
?

1'..,""....

..... .
~~
<o ..

~~

~

:a: l{l.., r~ ------------------------z·---------

1320E

;~

I

I

June July Aug.

I --

~

Fig. 8. Observation routes and sightings of the finless porpoise. June to August.
For marks see Fig. 7.

------ ------~)~---

131°E

U1

-

tTl

U'l

::;;

2l
2l.....

U'l

~
U'l

l'!j

z

~.;~

~~

~~ ~

"' "'::i:i;,,'.'.?; ~

~

~

::i:i

!"·

~

z

<'>

(¥')

z0

<'>

),

~

y'\

131°E

r-...__

c~/

.

•

.
~~ ~

I

132°E

I

I

Sept. Nov.

~-

• "°'i-1. o

;,~ .

I

Fig. 9. Observation routes and sightings of the finless porpoise (circle), and two
schools of Tursiops (T). September and November. For other marks see Fig. 7.

?~ ·"")J

r·--. 7 ~I___ ;I ......_______

I

!

;'

·

I

----------17
I '"J
~
--</
~.
~~
1
I ' ~~,~~' ~~r··~---../~-----~~r,,?

.t'

D(::~
7 &Ji

!\~·~

/

e., -

..

~

trj

~:;o

~

~

~
c

1JJ

o;

!""·

~-

~

~

"'
~

~~

......

~~..."- ~~~~\,...._"'.I>1,I

132°E

Fig. 10. Observation routes and sightings of the finless porpoise.
marks see Fig. 7.

,!:_.
~-- ~St ;a~/~-~ ~~<

\

I ·~

~~-~~

I

I

I

131°E

February.

~

For

-"

tr:!

u:i

0
.....

"C

:;d

0

"C

u:i
u:i

>'rj

zt;;

~

:-·

<.,

~.:

to ~

~ ::tl..."- ~

"'

~~

~

~

!:ti

-···--r----

~
<')

0

1JJOE

<')

-

z
0

·---

"··--·-. --1L-.

I

"'---

""\

~~ (

'~~

Fig. 11. Observation routes and sightings of the finless porpoise. March to May.
The routes indicated by dotted line are those observed by Kureha for the entire
study period. For other marks see Fig. 7.

"'...:.~B-f)·.,...v····~:;;>':·-~-c.,,/:-···,

13411E

.

~-

\

I

I

I

135°E

··, a/J;'.,,_1J,.

Mar.Apr.May-~

t:°':I

~~

~

~

c::
~

.IJJ

00

*

'?:
~ ~·

.r-

S'

~

"'

~~
.,...
"'

~~

..""'::.::,
.....

..,

·---

~

0

--------~

/

"

!'
I

------

I
I
I

'

%

~V"'
-)
"
~.., ----·--./
De)r::;J)·--/:C.,,/""'".

"'2·

J

r

,,..,v-~:~

Joo•J,lyA"g;;;?"'
.-4
~

/~.

·

A

-

I

-- ·--- · - .•. ·-

---

'---

.

.··I

J

~;;··•~->(JI

/ ;?

0

·n{~

-~~;~-~

~

~"­

v-"'~

i

i
I

;
!

/]

