THYSANOESSA MACRURA AS A FOOD OF BALEENWHALES IN THE ANTARCTIC
TAKAHISA NEMOTO AND KEIJI NASU
A giant euphausiid, Euphausia superba has been only considered as
the staple food of baleen whales in the Antarctic waters, because almost all baleen whales in the Antarctic feed exclusively on the swarmsof Euphausia superba. Some other euphausiids, such as Euphausia
crystallorophias, E. frigida, E. triacantha also widely distribute from thesub Antarctic to high Antarctic zone. But few of above species havebeen noted as the food of Antarctic baleen whales. The Antarctic
neritic species, Euphausia crystallorophias is considered to bear somevalue as a food of little piked whales, some blue and fin whales in thehigh latitude of Ross Sea (Marr, 1956), however, it has never been
observed in waters out of the pack ice.
An Antarctic Thysanoessa, Thysanoessa maerura G. 0. Sars distributes largely in the Antarctic waters and it is a very common euphausiid
next to E. superba (Rustad, 1930 ; Ruud, 1932), though it has neverbeen observed in the stomachs of whales in previous studies except threecases by Peters (1956). Rustad (1930) describes on this point thatE. superba and Thysanoessa maerura play the predominant part as foodfor larger animals, e.g. whales seals, and birds. Of the two species
E. superba seems to play the greater part, this species alone being
recorded from almost all stomach contents containing euphausiids.
And T. macrura has never been found as a staple diet of baleenwhales.
In 1956, Japanese whaling expeditions operated in the so called whaling area I and VI where the whaling operation had been forbidden untilthat year. In some euphausiids samples collected through above operations, dominant appearances of Thysanoessa maerura are observed.
These Japanese collections covered wide areas from 50° east to 100°
east longitudes, from 170° west to goo west longitude. And so many
numbers of samples have been collected in the following season of 1957.
T. maerura is found again in considerable number of samples. Thus,
T. maerura is considered to play some part as the staple food of
Antarctic baleen whales, though in has never been noticed by any investigations before this report.
The result that Thysanoessa macrura was not observed in collectionsin 1955, might be due to the fact that the samples of 1955 were restricted to the waters from goo east to 130° east longitude in the so-called
193

K. NEMOTO AND K. NASU

194

whaling area IV. The numbers of whales examined and samples collectedin the successive years are listed in tables from 1 and 2.
TABLE 1. NUMBER OF WHALES EXAMINED AND SAMPLES COLLECTED IN
THE WATERS WEST OF 100° E IN 1956 AND NUMBER OF WHALESEXAMINED AND SAMPLES COLLECTED IN THE WATERSEAST OF 170° W IN 1956
WestWhale species

East

Whale species

Number of whales

Sei
Fin Blue Humkback

Number of whales

Fin BI ue Humkback Sei

Whales examined
Whales fed
Collected samples
Unknown

978496258Whales examined
Whale fed
Collected samples
Unknown

3535
2477
69

TABLE 2.

9752
419555111278
148
37145
92
365

NUMBER OF WHALES EXAMINED AND SAMPLES COLLECTEDIN THE WATERS EAST OF 170° E IN 1957
Whale species

Number of whale

FinBlue

Humkback

Sei

Whales examined
Whales fed
Collected samples
Unknown

5832
2478
301
1611
311
3771474133555Description of T. macrura G. 0. Sars
The rostrum is narrow and lanceolate, reaching to a little back to theend of the first antenuular segment. Lateral margin of carapace beara denticle on its two-third from the tip of the margin. Eyes are large
with a transverse constriction above the middle. Antennulae with theupper flagellum is somewhat shorter than the sum of the two distal peduncular joints. Second thoracic legs are very elongate, with the merus
reaching beyond the end of the antennular peduncle. Oschium and merus
are very strong and heavy. Carpus somewhat is curved distally bearing
about 6 or more setae. The propodus is about one-fourth as long as
carpus, bearing about 7 to 14 setae on both margins. The dactylus isbroad and bears 4 to 5 strong setae and 3 to 5 slender setae. Abdomen without any keel or spine, telson bears two pairs of dorsal spines.
Six abdomnal segment is fully as long as the sum of the two preceedingsegments. Preanal spine of females is indented, but rather smooth inmales. This sexual distinction is well developed in young specimens.
Terminal process of the copulatory organ distally expanded in both sides
and especially outwards. Proximal process and lateral process are rather

