OCEANOGRAPHIC CONDITIONS OF THE WHALINGGROUNDS IN THE WATERS ADJACENT TO
ALEUTIAN ISLANDS AND THE BERINGSEA IN SUMMER OF 1955
KEIJI NASU
INTRODUCTION

The present paper gives the outline of the results investigated by Japanese research members in the waters adjacent to Aleutian Islands andthe Bering Sea during the Whaling Survey including whale-marking experiment in the summer of 1955 on boad of the "Konan-maru No. 5 ", belonging to the Nippon Suisan Co. Ltd. During the season, 73 Stations
were occupied by the boat as shown in figure 1, the observed data atthese stations are compiled with respect to the oceanographic elements
such as water temperature, salinity (chlorinity), transparency of the sea
water, colour of the sea water, dissolved oxygen, planktons, and other sealiving organisms sampled from various depths, and also with the weather
elements such as air temperature, sea-fog etc. Above materials arecollected on board by the author and Takehiko Kawakami of the Japanese Fisheries Agency.
The author wishes to express his hearty thanks to Dr. Michitaka Uda,
Professor of the Tokyo University of Fisheries and also to Mr. Makoto
Ishino for their instructions and aids given during the preparation ofthis report.
WATER TEMPERATURE AND SALINITY AT THE SEA SURF ACE

The surface temperature in the period during the survey from earlyJuly to late September in the Bering Sea and the southern Aleutian
Waters in the North Pacific vary from 11.8°C at its maximum to thelowest value 6.5°C. In general the isothermal lines run parallel to the
Aleutian Islands from west to east. On the other hand a warm watermass flows in the sea-region on the northern side of the eastern AleutianIslands from .the continental shelf-water on the Alaskan side in the
period from middle to late decade of August at its most prosperious
extention, and converges to the easterly-going stream along the northern side of Aleutian Islands at about 170°W longitude. Apparently
the boundary line of convergence shifts month by month in accordancewith the fluctuation of the two water masses, i.e. in July lying near at
91

so'N

43

0

ss N

170°E

Fig. 1.

·.46

35

"'l

-

'V>~:ttu I.

~

BB1.\\.'N~

180°

'-o5Q

22

S'B~

~
\

~

I

""'

·~-·~·

. I.

24

110°w

""
og1

•60

-;; Pribilof ls.

ovu
~

0

1so w

~'\\)'\> ~~

A_

jt.

µ/

Dd

NORTH AMERICAALAsKA1·~

7~···-~~

r7o'w'

Hydrographic Stations Carried out by Konan-maru No. 5 in the Summer Season of 1955.

~ Komanaorski Is.

~~\.: _ _/'180°

ZJ~

170°E.

i

I

so N

0

6d'N

j

c::::

(fJ

z!J:>

r

Nl

~

STUDY ON WHALING GROUNDS

93

about 170°W and in August lying near at 171°W due to its shift tosouthernmost and westerly location by the stronger inflow of water massfrom the continental shelf region, and in September it lies at about
168°W after its easterly shift. Also, the water along the Islands shows
lower temperature than that of the open sea, especially it shows a comparatively extensive cold water area in August near the Amchitka I.
lying about at Lat. 52°00'N, 180°Lg. It seems that those cold water
areas are formed by the upwelling due to the effect of the submarine
topographical conditions. Moreover it is observed the increased rate ofsea-fog occurrence over those Aleutian cold water areas on the inflowing occasion of warm and moist air current through southerly wind.
It was already proved that such dense sea-fog regions are the favourable whaling grounds, especially of sperm whales (Uda & Nasu, 1956).

170°E

170°W

180°
7S°c

-

-------- -- ...

... ,.............
'-..

BERING SEA

80°C--"' Pribilof Is.

8°C --

0

SSN~

~
/= .
10.0

170°E
Fig. 2.

Atlu I.

170°W

Horizontal Distribution of Surface Temperature (Aug., 1955) ///: dense sea-fog.

In next, glancing over the isotherms in August in the whole area of
Bering Sea, the 8°C-isothermal line running from St. Lawrence I. isfound in the central Bering Sea toward south to the western part ofthe sea along 58°N-line. In general the water temperature in the deeper central sea-region is lower than that in the shallower sea-region on

94

K. NASUthe continental shelf (see Fig. 2). Such a thermal difference in thoseregions may be due to the different conditions of bottom depths in therising stage of water temperature in summer. Also a very cold waterin the layer of 25-50 m depths is observed along the Siberian Coast.
On the other hand, the hydrographical conditions of the monthly whaling
grounds lying along the northern side of Aleutian Islands in the westlongitudes, (those found on the north to the Unalaska I. in the Aleutian chain) are following: A separated warm water area (centred at
8°C area) covers the western whaling grounds nearly along 55°N-line
north to Unalaska I. in July (in Aug. of 1954 the corresponding warm
water area around 9.0°C was also recognized).
no'w

lBO'

--

/

3250%01'00°W-------//~ERING SEA

330~

3300<

ss'N ~.,.,

170'E

s:;,,.
=

1 0°

33.00%0

Fig. 3. Salinity (S %0) at the Surface (July to August, 1955).