135°E

1·~~-----~7--------;---__
I

',/

;{

l«J/,f(F--,,.__·v~--~)----(-Ji/fi~';,~/ /

I

I

134°E

Fig. 12. Observation routes and sightings of the finless porpoise. June to August.
For marks see Fig. 7.

~~~--/-----•-_<!)·_:_\

'

133°E

~1---)

"?-

<.O

-

ti'l

rJJ

0.....

'"d

l:d

21

rJJ
rJJ

~

"l
.....

~

~ _;~

~~

.............

~~
~

~~

~

~

~

:-'·

"""

0

z

?;..,

b

z

\

\I
~

134°E

Fig. 13. Observation routes and sightings of the finless porpoise.
November. For marks see Fig. 7.

~'l..i>:'

1330E

September to

1JJ

of""

Sl'pt. Oct. Nov .

135°E

>

~

ti::I

~i'.:I

tl

~
z>

c:::

CFJ

:;>:1

""
0

!"'·

~-

~

~

"'

"~

~ ;,§

.....

""~
............
~

~

~ f<>

m·

I
I

133°E

1

I
I

D.o.J•oH

I

i

135°E

I
>rj

December to

0

ci

'1"

'\,_,r

ef~

1"'

~

~ ~ _Jf · I

.

~I

•

Fig. 14; Observation routes and sightings of the finless porpoise.
February. For marks see Fig 7.

,/

I

134°E

KASUYA AND KUREHA

22

-- --

------ /i:--.-_

I--~/'----.

/---------------------•

Fig. 15. Aerial sighting record, poisition of the occurrence of the finless porpoise.
Each circle indicates one encounter. For effort data see Fig. 20.

135°E

134°E

z

g
~ ---::-/-:~·""·~------~
I?'-~_~.

_,,, ..

-.)•

Fig. 16. Aerial sighting record, position of the occurrence of the finless porpoise.
For other explanations see Fig. 15.

Sci. Rep. Whales Re~. Inst.,
No. 31, 1979

FINLESS PORPOISE

23

300

en

ti

::J

u

·::; 200
u

c

.....
0

100

0

z

0

0

2

0.5

Distancefrom3coast in miles

Fig. 17. Distribution of the finless porpoise and the distance from the coast. Closed
circle and solid line indicate the actual number at actual position. Dotted line
indicates sightings per 1,000 nautical miles of observation, where the position of
the vessel was used as that of the porpoise.

-

>'iil

- - Areas 11 to 14--o-- Areas 21 to 23

c

~ 1.0

0

0

~

0::

J

FMAMJJASOND

Month
Fig. 18. Seasonal change of the relative density of the finless porpoise in intermediate (areas II to 14) and offshore (areas 21 to 23) strata indicated by the ratio
to the density in the nearshore stratum. Numeral indicates the expedition number.

intermediate strata in October to December will be the result of the migration to
the nearshore stratum. This is followed by the immigration from the external
waters to the Inland Sea in December to April mentioned below.
Figure 19 gives the geographical and seasonal fluctuation of the finless porpoise. density in the Inland Sea. The density is expressed by the minimum estimate persquare mile (tentative assumption of k= 1). For the estimation of real density,
this has to be divided by k or about 0.5. Two or three expeditions are grouped toaccumulate sufficient amount of data for each area. Generally speaking, thedensity is low in the eastern and western areas, through which the Inland Sea isconnected to the outer ocean. In the areas of the nearshore stratum the density
is highest in March and April, and the highest density is observed in the areas
3 and 4. However the density continues to decrease in all the areas of the nearSci. ]lep. Whales Res. Inst.,
No. 31, 1979

24

KSAUYA AND KUREHA

shore stratum until July-September. The decreasing trend is faster in area 4 inthe east than area 2 in the west. This makes, in May to September, the density
in area 2 higher than that in area 4, though the actual density is certainly decreasing.
In November-February season the density in the nearshore stratum start to increase, again at a higher rate in eastern areas. These features indicate that thelarge scale seasonal migration in the population starts in the eastern part andis spread to the west.
In the intermediate stratum, the decrease of the density from March to September is not clear, but there is observed a slight increase in the area 13 in the

1.Sf Mar.-Apr.
.5
14

":~
:!,,~,:,:,:,:,:,:,,,,~ I

!

i:[~J
Nov.- Feb.

west

Area

east

Fig. 19. Seasonal change of the density distribution of the finless porpoise in the
Inland Sea.

eastern part of the Inland Sea. In November-February the density in area 12
reaches to the minimum, however in the same season there is observed an increase of density in areas 13 and 14 at the eastern part of the Inland Sea, a possible
suggestion of movement to nearshore stratum. The abrupt increase of the density inthis season in area 11 at the western Inland Sea is difficult to be concluded becauseof the scarcity of the observations. However it will be reasonable to suspect fromthe seasonal trend of the density in both intermediate and offshore strata, and fromthe presence of similar trend in the aerial sighting records (Fig. 20), that the density
in the western part of the Inland Sea stays slightly high in summer and autumn
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

25

FINLESS PORPOISE
K1i Channel

~

4

8

~ 0
Osaka

Bay

4
0

14

InlandEast of~133.5°E

12

3

10

~
Vl

c

Cl1
Inland

12

2 0

\

6
4

0

-....

8

Sea

132°-133.5°E

Cl1

OI

0 .i:

:c

OI

2 Ji

8
6
4

0
2

12

8
4
Ql--l-~-+---.1~-'---''-""==---i.~-'-~-'---'-~...:L.~.L..1

0

4o~~~__,--=~~~--~-+-~+---'-~-'-~.w

A

M

A

s

0

N

D

F

Month

Fig. 20. Aerial sighting records of the finless porpoise. Seasonal change of thenumber of encounters per 1,000 nautical miles (closed circle and thick solid line)
and number of individuals (open circle and thin solid line) per 100 nautical miles.
Amount of effort are shown by dotted line (thousand nautical miles).

season and the spring concentration of the species in that part of the Inland Sea
seems to start slightly earlier than eastern Inland Sea (see Discussion and Conclusion).
jVfovements between outer waters

Observations were made at four passes connecting the Inland Sea with outerwaters. The intention was to get direct informations on the migration route of
the finless porpoise. The season covered both before and after the peak of the
population in April. Though the swimming direction was examined, it was foundto be insignificant as the indication of migration.
At the Kanmon Pass, 6.4 hrs (15 March 1978) and 11.5 hrs (2 May 1978) land
based observations at the narrowest point of the pass provided no sighting.
At the Hayasui Pass, five cruises made on 11 and 14 March 1978 provided
no sighting. Two cruises made on 24 and 26 April across the pass did not show
the presence of the porpoise, except for the three individuals off Beppu (Fig. 7).
Some ancillary cruises in the Bungo Channel gave no sighting of the finless porpoise.
The observation at the Akashi Pass was made by Kureha on board of small
Sci. Rep. Whales Res. Inst.,

No. 31, 1979

26

KASUYA AND KUREHA

ferry boat connecting Akasi and I waya across the pass.
Hour
0800-1826
0800-1820
0800-1823
0800-1720

Date
17 Mar., '78
20 Apr., '78
26 Apr., '78
12 Oct., '78

The result is as follows.

No. trips
16
16
16
14·

No. sighted
5+1
0
0
0

The larger school was sighted at 1040 when the current was flowing eastward.
The school was moving westward at the position about 400 m off the coast (Fig.
