DISTRIBUTION OF MOTHER-CALF DALL'S PORPOISE PAIRSAS AN INDICATION OF CALVING GROUNDSAND STOCK IDENTITYTOSHIO KASUYA * AND HARUO OGI**
ABSTRACT

Eighty nine mother-calf Dall's porpoise pairs were sighted in Augustand September 1982, 1983 and 1985 in the Bering Sea and the western
North Pacific (outside the principal range of the truei-type population).
These sightings were analyzed with an attempt to determine the range ofthe calving ground and the identity of the stocks. Three discrete concentrations of such pairs were found in the study area, two in the Pacific area
north of 45°N and another in the central Bering Sea. The dalli-type Dall's
porpoises in the surveyed area represent at least two local stocks each
breeding to the north and south of the western Aleutian Islands. In addition to these, there is probably another stock which calves off the east
coasts of the northern Kuril Islands, although its relationship with the Sea
of Japan-Okhotsk Sea stock needs additional examination.
INTRODUCTION

Using sightings data of Dall's porpoise, Phocoenoides dalli (True, 1885), fromthe western North Pacific south of the Aleutian Islands obtained between
August and September 1982 (which corresponds to the mating season after
the parturition peak of the species (Newby, 1982)), Kasuya and Jones (1984)
indicated that mother-calf pairs occurred north of the Subarctic Convergence.
They also noted the dominance of weaned juveniles and presumably of males
in the Subarctic Convergence zone, and their behavior of approaching vessels.
Ogi and Fujise (1984) conducted a cruise during the same season in 1983 andrecorded similar geographical behavior differences (Kasuya and Shiraga,1985).
Miyazaki and Fujise (1985) reported the results of a similar cruise in May
and June 1984, south of the western Aleutian Islands. Although their sightingsof mother-calf Dall's porpoise pairs were limited due to the period before theparturition peak, their data indicated the presence of latitudinal difference ofcatchability of the species which probably reflected the difference in the bow
riding behavior. This suggests that the Dall's porpoise segregates by growthstages, sex and reproductive status even prior to the parturition peak.

* Far Seas Fisheries Research Laboratory, 5-7-1, Orido, Shimizu-ski, Shizuoka-ken, 424 Japan** Faculty of Fisheries, Hokkaido University, 6-1-1, Minatomachi, Hakodate-shi, Hokkaido, 041 Japan
Sci. Rep. Whales Res. Inst.,
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KASUYA AND OGI

The above studies brought to question if such segregation within thespecies, especially that of the calving individuals extends further north into
the Bering Sea. In order to resolve this question, Japan Fisheries Agency
conducted in 1985 a 47 days cruise of the Hoyomaru No. 12 in the Bering Sea
for sighting and collecting biological sample from the species by harpooning(Ogi, Tanaka, Kuramochi and Yamamoto, 1986).
Using data obtained during these three cruises conducted after the
parturition peak for Dall's porpoises, the present study analyzes segregationof their breeding population, and attempts to identify the local stocks of thespecies in the western North Pacific and Bering Sea.
MATERIALS AND METHODS

Materials used are sighting records of Dall's porpoises obtained during three
cruises ( 17 August to 17 September 1982, 10 August to 16 September 1983,
and 6 August to 17 September 1985) of theHoyomaruNo. 12. This vessel waschartered by the Japan Fisheries Agency for the purpose of studying thebiology of the Dall's porpoise incidentally taken in the Japanese salmon gillnet
fishery. During these cruises sightings were conducted in the same way as
those described by Kasuya and Jones (1984). Most of the Dall's porpoiseschools were chased for possible harpooning, although the length andmethod of the chase were not the same between the cruises and the proportion of passed schools (schools neither chased or closed for harpooning or for
further observation) were significantly higher in the 1985 cruise as mentioned
below. In the following section the former survey mode (i.e., research vessel
stops ordinary sightings activity and to approach the porpoise schools forobservation or harpooning) is expressed as closing mode, and the latter (i.e.,the vessel continues sighting on the prefixed track line even after finding aschool) as passing mode.
Biologists on board the 1982 cruise were Y. Fujise, T. Kasuya and C.
Thomson. Outline of the cruise track line and proportion of individuals
constituting mother-calf pairs in the daily sightings of the Dall's porpoise are
given in Fig. 1 and Appendix Table 1. Further details of the cruise andsightings are in Kasuya and Jones (1984).
Y. Fujise, H. Ogi and S. Shiraga were on board of the 1983 cruise, except
for the two days period (14 August and 8 September) when it cruised within
fishery conservation zone (FCZ) of the Union of Soviet Socialist Republics(USSR), the survey was conducted in the Pacific area south of the FCZ of theUnited States of America (USA) and all Dall's porpoise schools encountered
were chased. Sightings were discontinued on 2 days of rough weather, but
continued on days of poor visibility. Results of the sightings and the cruise
track line are given in Fig. 2 and Appendix Table 2.
The 1985 cruise was conducted with four biologists on board, H. Ogi,
H. Tanaka, T. Kuramochi and Y. Yamamoto. Most of the period of the northSci. Rep. Whales Res. Inst.,
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127

bound cruise and days spent in the northern Bering Sea the vessel cruised the
FCZ of the USA or the USSR, and the chasing or harpooning was not conducted (8-12 August, 16-21 August, 5-6 September, 11-12 September).
Sightings were discontinued in rough weather (27 August), but continued onsome days of poor visibility (7 to 11, and 25 August). The sighting track line
and sightings of Dall's porpoises are shown in Fig. 3 and Appendix Table 3.
