SOME ASPECTS OF THE DISTRIBUTION OF CALANUS
CR/STATUS AND C. PLUMCHRUS IN THE BERINGAND ITS NEIGHBOURING WATERS, WITH
REFERENCE TO THE FEEDING OF
BALEEN WHALESTAKAHISA NEMOTO
Generally speaking, copepod crustaceans are one of the most important foods forsome baleen whales as well as other marine fish. They occupy the most part of
the abundance of the zooplanktons in the sea. In the Bering sea and in thenorthern part of the north Pacific, copepods are one of the most important foods
for baleen whales along with euphausiids and fish. Among baleen whales, fin
whales usually take Calanus cristatus besides euphausiids, and right and sei whales
are feeding on C. plumchrus favorably (Nemoto, 1959). These selections of theirfoods are closely related to the feeding apparatus of baleen whales (Tomilin, 1954 :Nemoto, 1959). The distribution of the copepods as a food of baleen whales is
examined here from the observation of stomach contents of baleen whales in relation
to. their feeding.
MATERIALS

The materials treated in this paper have been obtained from the collected samples
of stomach contents of baleen whales caught from 1952 to 1961. Plankton samples
collected in 150 and 200 meter vertical tows with 45 cm diameter and 0.33 mm
net have been also included with other data published by Anraku (1954) and
Minoda (1958). The measurements of cephalo-thorax length are only made on
the fresh unbroken specimens in plankton net samples or stomachs of baleen
whales saved from digestion. Oceanographical materials of the Bering sea andadjacent waters are based on following data.
Data collected by Whales Research Institute,
Data record of oceanographic observations and exploratory fishing. No. 1-5 by
Hokkaido University.
Oceanographic data on the northern part of the north Pacific. No. l'-3.

DISTRIBUTION OF FIN AND SEI WHALESThe distribution of baleen whales in the Bering sea and its adjacent waters is
considered from the charts of the catch distribution to some extent. As alreadydiscussed by Nemoto (1959) sei whales belong to Ocean denizen type and comparatively rarely penetrate into the marginal sea. The observation of sei whales has scarcely been recorded in the Bering sea in the whaling these days except some Japanese
157

158

T. NEMOTO

records. The number of sei whales found by the whale searching is also very few
in the Bering sea in high latitudes (Nemoto, 1959). On the other hand fin whales
are considered to be Ocean and Marginal sea denizen which distribute widely in the
Bering sea and even penetrate into the Arctic sea. From the catch statistics inJapanese operations in recent 10 years, 8 main whaling grounds for fin whales havebeen drawn in the Bering sea and adjacent waters. As illustrated in Fig. I, themost heavy catch is observed in the north waters of the east Aleutian Islands, where
euphausiids Thysanoessa inermis and T. longipes are very abundant. Thysanoessa
inermis distributes along the Alaskan continental shelf and T. longipes in the offwaters of the north waters of the east Aleutian Islands. In this off waters of thesaid area, Calanus cristatus also appears as a food for fin whales (Nemoto, 1959).

•
•
E

160'

Fig. 1.

170°

180°

170°

160>

•
•
•

1-20
21-50
51-100•101-20050
201-5001

501~ i150°w

Distribution of fin whales caught by Japanese whaling from 1952 to 1961.

It has occurred very often in the stomachs of fin whales in 1955 and 1956 seasons,and many fin whlaes have swarmed to feed Calanus cristatus. In the northern partof the Bering sea, there have been observed three regions of the concentration of
fin whales as illustrated in Fig. I. Along the Alaskan continental shelf waters,
considerable number of fin whales have been taken where Alaska pollack is thefood for fin whales (Fig. 1-B.) In other grounds C and D, fin whales sometimes
have fed on Thysanoessa raschii and caplin which distribute in the waters off capeN avarin (Fig. 1-C). A few catch of fin whales is also observed in Olyutorskiy
Bay, where the abundand crop of Calanus cristatus far baleen whales was alreadyreported by Brodsky (1950). But fin whales which have been caught by Japanesewhaling expeditions in the Olyutorskiy bay in June in 1960 have scarcely taken
Calanus cristatus. Fin whales caught in Olyutorskiy bay have fed on herring (Clupea
pallassi) and caplin (Mallotus caterverieus). It is safe to say that fin whales feedingin the said areas feed mainly on fish or euphausiids and few occurrences of Calanus