11 ). The other solitary individual was found at 1707 at the same position withanother school. Both the current and the swimming direction were eastward.
The position of these porpoises is same with that of a school of two individuals
found by Kasuya and Mr T. Hiwatari during the land based observation madeon 7 March 1978. The school was moving westward.
TABLE 2.

DISTRIBUTION OF FINLESS PORPOISE AT THE NARUTO PASS

Expedition no.

9 (two observers)

10 (one observer)

Date

8-9, March, 1978

30, Apr.-1, May, 1978

Current, flowing toNorth side

{ n. miles
no.
no./10 miles

South side

{ n. miles
no.
no./10 miles

North

South

Total

North

South

Total

8.9
15
16.9
30.7
47
15.3

11.9
26
21.8
21.9
22
10.0

20.8
41
19.7
52.6
69
13. 1

17.8
41
23.0
8.1
24
29.6

14.8
2
1.4
25. l
56
33.3

32.6
43
13.2
33.2
80
24. l

North side : Inland Sea, South side : Kii Channel.

The observations at the Naruto Pass were made in early March, and April
to May (9th and lOth expeditions). The former was done by Kasuya and Mr
T. Hiwatari, and the latter by Kasuya. The frequency of the swimming direction seemed to be influenced by the current, turbulance, and topography of thesea than the migration direction. Large concentration of porpoise was usuallyfound in the rapid current flowing from the pass. The presence of large concentration of the porpoise at the Naruto Pass suggests the migration of the species
through the pass. For the comparison of the porpoise densities between the two
expeditions, the number of observers must be corrected. The number of porpoises
sighted by Kasuya at the Naruto Pass was only 73 (9th expedition). This gives
the number of sightings per 10 nautical miles as 73-;-73.4X 10=9.9. This is about
half of the density observed in April/May expedition. The weather condition
will have no relation with this difference, because the wind was between 0 and
1 in both expeditions.

Population estimation
As the data was insufficient to calculate the population size by expeditions
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

27

Areas 21-23.5
Areas 11-14
2

lll

"O

c:

<IS

lll
:::J
0

0

:5
c: 2

8)

·ollla.
'-

0

-

a. 0

oc
Total

0

~

.c
E
:::J

z

28

I

4
T

1

i

3

20

12

T

:,

.....

2

4

0

F

M

A

M

J

J

A

s

0

N

D

Month
Fig. 21. Seasonal fluctuation of the finless porpoise population in the Inland Sea.
Mean population estimates and the 90% confidence range (closed circle and solidline), and range and mean of the surface water temperature (open circle anddotted line) are indicated. Since k= 1 is tentatively assumed, the population size
expressed here is close to the half of the actual estimation. Curves are drawn
by eye.
TABLE 3.
Month

2

SCHOOL SIZE FRFQUENCY OF FINLESS PORPOISE IN THE
INLAND SEA, AND ADJACENT BAY AND CHANNELS
3

4

5
1
Jan.
1
11
Feb.
9
101
41
Mar.
9
3
15
126
Apr.
19
95
38
38
13
4
May
25
19
8
2
June
4
12
July
4
1
3
Aug.
6
Sep.
9
2
::!
2
Oct.
12
Nov.
10
2
6
Dec.
4
341
Total
243
57
25
Total,% 48.1 34.3 8.0 3.5

5

4
4
2
2
2

15
2.1

6

7

8

9

11

12

13

Total

Mean

1
0.1

6
21
163
271
97
57
22
10
21
5
25
11
709
100

1.17
1.52
I. 74
2.03
2.04
1.95
2.73
3.10
2.71
1.40
1.84
1.55
1.97

1

3
4

10

3

3

2

9
5
1.3 0.7

5
0.7

0
0.0

5
0.7

2
0.3

0.1

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

28

KASUYA AND KUREHA

and by areas, data of some expeditions or of some areas were combined. The
first method is to group the data of one expedition into three strata and to estimate
the population for each stratum. The second is to group the data of two or three
expeditions to calculate the population in each area. As shown in Appendix, thetwo kind of estimations give a reasonable coincidence.
The population abundance in nearshore stratum attains the maximum in
April and followed by the decrease to the minimum level in September (Fig. 21).
The population level in the intermediate stratum, however, seems to continue todecrease until December. Though this differs in the expression with Fig. 19,
both of them indicate the same phenomenon of the porpoise migration. Further
discussion on the migration of the species will be made in the later section.
When the value of k is considered as 0.5 (see page 10), the population of
finless porpoise in the Inland Sea is estimated as about 2,450/0.5=4,900 in the
maximum season in April and decreases to the minimum level of about 780/0.5=
1,560 in early winter. The overall population density in April is 4,900/14,260=
0.34 individuals/km 2 • The approximate density in each stratum in this monthis given as 3,710/4,805=0.77 for nearshore stratum, 928/5,061=0.18 for intermediate stratum, and 260/4,394=0.06 for offshore stratum. In the intermediate
stratum, however, the highest density of 1,470/5,061=0.29 individuals/km2 will beattained in August (Fig. 21 ). Though the direct comparison will not be meaningfull because the body size, food requirement, and the environment can be different,
it is worth to note that the above densities are close to those of the Atlantic Tursiops
truncatus, 0.23 to 0. 75 dolphins/km 2 , calculated for coastal or semienclosed waters(Barham, 1979).

School size
In order to avoid the influence of the preoccupation, the analyses concernig
the school structure and the size frequency of the porpoise were made after thecompletion of all the expeditions.
The largest school encountered in the present study was composed of 13 individuals. As shown in Table 3, however, most of the schools of this species areso small to give the overall mean school size of 1.97 individuals. About 50%of the encounters were solitary individuals, and the school of 3 or fewer numberof animals comprises 90.4%. These figures suggest that the school of this species
is slightly smaller than that of Phocoenoides dalli which shows the mean school sizeof 4.62 (Kasuya, 1978).
The seasonal fluctuation of the school size is shown in Fig. 22. The ratioof solitary individuals in the total encounters shows an annual cycle with the highest
in January and the lowest in July. The mean school size shows the similar annual
cycle.
School structure
The body length of the porpoises in a school is variable, and the relative distance between the members is not same. These characters are considered in theSci. Rep. Whales Res. Inst.,.No. 31, 1979

FINLESS PORPOISE

65

Jan.

N=6

Feb.

N=21

Mar.

N=163

Apr.

N=271

May

N= 97

Jun.

N=57

Jui.

N=22

Aug.

N:10

25
50

25
~ 25

29

c
>.

u

25

c

~

---

50

er

._
u..
QI

•

•

Sept. N:21

25
50

•

•

~

Oct.

N=5

Nov.

N: 25

Dec.

N=11

9

11

--+-

25

-+3

5

7

13

School size
Fig. 22. Seasonal fluctuation of the school composition (closed circle and solidline), mean school size (vertical bar), and 90% confidence range (holizontal bar).
All the data obtained in the present study included.

present study as an indication of the internal structure of the school.
Though there was found solitary calf or juvenile (Fig. 23, type 1-b, 1-c),
more frequently they were found with another individual of various growth stages.