RESULTS

Density distribution
Kasuya and Ogi ( 1986) analyzed segregation between the two color typesof Dall's porpoise (dalli-type and truei-type, terminology after Kasuya (1978)),
using data which became available after Kasuya (1978), i.e. Kasuya and Jones(1984), Miyazaki, Jones and Beach (1984), Miyazaki, Fujise, Komuro and
Taketomi (1984), Ogi and Fujise (1984) and Ogi et al. (1986). Recently
Miyashita and Kasuya (1987) made similar analysis using additional dataobtained during several whale sighting cruises, and indicated that although
the ranges of the two color types overlap the truei-type predominates in thesummer season in the Pacific area between 40°N and 45°N latitude and between 145°£ and 155°£ longitude and that the northern boundary does notchange significantly during May to September when the Japanese coastal
Pacific is predominated by dalli-types from the Sea of Japan-Okhotsk Sea
Stock.
Our survey data do not show clear density change in the northern boundary area of truei-types (Appendix Tables 1 to 3). Additionally, distribution of
the Dall's porpoise in the surveyed area did not show clear density gap which
may correspond to the stock boundary deduced in the present study, although
there were detected some apparently high density areas, i.e. around thewestern Aleutian Islands (Appendix Table 3) and in the Pacific area at around
45°N latitude and 160° to 165°£ longitude (Appendix Tables 1 and 2; Kasuya
and Jones, 1984). The density was low in the northern Bering Sea north of
59°N latitude (Appendix Table 3).
Dall's porpoises are reported to be uncommon to the north of the capeN avarin (Anon., 1986) and on the continental shelf in the eastern and northeastern Bering Sea (Anon., 1985). Our survey in 1985 confirmed this (Appendix Table 3).
Mother-calf pairs in the western North PacificIn the 1982 cruise there were 39 sightings of mother-calf pairs in thewaters predominated by the dalli-type and three of unidentified type in thetruei-type area (Kasuya and Jones, 1984). None of the former sightings was
identified as the truei-type. The majority of them (36 pairs) were concentrated
in a small area between 165°£ and 174°£ (eastern end of the research area)
longitude and north of 45°N latitude (Fig. 1). The remaining three pairs were
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KASUYA AND OGI

0~30 - - - - - - , 50°N,,.,-........ __71,;/'"'"-.c_).,o,.,I/?'
7 I ~ t:'-'?.
~~~
I------S!;ls------7---~~~---~~~', -~,'-'9 '11 '
0

0

O

9

{/ 9

70

0

II /_,,-'/\

0'\, '\\ Se~.N
'

-~

0

I

0

.._ '+--------1 4 OoN'o--Aug.18---=-=--!.-"''-------140°E

Aug.30 13

5-.:,---...

150°E

Fig. 1. Distribution of mother-calf pairs of the Dall's porpoise indicated by thepercentage of individuals constituting such pairs in the daily number of individuals
sighted. Hoyomaru No. 12 Cruise, 17 August to 17 September, 1982. Solid line
indicates track line surveyed, dotted line track line not surveyed, and closed circle
noon position. No mother-calf pairs of the truei-type were identified during the cruise.

d•• ~ • DaD

.

•o
0

~~-+~~-A-~f~~--lo-~~~~~~~~-+-~~--jsooN

2r-----·

0 :I

----~

/~

~ (/
'.Y-- 0 t'-./ ,/'cf ~------~-----_j 0 0f Sep.1____~-----

140°E

--~
Sep.8

o

'

't'

'-......

I31-u_; ~------2----1

IJ_,..-----_..---------------

o o+.----"'-----..
05

Aug.27

o

o

0

170°E

Fig. 2. Distribution of mother-calf pairs of the Dall's porpoise indicated by thepercentage of individuals constituting such pairs in the daily number of individuals
sighted. Hoyomaru No. 12 cruise, 10 August to 16 September, 1983. Solid line
indicates track line surveyed, dotted line track line not surveyed, and closed circle
noon position. No mother-calf pairs of the truei-type were identified during the cruise.

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DALL'S PORPOISE STOCKS

,.
f

IO

0

J_j.o. .__o~
39 /~·,,,,~ 32ok.13 E~-------

9...-..--~- ,/, ,- '

29,/or-1s,'. . 0. . la1016a-----i-----s_ _f';> ••••

.r'°' . . \~S.ep.S
.0
co

170°E

140°E

180°

160°E

170°E

Fig. 3. Distribution of mother-calf pairs of the Dall's porpoise indicated by thepercentage of individuals constituting such pairs in the daily number of individuals
sighted. Hoyomaru No. 12 cruise, 7 August to 17 September, 1985. Solid line
indicates track line surveyed, dotted line track line not surveyed, and closed circle
noon position. No mother-calf pairs of the truei-type were identified during the cruise.

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KASUYA AND OGIsighted in the dalli-type area but occurred in the three isolated positions, i.e.
approximately in 47°N, 160°E; 44°N, 168°E; 43°N, 159°E.
The 16 mother-calf pairs recorded during the 1983 cruise in the Pacificarea occurred in the dalli-type area and none were identified as the truei-type.
One of them was sighted on 18 August in 47°N and 160°E, which was about
500 nautical miles (nm) west of the western limit of the rest of the pairs (Fig.
2), but it was close to the position of one of the three isolated records ofmother-calf pair in the 1982 cruise (see above). The remaining 15 pairs weresighted in the Pacific area east of l 72°30'E and north of 45°N. The westernboundary of this range is located about 300 nm east of the possibly corresponding calving area identified in the previous year (east of l 65°E and northof 45°N, see Fig. 1) and these two identified ranges overlapped only in thearea east of l 72°E.
