_/AN AMPHIPOD, (PARATHEMISTO GAUDICHAUDII)
AS A FOOD OF THE ANTARCTIC SEI WHALE
TAKAHISA NEMOTO* AND KWANG IL YOO*

An Antarctic amphipod, Parathemisto gaudichaudii (Guer.) is extremely abundant in
the circumpolar belt around the Antarctic convergence (Baker, 1954; Kane, 1966).
It forms a considerable part of the food of sei whales in the Antarctic as well as in thewaters between the Antarctic and subantarctic convergence (Nemoto, 1959; 1962).
All materials treated here have been collected mainly from the stomach contentofsei whales caught by Japanese whaling expeditions from 1964 to 1967 in the Antarctic. Some other specimens collected from plantkon tows carried in 1957 and thestomach content of baleen whales were also examined.
These data on the food of sei whales reveal the distribution of P. gaudichaudii
which is very important as the food of sei whales, and covers the lower subantarctic
waters. A short discussion on the feeding habit of this species is also given.
FOOD OF SEI WHALES

P. gaudichaudii was reported as the food of sei whales in the Antarctic waters byNemoto (1959), and its occurrence has been summarized in recent works (Nemoto,1962; Doi, Ohsumi, and Nemoto, 1967).
The occurrence of P. gaudichaudii as the food of sei whales (Balaenoptera borealis)is shown in Table 1 and 2, in which the amphipod forms a considerable part of thefood. The occurrence of this amphipod as the whale's food in recent years isevidently due to the shift of the whaling ground from the higher Antarctic wates tothe comparatively lower latitudes of the Antarctic and northern waters of the Antarctic convergence.
The catch of sei whales in 1964-1965 season was concentrated somewhat in thewaters south of the Antarctic convergence, but the main catch of sei whales in 19651966 was obtained from the northern waters of the convergence. This may be dueto the fact that the copepods and amphipods form a major part of the food species,
although there may be some misidentification of food species. In 1964 most of theoccurrence of P. gaudichaudii was observed along the Antarctic convergence (Figs. 1and 2).
DISTRIBUTION OF P. GAUDICHAUDII

P. gaudichaudii is an oceanic swarming species of the Amphipoda-Hyperiidea and isfound mainly in surface waters (Kane, 1966). This species has been described not
only in plankton collections, but also in many fish stomachs (Hurley, 1959). The* Ocean Research Institute, University of Tokyo.
Sci. Rep. Whales Res. Inst.,
No. 22, 1970, 153-158

154

NEMOTO AND YOO

southern limit of this species has been discussed by various authors (Bowman, 1960;Hurley, 1961; Kane, 1966). It is suggested that it might occur south of the Antarctic convergence or divergence (Barnard, 1930). Bary (1959) also described theoccurrence of P. gaudichaudii in the south of subtropical convergence according totemperature-salinity and plankton diagram. Hurley (1961) and Kane (1966)
considered further that P. gaudichaudii is the species distributing in warm water northof or in the subtropical convergence region, in the oceanic cold water south of thesubtropical convergence region and colder water south of the Antarctic divergence.
TABLE I. STOMACH CONTENTS OF SEI WHALES CAUGHT BY TWO JAPANESEWHALING EXPEDITIONS IN THE SOUTHERN OCEAN IN RECENT YEARS

None
Copepods
Euphausiids
Decapods
SquidsFishAmphipods
Total

1964-'65 season

1965-'66 season

5356
23369360161119205

7152
2180
774
65
52113811316

TABLE 2. STOMACH CONTENTS OF SEI WHALES CAUGHT BY JAPANESEWHALING EXPEDITIONS IN THE SOUTHERN OCEAN IN 1966/1967 SEASON
Quantity*Food Species
0None
Copepods
Euphausiids
Amphipods
Amphipods and Copepods

r

rr

rrr

R308
24434190
161747331834472121130* R : Much, rrr : More than half,

rr : less than half,r : little.

In the north hemisphere, the records of P. gaudichaudii was only from the Atlantic, but has not been recorded in the North Pacific (Dunbar, 1954; Kane, 1966), andthis would be one problem to be solved in the future investigation.