The most common was the combination of a calf and an adult, presumably corresponding to the mother and calf. The less common was the school of adultand juvenile, some of which may represent the combination of the mother andelder calf of the previous season. The school of weaned individuals (types 2-d,2-e, 3-h), and that of one cow and two juveniles (type 3-g) are scarce.
Most of the adult individuals encountered were solitary or in a pair withanother adult individual (types 1-a and 2-a). In some cases, the adult porpoisesof up to five individuals were found to aggregate to form a school (types 2-a, 3-a, b,
4-a, b, c, 5-a, b ). However, it was more common for the schools of three or more
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

KASUYA AND KUREHA

30

3

4

5

------11

~
a~

2
::::=
ao------

2a~bo--- 1317c.-a~ a:==--::::=

b-----11 ------2 _____!
b==== b = -------2
b:::==
c._ GOd::::::=,.______lc::::=_

4

~

__-2
c-~

":=

4

d--

-- :=--1
1

t:=--

e--

,.______l:::--1

g:=

f

7

---2.

.__l

a ,.____,.____
o---------

0---------·

o-------_1-------- b====~c:=---~

3----:=-------1

a::==

b====

---- ::::-1

Co---

d~

-----1eo--

---1

6

0---------0----------d~~:::::::~:\

co---------0----------·
o---------·

L~~~~~}=

do-----------

:=---

h~

11

12

&::.·.::.::~--imt~{~{t8b--8:::::::::::.
8::::::.:::::

0---------..
0------------

0----------()-......... .

o-----------

10...._.
,._

13::::--1o----------0.-----------------

0-------·-- .....--

Fig. 23. Schematic figure of the school of the finless porpoise, relative size of theschool members and subgroups are indicated. Numeral at the top of column indicates school size, numerals by each type the number of encounters. Two dimensional arrangement of subgroups is indicated only in cases of type 8-b and 10.
Long bar, adult; intermediate, juvenile; short bar, calf; open [ircle and dotted
line, size unknown.

individuals to contain the combination of cow and calf. It was frequently observed that a cow with calf was followed by one or two adult individuals. Presumably they represent the case where, after certain length of nursing period, a
cow accompanied by the calf (type 2-c) approaches the next oestrous cycle andis attended by adult male(s) (types 3-c, f, 4-d). The number of such schools was
22, or about one third of the number of schools of the cow and calf. This indicates that most of the cows accompanied by the calf, consequently for most of
the nursing period, are not attended by adult male.
Another information on the school structure was obtained from a land based
observation on 5th March 1977 at Teshima (34°23.5'N, 133°40.5'E) in the Inland
Sea. Several finless porpoises, varying between 1 and 6, fed in a small rocky
inlet open to south. Their position was about 20 m from the beach. It seemed,
at a glance, to be one feeding school with several internal structures. However
the subgroups were continuously changing. The subgroup, two or three individuals
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

31

in it, arrived one after another from the southwest direction, fed together for 20
to 30 minutes in the same area with other subgroups, and then slowly left the place
toward southeast offshore direction. Their leaving passage was traced for morethan 1 km by the presence of a flock of sea gulls. By this way total of 5 subgroups
were confirmed by 2 hours' observation.
From above informations we suspect that the most stable basic unit of theschool will not exceed three individuals in number, and they are combinationsof the cow and calf or of adult male and female. Probably the school of morethan four individuals would have been formed through the aggregation of thesefundamental units. An example of the transitional stage is shown in Plate I, Fig.
2, where all the seven individuals will be considered without doubt as one school
if the three units were situated slightly closer.

GO
~
0

c
~ 40

c

Cl.I
:::J

O"'

J: 20
J

F M A M JJ

A S 0 N D

MonthFig. 24. Seasonal change of the solitary adults. Closed circle and dotted line
indicate the ratio of solitary adult to total number of the adults, dotted line themoving average of the three. All the data obtained in the present study included.

Mating Season
Though the copulation was not confirmed, there were several occasions toobserve the probable precopulatory behavior of the finless porpoise in the Inland
Sea. They were one couple in March, four in April, two in July, and one in
September. They suggest that the mating occurs from March to September.
Another indirect indication was obtained from the seasonal change of thefrequency of solitary adult. The number of solitary adults was about 40% of thetotal adults in any months between October and March, but decreased below 30%
in April to September, with the lowest frequency in June to August (Fig. 24).
This season coincides with the peak of mean school size, and is considered as themating season of the species in the Inland Sea.
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

32

KASUYA AND KUREHA

Parturition and weaning season
The parturition season was estimated from the seasonal change of ratio ofcows accompanied by the calf to all the adult individuals (Fig. 25 ). The ratio isstable from November to March at a level of about 10%, and start to increase in
April to attain the maximum of about 27% in September, which is followed bya rapid decrease to initial level in October and November. The increasing season,
April to August with the center in June, will correspond to the parturition season.
1

15 147 213 122

7

2

13

10

2

5

24

14

Juvenile0
Solitary calf

-!

20

•

c

u>-

10

c

~ 0
CT
Cl>

~

[J..

20

to
QL--'-__.,~..___.___.~_.____.____.....__.....___._~~~JF M A M JJ

A S 0 N D

MonthFig. 25. Seasonal change of the frequency of juveniles, solitary calves, and cows
with calf. Frequency is shown by the ratio to the total number of the adultshown at the top. Months with small sample size are grouped.

The rapid decrease of the cow with calf in October and November is followed
by a rapid increase of solitary calves in November and December, which tails off
towards next summer. This will be the indication of the weaning season. Namely
most of the weanig will occur in October and November, but some calves seemto accompany their mother until next spring or summer.
The decrease of solitary calves after December is followed by the high levelof juveniles, which will indicate the growth of the weaned individuals.

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

33

DISCUSSION AND CONCLUSION

Seasonal movements
The continuity of distribution of the finless porpoise between the Inland
Sea and the Kii Channel through the Naruto Pass suggests that the annual migration of the species will be done through this pass. The seasonal change of thedensity in the Kii Channel appeared in the aerial sighting records suggests a peak
before July, low density in August and September, and the winter increase inJanuary and February. This change is similar to that in the Inland Sea. The