Of the 34 mother-calf pairs identified in the 1985 cruise, 12 pairs weresighted in the Pacific area (6 pairs on 11 August, 5 pairs on 7 September, andone pair on 9 September, see Appendix Table 3). They were found north ofthe major range of the truei-type distribution (Fig. 3), and none of them wereidentified as the truei-type. The positions of the 5 pairs encountered on 7
September (50°N, 165°E) were situated on the western limit of the aggregation of 36 mother and calf pairs encountered during the 1982 cruise (seeabove), but the remaining 7 pairs (11 August and 9 September) situated westof l 60°E longitude and were close to the position of two isolated western records in 1982 and 1983 cruises.
We conclude from the above data that the distribution of mother-calfpairs suggests the presence of two discrete calving areas for dalli-type Dall's
porpoise in the western North Pacific. One is found approximately between
45° and 49°N latitude and west of 160°E longitude. This was deduced fromonly 9 sightings and additional data are still needed to confirm the range andmagnitude of this area. However, we consider the presence of this calving
area to be reliable because it was confirmed during the three survey cruises.
The other is the area east of 165°E longitude and north of 45°N latitude. Thiscalving area extended at least to l 78°W longitude, but the eastern limit is notknown because of the limitation of survey area. The identified western rangeof this calving area was variable. In 1982 it was situated at l 65°E longitude,
possibly as in the case of 1985 season when only western portion of the range
was surveyed. The apparent eastern shift of this area in 1983 was possibly due
to the northward shift of the area into the USA FCZ (see Discussion). We do
not consider that two mother-calf pairs sighted in isolated locations south of
44°N and east of 159°E on 3 and 14 September (Fig. 1 and Appendix Table 1)
represent another breeding area, because it has not been confirmed bysubsequent cruises in the area (Appendix Tables 2 and 3, Figs 2 and 3).
The two calving areas in the western North Pacific described above are
separated by about 5 degree in longitude or about 250 nm in the minimum
linear distance (distance between the sightings on 11 August 1985 (48°16'N,
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131

158°32'£) and that on 7 September (49°59'N, 164°10'£)). They were further
separated in 1982 and 1983. This indicates the discontinuity of these twocalving grounds.*

Mother-calf pairs in the Bering Sea
The Bering Sea was surveyed in 1985, and there were sightings of 22
mother-calf pairs. None of these pairs were identified as truei-type. The
southern most sighting of a mother-calf pair in the Bering Sea occurred on
13 August in 54°27'N and 170°04'£, or just on the southern boundary of theBering Sea. The other 21 pairs were sighted in the central portion of theBering Sea. No mother-calf pairs were sighted in the northern Bering Sea(north of the 59°N) in spite of the sightings of 82 Dall's porpoises in this area
(Fig. 3).
The proportion of mother-calf pairs in the Bering Sea declined toward
the Aleutian Islands (Fig. 3), from the highest figure of over 39% in the middle
part of the Bering Sea at 58°N latitude (24 August) to 8% at 55°N latitude (2September). During this time the survey method was the closing mode. During
the five day period in the FCZs of USA and USSR around the Aleutian Islands(12-13 August and 4-6 September), the passing mode was used and only one
mother-calf pair (mentioned above) was identified among 396 Dall's porpoises.
This apparently low proportion of mother-calf pairs in the Aleutian Islands
area can not be fully explained by the difference of detectability between thetwo survey methods.
On the other hand, mother-calf pairs of Dall's porpoise were identified
even on the days of passing mode survey when no porpoise schools wereclosed or chased (nine mother-calf pairs in the total of 322 individuals sighted
on 11 and 13 August, and 3 and 9 September 1985, see Fig .. 3), but nomother-calf pairs were sighted on some of the subsequent days of closing
mode (six days of 14, 15, and 23 August, and 10 and 12 September 1985,
when total of the 134 Dall's porpoises were sighted). Therefore, not denying
the possibility that more mother-calf pairs might have been identified if we
had used the closing mode in the Aleutian Islands area, we believe that theapparently low abundance of mother-calf pairs in the area reflects the geographically biased distribution of calving individuals, and that the calving
ground in the Bering Sea is discrete from those in the Pacific Ocean.
•: After this manuscript was sent to printer, Yoshioka, Ogura and Shikano (1987) completed a transpacific researchcruise on board of the Hoyomaru No. 12 in August through October 1986 for sightings of Dall's porpoises. They
confirmed calving grounds off the east coast of northern Kuril Islands (represented fry four mother-calf pairs in 43° to
46°N latitude and 155° to 165°E longitude) and south of the Aleutian Islands (seven mother-calf pairs in 47° to 49°N
latitude and 180° to 165°W longitude), and found the third calving ground in the Gulf of Alaska east of 153°W (eightmother-calf pairs). Although the ranges of the two western calving grounds were located considerably to the east of theranges indicated fry the present study, they were apart for over 500 nm and the boundaries were distinct. Thus the cruiseof Yoshioka et al., (1987) provided an additional support to our conclusion on the presence of two calving grounds ofthe dalli-type Dall's porpoise in the northwestern North Pacific.