DISTRIBUTION OF CALANUS IN THE BERING SEA

159

cristatus. In the southern Kamtchatka side of the Bering sea, C. criatatus is one of
the important food for fin whales as illustrated in Fig. 2. In the adjacent waters
to Attu Islands (Fig. 1-F), fin whales swarm to feed on C. cristatus every year from
June to July especially in the late of July. The stage of the C. cristatus is copepodite
5 in generall and it coincides with the cycle of it in the waters as established byHeinrich ( 195 7). The considerable part of the copepodite stage 5 Calanus cristatus
distributes in the surface strata of the north Pacific. (Vinogradov, 1955). In thesouthern waters of Sagami Bay of Japan, the immature C. cristatus also inhabits in
the intermediate layers between 300-500 meter and adult specimens are usuallyfound in the depth deeper than 500 m (Tanaka, 1956).

. ·•If·11-14
.15-

160'

170'

180'

no·

160'

150'

140"

Fig. 2. Distribution of Calanus cristatus and C. plumchrus in the stomachs of fin whalesin the Bering sea and Adjacent waters. Black-C. cristatus, Open-C. plumchrus.

The swarm of C. cristatus is considered to sink to the deeper waters to attaintheir growth and to spawn. Generally, C. cristatus spawn in the waters deeper than
500 m in the Bering sea and adult C. cristatus is also found in the deeper watersin Kuril-Kamtchtka region (Vinogradov, 1955). Fin whales can dive as far as
about 300 m (Scholander, 1940), and it is considered usual feeding range of thebaleen whales do not exeed 300 m. Thus swarms of adult Calanus cristatus escapethe swallowing of baleen whales. In other two waters, Copepodite 5 stage ofC. cristatus stay in the upper layer waters later than July. As a second important
copepoda, Calanus plumchrus occurs in the south waters of the Aleutian Islands from
June to August. The occurrence is also observed in July and August in the northwaters of the east Aleutian Islands (Fig. 2).
The whaling grounds formed by Calanus cristatus extinct as soon as the subsidingof C. cristatus to reproduct in the unattainable depth of fin whales. In the ' Calanus

T. NEMOTO

160

year' (Nemoto, 1959), fin whales heavily swarm in the area F and E in Fig. 1 inJune and July, however, blue whales usually do not come to the areas by the lateof August and September. On the other hand, fin whales have not been attracted
by C. cristatus, and feeding on the heavy shoals of euphausiids in the waters E, in' Euphausiid year '. In I 954, many fin whales were feeding in waters along the
Alaskan continental shelf but they were feeding in the off waters of the shelf on
Calanus cristatus in I 955 when euphausiids were rather scarce along the shelf.
The second Calanus feeder is the sei whale in the northern part of the North
Pacific. Sei whales are the Ocean denizen and majority of them come only as far as
the Aleutian archipelago. The catch of sei whales, however, usually have been donein the south of the Aleutian Islands as the main herd of sei whales do not penetrate
into the Bering sea. As it is shown in Fig. 3, the main concentrations of sei whales
catch are observed in the waters off Kamtchatka and along the Aleutian Islands.
E

1so·

170·

160'

160'

~~ l
"I
~

/ j -\

150"'\~~ . ( ""' . J<f'':>:;J'l, ~; <?iJ~~vf"~ :X·rx'\ .

••••• • •
• •

(/

• /}a

····•··· ~~ -_, ,~ ~.

• •••••••••,,..

·••·. .

• e e **\!
0

\'.