FEEDING HABIT OF P. GAUDICHAUDII

Three forms of the species P. gaudichaudii have been considered by recent investigations (Hurley, 1959), however, most of the observed specimens are f. thomsoni or"long-legged" form, which is referred to as f. bispinosa (Kane, 1966).
The observation offeeding habitin living specimens shows that the third peraeopod acts very quickly to seize zooplanktons, the action ranges of each peraeopod areSci. Rep. Whales Res. Inst.,
No. 22, 1970.

ANTARCTIC AMPHIPOD, PARATHEMISTO GAUDICHAUDII

155

schematically in Fig. 3, as semi-circle. The fourth and fifth peraeopods also
play some part in the action, but their spines and setae along the inner edge of thelegs are not so well-developed as third peraeopod. The third peraeopod has welldeveloped seizing setae and spines (Plate I-1), the wide range of the reach is effective
for the active zooplanktons. The first and second peraeopods have well-developed
sickle-shaped terminal segments and they are considered to hold the caught prey30°

150°

Fig. 1.

w 1ao E
0150°

Distribution of amphipods as the food of sei whales in the southern hemisphere.

and carry it to the mouth-part. The chellae in the terminal segment of the second
gnathopod may tear the prey and carry to the mouthpart. The chellae in gnathopods confirm it. In addition to the feeding action, the sixth peraeopod keeps
the body in right position in their swimming and feeding. The feeding habit inP. gaudichaudii is very similar to that described for P. gracilipes by Kane (1963)
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

156

NEMOTO AND YOO

who says " The posterior peraeopods were used to grasp and hold the prey and thefirst two peraeopods to hold it in place and direct the part to be eaten towards thegnathopods. These in turn seemed to be tearing off pieces which were pushed
towards the continuously active mouthparts ".
The mandible of P. gaudichaudii is typical carnivorous one. It completely lacks
the pars molaris of the same type of euphausiids which is very effective in crushinghard shells like diatom.
s40

4550_,, ,

55

Amphipods

60
3060

40

40
45

.... ,

50..... ---- - - - - --'A.O .
100

55

300 500

Copepods

30

40

45

, ...

SUSS

--Euphausiids

606LO~~..l!::.~---1..~~.J.._~-1=-~~:':--~-:--~:--:';:--~-7,:-~---;3~0~:--4~0~---;~~45:;:.-~--=&,--____:~~--=&:------'i:-~-'ii;~~'I07'"~--..::--~.-~,-~~,-~~~~

so--A.O.

55
LOOO

60

Catchsowso

4.0

30

20

1010203040SOE

Longitudes

Fig. 2.

Occurrence of food planktons in the stomach of sei whales in the Antarctic in 1964-65
and 1965-66 seasons.

The stomach also lacks the inner spines and mill-like cluster spines (Plate 1-2)
which are common in herbivorous euphausiid species such as Euphausia superba (Nemoto, 1967). The examination of stomach contents of P. gaudichaudii reveals thatthey mainly feed on zooplankton, especially copepod (Plate 1-3, 4,). In thestomach of large P. gaudichaudii three or more copepods of 3 mm in cephalothorax
length were often observed (Plate 1-3). In some cases, appendages of euphausiid
were also found in its stomach (Plate 1-5). Plate 1-6 shows diatoms in the stomach
Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

ANTARCTIC AMPHIPOD, PARATHEMISTO GAUDICHAUDII

157

of young amphipod, and it suggests that the phytoplankton fragments are originatedfrom the fed copepod or else, that the young P. gaudichaudii might take phytoplankton.
The specimens in the same patch were often found to have fed on equal quantityof copepod, suggesting that they came across the patch of copepod and took the patch
all at once.

Fig. 3.

Schematic illustration of movement of thoracic legs of Parathemisto gaudichaudii in feeding.