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KASUY A AND OGIDISCUSSION

Dall's porpoises in the calving ground tended to avoid vessels and weredifficult to harpoon (Kasuya and Jones, 1984). This was supported by latercruises in the western North Pacific with similar purpose (see above). However,the survey of closing mode in the central Bering Sea in 1985 showed that the
number of Dall's porpoises that rode the ship's bow wave ranged from 0 to
69% (mean was 21 %) of the total number of individuals sighted daily. This
was apparently higher than the figures below 30% in 1982 (Appendix Table 1)
and in 1983 (Appendix Table 2) cruises recorded in the same season for thecalving ground in the south of the western Aleutian Islands. This can be
attributable to two reasons. The first is that the segregation of breeding population may not have been so distinct in the Bering Sea as in the western North
Pacific reported by Kasuya and Jones (1984). This was deduced from the factthat the proportion of mother-calf pairs declined from the highest value at
58°N latitude to the lowest near the USA FCZ (55°N) (and then to almost zeroof the passing mode survey in USA FCZ, 49° to 54°N). The second reason canbe a possible higher intensity of chasing schools during the 1985 Bering Sea
cruise. Few members of a school could have approached the vessel and eventually been harpooned after a long intense chase. During the 14 day cruise ofclosing mode in the central Bering Sea, they caught only 12 Dall's porpoises(0.86 individuals/day). This is considerably lower than the total catch madeduring about one month cruises in the Pacific area including both calving
grounds and other areas, i.e. 72 individuals in the 32 days cruise in 1982
(Kasuya and Jones, 1984), 95 in the 38 days cruise in 1983 (Kasuya andShiraga, 1985), and 187 in the 43 days cruise in 1984 (Miyazaki and Fujise,1985). Therefore, it will be accepted, in general, that the central Bering Sea
area is one of the calving grounds for Dall's porpoises and the individuals in
the area tended to avoid vessels.
Using the incidental take rate from 1981 to 1984 salmon gillnet fishingseasons (June and July) as an index of abundance, Ferrero and Jones (1986)
analyzed distribution of Dall's porpoises by sex and maturity in the western
Aleutian Islands area of the USA FCZ which was bounded by 168°E andl 75°E longitude and 49°N and 55°N latitude. This area is between the two
major calving areas in the Bering Sea and western North Pacific identified
above, and partially overlaps with the latter. Their data indicate that (1) thedensity of immature individuals was higher in the northern latitude in all
years/months and in both sexes, (2) adult female density in July was higher inthe southern latitude except for the opposite trend in July 1983 (the density
was low and had less distinct latitudinal change in June of these years), and(3) the density of the adult males was always lower than that of the adultfemales and the latitudinal trend was indistinct. The first two of these features
can be explained by assuming that the segregation by sex and growth stagesof the Dall's porpoise occurs parallelly in the Bering Sea as in the western
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DALL'S PORPOISE STOCKS

60°

1600

Fig. 4. Calving grounds of the dalli-type Dall's porpoise identified in the present
study (shaded areas). Chain indicates ordinary summer range of the species where
dalli-type predominates, and dotted line that of truei-type predominance. Triangles
indicate three mother-calf pairs of truei-type sighted in July 1984 (Toshimaru No. 25
cruise, Kasuya unpublished) and three mother-calf pairs of unidentified typesighted in the truei-type area in September (Hoyomaru No. 12 cruise in 1982, Appendix Table 1). Information is not available on breeding ground of the Dall's porpoisein the Okhotsk Sea. Some dalli-types from the Sea of Japan-Okhotsk Sea stock summer in the southwestern coastal portion of the truei-type range (Miyashita andKasuya, 1987)

North Pacific, and that the northern range of the Pacific stock (inhabited by
the calving population) overlaps partially with the southern range of theBering Sea stock (predominated by immature individuals). Therefore, we
consider that the two independent calving grounds of Dall's porpoises are
utilized by two isolated local stocks of the species. The adult males of thestocks probably live further north and south of the study area of Ferrero andJones (1986).
The 1983 season was characterized by both the unusual distribution of
adult female density (Ferrero and Jones, 1986) and the apparent eastern shiftof the range of the calving area observed outside the USA FCZ south of thewestern Aleutian Islands (present data). These can be explained by assumingthat the western portion of the calving ground of the western North Pacificstock was located further north during the 1983 season than other seasons.
The apparent overlap of the range of the two local stocks will offer only
a limited chance of interbreeding because the breeding populations of the twostocks do not usually meet in an area (Fig. 4). The similar, but less influential,
effect is also expected in the possible earlier occurrence of the mating season
in the western North Pacific stock. Among 29 adult dalli-type Dall's porpoise
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KASUYA AND OGI

females taken during the 1982 and 1983 cruises in the south of the western
Aleutian Islands, five were pregnant (with fetal body lengths 0.32 to 13.1 cm
and the mean of 4.0 cm), eight had embryonic membrane containing noidentifiable embryo, and 16 females had only corpus luteum of ovulation(Kasuya, unpublished). However, among nine adult females in the Bering Sea
collected in the same season and by the same method, seven had corpus
luteum of ovulation and no fetus or embryonic membrane. The remaining
two adult females had no corpus luteum (Yoshioka, 1986). Therefore, it isprobable that the mating peak occurs late in the Bering Sea.