_/ J?

•

.

••

. .••·If•••,..~.<,•·•a...
0 0

I

•·

••

t

11-20

~~
l,,

21-30

f

• 6-10
1-5

•
•

0

•

.31E

160'

Fig. 3.

170°

180'

170

160"

.
I

/?.' , . .
~\ '1-·~~..

·· -·~~, .., 0 · -tjl(,Y;.~··· · ·"".iic .~ e ee * •• * e e e

·•··

t

/?; ••_,........-

150'

i
\\

Distribution of sei whales caught by Japanese whaling from 1952 to 1961.

As a generall tendency, sei whales come to the waters off Kamtchatka in summer
when the height of Calanus plumchrus is observed (Heinrich, 1957), Heinrich shows
two groups of C. plumchrus in the waters and sei whales mainly feed the group which
attains their copepodite stage 5 in August. But sei whales are already feeding inthe south waters of the east Aleutian Islands in June. This also suggests that C.
plumchrus is abundant in this area in June.
In the stomachs of sei whales, the majority of Calanus plumchrus is in copepodite
5, and a few specimens of copepodite 4 are also found among copepodite 5. Thisdiffers the case of Calanus cristatus found in stomachs of fin whales in which very few
copepodite 4 is found in the mass of Calanus cristatus.
The food of sei whales in the northern part of the north Pacific is already discussed by Nemoto (1959), and the most sei whales have been feeding on copepods.

DISTRIBUTION OF CALANUS IN THE BERING SEA

161

The number of sei whales fed on other foods, euphausiids and squids are rather
scarce when the data are compared with the one in the adjacent waters to Japan.
The destribution of Calanus copepoda identified in the stomachs of sei whales areillustrated in Fig. 4. Although the collected number is not so many, the mainpart of the food Calanus is Calanus plumchrus. It is suggested these main concentrations of sei whales fairly coincide with the waters where Calanus plumchrus areabundant.

•.·

o. 0

.
0

m

~

~o~ • 1-2.~E;:;0..2
0.
u

u

E

160'

170°

180°

I'iO'

160°

150°

•

Ii,

ij50

3-5

·6- I
w

Fig. 4. Distribution of Calanus cristatus and C. plumchrus in the stomachs of sei whalesin the adjacent waters to Aleutian Is. Black-C. plumchrus Open-C. cristatus.

DISTRIBUTION OF CALANUS CR/STATUS AND C. PLUMCHRUS
IN THE SURFACE STRATA

According to Bogorov & Vinogradov (1960), Calanus cristatus, C. plumchrus andEucalanus bungii occupy the 80 per cent of biomass of the Kuril-Kamtchatka region.
In the surface collecteons of copepods by the vertical plankton net, both Calanus
cristatus and C. plumchrus are found most commonly in the waters investigated.
These occurrences of both species show, however, some interesting features as
discussed following.
Calanus cristatus found in the stomachs of fin whales usually consists of copepodite
stage 5, and adult C. cristatus has not been found in the stomachs of baleen whales.
The positions where copepodite stage 5 of C. cristatus is found in the net collections
are plotted in Fig. 5. As it has been considered, C. cristatus distributes mainly inthe waters which have depth deeper than 500 m and naturally it is found in the
deeper waters in the Bering sea. Calanus cristatus has not been found in some plankton net towed along the Alaskan continental shelf and Chukchi sea as shown inT. NEMOTO

162

Fig. 5. C. cristatus has not been collected in the stations within the Alaskan shelfand 5 station in the Siberian side of the Chukchi sea. Of course both areas are little
influenced by the Bering sea current which may bring C. cristatus from the off water.
In the Chukchi sea, Johnson (1956) already reports the occurrences of C. cristatus
as the visiter from the southern fauna in the Alaskan side of the Chukchi sea. The
clear segregation in occurrences of C. cristatus in the Chukchi sea is apparently affected by the sea current through the Bering strait and shore waters along theSiberian side.
The number of Calanus cristatus in the shallower waters of Chukchi sea is very
scarce in the vertical net from the bottom, and adult spectmens have not beencollected. The adult Calanus cristatus has not been collected by surface plankton
nets in other waters of the Bering sea (Anraku, 1954: Minoda, 1958), and it is considered it usually distributes in the waters lower than 500 m.