In conclusion it can be said that P. gaudichaudii is one of the typical voracious
carnivorous zooplankton species, and it constitutes a considerable part of sei whale's
food in the Antarctic. Sei whales feed also on carnivorous zooplankton, P.
gaudichaudii in the southern hemisphere, and their feeding behavior is different fromthat of the other baleen whales such as blue and fin whales that feed on herbivorous
euphausiid, Euphausia superba and Euphausia vallentini.
It is also suggested that P. gaudichaudii consists of another pathway in food chain
as well as euphausiid groups in the southern hemisphere (Nemoto, 1966), while
correlations in food web are present as following series: Phytoplankton-smallsized zooplankton, Copepod-carnivorous Amphipod, P. gaudichaudii-Sei whales.
This chain is the typical one which is related to the carnivorous zooplankton in theopen ocean.
Sci. Rep. Whales Res. Inst.,

No. 22, 1970.

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NEMOTO AND YOO

REFERENCESBAKER, A. DE C., 1954. The circumpolar continuity of Antarctic plankton species. Discovery Rep., 27: 201218.
BARY, B. M., 1959. Ecology and distribution of some pelagic Hyperiidea (Crustacea, Amphipoda) fromNew Zealand waters. Pacific Sci., 13: 317-334.
BARNARD, K. H., 1930. Amphipoda, Nat. Hist. Rep. Brit. Antarct. ('Terra Nova') Exped. 1910, .(ool. 8(4):307-454, text-figs. 1-63.
BOWMAN T. E., 1960 Thee pelagic amphipoda genus Parathemisto (Hyperiidea: Hyperiidae) in the North
Pacific and adjacent Arctic Ocean. Proc. U. S. nat. Mus., 112: 343-392.
D01, T., S. 0HSUMI, and T. NEMOTO, 1967. Population assessment ofsei whales in the Antarctic. Norsk Hvalfangst-Tid., 56(2): 25-41.
DUNBAR, M.J., 1954. The amphipod Crustacea of Ungava Bay, Canadian Eastern Arctic. J. Fish. Res.
B. Can., 11(6): 709-798.
HURLEY, D. E., 1955. Pelagic amphipoda of the sub-order Hyperiidea in New Zealand waters. I. Systematics. Trans. roy. Soc. N • .(., 83(2): 119-194.
HURLEY, D. E., 1959. Amphipoda Hyperiidea.B.A.N..(. Antarctic Research Expedition Rep., Ser. B, 8(5): 107114, figs. 1-2.
HURLEY, D. E., 1961. Pelagic Hyperiidea (Crustacea: Amphipoda) collected by the yacht' Magga Dan'between Australia and Antarctic with some notes on their distribution. N . .(. J. Sci., 4(3): 597-603.
KANE,]. E., 1962. Amphipoda from waters south of New Zealand. N. Z· J. Sci., 5(3): 295-315.
KANE, J.E., 1963. Observations on the moulting and feeding of a Hyperiid Amphipoda. Crustaceana,6(2): 129-132.
KANE, J.E., 1966. The distribution of Parathemisto gaudichaudii (Guer.), with observations on its life-history
in the 0° to 20°E sector of the Southern Ocean. Discovery Rep., 34: 163-198.
MACKINTOSH, N. A., and J. F. G. WHEELER, 1929. The southern blue and fin whales. Discovery Rep., 1 :257-540.
NEMOTO, T., 1959. Food of the baleen whales with reference to whale movements. Sci. Rep. Whales Res. Inst.,
14: 149-290.
NEMOTO, T., 1962. Food of baleen whales collected in recent Japanese whaling expeditions. Sci. Rep.
Whales Res., Inst., 16: 89-103.
NEMOTO, T., 1966. Feeding of baleen whales and krill, and the value of krill as a marine resource in theAntarctic. Symposium on Antarctic Oceanography, 240-253.
NEMOTO, T., 1967. Feeding pattern of euphausiids and differenciations in their body characters. Inform.
Bull. Planktology Japan, Comm. No. of Dr. Y. MATSUE 60th Birthday, 157-171.

EXPLANATION OF PLATE
I-Seizing spines in third peraeopod. 2-Stomach wall of Parathemisto gaudichaudii. 3-Stomach contentsof P. gaudichaudii. 4-Stomach contents of P. gaudichaudii. 5-Stomach contents of P. gaudichaudii.
6-Stomach contents of P. gaudichaudii.

Sci. Rep. Whales Res. Inst.,
No. 22, 1970.

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