SURFACE TEMPERATURE FIELD IN THE CROZETAND KERGUELEN WHALINGGROUNDSSABURO MACHIDA
Whales Research Institute, Tokyo

ABSTRACT

Some oceanographic conditions in the summer season at the surface in the
Crozet and Kerguelen Ridge regions, where the good whaling grounds ofbaleen whales occur, are discussed on the basis of the distribution of the surface
temperature observed by the Japanese whaling fleets in the 1965/66 to 1972/73
Antarctic seasons.
The surface isotherms bend northwards over the submarine rising aroundthe Prince Edward, Crozet and Kerguelen Islands. These bends of the isotherms suggest to reflect the bending of the surface current, and that it ispresumably influenced by the bottom topography. They may be also suggested that the convergence efficiency of the current is comparatively intense
north and east of these submarine risings.

INTRODUCTION

It is well known that the good whaling grounds of baleen whales occur in the Crozet
and Kerguelen Ridge regions. In these two regions right whales were taken by
the old American whalers mainly in the 19th century and pigmy blue whales werealso taken there in the early 1960's. Recently the Japanese whaling fleets havebeen often searching for the favorite haunts of the sei and fin whales in the regions.
We have little knowledge of the general oceangoraphic conditions in the Crozet
and Kerguelen whaling grounds, though the oceanographic conditions are theclose living evnvironment to the whales. A knowledge of oceanographic conditions
is fundamentally necessary to think systematic study on the environment of thehabits of various marine organisms. From this point of view, therefore, the purposeof the present study is to discuss the oceanographic conditions at the surface in the
Crozet and Kerguelen Ridge regions on the basis of the surface temperature distribution, which was observed by the Japanese whaling fleets.
MATERIAL AND METHOD

The whaling fleets have been supplying us with the data of the oceanographic conditions in the different whaling grounds. They are temperatures observed by anelectric thermometer, of which sensor is fixed to the bottom of a factory ship (ea.
10 m depth) and a scouting boat (ea. 5 m depth). As the surface layer down to a few
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MACHIDAten meters in the Antarctic Ocean is roughly homogeneous in temperature, it seems
to be reasonable to consider that there is no difference in the temperatures between
5 and 10 m depth. Therefore, they are taken as same and defined here as the surface temperature.
The surface temperatures were derived from " The survey report of the whaling grounds by a scouting boat" in the 1965/66 to 1972/73 Antarctic seasons and" The weather and oceanographic conditions at the noon position of a factory ship "in the 195 7/58 to 1972/73 Antarctic seasons. A one degree square grid was adopted
in making a monthly chart of the mean surface temperature, and isotherms weredrawn by interpolation.
The Far Seas Fisheries Research Laboratry, Fisheries Agency of Japan kindly
supplied me with the materials for this study.

50

s

0

0

Fig. I. Chart of the Crozet Ridge region showing general bathymetry.
in the 100 fathoms. (After U.S. Chart H.O. Misc. 15, 254-12).

DepthsThe Crozet and Kerguelen Ridge regions are shown with bathymetric contours in Figs. 1 and 2. Although the submarine rising around the Prince Edward
and Crozet Islands is not generally termed the Crozet Ridge (Herdman, Eiseman
and Overy, 1965 ), the Crozet Ridge is named in this study after "Atlas zur Ozeanographie" by Dietrich and Ulrich (1968).
Sci. Rep. Whales Res. Inst.,
No. 26, 1974

CROZETAND KER
GUELE
N もVHALING GROUNDS

60

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MACHIDA

274

LOCATION OF WHALING GROUNDS
Before discussing the features of the temperature distribution at the surface in the
Crozet and Kerguelen Ridge regions, the features of the catch distribution of the sei
and fin whales, which are the most important baleen whales as well as the minke
whale for the recent whaling industry, is summarized.
In these two regions right whales were abundantly caught by the old American
whalers mainly in the l 9th century, and pigmy blue whales also were bulkly caught
there in the early 1960's. The chart of the catch distribution of the right whale byTownsend (1935) and one of the pigmy blue whale by Ichihara (1966) are very usefull. According to them, the good whaling grounds of the right whale were locatedin the waters adjacent to the Crozet and Kerguelen Islands and ones for the pigmy
blue whale were rather distributed over the Kerguelen and Crozet Ridges. Sei
whales have been abundantly caught in these regions since the 1964/65 Antarctic
season and fin whales have been frequently caught in the north of 60°S since the
195 7/58 Antarctic season. The catch distribution of the sei and fin whales areshown in Figs. 3, 4, 5 and 6.
30

40
1-25
26-50
51-75
76-100
101 -

•

•

•• •·
•

•• ·•
•

SEI

..