Since after about middle August the isolated water mass, combined
together with the tongue-like inflow in warm water of about 10°C fromthe continental shelf on the side of Alaska extends to about 171 °W
toward south along the Aleutian Islands. In September the isolated
warm water area of about 8°C which disappeared once in August appears again, and moreover in smaller scale than those in July to August.
At present the origin and its process of formation of the warm watermass is not clear and is left for future study.
The hydrography of the Bering Sea basing on the distribution of salinity
is as follows; the isohaline of 32.50 %0 runs nearly along the 200 m isobathymetric line, showing an arc from nearly Lat. 60°N, 180°Lg. to the
middle part of the Kamchatka Peninsula with the parallel distributionof 32.00 %0 lines on both sides of it. The sea-region of waters having
lower salinity less than 32.50 %;; in the Bering-Sea covers an extensive
area on the western side of Alaska compared than that on the easternside of Siberia-Kamchatka (except the vicinity of Anadir Bay). The

STUDY ON WHALING GROUNDS

95

above phenomena are explained by the discharge of Yukon River,
Kushokwin River on the side of Alaska and of the Anadir River on theside of Siberia (Barnes & Thompson, 1938). Referring to the pilot chart
published by the H.0. of U.S. Navy the limit of sea-ice distribution inits melting period resembles very well to the location of 32.50 %c isohaline, suggesting the dominant influence of ice-melted water on the surface
distribution of salinity (see Fig. 3).
DICHOTHERMAL WATER AND THERMOCLINE

It is wellknown fact that in Bering Sea and North Pacific Ocean the
dichothermal water (intermediate cold water) in summer has been formedby the sinking of surface water cooled in winter. Also the results ofour survey ascertained it and added some new data to it. The outline
is as follows; on the whole in Bering Sea, excepting the shallower searegion on the continental shelf and the waters around the Aleutian Is.,the dichothermal water lying in the depths from 25 m to 150 m andhaving its core water temperature ( -1.5°'""" + 4.0°C, and only one station 4.83°C recorded) are found evidently almost everywhere in thearea and also in the northern part of North Pacific Ocean along thesouthern side of Aleutian Islands.
TABLE 1.
Position
Depth (m)POSITION AND DEPTH OF DICHOTHERMAL WATER

62-28N
179-lSW25

61-12N
178-57W
75

58-45N
179-40W
100

57-00N
178-55W
146

53-31N
172-59W
150

Generally the dichothermal depth as shown in table 1 is shallower in
the northern region, moderately deeper in the central region and deeper in the southern region. In the western Bering Sea the dichothermal
depth near the water of 57°N (56°54'N, l 73°17'E. St. observed by
Oshoro-maru) shows deeper than the north waters, and shallower again
as it goes to south (e.g. St. 48).
On the other hand the distribution of water temperature varies gradually from the eastern region passing through the central region around180°Lg. to the western region, i.e. the temperature in the dichothermal
layer of the central region (east to C. Navarin-60°N) rises from -1.5
to 3.32°C, moreover coming on the oceanic plateau near 57°N it falls
and it rises again near the Aleutian Is.
In the western Bering Sea the minimum dichothermal temperaturerises from -0.58°C (St. 27) at the south to C. Olyutorskii towards thevicinity of Aleutian Is. Next in the Northwestern Part of North Pacificsouth to Komandorskii Is. the depth of the intermediate minimum water