decrease of the density from April to September in nearshore stratum is faster ineastern areas than western areas, but both the speed of the density decrease andthe areal difference of the speed are not large in the intermediate stratum. Theseobservations suggest that most of the migratory individuals start to move, in April,from the coastal stratum to eastern areas of offshore stratum, and then to the Kii
Channel. The low porpoise density in the Kii Channel (Table 4) suggests thatthe finless porpoise will not spend summer in the channel but will be dispersed inwide coastal area facing to the Pacific. The migration into the Inland Sea will
occur from January to April (Fig. 21 ). However the concentration of the porpoise
into the nearshore stratum seems to start in November (Figs 18 and 21). In otherwords, the seasonal migration of the species seems to start in the nearshore areas.
TABLE 4.

AERIAL SIGHTING DENSITY OF FINLESS PORPOISE, BASEDON RECORD OF FISHERIES AV. CO., 1972-1978
Distanceflown(n. mile)

Bungo Channel
Western Inland Sea
Central Inland Sea
Eastern Inland Sea
Osaka BayKii Channel
I)

3,387
7,471
12,025
12,0333,310
6,666

Schools
no.
21>
45
97
137
9
14

Individuals

no./100 miles

no.

no./100 miles(0.06)
0.60
0.81
1.14
0.27
0.21

2Jll
376
659
863
37
50

(0.62)
5.03
5.48
7 .17
1.12
0.75

A school of 20 individuals of doubtful identity included.

The porpoise density in the summer season is slightly higher in western area
than in eastern area. This will mean that the coast of oceanic western Inland
Sea is in some degree used as the summering ground of the species.
The presence of small number of sightings in July and August in the Bungo
Channel (Fig. 20), and the increase of the density in the western Inland Sea in
October to November (Figs 19 and 20) suggest that some individuals of the finless
porpoise in the Inland Sea will migrate to and from the Bungo Channel throughthe Hayasui Pass. However, the low density of the porpoise at the Hayasui Pass
and large water depth in the Bungo Channel will not give suitable reason to expect
such a large number of migrating porpoises as expected for the Naruto Pass andthe Kii Channel.
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

34

KASUYA AND KUREHA

Considering the several sightings at the Akashi Pass and the relatively highdensity of the porpoise in the Osaka Bay (Table 4), it will be reasonable to consider
that the pass is one of the migration routes of the species.
According to the record of the Toba Aquarium, the incidental capture of 30
individuals in the past 13 years in the Ise Bay occurred from September to April
with one peak in February to April. This pattern resembles the seasonal density
fluctuation in the Inland Sea, and it is suggested that the species migrates seasonally between inshore and open waters. However it is unreasonable to. suspectthat the species migrates to the offshore open waters, because the species is often
sighted or captured within a few hundred meters from the beach facing the Pacific(Kasuya, unpub.) and has not been sighted in the true offshore water.
Any environmental factors controlling the migration of the species mentioned
above are not certain at present. In the Inland Sea, the species is found in thesurface water temperature between 6°C and 28°C. Such a wide adaptability is
uncommon in the pelagic delphinids (Kasuya, 1976). The migration into Inland
Sea start in January before the lowest peak of the water temperature, and attains
the population peak in April when the water temperature is still lower than theouter waters. These are indications that the migration is not controlled by thewater temperature.
It is generally believed by the Inland Sea fishermen, that the finless porpoise
migrates to the Inland Sea to eat Ammoqytes personatus. The fishing ground of A.
personatus and the distribution of the finless porpoise coincides well. As far as
investigated, only the peak of fishing season of A. personatus in April or May showssome degree of coincidence with the density of the finless porpoise in the Inland
Sea. Though some of the finless porpoises in the Ise Bay were found to feed A.
personatus (Kataoka et al., 1976) and the porpoise in the Inland Sea had the fish in
the stomach (Kureha and Kasuya, unpub. ), the frequency is not high to support the
hypothesis. Alternative explanation is made below in relation to breeding season.

Breeding season and reproductive cycle
Table 5 gives 17 records of the finless porpoise born in aquarium, incidentallykilled, or stranded. The individuals below 100 cm were listed. The higher
frequency between 65 and 85 cm suggests the mean length at birth in this range,
and the parturition season from April to June. Perrin et al. (1977) and Kasuya(1977) gave some methods to estimate the gestation length of odontoceti based on
the neonatal length. The former method and the neonatal length of 75 cm givethe estimated gestation time of 10.6 months. The lattter gives 10.5 months,
assuming 0.135 X gestation time for x-intercept of linear growth line. The mating
and parturition seasons estimated from the analyses of the school structure are from
April to September and from April to August respectively. They give the roughestimation of gestation time of 11 to 12 months. As this value is close to the estimations made above, it will be safe to conclude in the present study that the
pregnancy will last for about 11 months in the finless porpoise.
Furuta et al. (1977) state on this species kept in the Toba Aquarium in theSci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

35

Ise Bay that the copulation occurred most frequently in every April and May inrecent several years and this led to a birth in April 1976 (Table 5). This datum andthe gestation time of about 11 months suggest the parturition season in March andApril. Though this gives a good coincidence with the parturition season indicatedby the newborn calves in Table 5, it does not well agree with the season estimatedfrom the frequency of the cows accompanied by the calf. The difference exist in
the prolongation of the parturition season until August. An important fact wemust remind with this connection is that the analyses of seasonal change of theschool structure are not based on the same group of individuals. The most of the
porpoises leave the Inland Sea after April, and do not come back to the area until
early winter. If it is assumed that the main peak of parturition of the Inland Sea
TABLE 5.

RECORDS OF NEWBORN FINLESS PORPOISE BELOW
100 CM IN BODY LENGTH

Body length

Sex

Date

Locality (latitude)

Author60.0 cm
94.8 cm
96.4 cm
68.8 cm
71.5 cm
72.0 cm
65. 3 cm
79.0cm
83.0 cm
85. 5 cm
85.0cm
81.5cm91.3 cm
80. 0 cm
69.0 cm
71.5 cm
97 .6 cm

S
S
S

20, Mar., 1924
26, Mar., 1924
24, May, 1924
14, Apr., 1977
24, Apr., 1974
3, May, 1976
4, June, 1976
11, Apr., 1973
22, Apr., 1976
27, Apr., 1966-, Apr., 1964
17, Apr., 1976
20, May, 1979
5, June, 1969
16, May, 196327, June, 1973
18, June, 19:33

China
China
China
Omura Bay, 33°N
Inland Sea, Fetus
Inland Sea
Inland Sea
lse Bay, 34°40'N
Ise Bay, 34°40'N
Ise Bay, 34°40'N
Born in Toba Aquar.
Born in Toba Aquar.
Shimizu, 35°N
Sagami Bay, 35°15'N
Yokosuka, 35°14'N
Yokosuka, 35°14'N
Sendai Bay, 38°20'N

2
TK 415
KS 76-7
TK 478345567
TK 296
8
TK 396