There are no direct data on migration of adult individuals between
calving grounds in successive years, but we consider it uncommon from theregularity of reproduction of the species, i.e. narrow and successive parturition and mating seasons and one year cycle of female reproduction (Newby,1982). Support for this was found for the dalli-type Dall's porpoise in the
Bering Sea and western North Pacific in the concentration of heavy metals
and organochlorines, and in the parasite load. Walker (1987) compared theoccurrence of cestode, Phyllobothrium sp., and nematode, Crassicauda sp., between the Dall's porpoises of the same growth stage taken in the western
North Pacific and the Bering Sea, and found significant difference of theinfectation rates between the two areas. Subramanian, Tanabe, Fujise andTatsukawa (1986) found geographical difference in the PCB and DDE concentrations and their ratios between individuals taken during the summer inthe Bering Sea and north western North Pacific, and concluded that thoseindividuals used different feeding grounds although two individuals from thewestern Aleutian Islands had intermediate values. Tatsukawa, Fujise, Honda
and Mishima (in prep.) discovered higher cadmium concentrations and lower
mercury concentrations in individuals from the Bering Sea and opposite
ratios from individuals south of the western Aleutian Islands, and arrived at aconclusion which was similar to that of Subramanian et al. (in press). They
also suggested the Aleutian Islands as an intermingling area. Their results
agreed with the possible distribution of two stocks in the Aleutian Islands area
deduced in the present study.
Our study indicated that dalli-type Dall's porpoises also calves in an areaof the Pacific west of the major calving ground south of the western AleutianIslands which was discussed above (Fig. 4). The two calving grounds in thewestern North Pacific did not merge each other, although the ranges probably fluctuated annually. This suggests that these calving grounds are used by
two different populations of the dalli-type Dall's porpoise. Further study isneeded on the extent of this calving ground along the east coast of the northern Kuril Islands and southern Kamchatka Peninsula. Additional research isalso needed on how the Dall's porpoises in this calving ground are related to
the Sea of Japan-Okhotsk Sea stock proposed by Kasuya (1978), because
there remains a possibility of a local intrusion of the Sea of Japan-Okhotsk
Sea stock as well as the possibility of existence of a local stock.
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We found substantial agreement between the major ocean current systems
and the calving grounds of the presently accepted stocks of Dall's porpoise.
The majority of the Sea of Japan-Okhotsk Sea stock (dalli-types) seem to stayin the Okhotsk Sea Gyre during the breeding season, although some individualsof unknown reproductive status from the stock might summer off the Pacificcoast of southern Hokkaido (Kasuya, 1978; Miyazaki and Fujise, 1985;
Miyashita and Kasuya, 1987; Subramanian et al., 1986). Distribution of thestock off the Pacific coast of Ja pan is limited to the waters under the influenceof the Oyashio Current, with the Kuroshio and Tsugaru Currents as thesouthern and western boundaries, respectively. We are still unclear if thisstock is composed entirely of the truei-type individuals (i.e. all the dalli-types
found in the area are migrant from other stock), or a small proportion ofdalli-type individuals are contained in it. We found that the breeding groundof the Bering Sea stock (dalli-types) is limited to the Bering Sea Gyre, and its
breeding population does not intrude into the Wester~ Subarctic Gyre southof the Aleutian Islands, which is inhabited during the summer breeding
season by the breeding population of another stock of the dalli-type Dall's
porpoises (western North Pacific stock). The non-breeding member of thiswestern North Pacific stock is known to segregate in the Subarctic Convergence
Zone south of the breeding ground (Kasuya and Jones, 1984).
Not denying the possibility of some additional local stocks or small scaleintermingling across the current system as suggested by the breeding groundin the East Kamchatka Current area, we consider the above correspondence
is important and presume that the eastern boundary of the calving ground of
the western North Pacific stock will not extend into the Alaskan Gyre. The
ranges of the Western Subarctic Gyre and Alaskan Gyre extends at least
approximately to 160°W and 180° longitude, respectively (Favorite,
Dodimead and Nasu, 1976). Therefore the eastern boundary of the western
North Pacific stock (which breeds in the area east of 165° E) seems to belocated somewhere between these longitudes. Recently the breeding groundof this western North Pacific stock has been confirmed to extend to 165°W(Yoshioka et al., 1987) rather than l 78°W (confirmed in the present study).
Available records of mother-calf pairs in truei-type area are scanty. Three(truei-types) were sighted by myself during the cruise of the Toshimaru No. 25
in July 1984 (southern three records in Fig. 4), which scanned the major
range of the truei-types outside the USSR FCZ (Kasuya, 1986). Other threesightings of mother-calf pairs of unknown type occurred during the 1982
cruise of this study off the east coast of Hokkaido at about 43°N (Fig. 4).

ACKNOWLEDGEMENTS
All the biologists on board of the Hoyomaru No. 12 cruises cooperated incollecting sightings data while many of them were conducting their own
biological tasks. Captain F. Ito and his crew supported every research activity
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KASUYA AND OGI

on the vessel. The principal planning and organization of the cruise weredone by Drs S. Odate, K. Takagi, J. Ito and M. Kato of the Salmon Division of
the Far Seas Fisheries Research Laboratory. Dr R.L. Brownell and Mr W.A.
Walker critically read the draft and corrected English.
REFERENCES
ANON., 1985. Survey of fur seal stocks and ocean environment in the Bering Sea in 1984. Far Seas Fish.
Res. Lab., Shimizu (Japan). 7lpp. (in Japanese).
ANON., 1986. Draft environmental impact statement and economic impact analysis on the incidental takeof Dall's porpoise in the Japanese salmon fishery. Nat. Mar. Fish. Ser. (USA). 240pp.
FAVORITE, F., A.J. DODIMEAD and K. NASU, 1976. Oceanography of the Subarctic Pacific region 1960-71.
Bull. Int. North Pac. Fish. Comm., 33: 1-187.
FERRENO, R.C. and L.L. JONES, 1986. Distribution and movement patterns of Dall's porpoise (Phocoenoides
dalli) in the western North Pacific Ocean during June and July 1981-1984. Document submitted to
the Scientific Subcommittee, Ad Hoe Committee on Marine Mammals, International North PacificFisheries Commission, Tokyo. 24pp.