96

K. NASU

temperature lies uniformly about at the 100 m depth and it is relatively
low except some station in Bering Sea, especially low near the coast of
Kamchatka Peninsula. Moreover in the waters south to Aleutian Islands in the west Longitude the depth of 100 m, showing comparatively
warmer values of about 3°-5°C. At this place, comparing the generalfeature of dichothermal layers in the Bering Sea and that in the Pacific
Ocean north to 50°N (except those east to 160°W), the layer lies uniformly at about 100 m depth in the east and west longitudes contrary
to the 25-150 m depths in the Bering Sea. This fact may be due tothe somewhat conspicuous effect of topographical conditions. The watertemperature shows its highest value in the area of west longitude on
the Pacific side and lowest value in the area of east longitude (partly
lowest in the Bering Sea) and rising gradually from west to east in
general. In the Bering Sea from spring to autumn season the rise of
surface water temperature by solar radiation causes the remarkable development of thermocline (spring layer), in almost all sea-regions except
some few areas. Thermocline has not been found in the waters of west
longitudes whaling grounds north to Unalaska I. in this research andits most remarkable development was found near the east coast of Kamchatka south to Komandorskii Is. Also in the central region of Bering
Sea (e.g. St. 19) and the northernmost oceanographical station (St. 23)
locating north to St. Lawrence I. thermocline developes very remarkably
showing its depth at about the 10-15 m on the shallower portion of thecontinental shelf and about 50 m in the central part of Bering Sea
together with the region south to Komandorskii Is.
DISSOLVED OXYGEN

The quantity of dissolved oxygen at the sea surface in the Bering Sea
and its adjacent Pacific areas amounts from 4.43 to 11.05 cc/L. In
general its distribution shows higher quantity near to the side of Kamchatka Peninsula and Siberian Coast compared to the Alaskan side, in
the region from Attu I. to Boweres Bank on the east the richly dissolved exygen area more than 10 cc/L. On the other hand in the region
around Boweres Bank and from near Amchtka Pass to U mnak I. On
the both sides of Aleutian Islands the poorest area of dissolved oxygen
is found in the surveyed region of Bering Sea. Its pattern resembles
well to the prescribed distribution of cold water area denoted by surface isotherms, representating the effect of upwelling by the Aleutianridge (see Fig. 4).
Regarding to the vertical distribution of dissolved oxygen in the East
Longitudes Whaling Grounds, the distribution of dissolved oxygen differs

STUDY ON WHALING GROUNDS

97

180'

]I) more than I aceI L.D I ess than 7rxh
Fig. 4.

Horizontal Distribution of Surface Dissolved Oxygen.
(Aug. to Sep. 1955)

Dissolred oxygen
3
5
6
7
8
9
10 (C91,)(m)r-~~~~~-----''--~-'-~-"-r~~~~~~..:..;::__:__,~

50

100
Q)

L

1ii
E

c

=t_
Q)

0

150·

200
Fig. 5.

Vertical Distribution of Dissolved Oxygen.
(Aug. to Sept. 1955).

98

K. NASUconsiderably between the upper and lower layers separated by theboundary layer at about 100 m depth. In short, in the upper layer lessthan 100 m depth a maximum dissolved oxygen layer is found at about
25 m depth (St. 46) which may be produced by the blooming of phytoplankton in the euphotic layer due to photosynthesis, and on the other
hand the dissolved oxygen decreases with the depth at 80 m and again
increased at 110 m depth. Roughly speaking, in the above mentioned
area the value of oxygen keeps nearly constant at the depths less than
100 m and shows spring layer in the depths from 100 to 200 m (there is nodatum of below 200 m depth due to the lack of observation) (see Fig. 5).
Next, in the West Longitudes Whaling Grounds the distribution ofdissolved oxygen somewhat varies to the depth of 100 m, however below
100 m depth it decreases with the increase of depth gradually. The
saturation percentage of dissolved oxygen shows supersaturation over
the almost whole area (except the poor dissoloved oxygen areas in theregion near Boweres Bank and the region along the Aleutian Islands
from 180°Lg. to 168°W), especially the higher supersaturation % in theregion south to C. Olyutorskii. Though there is no datum of dissolved
oxygen in the region north to 56°N in the summer of 1955 owing to
the lack of water sampling for oxygen analysis, referring to the surveyof U.S. Navy in 1933 and that in 1934 by U.S. Coast and Geodetic
Survey, it may be concluded that in the waters along the 170°W line
extending to St. Lawrence I. except the vicinity of Pribilof Is. the richdissolved oxygen amounts to supersaturation. Generally the oxygen at
the sea surface of Bering Sea shows almost supersaturation over thewhole area of the sea except the regions near Boweres Bank and on
the both sides of Aleutian Islands from 180° to 168°W together with
Pribilof Is.
WHALING GROUNDS IN RELATION TO HYDROGRAPHIC CONDITIONS