9

S
S
~

S
J
J
S
S
J
J

S

1) Howell, 1927. 2) Takemura, p.c. 3) Kataoka et al., 1974 4) Toba Aquarium, unpub. data.
5) Kataoka et al., 1969. 6) Furuta et al., 1977. Measured after death on 3 May. 7) Masaki, p.c.
8) Nakajima, 1963. 9) Ogawa, 1950.

population of the species is in April and May, and that the cows accompanied by
the newborn calf leave the sea for the summering ground, then the above disagreement will be explained. This also explains the rapid drop of the ratio of
the cow with calf in May. We can, by this hypothesis, duly evaluate the ratio of
the nursing cows represented by large number of samples in the months fromMarch to May. Most of the small number of cows which gave birth to the cow
after May will spend the summer in the Inland Sea and will contribute to the apparent increase of nursing cows in the waters. Accordingly it will be most reasonable to suspect that at least one of the main factors controlling the migration of
the species into the Inland Sea could be the breeding.
Sci. Rep. Whales Res. Inst., 'No. 31, 1979

36

KASUYA AND KUREHA

Mizue et al. (1965) estimated for the finless porpoise in the waters off the west
coast of Kyushu that the parturition season will be from late August to early September. Their estimation is based on one lactating female caught in October
1962 and unconfirmed information of the fishermen on the occurrence of newborn
calves in early September. It is strange that they did not refer, for the conclusion,
their specimens collected in late September to early October mainly from theincidental catch in set net and amounting more than 50 individuals. They writethat the smallest individuals they collected were 101.6 cm in females and 112 cm
in males. We are not going to deny the possibility of the tailing off of parturitionseason in September or the presence of small number of newborn calves in themonth. However it will be reasonable to consider that if there is a main peakof parturition in August and September, they should have obtained smaller calvesin their collection. We feel that it is unrealistic to expect for the finless porpoisein the western Kyushu a parturition season different from that in the Inland Sea.
The length of nursing period is estimated from the seasonal change of thefrequencies of nursing cows, of solitary calves, and of juveniles. The ratio of cows
with calf decreases and that of solitary calves increase in October and November.
This season is a time when the migrating porpoises are still outside of the Inland
Sea. Accordingly the change seems to have happened on the resident population.
The decrease, from 27% to 7%, is too large to be explained by the weaning of
calves which have been nursed since previous winter or about 10% of the adultof that season. Accordingly it must be considered that the calves born in thepreceding season are weaned in October and November. Some calves born inthe season will be nursed until next June or July as suggested by the increase ofsolitary calves in the months. This implies that the nursing period will last from
6 to 15 months.
The total number of weaned or suckling calves and that of juveniles attains theequal frequency of about 10% of the adults in March (Fig. 25). The body length
separating the two categories is roughly 120 to 130 cm. The age of individuals at
this body length can be deduced as follows. Firstly the body length frequency of theindividuals stranded or accidentally captured in March to June shows three groups.
The smallest is of 14 individuals ranging from 65.3 cm to 97 .6 cm and consideredas the newborn individuals. The intermediate is composed of total of eight individuals with the distribution of one at 117 cm, three in the range from 125 to
129 cm, one at 130 cm, two from 135 to 139 cm, and one at 141 cm which was anadult female. At least most of the individuals at the lower part of this group will
be one year old. The third group is composed of 22 individuals ranging from145 cm to 188 cm. They must represent older and presumably adult individuals.
Secondly, if the body length of 120 to 130 cm is attained at one year after birth,the mean annual growth rate is from 60 to 73%, which is sufficiently close to thecorresponding values, 55 to 65% known on several delphinids (Kasuya, 1972;
Kasuya et al., 1974) and phocoenids (Nielsen, 1972; Kasuya, 1978). They suggest
mean nursing period not exceeding one year and average body length at weaning
below 120 or 130 cm.
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

37

Though the study of age determination and growth of the species is in progress, the exploratory examination of 25 strandings and accidental catches madeafter completion of this study shows that the dentine deposition is annual. Namely
a narrow layer strongly stainable with haematoxylin is deposited between September and June, and a wide weakly stainable dentine in June to September. Thisrate is same in cemental layers. The age frequency of the sample is as follows(both sexes); eight individuals between 0 and 0.9 years (65.3 to 130.2 cm in bodylength), four between 1.0 and 1.9 years (119.8 to 128.0 cm), and one at 3.0 years(length unknown) and 13 between 8 and 23 years. All the individuals in the last
category were sexually mature. This supports the above deduction on the growthof juveniles, and indicates low mortality rate after weaning and before 8 years ofage. These samples were obtained both inside and outside of the Inland Sea.
Most of the females which have weaned the calf before April will start thenext gestation in the mating peak in the April and May. The cows which do
not wean the calf before the mating peak will also be attended by some males as
analysed in the school structure, and will start the nexst pregnancy by the endof August, or in some cases in the next mating season.
TABLE 6.
Month

FREQUENCY OF GROWTH STAGES OF FINLESS PORPOISE
IN THE INLAND SEA AND ADJACENT WATERS
Jan. Feb.

Mar.

Apr.

May

213
20
62
295

122
4
19
145

19
102

49

18
26

14
19

Adult
Juvenile
Calf
Total

7
1
0
8

21

147
13
13
173

Cow with callSingle adult

0
3

3
6

10
61

15
1
5

57

Jun.

Jul.

Aug.

Sep.

78

20
0
8
28

13
0
2
15

28
0
9
37

6

2
4

9

5

5

Oct. Nov.

Dec.

5

24
0
10
34

14
0
2
16

0
3

3
9

0

5

0
0

5

The ratio of the females which breed in two successive years, or that of thefemales which do not breed more than two years are not known. However, thelow ratio of cows with calf attended by adult male, rather sharply defined mating
season, and relatively short nursing period suggest that the most usual breeding
cycle of the population will be about 2 years. Among the five records of the adultfemales, the three individuals caught in June were not lactating nor pregnant
and were either before ovulation with large follicle in the ovary or after recent ovulation, one female caught in November was lactating and simultaneously pregnant
with 43.5 cm fetus, and another female in April was not lactating but pregnant
with 71.5 cm fetus. These informations suggest that the overlapping of lactationand pregnancy is not common (20% of five females).