THYSANOESSA MACRURA AS A FOOD OF BALEEN WHALES

195

slender and terminal parts curved. Spine-shaped process is curved
through about 90° angle. Females attain to about 29 mm from the tipof the rostrum to the last of telson, on the other hand the adult males

Fig. 1. Adult female of Thysano(issa macrura G. 0. Sars.

AFig. 2. Male copulatry organs of T. macrura A.

AB

inmature male B mature male.

BcFig. 3. Preanal spines of T. macrura. A. inmature female. B. maturefemale C. mature maleare far smaller, only 20 mm in the largest specimens as described byHansen (1911). Females are always dominant in number among thepatches of T. macrura like northern Pacific euphausiids.

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K. NEMOTO AND K. NASU

OCCURRENCE

Thysanoessa macrura is found in our collections as shown in tables 3and 4. In 1956, 5 samples are found containing T. macrura in 105 ones.
No other euphausiid is observed in these 5 samples, and observations bybiologists on board confirm that the stomachs were satiated only withthis T. macrura in above 5 samples. The further collections in 1957, show
also such ratio of occurrences as in the previous year. Of course othercollected samples consist of only Euphausia superba in various stages.
The mingled collections with E. superba and T. macrura are also observedin less number in both years. In these mingled collections, specimensof E. superba are rather young ones and full grown euphausiid havenever been observed. So the sizes of E. superba is not so large as adultspecimens in these mingled samples.
The eyes of T. macrura is fragil like the North Pacific Thysanoessa
T. longipes (Nemoto, 1957). When T. macrura is found among Euphausia
superba, the eyes of T. macrura are nearly digested. On the other hand,those of E. superba remain undigested.
As shown in table 5, the occurrences of T. macrura differ in eachmonth of the whaling season. The most dominant appearance is observed in the late decade of January and the first decade of February.
In other decades, comparatively few samples of T. macrura are observed,
and we see none of them in many samples in March. From above facts,some seasonal or distributional pecuriarity of T. macrura is suggested.
In 1956, a Japanese fleet operated in the waters from 40° east to 90°
east longitudes so called whaling area III. From these 30 samples,
T. macrura is found in two samples collected in the waters near 40°
east line, and none of T. macrura is found in other collection from 50°
90° east longitude as shown in figure 4. And 5 samples of T. macrura
are found in the waters near 130° east longitudes
In 1957, many samples of T. macrura are collected in the area from135° west to 100° west longitudes. Except the waters near the pack ice
in this area, T. macrura is considered to be important as a food ofwhales as shown in figure 5. In the waters from 170° west to 140°
west, many collections of stomachs of whales are all E. superba but one
T. macrura. In this area we have also none of T. macrura in the previous year. It may be considered from above facts that E. superba
does not distribute so uniformly, and perhaps E. superba is scarce orT. macrura is very common in this area. Thus many whales that fedon T. macrura may be found in our researches.
During the Antarctic whaling season in 1957, oceanographical data
were collected on the board of the factory ship "Nisshin-maru" at in-THYSANOESSA MACRURA AS A FOOD OF BALEEN WHALES

197

terval of 4 hours, the discussion of which will be published after the examination and we may state simply its quatation here for our study.
Oceanographic conditions of January and February show, generally, water
masses of the lower temperature and salinity are formed by melting ice
towards the north. On the other hand, water masses of the higher
temperature and salinity run towards the south.
TABLE 3. OCCURRENCE OF THYSANOESSA MACRURA IN THE JAPANESECOLLECTION OF STOMACH CONTENTS OF BALEEN WHALES IN 1956
East of 170° W
Whale species