It is well-known that in the waters around the line of convergence as
the boundary of two currents a favourable fishing grounds is formed by
the accumulation of concentrated planktons (phyto- and zoo-plankton)
and other sea-livings attracted to them. The good example is seen also
in northern waters i.e. as already mentioned above the concentrated
abundance of whales are shown around the line of convergence in thefishing grounds north to Unalaska I. and the movement of whales following the shift of the line of convergence is seen.
These features may be explained as follows : the dense populations ofphyto- and zoo-plankton due to blooming in the richly fertilized region
along the Aleutian Islands due to the upwelling of deep water having

STUDY ON WHALING GROUND

99

rich nutrient salts are transported by the east-going Aleutian current
and then collides with the fresh water mass inflowing from Alaskan coastal
area, where the densely concentrated food-planktons of whales may be
resulted near the boundary of two water masses. In order to estimate
the rate of whales sighted (Sw) in relation to water temperature, we
may put the following quantity,
Sw= }Ve X 100(%0)

Newhere We: the observed frequency of whales for each 1°C of watertemperature.
Ne : the observed frequency of water temperature for each 1 °C.
Calling Sw-curve as the Appearance Curve of whales and then plotSt#

whale plerrl-_y

St45

st4ti

,.....6.6\
I
I

I
J

\_/ 6.5
6.0
55

150

150
200
Fig. 6. Relation to the DichothermalCore Water and the Whales. (Aug.
1955).

Fig. 7. Vertical Distribution of Dissolved Oxygen (cc/L) and the Whaling Ground. (Aug. 1955).

100

K. NASU

them for each species of whales during the whole fishing period, themode of the Sw-curve can find at (8.0±1.0°C) with respect to thesurface water temperature statistically i.e. the highest rate of whale
appearance at the temperature. The distribution of whales in relation
to dichothermal water was noticed already by Uda (1956), and in thisinvestigation also the same is proved. In other words, except the relatively cold water area at the surface influenced by the intermediate
cold water. Comparatively many whales are found on both sides of it
in somewhat warmer water area (see Fig. 6). In the Northeast searegion of Japan off Sanriku a similar feature of whaling grounds, especially of sperm whales, is conspicuously noted by the result of whalemarking survey in 1955.
Next, regarding to the relation of dissolved oxygen, the concentrationof whales is observed in the narrow zone denoting the steep horizontal
gradient from very rich oxygen water mass to poor oxygen water massin the layer of depths from 10 m to 150 m (see Fig. 7). With respect
to the relation between the abrupt change of dissolved oxygen in thelayer about at 10 m depth and the distribution of whales, Marr (1956)
has pointed out the densely concentrated krills as the favourite food of
whales in the very surface layer within 10 m depth in the Antarctic.
And author also observed many swarms of euphausiids in the surface
areas south by east off Komandorskii Islands. The distribution of whales
are considered to show its denser concentration in the such region slightly shifted from the maximum portion of the phytoplankton quantity.
DEEP SCATTERING LA YER AND WHALING GROUNDSThe author has observed the deep scattering layer on echogram with
its evening ascent and morning descent in the fishing grounds such asof Sergestes shrimps etc. (Uda, 1956). In this investigation we recorded
it off the cape of Olyutorskii and euphausia (T. inermis) was sampled byplanktonnet hawl at the same time, of which creature was not sampled
at the St. 27 (59°18'N, 170°52'E). The author hopes in the indirect
searching method of whales during the night by utilizing the echo-traceof deep scattering layer due to the food plankton of whales may be put
to practical use.
REFERENCESBARNES, C. A. & THOMPSON, T. G. (1938). Physical and chemical investigation in Bering
Sea and portions of the northern Pacific Ocean. Univ. Washington Publ. Oceanogr.
3 (2): 35-79.
MARR, J. W. S. (1956). Euphausia superba and the Antarctic surface currents (an advancenote on the distribution of the whale food). Norsk Hvalfangst-Tid., no. 3: 127-34.

STUDY ON WHALING GROUNDS

101

MOTODA, s., KOTO, H., KATO, K., & FUJI, T. (1956). Hydrographic data obtained principallyin the Bering Sea by "Oshoro-maru" in summer of 1955. Fae. Fish. Hokkaido Univ.
UDA, M. (1954). Studies on the relation between the whaling grounds and the hydrographic condition (1). Sci. Rep. Whales Res. Inst., no. 9: 179-87.
(1956). Researchs on the fisheries grounds in relation to the scattering layer ofsupergonic wave. J. Tokyo Univ. Fish., 42 (2): 103-11.
UDA, M. & NASU, K. (1956). Studies of the whaling grounds in the northern sea-regionof the Pacific Ocean in relation to the meteorological and oceanographic conditions(Part 1). Sci. Rep. Whales Res. Inst., no. 11: 163-79.