FOODS OF BALEEN WHALES IN THE GULF OF ALASKA
OF THE NORTH PACIFIC
TAKAHISA NEMOTO AND TOSHIO KASUYAThe foods of baleen whales in the North Pacific have been studied by Banner (1949),Ponomareva (1949) and Nemoto (1957: 1959: 1962). But these are results on thewhales caught in the north west part of the North Pacific in general. In recent Japanesewhaling, comparatively many baleen whales have been caught in the Gulf of Alaska
and the foods of those baleen whales have been collected as the continuance ofthe works carried out up to these days.
The materials of foods of baleen whales have been collected in 1961, 1962 and1963 on the factory ships as it has been done. Some materials were also collected
on right whales in 1961, which were permitted to catch under the special permission for the scientific research.
The distribution of euphausiids, which is important for whales foods, have beenstudied by Banner (1949), Nemoto (1959: 1962) and Brinton (1962), and theseresults are of great help for the general consideration of the distribution of foodsof baleen whales.
DISTRIBUTION OF BALEEN WHALESThe Gulf of Alaska waters was famous for the whaling ground for right whales in 19
century (Townsend, 1935). Fin and sei whales, however, mainly constitute therecent catch of baleen whales as illustrated in Fig. 1 and Fig. 2. Both fin and sei
whales are common in the mid-gulf where right whales were caught, but the fin whale
catch is sometimes restricted in the shore waters in a certain year, for example 1963,
as shown in Fig. 1. But fin whales were caught in the off waters in 1962 possibly
owing to the foods distributions in the Gulf of Alaska.
The distribution types of baleen whales were discussed in a previous report(Nemoto, 1959). Sei whales are ocean dinizen and they seem not to approach
shallow inshore waters and the marginal sea. This is also confirmed in the recent
catch as shown in Fig. 2. On the other hand, fin whales feed also in the shallow
coastal waters and marginal seas as in the open ocean.
Blue whales, the euphausiids feeder and ocean denizen, are caught in the edge of
Alaskan continental shelf where euphausiids are most prosperous through the summer season.
FOODS OF BALEEN WHALES

Collected stomach contents of baleen whales have been examined and plotted inFigs. from 3 to 6. The occurrences of euphausiids and copepods in fin whales
are given as the percentage occurrences in each 1 latitude and 2 longitudes squarein Fig. 3. As it is clearly shown, copepods are observed in the off waters and45

46

T. NEMOTO AND T. KASUYA

euphausiids are mainly distributed in the shore waters as the foods of fin whalesin 1963.
Three species of euphausiids, Euphausia pacijica, Thysanoessa inermis and T.
spinifera are main euphausiids occurred in the stomachs of baleen whales in thecoastal waters.
The distributions of North Pacific euphausiids also have been discussed byBanner (1949), Brinton (1962) and Nemoto (1962). Six northern Pacific euphausiids Euphausia pacijica, Thysanoessa inermis, T. longipes, T. raschii, T. spinifera andTessarabrachion oculatus are all common in the Alaskan Gulf although the depth andhorizontal distributions are somewhat different.
w

16CI°

w

140°

Fin Blue~G\10.
-•55'60°

51-_60---Fig. 1. Catch distribution of blue and fin whales by Japanese whaling expeditions in the Gulfof Alaska in 1963.

Euphausia pacijica is recorded from the most northern Gulf of Alaska by Banner( 1949). The geographical distribution of Euphausia pacijica established by Brinton( 1962) endorces the wide distribution of this species in the subarctic Pacific, and its
importance for marine animals may be valid in the southern waters (Nemoto, 1959:Brinton, 1962). Euphausia pacijica is found in both oceanic and neritic waters invast swarms (Banner, 1949), but baleen whales in the Gulf of Alaska took it mainlyin the continental shelf edge of the gulf. The size of the collected specimens islarger comparing with specimens in southern waters (Unpublished data in theWhales Research Institute).
Thysanoessa spinifera is one of the most important euphausiids in the Alaskan Gulf
as a food of baleen whales. It was found in the shore waters of the Aleutian Islands
only in the eastern side (Nemoto 1959: 1962), but it was never found in the west

47

FOODS OF BALEEN WHALES

waters of the Bering sea and the North Pacific (Nemoto, 1959: 1962: Brinton, 1962).
It distributes from the eastern part of the Aleutian Islands to the southern California
along the shelf waters. It is considered to be the most dominant euphausiids species
in the neritic waters of the Gulf of Alaska. Baleen whales, blue, fin and humpback
whales, which are swallowing type in feeding (Nemoto, 1959) are possibly feed on
this T. spinifera in those waters. T. spinifera appeares to be restricted to depths ofless than 100 meters (Brinton, 1962), and it is found also in the daytime in theshallower waters in near-shore waters.

••,,.,,.

----x55'

50'50'150•140°w

Fig. 2. Catch distribution of sei whales by] apanese whaling expeditions in the Gulf of Alaska
in 1963.