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., 1986. Distribution and behavior of Baird's beaked whales off the Pacific coast of Japan. Sci.
Rep. Whales Res. Inst., 37: 61-83.
KASUYA, T. and L.L. JONES, 1984. Behavior and segregation of the Dall's porpoise in the northwestern North Pacific Ocean. Sci. Rep. Whales Res. Inst., 35: 107-128.
KASUYA, T. and H. Oc1, 1986. Segregation of Dall's porpoise in the Bering Sea and western North Pacificby color type and reproductive status. Document submitted to the meeting of the ScientificCommittee, Ad Hoe Committee on Marine Mammals, International North Pacific FisheriesCommission, Tokyo. llpp.
KASUYA, T. and S. SHIRAGA, 1985. Growth of Dall's porpoise in the western North Pacific and suggested
geographical growth differentiation. Sci. Rep. Whales Res. Inst., 36: 139-152.
MIYASHITA, T. and T. KASUYA, 1987. Distribution of Dall's porpoises off Japan. Document submitted to themeeting of the Scientific Committee of Ad Hoe Committee on Marine Mammals, International
North Pacific Fisheries Commission, Tokyo, March 10-14, 1987. 24pp.
MIYAZAKI, N. and Y. FUJISE, 1985. Report of the survey by the dedicated vessel, Hoyomaru No. 53, in 1984.
Document submitted to the meeting of the Scientific Subcommittee, Ad Hoe Committee on Marine
Mammals, International North Pacific Fisheries Commission, Tokyo. 25pp.
MIYAZAKI, N., Y. Fu11sE, T. KoMURO and H. TAKETOMI, 1984. Outline of the survey of the porpoises in
the northern North Pacific by the Hoyomaru No. 53 dedicated for the study of Dall's porpoise (10May to 20 June 1984). Far Seas Fis. Res. Lab., Shimizu. 47pp.
MIYAZAKI, N., L.L. JONES and R. BEACH, 1984. Some observations on the schools of dalli- and truei-type
Dall's porpoises in the northwestern Pacific. Sci. Rep. Whales Res. Inst., 35: 93-105.
NEWBY, T.C., 1982. Life history of Dall porpoise (Phocoenoides dalli, True 1885) incidentally taken by theJapanese high seas salmon mothership fishery in the northwestern North Pacific and western
Bering Sea, 1978 and 1980. Doctoral thesis submitted to University of Washington. 155pp.
OGI, H. and Y. FUJISE, 1984. Outline of the research on marine mammals by the Hoyomaru No. 12 in 1983
(August 10 to September 11). Document submitted to the meeting of the Scientific Subcommittee,
Ad Hoe Committee on Marine Mammals, International North Pacific Fisheries Commission, Tokyo.
14pp.
OGI, H., H. TANAKA, T. KuRAMOCHI and Y. YAMAMOTO, 1986. Outline of the research on Dall's porpoiseby the Hoyomaru No. 12 in 1985. Document submitted to the meeting of the Scientific Subcommittee,
Ad Hoe Committee on Marine Mammals, International North Pacific Fisheries Commission, Tokyo.
20pp.

Sci. Rep. Whales Res. Inst.,
No. 38, 1987

DALL'S PORPOISE STOCKS137

SUBRAMANIAN, A., S. TANABE, Y. FUJISE and Y. TATSUKAWA, 1986. Organochlorine residues in Dall's andTrue's porpoises collected from northwestern Pacific and adjacent waters. Mem. Natl Inst. Polar Res.,
Spee. Issue, 44: 167-173.
WALKER, W.A., 1987. Geographical variation of the parasites Crassicauda (nematoda) and Phyllobothrium(cestoda) in Phocoenoides dalli in the northern North Pacific and Bering Sea. Document submitted tothe meeting of the Scientific Committee of the Ad Hoe Committee on Marine Mammals, International North Pacific Fisheries Commission, Tokyo, March 10-14, 1987. 17pp.
YOSHIOKA, M., 1986. Report on biological studies of Dall's porpoise taken by the dedicated vessel, Hoyomaru
No. 12, cruise in 1985. Document submitted to the Scientific Subcommittee, Ad Hoe Committee on
Marine Mammals, International North Pacific Fisheries Commission, Tokyo. 12pp.
YosHIOKA, M., M. Ogura and C. Shikano, 1987. Results of the transpacific Dall's porpoise research cruiseby the Hoyomaru No. 12 in 1986. Document submitted to the meeting of the Scientific Committee,
Ad Hoe Committee on Marine Mammals, International North Pacific Fisheries Commission, Tokyo.
22pp.

Sci. Rep. Whales Res. Inst.,
No. 38, 1987

138

KASUYA AND OGIAPPENDIX TABLE l. SIGHTINGS OF DALL'S PORPOISES DURING THE
CRUISE ABOARD HOYOMARU NO. 12 IN 1982 5l
No of individuals6l

Date
Noon position
mo.

day

8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.