The examination of gonads provided the following provisional result. In males,.
a 144 cm (1.5 years old) individual seemed to be at early pubertal stage, but otherfour males of 148, 157, 166, and 187 cm were undoubtedly mature. In females
all six females from the Inland Sea measuring 141 cm or more were sexually mature.
Their body lengths were 141, 154, 162, 163, 164, and 164.2 cm. Though, becauseof the underrepresentation of weaned immature individuals, the correct estimation
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

38

KASUYA AND KUREHA

of the body length or age at the onset of sexual maturity is impossible, it will bepossible to conclude that the individuals clasified as " adult " in this study will besexually mature so far as they are concerned with the females. Then the roughestimation of the annual gross production is calculated by assuming the equalsex ratio. As shown in Table 6 the ratio of the adult individuals is 71.5% of thetotal individuals in April. If the " adult " is assumed to be sexually mature, thenumber of adult females will be 4,900x0.715X0.5=1,751. The two years breeding cycle gives calves produced in the Inland Sea in one season as 1,751 x0.5=875
individuals of both sexes. In other words the gross annual reproductive rate seems
to be 17.9%. The annual calf production, 25% of the total adult, is consistent
with the number of calves and juveniles in the following March, 20% of the total
adults (p. 36).
Nothing is known on the popul~tlon discreteness of the species in the Japanese
coastal waters.
ACKNOWLEDGMENTS
This study is greatly indebted to the World Wildlife Fund Japan and Professor
M. Nishiwaki of the University of Ryukyus, who offered the research fund and led
the project. Dr I. Uchida, Director of the Himeji Aquarium provided many
porpoise carcasses in his collection and offered the aquarium facilities for theprocessing. Thanks are also due to the Fisheries Aviation Co. Ltd. for giving theprivilege to analyse their aerial sighting records, and to Mr S. Sudo, Chief Managerof the Shikai Fishermens Cooperative Union for offering a fishing vessel for the
porpoise observation. Mr T. Kataoka of the Toba Aquarium, Dr Y. Naito of
the Polar Research Institute, Dr Y. Masaki of the Far Seas Fisheries ResearchLaboratory, Mr T. Shimoyama of the Matsushima Aquarium, and Mr S. Kondo
in Tadotsu City presented the specimens or unpublished data of the finless porpoise.
Dr. S. Ohsumi of the Far Seas Fisheries Research Laboratory critically read themanuscript. This study was technically assisted by Mr T. Hiwatari, Ms M. Nakagiri, Ms Y. Oka, Ms S. Wada, and Ms K. Iwata. We would like to express our
sincere thanks to all who helped the present study.
REFERENCES
ANON., 1965. On the rearing and ecological observation of the finless black porpoise (Neophocaena phocaenoides). pp. 31-40. In: T. Kataoka (ed.) Ten years history of Toba Aquarium, Toba Aquarium, Toba.
(In Japanese)
ANON., 1978. Annual report on the trend offisheries presented to the 87th congress, 53th year of Showa [1978]. Tokyo,
159 pp. (In Japanese)
BARHAM, E. G., ]. C. SWEENEY, S. LEATHERWOOD, R. K. BEGGS, and C. L BARHA11, 1979, Aerial census
of the bottlenose dolphin, Tursiops truncatus, in a region of the Texas coast. Fish. Bull. 77 (3) : (inpress).
CHUGOKU SHIKOKU NosEIKYOKU [C. S. AGRICCL. ADMINIS. BuR.], 1978. Fisheries statistics of the Inland
Sea indicated by areas, pp. 86-97. (In Japanese).

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

39

Dm, I., 1974. Further development of whale sighting theory. pp. 359-368. In: W. F. Schevill (ed.) The
Whale Problem, A Status Report, Harvard Univ. Press, Cambridge, Massachusetts, 519 pp.
FURUTA, M., 0. TsuKADA, and T. KATAOKA, 1977. On the birth offinless porpoise, Neophocaenaphocaenoides
in captivity. pp. 1-12. In: Toba Aquarium (ed.) Report on the rearing and behavior of finless porpoise(Neophocaena phocaenoides) in Toba Aquarium, Toba Aquarium, Toba, 50 pp. (In Japanese withEnglish summary)
HosmNO, Y., 1972. Pollution of the Inland Sea. Iwanami, Tokyo. 202 pp. (In Japanese)
HOWELL, A. B., 1927. Contribution to the anatomy of the Chinese finless porpoise Neomeris phocaenoides.
Pros. U.S. Nat. Mus., 70 (13): 1-43, pl. !.
KABURAGI, T., 1932. The migrating place of the Indian porpoise (Neophocaena phocaenoides) and fishery,
Hiroshima Prefecture. pp. 72-75. In: Ministry of Education (ed.) Report of the survey of natural monuments, animals part 2, Min. Education, Tokyo, 114 pp.
KASUYA, T., 1972. Growth and reproduction of Stenella caeruleoalba based on the age determination by meansof dentinal growth layers. Sci. Rep. Whales Res. Inst., 24: 57-79.
KASUYA, T., 1976. Preliminary report of the biology, catch, and populations of Phocoenoides in the western
North Pacific. FAO/ACMRR/SC/21, 20 pp.
KAsuYA, T., 1977. Age determination and growth of the Baird's beaked whale with a comment on the feta!
growth rate. Sci. Rep. Whales Res. Inst., 29: 1-20.
KASUYA, T., 1978. The life history of Dall's porpoise with special reference to the stock off the Pacific coastof Japan, Sci. Rep. Whales Res. Inst., 30: 1-63.
KASUYA, T., N. MIYAZAKI, and VV. F. DAWBIN, 1974. Growth and reproduction of Stenella attenuata in the
Pacific coast of Japan. Sci. Rep. Whales Res. Inst., 26: 157-226.
KATAOKA, T., M. FURUTA, and S. KITAMURA, 1974. On the feeding to newly captured finless black porpoise,
Neophocaena phocaenoides. J. Jap. Ass. Z,ool. Garden. Aquariums, 16 (1): 1-5. (In Japanese with English
summary)
KATAOKA, T., S. KITAMURA, M. SEKIDO, and K. YAMAMOTO, 1976. On the feeding habit offinless porpoise(Neophocaena Phocaenoides). Mie Seibutsu, 24 and 25: 29-36. (In Japanese with English summary)
KATAOKA, T., S. KITAMURA, K. YAMAMOTO, S., MANABE, and M. SEKIDO, 1969. On the external proportions of finless black porpoise, Neophocaena phocaenoides. J. Jap. Ass. Z,ool. Garden. Aquariums, I I (3):54-56.
KURODA, N., 1940. On the cetacean in the Suruga Bay. Shokubtsu o_yobi Dobutsu, 8 (5): 1-10. (InJapanese)
MIZUE, K. A. TAKEMURA, and K. NAKASAI, 1968. Studies on the little toothed whales in the west sea areaof Kyushu-XV, underwater sound of the Chinese finless porpoise caught in the Japanese coastal sea.
Bull. Fae. Fish. Nagasaki Univ., 25: 25-32.
MizuE, K., K. YosHIDA, and Y. MASAKI, 1965. Studies on the little toothed whales in the west sea area of
Kyushu-XII, Neomeris phocaenoides, so-called Japanese "sunameri ", caught in the coast of Tachibana
Bay, Nagasaki Pref. Bull. Fae. Fish. Nagasaki Univ., 18: 7-29. (In Japanese with English summary).
NAKAJIMA, M., 1963. A lost infant of finless porpoise. Geiken Tsushin, 147:1-4. (In Japanese)
NIELSEN, H. G., 1972. Age determination of the harbour porpoise Phocoena phocoena (L.) (cetacea). Vidensk.
Meddr. Dansk Naturh. Foren., 135: 61-84.
OGAWA, T., 1950. A dolphin research trip in the summer of Showa 9th. pp. 28-37. In: T. Ogawa A
tale of whales, Chuo-koron, Tokyo, 211 pp. (In Japanese)
PERRIN, W. F., D. B. HOLTS, and R. B. MILLER, 1977. Growth and reproduction of the eastern spinner
dolphin, a geographical form of Stenella longirostris in the eastern tropical Pacific. Fish. Bull., 75 (4):725-750.