160

170 ~

180"

110·

160

150°

Fig. 5. The occurrences of Calanus cristatus in the vertical plankton Net in the surface
strata above 150 m and 200 m in the Bering sea and Chukchi sea.

The general distribution layers of the two Calanus species are defferent. Copepodite 5 stage of C. plumchrus distributes shallower waters than C. cristatus (Vinogradov,1956). This coincides with the swimming depth of fin and sei whales in their usual
feeding. (Nemoto, 1959).
The occurrences of Calanus plumchrus in the vertical plankton nets towed insurface layer in the Bering sea are plotted in Fig. 6. Both adult and copepodite 5
stage of C. plumchrus are more commonly found in the Bering sea and the latter
appears in the almost all collections in the investigations. It also occurs in the Chucki
sea in several stations. Especially adult C. plumchrus is observed in shallow stations

DISTRIBUTION OF CALANUS IN THE BERING SEA

163

of Chukchi sea and Alaskan shelf as shown in Fig. 6. Adult Calanus plumchrus has
been found only three net collections towed in stations in the deeper waters off the
Alaskan shelf and the west waters, however, it occurs in several shallower stations
in Alaskan shelf and Chukchi sea. The adult Calanus plumchrus is found in the deep
waters of the Bering sea and usually deeper than 200 m (Anraku, 1954). Thissuggests that Calanus plumchrus becomes adult in the shallower waters if it can't
subside to deeper waters, although the adult Calanus plumchrus spawns like Calanus
cristatus in the deeper waters. Anraku (1954) reports the adult Calanus plumchrus
distributes usually in the waters deeper than 150 m or 200 m in the west side of
the Bering sea.
60"

170'

180"

110·

1 o·

w

"1

N

• Adult

0 Present
C!> Absent

,56

160"

180'

110·

160'

150'

Fig. 6. The occurrences of Calanus plumchrus in the vertical plankton net in the surface strata avove 150 m and 200 m in the Bering and Chukchi sea.

In the stomach contents of fin and sei whales caught, there has been norecord of adult Calanus plumchrs not to say Calanus cristatus. It may be reasonable toconsider that those baleen whales usually not to feed in the deeper waters where theadult Calanus plumchrus and Calanus cristatus are reproducing. The number of adult
Calanus plumchrus sometimes amounts considerable number in the plankton net towed
in the Alaskan shelf waters (Minoda, 1958). Calanus plumchrus has been collected
in almost all stations in the Bering sea as stated above, but it has not occurred in
3 stations along the east Aleutian Islands, 3 stations in the Alaskan continental shelfand 2 stations in the Siberian side of the Chukchi sea. These waters are also shallower and the number of Calanus plumchrus is restricted by the environmental conditions.

164

T. NEMOTOBODY LENGTH VARIATION

The variations of body length of Calanus plumchrus and C. cristatus are discussed byHeinrich (1957). The materials collected in Whales Research Institute during
1952 to 1956 are measured, the positions of collections of which are also illustratedm Fig. 7.
,FE===.,,,,,,,,1~60~·~~~-=="1~10~·~~~~1s~o·~~~~7
11~0·~~~~~16~0·~~~~~15~o·~~~~~w,\-'(__"1
~
£0

N

6

E

160"

170"

Fig. 7. Stations where Calanus cristatus and C. ptumchrus have been collected in the
Bering sea and adjacent waters to Aleutian islands. Black symbols and capitals-C.
cristatus, Open symbols and C. pl!imchrus.