The third species, Thysanoessa inermis is the most important euphausiids species
in the waters of the east Bering Sea and off Kamtchatka waters (Nemoto, 1959), but
it is rather scarce as the foods of baleen whales in the Gulf of Alaska. Bannerreported it from the Gulf of Alaska and Brinton also noted the main range of T.
inermis covers arctic boreal regions of the North Pacific north of 52°N in the eastern
part. As for the morphorogical types of T. inermis, two spines form is dominant inthese areas as considered in a previous report (Nemoto, 1959: 1962), and it amounts
about 75% or more in the Gulf of Alaska waters, in the east side of the Pacific.
Another neritic species Thysanoessa raschii has been recorded in the shore watersof the Alaskan continental shelf by Banner (1949), but it has not been observed as
foods of fin and other baleen whales in the Gulf of Alaska. Perhaps it distributes
shallower and colder neritic waters along the Alaskan continent throughout winterand summer seasons.
Thysanoessa longipes on the other hand, distributes in the off waters. In 1962,

T. NEMOTO AND T. KASUYA

48

comparatively many fin whales had been caught when they were feeding onT. longipes in the mid-gulf. The concentration of T. longipes in the mid-gulf is also
shown by plankton investigations (McAllister, 1961: Brinton, 1962). It is preliminarily suggested that the relative abundance of off shore species T. longipes may
affect the migration of fin whales to those areas. The close related species, T.
inspinata has not been found in the stomachs of baleen whales caught in the Gulf ofAlaska. In 1963, T. longipes has not been found in the mid-Alaskan Gulf and fin
whales had not been observed in the area in swarms. T. longipes is also important in
the Bering Sea and southern waters of the Aleutian Islands, and annual fluctuations

60'55'55'

Fig. 3. Percentage occurrences of euphausiids (Black) and copepods (White) in the stomachsof fin whales caught in the Gulf of Alaska in 1963. Cross-Position of right whale capture.

were also observed in comparing with other euphausiids such as T. inermis and T.
raschii (Nemoto, 1959), which form the stable feeding grounds every year. Two
species of copepods, Calanus cristatus and C. plumchrus, are common as the foods ofbaleen whales in the Gulf of Alaska as in the Bering Sea (Nemoto, 1962). Fin whales
prefer Calanus cristatus as the swallowing feeding type, but a few fin whales also
take Calanus plumchrus.
Sei whales are mostly skimming feeder in the North Pacific (Nemoto, 1959),
feeding on copepods. As it is illustrated in Fig. 4, they exclusively feed on copepods
in the off waters of the Gulf of Alaska. Calanus cristatus and Calanus plumchrus areobserved as the foods of sei whales. C. cristatus is more dominant in the off waters,
although sei whales have taken C. plumchrus in the western waters of Kamtchatka
region and southern off waters of the Aleutian Islands.
Two cases of right whales which have taken Calanus prumchrus in the coastal

49

FOODS OF BALEEN WHALES
140°w

60'55'

00000
050'50'w

160°

140°

150'w

Fig. 4. Percentage occurrences of copepods (White) and euphansiids (Black) in the stomachsof sei whales caught in the Gulf of Alaska in 1963.

160'140°

150°w
N60'~

DI~'QJ' Q_\\?'
0xxxx xooo'7"'

1-f:::,,Lo.

01r-:

oOD
L:o.

55"

ft55'

D

D0DDD,,.

5G'Vi

160°

Fig. 5.

150'

140°

Euphausiids occurrences in the stomachs of baleen whales in 1962.

v:

T. NEMOTO AND T. KASUYA

50waters of Kodiak Islands show that they were skimming feeder, which coincides
with the results obtained in the waters off Japan.
1.:0·w

w

60'co'55•

660Fig. 6.

0Euphausiids occurrences in the stomachs of baleen whales in 1963.

Fig. 7.

Water masses in the Gulf of Alaska (After Doe, 1955).

The water mass of the Alaskan Gulf is described by many authors, and one
example is given by Doe (1955). It fairly well coincided with the main distributionsof the euphausiids species and copepods. Thysanoessa spinifera, T. raschii and T.
inermis are coastal species, whereas T. longipes is offshore species. The life cycle ofthe former species may be brought up in the neritic domain, but T. longipes has some

FOODS OF BALEEN WHALES

51

connections with the west waters where it is found along the boundary of the water
masses, between subarctic and Aleutian neritic waters.
SUMMARY

The foods of baleen whales in the Gulf of Alaska have been examined. The main
species of euphausiids are Euphausia pacifica, Thysanoessa spinifera, T. longipes and T.
inermis. Calanus cristatus and C. plumchrus are also important as foods of baleen whales.
The distribution of each species is discussed and possible relations between thenatural regions of the Gulf of Alaska waters and euphausiid distributions are stated.
REFERENCESBANNER, A. H. (1949). A taxonomic study of the Mysidacea and Euphausiacea (Crustacea) of the North
Pacific. Pt. 3. Euphausiacea. Trans. Roy. Soc. Canadian Inst., 28 (58) : 2-49.
BRINTON, E. (1962). The distribution of Pacific euphausiids. Bull. Scripps Inst. Oceanogr., 8 (2): 51-270.
DoE, L. A. E. (1955). Off shore waters of the Canadian Pacific coast. ].Fish. Res. Bd. Canada. 12 (I): 1-34.
McALLISTER, C. D. (1961). Zooplankton studies at ocean weather station Pin the northern Pacific ocean.
]. Fish. Res. Bd. Canada, 18 (I): 1-29.
NEMOTO, T. (1959). Food of baleen whales with reference to whale movements. Sci.Rep. Whales Res. Inst.,
14 : 149-290.
- - (1962). Distribution of five main euphausiids in the Bering and the northern part of the North Pacific.
]. Oceanogr. Soc. Japan 20th Ann., 1962: 615-27.
- - (1963). Some aspects of the distribution of Ca/anus cristatus and C. plumchrus in the Bering and its
neighbouring waters, with reference to the feeding of baleen whales. Sci. Rep. Whales Res. Inst., 17:
157-70.
PONOMAREVA, L. A. (1949). On the food planktons of baleen whales in the Bering sea. Dokal. Acad. Sci.
U.S.S.R., 68 (2): 401-3.
TowNSEND, C. H. (1935). The distribution of certain whales as shown by logbook records of American whaling. :(_oologica, 19 (1): 1-50.