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

40

KASUYA AND KUREHA
APPENDIX I.
Expedition

no.

date
12, IV, '76

I
223, IV, '76
22, VII, '76

I
34, VIII, '76
12, XI, '76

4

2, XII, '76
2, Ill, '77

515, III, '77
8, v, '77

6

19, v, '77
14, VI, '77

725, VI, '77
15, IX, '77

828, IX, '77
27, I, '78

910, II, '78
6, III, '78

10

15, III, '78
15, IV, '78

I
I

I
I

I

I
I
I

x 6

30, IV, '78
17, I, '77

Xl39, VIII, '77

Xl525, x, '77

Xl615, XI, '77

Xl7

13, XII, '77

Area
N. mile 2
km 2
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles

RESULT OF SURVEY OF

1

2

3

4

5

Sum

245.2
841

433.7
1,488

255. l
875

358.8
1,231

108.0
370

1,400.8
4,805

17.5
0
0
17.4
0
0
13.8
0
0
12.8
0
0
13.8
0
0
14.0
2
1.429
13.7
0
0
26.5
0
0
16.0
10
6.250

130.7
83
6.350
135.2
35
2.589
141.6
17
1.201
135.5
46
3.395
122.8
40
3.257
134.4
27
2.009
142.5
14
0.982
98.7
2
0.203

119.4
74
6.198
123.7
12
0.970
138.4
19
1.373
142.7
44
3.083
111.5
24
2.152
109.0
30
2.752
95.4
6
0.629
67.3
19
2.823

144.5
65
4.498
122.4
13
1.062
88.6
13
1.467
123.4
43
3.485
102. l20
1.959
117 .5
21
1.787
144.4
12
0.831
86.6
10
1.155

156.2
32
2.049

136.3
81
5.943

108.4
72
6.642

4. 7
0
0
5.0
4
8.000
5.2
0
0
4.7
0
0

22.9
0
0
19.0
2
1.042
51.0
0
0
71.0
7
0.986
28.5
2
0.701
60.4
0
0
33.2
0
0
29.8
0.336
20.8
41
19.71255.6
44
7 .914
29.8
0
0
29.7
0
0
31.0
0.323
22.2
5
2.252
21.4
0
0

417.5
222
5.317
417.8
62
1.484
437.0
49
1.121
486.4
140
2.878
377.7
86
2.277
435. l78
1. 793
429.5
34
0.791
296.1
32
1.081
47.3
41
8.668
472.5
239
5.058
29.8
0
0
34.4
0
0
36.0
5
1.389
27.4
5
1.825
26.1
0
0

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

41

FINLESS PORPOISE IN THE INLAND SEA
11

12

13

14

Sum

21

22

23

Sum

Grand total

332.7
1, 141612. l2,099

327.6
1, 124203.1
697

1,475.5
5,061

894.6
3,068

87.7
301

298.9
1,025

1,281.2
4,394

4,157.5
14,260

34 .2

17 .2

0.2

0.2

0
0

0
0

10.0
0
0
24.1
0
0
24.4

13.0
26
20.000
53.2
4
0.752
97.3
0
0
92.2
6
0.651
71.9
0
0
95.2
27
2.836
81.2
19
2.340
51.0

4
1.170
35.9
12
3.343
47.2
2
0.424
34.2
13
3.801
25.3
16
6.324
35.4

0.581
16.3
0
0
32.1
0
0
50.4
1
0.198
22.4
0
0
57.9

64.4
31
4.814
115.4
16
1.386
200.7
2

3

2

1.840
17.0
0
0
34.5
3
0.870

0.392

0.565
41.2
2
0.485
21.9
0
0

91.3
12
1.314

'.29. 74
1. 347

20.4
0
0

0.100
201.3
22
1.093
141.8
20
1.410
211.2
30
1.420
174.8
21
1.201
131.0
8
0.611
17.0
0
0
175.9
19
1.080

5.3
0
0
4.3
0
0
4.0
0
0
4.7
6
12.76628.0
5I. 786
25.2
0
0
20.9
0
0
21.2
3
1.415

33.3
5
1.502
29.5
0
0
24.9
0
0
25.9
9
3.475

2

0.820
22.2
4
1.802
22.7
0
0
19.6
0
0
16.3

2

0.173
32.8
0
0
41.8
3
0.718

7.2
0
0
15.2
0
0
50.0
0
0
49.6
4
0.806
43.8

0
0
57.7
2
0.347
29.8

2.2
0
0
11.2
0
0
2.2
0
0
4.4
2.273
4.4
0
0
2.1
0
0

0

0

86.5
0
0

4.4
0
0

0

9.4

0
0

0
0

28.3
0
0
3.0
3
10.000
1.6
0
0
22.9
0
0
25.3
0
0
0.4
0
0

54.7
0
0
55.2
3
0.543
55.6
5
0.899
71.1
0
0
85.1

2.1
0
0

93.0
0
0

2

0.235
30.2
0
0

482.1
253
5.248
542.6
78
1.438
692.4
51
0. 737
742.9
165
2.221
575.1
111
1.930
717.4
108
1.505
689.4
57
0.827
457.3
40
0.875
64.3
41
0.638
741.4
258
3.480
29.8
0
0
67.7
5

0.4
0
0

0.4
0
0
0.4
0
0

0.4
0
0
0.4
0
0
0.4
0
0

0.739
65.9
5
0.759
52.7
5
0.949
52.4
9
1. 718Continued ...

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

KASUYA AND KUREHA

42

APPENDIX I.
X2121, VII, '78

X22

17, VIII, '78

X23

19, IX, '78

X24

17, x, '78

N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles
N. milesNo. sighted
No./10 miles

4.5
0
0
4.4
0
0
4.9
0
0
7.0
0
0

39.7
4
1.008
33.5
0
0
30.6
0
0
34.0
0
0

35.2
4
1.136
29. l
0
0
25.7
0
0
27.0
0
0

X : Survey conducted by K. Kureha in the areas 4, 5, 13, and 14. Four surveys conducted at Akashi
and Kanmon passes not listed.
1 : Includes Xl, May 5, 25.7 miles, 0 porpoise. 47 individuals in 16 schools observed on a fishing vessel
not included (area 4).
2: Includes X2, Aug. 8, 18.8 miles, 2 porpoises.
3: Includes X3, Oct. 20, 25.5 miles, 0 porpoise, X4 Nov. 18, 10.2 miles, 0 porpoise, and X5 Dec. 16,
42.3 miles, 0 porpoise.
4: Includes X7, Feb. 23, 20.4 miles, 0 porpoise, and X8 and X9 Mar. 1 and 22, 116.4 miles, 9 porpoises.

APPENDIX II.
Expedition
no.

date

4
1
9
5
6
2
7
3
8

2, III-15, III, '77
12, IV-23, IV, '76
15, IV-30, IV, '78
8, V-19, V, '77
14, VI-25, VI, '77
22, VII- 4, VIII, '76
15, IX-28, IX, '77
12, XI- 2, XII, '76
27, I-10, II, '78

11

MINIMUM ESTJMATION OF PORPOISE

Nearshore stratum
3

5

sumo

421

325

438

94

1,488

257

143

149

6

555

250

69

110

14

494

193

265

239

7

704

210

} 0
} 51
} 0

}

Intermediate42

sum 2l
1,170(201)
1, 574 (279)
1,970(380)641 (143)
665 (146)
744 (190)
335 (97)950 (261)
796 (215)

11

12

13

60

350

179

68

226

221

0

343

194

139

46

53

Calculated for each area after combining the data of two or three expeditions. The r values used are
0.391 (March to April), 0.438 (May to June), 0.306 (July to September), and 0.178 (November to

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FINLESS PORPOISE

43

Continued
4.1
0
0
4.4
0
0
4.0
0
0
4.4
0
0

25.5
4
1.569
25.0
0
0
26.9
0
0
29.0
0
0

29.6
4
1.351
29.4
0
0
30.9
0
0
33 .4
0
0

0.4
0
0
0.4
0
0
0.4
0
0

0.4
0
0
0.4
0
0
0.4
0
0

69.7
8
1.148
63.3
0
0
61.9
0
0
67.4
0
0

5: Includes XlO May 12, 59.5 miles, 2 porpoises.
6: Includes Xll Jul. 14, 66.0 miles, 2 porpoises.
7: Includes Xl4 Sept. 18, 66.4 miles, 0 porpoise.
8: Includes Xl8 Jan. 20, 517 miles, 1 porpoise, and Xl9 Feb. 17, 28.7 miles, 3 porpoises.
9: Survey conducted mainly at four straight and waters adjacent to the Inland Sea. Only the Inland
Sea records are listed.
10: Includes X 20 Apr. 13 49.3 miles 0 porpoise. Surveys made outside of the Inland Sea excluded.

POPULATION IN THE INLAND SEA, k=l ASSUMED
Offshore stratum

stratum
14

sum 1>

12

601

6

521

0

537

46

284

sum 2>
469 (173)
1, 502 (752)444 (185)
418 (283)
555 (177)
732 (560)
536 (405)
89 (88)474 (248)

21

22

23

sum 1>

0

0

432

432

87

23

0

110

90

0

0

90

0

0

0

0

sum 2>
202 (200)00232 (135)

Febraury).
2> Calculated for each stratum after combining the data of areas.

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

60
91 (90)00Grand
totaP>

2,521
1,186
1, 121988

Grand
total2>
1,841 (332)
3,076 (810)2,414(432)
1,291 (344)
1,220 (230)
1,476 (591)962 (426)
1,039 (276)
1,270 (328)Standard error in parenthesis.

44

KASUYA Al'\D KUREHA

EXPLANATION OF PLATESPLATE I
Fig. I. Aerial photograph of seven schools of the finless porpoise. 1044 hrs, 12
July, 1976. 34°00'N, 132°25'E. Numeral and arrow indicate the position andnumber of distant individuals. Copyright, Fisheries Aviation Co. Ltd., Kojimachi,
Tokyo.
Fig. 2. Closeup of the three schools in Fig. I. It is also possible to consider themas one school. Copyright, Fisheries Aviation Co. Ltd.
PLATE II
Fig. I. Aerial photograph of two schools (two and seven individuals) of the finless
porpoise. Data are same with PLATE I. Numeral and arrow indicate the position and number of submerged individuals, all adult. Copyright, Fisheries
Aviation Co. Ltd.

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

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