78

-76

J

~74

2

70
68
ABCDEFGHIJKLMNOPQRSSSSTUVWXYZ.
Stations

Fig. 8. Cephalothorax length of C. cristatus in the Bering sea and djacent waters.
Rectangles represent means, plus or minus two standard errors.

The average body length (cephalothorax length) of Calanus cristatus in copeopdite
stage 5 is plotted in Fig. 8 with two standard deviations. From the figures, it isDISTRIBUTION OF CALANUS IN THE BERING SEA

165

suggested that there are 4-5 size groups in the waters around the Aleutian Is. Off
Kamtchtka group, South-west Attu Is. group, North-east Aleutian Is. group, andAdjacent waters to Aleutian Is. groups are them. Following points are noticed
from the illustration of the body length.
1) Calanus cristatus distribution in the off water of Kamtchatka Islands, has
the character of cold water form and has larger body length. This may be attributable to the intermedatte cold waters where Clanus cristatus develops from naupli
to copepodite stage. In the very adjacent waters to stations E and F, the small
sized Calanus cristatus occurs in G and H stations. This would suggest complicatedoceanographic conditions in the waters where the Kamtchtka shore waters, Aleutiancurrent and waters from the south meet one another.
2) From I to M stations, Calanus cristatus shows also comparatively smaller
values. As it is shown in Fig. 9, the water temperature in J-M waters is higher
than the waters A-B, C-D and D-F.
3) The length of C. cristatus in N-0 waters is larger than the specemens in
J-M waters of the north. The reason may be attributable to the fact that thosespecimens of cold water origin come from Kamtchatkan side4) Calanus cristatus collected in the water Q-R stations has the smaller bodylength and water temperature is higher as shown in Fig. 9. But station P has arather larger size Calanus cristatus in spite of the lower water temperature than stations
Q-R. This reverce correlations should be examined again in the further investigation.
5) In the north waters of the east Aleution Islands stations T-Z, the intermediate cold waters do not so develop. The surface water temperature is alsohigh and this tendency coincides with the small size of Calanus cristatus in thesewaters except stations X and S. It is interesting to note, further, the large sized
Calanus cristatus specimens are found in the station S and X in the very neighbouring
waters. Calanus cristatus in station S groups are collected from the stomachs offin whales caught in the neighbouring waters.
Although plus and minus standard erorrs overlap one another as a series distribution from the west to the east, there are some correlations between the watertemperature and body length of Calanus cristatus, as it has been established (Wiborg,1954).
These groups of Calanus cristatus constitute fin whales feeding ground fromspring to summer. And it has been observed that the prosperity of Calanus cristatus
in each whaling grounds is different in every season.
When the relation between the body length of Calanus cristatus and water temperatures is examined, the water temperatures below 500 m depth do not show somuch difference among stations. They are nearly constant values about 3°C at
800 m depth, however, the water temperatures at 300 m depth show lower values
at the stations where the larger Calanus cristatus has been collected. The watertemperaturs at stations A-B. and E-F are lower than the values at J-M and T-X
stations. It is more likely that if the development of Calanus cristatus affected by theintermediate cold waters in the Bering sea, then it is affected by the slight difference

T. NEMOTO

166

of water temperatures at 300 m level. The intermediate cold water generally
develops in the west waters of the Bering sea especially in the A-B and E-F areas.

AB

500

1,000,

r

f
CD

10

500 ·

EF
l'

sool

1,000

I

!.OOO·
l.000

!,OJ
1.000

Fig. 9. Water temperature profile in the Bering sea and the adjacent waters. Alphabet
shows the position in Fig. 7.
42

41

sa

40

-:5

"'c
"'
""

""
co

39

0

38

37

36
b

d

g

rn

Stations

Fig. 10. Cephalothorax body length of Calanus plumchrus in the Bering sea and adjacentwaters. Rectangles represent means, plus or minus two standard errors.