17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
162)
17
18
19
Total

Lv. Kesennuma
39°27'N, 146°30'E
40°36'N, 151°3l'E
43°32'N, 155°54'E
45°17'N, 158°2l'E
45°59'N, 159°15'E
46°49'N, 160°00'E
48°37'N, 162°22'E
49°4l'N, 163°58'E
49°46'N, 166°55'E
49°13'N, 169°22'E
48°38'N, 172°41 'E
46°58'N, I 74°02'E
44°55'N, l 73°47'E
43°08'N, 173°3l'E
40°59'N, 172°0l'E
43°09'N, 169°37'E
44°05'N, 167°44'E
45°10'N, 165°13'E
42°20'N, 167°48'E
40°00'N, 168°49'E
42°48'N, 165°23'E
43°58'N, 163°37'E
44°14'N, 161°4l'E
44°50'N, 16l 0 27'E
43°52'N, 161°30'E
41°29'N, 163°54'E
41°3l'N, 163°50'E
42°50'N, 158°52'E
42°56'N, 155°03'E
43°02'N, 149°5l'E
42°46'N, 144°52'E
42°14'N, 143°53'E
Ar. Kesennuma

T

D

0
0
0
4
I
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
27
23
43
24
10
12
15
22
15
13
7
0
17
31
7
I
0
4
23)

u

Mothercalf
pairs

0
0
0
0
0
0
0
0
0
0
0
33
I
41
8
0
0
28
12
3
4
12
34
20
11
8
I
3
0
0
0
0
0
2
I
7
0
2
0
0
0
0
0
0
0
0
23
0
2
0
59
25
No sighting surveys conducted
0
0
2
2
0
0
0
2
0
7
5
0
0
0
0
5
17
I
12
15
16
2
31
0
13
0
0
0
0
0
42
55
380
275

Rode
ship's 1l
wave
(%)

50
82
32
87
63
5
4
7
0
0
6
71
100
45
22
100
100
100
85
76
50
0
58
22
63
30

Surfacetem(oeratureOC)4)20.8-23.4
20.9-22.6
20.2-23.7
18.5-19.6
17.5-18.7
16.6-17.8
12.5-16.6
11.8-12.5
9.8-10.2
9.1- 9.5
9.2- 9.9
9.5-10.0
9.7-11.1
11.6-12.8
12.1-16.7
16.0-18.0
13.7-17.6
13.1-14.0
13.7-14.1
15.0-18.9
19.4-19.8
15.8-18.4
14.4-15.4
14.6-17.l
14.8-16.8
14.1-16.8
16.7-18.2
18.0-20.6
14.4-18.3
16.0-17.6
13.8-17.6
14.1-18.0
15.0-18.5
19.1-20.l

461) Porpoise came to the ship's wave, either at bow or side.
2) No porpoises were chased or caught by the vessel.
3) Porpoises were sighted on bow, but sighting survey was not conducted due to rough weather.
4) Temperature ranges during sighting surveys, or during the day if surveys were not conducted.
5) Reproduced from Kasuya and Jones (1984).
6) T, truei-type. D, dalli-type. U, Dall's porpoise of unknown type.

Sci. Rep. Whales Res. Inst.,
No. 38, 1987

?:
~
,....

~

~

"' .,

~~

.....

""~
_Oo~

~~

2
3
4
5
6
7
8
9
10

I

12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

Hakodate Port
42°11 'N,
145°00'E
43°43'N,
149°40'E
43°47'N,
155°14'E
43°49'N,
160°00'E
45°29'N,
160°04'E
47°12'N,
159°52'E
47°55'N,
164°01 'E
50°39'N,
165°00'E
49°28'N,
167°28'E
48°39'N,
168°34'E
48°39'N,
170°10'E
47°12'N,
171°08'E
48°07'N,
174°28'E
47°31 'N,
179°33'E
45°57'N,
178°05'W44°12'N,
178°13'W
44°01 'N,
177°53'E
43°37'N,
174°04'E
43°08'N,
169°38'E
43°17'N,
165°46'E
43°16'N,
163°04'E
44°04'N,
163°07'E
46°00'N,
164°33'E
45°06'N,
161°26'E
46°05'N,
160°21 'E
44°54'N,
156°11 'E
43°17'N,
151°0l'E
42°ll'N,
145°22'E
Hakodate Port

Noon
position
28
124
149
169
121
84
97
119
120
89
0
84
126
112
111
103
80
113
62
30
94
43
70
63
38
0
84
141
130
31

Distance
surveyed
(nm)

0
0
0
0
0
0

I

0
0
0
0
0
0
0
0
0
0
0
2
0

I

0
12
18
3
0
0
0
0
0

T

4
0
0
4
34
13
21
2
3
4
0
49
8351
96
65
20
0
45
0
0
0

I

59
2341
56
35
29

I

0
5

D
0
6
0
16
0
38
54
11
7
0
0
0
3
18
19
17
2
3
0
0
7
60
34
60
5
0
36
0
0
0

u
0
23
19
78
23
94
89
40
8
5
0
0
7
52
32
38
4
6
4
0
56
147
130
126
25
0
81
0
0
0

sum

No. of individua)s21

1) Includes secondary sightings. All the sightings were chased.
2) T, truei-type. D, dalli-type. U, Dall's porpoise of unknown type.
3) Surface water temperature range during sighting survey.
4) Includes one black type.
5) Includes two black types.

8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.

mo. day

---

Date

I

0
0
0
0
0
0
0
0
0
0
0
0
0
0

I

10
0
17
0
3
0
0
8
63
47
35
40
0
31
0
0
0

I

0
0
0
0

0
0
0
0
0
0
8
6

I

0
10
3
12
16
19
3

Porpoisesrode bow
wave

0
0
0
0
0
0

Mother/calf
pairs
19.2-22.8
12.5-19.9
13.3-16.2
11.5-15.0
13.0-18.4
11.7-12.6
10.5-12.0
10.0-10.9
9.9-10.9
9.4-10.3
no survey
9.2-9.7
9.6-9.9
9.8-10.8
10.9-11.5
11.6-13.2
13.3-16.2
13.1-14.9
13.9-15.9
13.9-14.5
12.4-13.0
13.3-13.8
12.6-13.8
11.6-12.7
13.3-16.2
no survey
11.8-13.8
12.1-17.3
15.2-20.0

Surface water31
temperature(Co)

APPENDIX TABLE 2. SIGHTINGS OF DALL'S PORPOISES DURING THE CRUISE ABOARD HOYOMARU NO. 12 IN 1983ll

<.O

""

......