Euphansiid
species~'E. superba
T. macrura

FinBlue

Hunpback

65433

West of 100° E
Whale species

Euphansiid
species

FinBlue

Hunpback

23141

E. superba
T. macrura
E. superba
T. macrura

1TABLE 4. OCCURRENCE OF THYSANOESSAMACRURA IN THE JAPANESECOLLECTION OF STOMACH CONTENTS OF BALEEN WHALES IN 1957
Whale species
Euphansiidspecies

E. superba
T. macruras_ superba &T. macrura
TABLE 5.

SpeciesE. superba
S. superba &T. macrura
T. macrura

FinBlue274
2136

Hunpback

Sei

13

5

6

OCCURRENCE OF THYSANOESSA MACRURA IN 1957
JanuaryFebruary,------'~,,-----------~

18

12
27

2March,-------''----,__123

1220

52

55

87

41

26

4298

3

13

Between the currents towards the north and the south the cycloniceddies are formed, therefore, the isotherms and the isohalines bend far
laterally, and the whaling grounds in the Antarctic waters is locatednear the cyclonic eddies, that is, whaling grounds are formed in thecenter of the water boundary forming cyclonic eddies as Ruud (1929) andUda (1954) describe. It seems that the krill T. macrura is concentrated by the water current on such areas.

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K. NEMOTO AND K. NASU

As above mentioned, in 1957 the area where T. macrura occurred wascovered on the waters from 135°W to 100°W longitude, and the greatest
concentration was observed at the adjacent waters of 110°W longitude.
Generally speaking in the area were T. macrura had been dominaratly
appeared the temperature and salinity were approximately 0°C and33.60°/ 00 respectively in our observations. So T. macrura may distribute
relatively high temperature and salinity and may be the food of baleen
whales of which are distributed off comparatively warmer waters in theAntarctic.
SUMMARY
An Antarctic Thysanoessa, T. macrura is found as a stable food ofbaleen whales. Considering dominant appearances of T. macrura instomachs of whales, it must bear significance for the Antarctic whalesin the certain Antarctic area.
T. macrura is considered to distribute relatively higher temperatureand salinity than Euphausia superba.
REFERENCES
HANSEN, H. J. (1931). The genera and species of the order Euphausiaces, with accountof remarkable variation. Bull. Inst. Oceanographique, Monaco, 210: 1-54.
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
NEMOTO, T. (1957). Foods of baleen whales in the Northern Pacific. Sci. Rep. Whales
Res Inst., no. 12: 33-89.
PETERS, H. (1955). Uber das Vorkommen des Walkrebschens Enphausia superba Danaund seine Bedeutung fiir die Ernahrung der siid!ichen Bartenwale. Arch Fishereiwissenchaft, 6(5): 288-304,
RUSTAD, D. (1930). Euphausiacea with notes on their biogeography and development.
Sci Res. Norw. Antarc. Exped. 1927-28 and 1929-30, co. 5. Olso.
RUUD, J. T. (1932). On the biology of southern Euphausiidae. Hvalriidets Skrifter no. 2.
UDA, M. (1954). Studies of the relation between the whaling grounds and the hydrographical conditions (1). Sci. Rep. Whales Res. Inst., no. 9: 179-87.

THYSANOESSA MACRURA AS A FOOD OF BALEEN WHALES

16o"WISO'W

140°W... ·.
.
. ....... "':. ··.:....

170W

JIO'W

IOO'W

.. . ... ...

- <Y-i.- ~....... ,,.,.....

.. • •=:-: :··!>'?:·· ••/~/

120'\v

130'\v

199

so'W

_,/

((;7'180° /Occurrences uf T. macrura in the collected samples in the Antarctic waters in 1956.

Fig. 4.

IScJw

140°w

130'\v

120'\v

II o"W

100'\v

·:·

90°w

170'W
os/i;,<:>,,/........

/:. "'o'°)/18o"'\I;:\?
//Fig. 5. Occurrences of T. macrura in the collected samples in the Antarctic waters in 1957.