The body length of Calanus cristatus found in J-M stations is smaller than thosein C-D stations, although the coldest point of intermediate cold waters is the nearly
the same. In the stations Q-R and T-X where the small length Calanus cristatus
is found, the intermediate cold water does not so develop. Further, the surface
water temperature shows l0°C or more. The body length of copepodite stage
5 Calanus plumchrus in the collected specimens is illustrated in Fig. 10. The different
body size in each Calanus plumchrus group is already discussed by Heinrich (1960).

DISTRIBUTION OF CALANUS IN THE BERING SEA

167

According to his description, the cephalo-thorax length ranging 3.3 and 4.1 mm is
obtained in the west Bering sea.
Calanus plumchrus specimens in the adjacent waters to the east Aleutian Islands
and Kodiak Is. have rather large body size than the west groups in general. Thistendency is attributable to the fact that the Calanus plumchrus treated here may
be the second group in Heinrich's materials, which attains to their copepodite stage
5 in the summer when the surface water temperature is considered higher. They
propagate and distribute in the surface in the western side of the Bering sea andconstitute feeding grounds of sei whales in summer.
SWARM OF CALANUS CR/STATUS AND C. PLUMCHRUS

In the feeding ground of the Bering sea and its neighbouring waters, fin whales like
Calanus cristatus as their food. But those fed on Calanus plumchrus are rather scarcein number when compared with other food taken. On the other hand, sei whales
feed usually on Calanus plumchrus (Nemoto, 1959). It is reasonable to consider that
two Calanus copepods have different attractions for fin and sei whales. Some examples of the weight of stomach contents found in fin and sei whales are given in
Table 1. This table shows a fairly good correlation between weight of stomach
contents and feeding quantity stage observed by naked eyes.
TABLE I.

THE WEIGHT OF COPEPODS CONTENTSIN STOMACHS OF FIN WHALESSpeciesCalanus cristatus

Calanus plumchrus

Metridia lucens

WeightStage

107 kg
87
75
"
45
"
30
"
30
"
26
"
18
"
72
"
64
25
16
"
80

rrr
R
rrr
rr
rr
rr
rr
rr
R
rrr

"

rr
rrr

Generally speaking, the quantity of Calanus plumchrus found in baleen whales
is smaller than Calanus cristatus, which suggests the patch of Calanus cristatus is heavier
than that of Calanus plumchrus in the sea. Fin whales usually take their food byswallowing method, which needs the food plankton patch to be in suitable density
and mass in the sea. Of course, Calanus plumchrus also sometimes may make heavy
swarms.
From the digestion stage of the stomach contents, it is considered the swarm
of Calanus cristatus and euphausiids are sometimes swallowed instantaneously or successively in the short period. In the stomachs of baleen whales, Calanus copepods

168

T. NEMOTO

sometimes have been found along with other euphausiid Thysanoessa longipes. Calanus cristatus is also found with Thysanoessa inermis and Euphausia pacifica, however,the number of occurrences is far small as given in Table 2. The shore living
euphausiids Thysanoeasa raschii and T. spinifera have scarecely been found with
Calanus cristatus, It is attributable to the fact that the main distribution of Calanus
cristatus has been restricted in the region of the sea where the bottom is deep as
it is discussed in the former part. Thysanoessa longipes is only a off shore euphausiids
in the north Pacific, the anual cycle of which has no relation to the shelf or theshallower sea. The possibility of the constituting mingled swarms of Calanus cristatus
and Thysanoessa longipes is also probable.
TABLE 2. MIXED SWARM FORMATION IN CALANUS COPEPODSAND EUPHAUSIIDS IN THE BERING SEA AND ADJACENT WATERS
Thysanoessa
longi pes

inermis38
3

10

Calanus cristatus
C. plumchrus
C. cristatus &C. plumchrus
170-E

Euphausia
pacifica

spinifera

3

4

172'E

170'E

17l'E

J-L

0

53'

0

53'

0

53'

0

0

0

0
0
•

I

52'i'==l================"52'
172'E
170'E

..

ooeo®O00•052 ll==============ll52'
170° E
17l'E

Fig. 11. Distribution of the foods of fin whales in the adjacent waters to Attu Is. in
1953. Black-Calanus cristatus, with dot-Euphausiids, Open-Vacant stomach.