(f)

~

n

0

(f)
....,

t'"j

c;;

0

"C

:io

0

"C

(f)

i:-:

t:l

>
t'"'

\0 ~
Oo
'l~

..... .....

,?a~'""::0

~~

~

::0
~

"'~-

7
8
9
10
11
12
13
14
15
16
17
I8
I9
20
2I
22
23
24
25
26
27
28
29
30
3I
I
2
3
4
5
6
7
8
9
IO
II
I2

42°I2'N,
42°52'N,
43°2l'N,
46°02'N,
48°46'N,51°30'N,
54°ll'N,
57°13'N,
59°02'N,
62°00'N,
61°00'N,
60°00'N,
60°02'N,
59°09'N,
58°59'N,
58°00'N,
58°00'N,
57°59'N,
57°30'N,
57°30'N,
57°0I 'N,56°30'N,56°30'N,
56°0I 'N,55°30'N,55°30'N,
55°00'N,
54°30'N,
53°28'N,
52°22'N,
50°5I 'N,
49°57'N,
47°59'N,
45°3I 'N,
45°13'N,
40°46'N,
40°40'N,

l44°02'E
l44°25'E
l49°22'E154°21 'E
l59°24'E
l64°44'E
l70°20'E
l75°32'E
I77°58'W
l74°00'W
174°46'W
I 77°00'W
I74°30'W
I73°oo·w
I77°27'W
I 78°20'W
I79°58'W
I 77°07'E
I 77°27'E
I 78°50'W
I 76°57'W
l 78°44'W
l 77°14'E
I75°00'E
I78°00'E
I78°34'W
I 75°58'W
I78°00'E
I73°I7'E
I76°lO'E
I70°24'E
I64°54'E
I60°53'E
I57°ll 'E
I53°50'E
I50°45'E
I47°ll 'E

Noon
position
131.4
68.5
160.0
160.l
167.2
166.9
167.0
156.2
149.3
150.I
159.2
I64.5
26.9
I44.5
I54.5
30.6
57.2
I I5.0
I08.2
97.0
69.7
99.2
I 15.I
I27.4
I24.8
I22.9
I66.4
I I l.9
I32.9
I24.2
I35.6
I l l.8
I09.6
45.0
89.5
I I 9.I
1 IO.ODistance
surveyed
(nm)
3
0
4
0
0
0
l
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
I
2
I9

T
5
5
10
10
6
3
52
16
15
7
0
11
I
0
II
I
I4
8
I5
II
0
0
I7
I2
3
I4
8
5
I5
16
5
I4
10
2
24
0
2

D
l

13
0
3
9
0
0
I2
0
I
I8
10
24
I2
4
8
I5
I7
8
I7
I7
44
I9
I6
40
I5
I
I2
0
6

11

8
3
13
53
40
I85

u
9
13
17
23
59
43
238
27
28
7
3
20
I
0
23
I
I5
26
25
35
12
4
25
27
20
22
25
22
59
35
2I
54
25
3
37
2
27

sum

No. ofindividuals2>I) Includes secondary sightings of 27 individuals in six schools.
2) T, truei-type. D, dalli-type. U, Dall's porpoise of unknown type .
3) Surface water temperature range during the sighting survey.

8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
8.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.
9.

mo. day

Date

0
0
0
0
6
0
l
0
0
0
0
0
0
0
0
0
0
5
4
5
l
0
2
0
I
I
I
I
0
0
0
5
0
I
0
0
0

Mother
/calf
pairs
0
0
0
0
0
0
0
24
10
0
0
0
0
0
0
0
I4
2I
23
35
12
2
23
I4
3
22
4
0
0
0
0
4I
15
0
37
0
26

Porpoiseschased

l
2
0
5
I
0
8
0
7
4
5
9
0
0
6
4
2
9
0
I
2
0
0
I3
5
0
II
0
II

l

l
0
5
4
0
3
28

Porpoisesrode bowwave
14.0-21.0
14.0-19.3
10.9-13.0
7.5-10.l
9.8-10.9
8.7-9.l
8.8-9.4
8.7-9.4
8.7-9.5
8.0-9.0
8.2-8.9
8.2-9.0
8.4-8.6
8.0-9.I8.6-9.0
9.0-9.2
8.6-9.I8.6-8.9
8.4-9.0
8.8-9.I
8.7-9.l
8.5-8.8
8.5-8.9
8.3-9.I
8.3-9.I8.6-9.0
8.6-8.8
8.6-9.I9.2-9.7
5.9-8.8
9.5-I0.2
I0.2-10.3
9.6-10.6
1 l.5-I2. I
I5.7-I7.7
I7.I-2l.0
I6.I-I9.9

Surface water3>
temperature(Co)

APPENDIX TABLE 3. SIGHTINGS OF DALL'S PORPOISES DURING THE CRUISE ABOARD HOYOMARU NO. 12 IN I985'>

t:I00......

~

>
r.n
e
-<::
>
z>

0

~

......