On the other hand, few cases of Calanus plumchrus have been found in thestomachs of baleen whales as a mingled swarm with other euphausiid as given in
Table 2. Only three cases of Calanus plumchrus are found in the stomachs of baleen
whales along with Thysanoessa longipes, and each one case with Thysanoessa inermis
and T. spinifera respectively.
As an example of the distribution of Calanus cristatus and euphausiids, the feeding
chart of fin whales is given in Fig. 11, which shows the stations where fin whalescaught with or without plankton contents in their stomachs in 1953. In the southwest waters of Attu Is. in 1953, the most part of fin whales had been feeding on
Calanus cristatus by the first in July. In the middle of July, there are cencentrations

DISTRIBUTION OF CALANUS IN THE BERING SEA

169

of Calanus cristatus and euphausiids in certain areas from the distribution of the catchof fin whales with them in their stomachs. Calanus cristatus in the waters where thedominant occurrences of Calanus cristatus were observed in the middle had extinctedin the late of July as shown in Fig. 11. The swarms of Calanus cristatus must havesubsided down deeper waters for reproduction. The surface water temperature isconsidered to be the direct reason for the subsiding of Calanus cristatus in this case
(Nemoto, 1959). The southern groups of Calanus cristatus appeared in the samewaters still in the late of July as shown in Fig. 11. This would suggest that thesubsiding of Calanus cristatus occurs successinely by physical condition of Calanus
and environmental factors.
SUMMARY

1. Based on the data of stomach contents of baleen whales and plankton nets,
the distributions of Calanus cristatus and C. plumchrus are discussed. The probablecorrelation between the distribution of fin and sei whales in their feeding grounds
and the distribution of Calanus cristatus and C. plumchrus is given. The main concentration of Calanus cristatus in spring and summer seasons of the Bering sea coincides with the feeding grounds of fin whales, and Calanus plumchrus with sei whales.
2. Adult specimens of both species have not been appeared in the stomachs
of baleen whales as their food. Some occurrences of adult C. plumchrus in the netcollentions are observed maninly in the shallower waters of the Bering and Chukchi
seas.
3. The cepharo-thorax body length of two Calanus is examieed. The fairly
close correlations between water temperature and body length are observed in
Calanus cristatus, and the related body size groups are found in the neighbouring
waters. But the different types of size groups are sometimes found in the very nearposition in the sea where the sea condition is rather complex.
4. Calanus cristatus sometimes may make mingled swarms with euphausiids
Thysanoessa longipes, or Calanus cristatus which often distribuetes in the very nearwaters to the swarm of Thysanoessa longipes.
REFERENCESANRAKU, M. (1954). Gymnoplea copepoda collected in Aleutian waters in 1953. Bull. Fae. Fish. Hokkaido
Univ., 5(2) : 123-36.
- - (1954). Copepods collected on the whaling grounds off northern Japan and around Bonin Islands. Bull.
Fae. Fish. Hokkaido Univ., 5(1): 1-8.
BRODSKY, K. A. (1950). Calanoida of the far eastern and polar seas of the U.S.S.R. Fauna of U.S.S.R., 35:
1-442.
BoGoRov, V. G. & VrNOGRADOV, M. E. (1960). Distribution of zooplankton in the Kuril-Kamtchatka
region of the Pacific ocean. Trudy Inst. Oeeanology., 34: 60-84.
HEINRICH, A. K. (1957). The propagation and the development of the common copepods in the Bering sea.
Trudy V. Gidrobiolog. 0., 8: 143-62.
- - (1960). Seasonal phenomena in plankton of high and temperate latitudes. Trudy Inst. Oeeanology.,
LI: 57-81.

170

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