•·
••••••••••••••

40.
·•·. . .
••••.
•••••••

050sFig. 3. Distribution of sei whales caught by Japanese Antarctic whaling fleets in
the Crozet Ridge region from the 1965/66 to the 1972/73 seasons. Light shading:
depths less than 1,500 fathoms (about 3,000 m).

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No. 26, 1974

CROZET AND KERGUELEN WHALING GROUNDS275

The Crozet Ridge Region
Sei whales were caught abundantly in the submarine rising around the Crozet
Islands, though their few catches are distributed widely on the Crozet Ridge. The
good whaling grounds of the sei whale are located in the adjacent waters to the
Crozet Islands. Although in the shallow waters around the Prince Edward Islands
it is somewhat similar in appearance to the Crozet Islands region, catches of sei
whales have been a little less than the former. The fin whale, on the other hand,also distributed widely on the ridge, and a great number of their catches is locatedon the far south-west waters to the Prince Edward Islands.
30

40

•

•••

1-25
26-50
51-75
76 - 100
100-

FIN

40

••
•

•

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••
•• ••

.. ..

0

• ••

••

"

50

s

•• ••••••. . ..

·•·

•• ••

••

Fig. 4. Distribution of fin whales caught by Japanese Antarctic whaling fleets in
the Crozet Ridge region from the 1957/58 to the 1972/73 seasons.

The Kerguelen Ridge Region
The catches of sei and fin whales are widely distributed on the ridge, though
the features of their eatch distribution is to some extent different from one on thesouthern part of the ridge. There are two heavy catches areas of sei whales over the
ridge. It appears that the whaling grounds of the sei and fin whales between 40°
and 45° S are related to the Subtropical Convergence. The fin whales seem to be
distributed dominantly south of about 53° S. These two species of whales have a
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MACHIDA

50

60

sFig. 5. Distribution of sei whales caught by Japanese Antarctic whaling fleets in
the Kerguelen Ridge region from the 1965/66 to the 1972/73 seasons. Light shading: depths less than 1,500 fathoms (about 3,000 m).

Sci. Rep. Whales Res. Inst.,
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277

CROZET AND KERGUELEN WHALING GROUNDS

•

•

50

•
••••••.......•• ..
•• • • • • •

..
••

•
'

• •••
•• •

•

••
•

...

•

•

• 60

•••• s

•

••
• ••
•

•

••

•

•

••
Fig. 6. Distribution of fin whales caught by Japanese Antarctic whaling fleets in
the Kerguelen Ridge region from the 1957/58 to the 1972/73 seasons.

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MACHIDA

278

strong tendency to be distributed on to the eastern slope of the ridge and a few ones
have been caught on to the western slope of it, except in the higher latitudes southof about 56° S, where the fin whales are widely distributed from west to east of theridge.
The different features of the catch distribution of the sei and fin whales as mentioned above may be partly caused by the difference of their foods and habitat segregation. In the Subantarctic regions of these two whaling grounds, the quantitatively important food organisms of the sei whale is Parathemisto gandichaudii, andEuphausia vallentini is important as a favorite food of the fin whale (Nemoto, 1959,
1962, 1970; Nasu, 1966; Kawamura, 1970). I do not intend to mention furthera pattern of their catch distribution, because it is not the main purpose of the present study.
SURFACE OCEANOGRAPHIC CONDITIONS
Figs. 7-21 show the distribution of the surface temperature in the 1957/58 to 1972/
73 Antarctic whaling seasons. Some oceanographic conditions in the Crozet and
Kerguelen Ridge regions are discussed on the basis of these distribution of the surface isotherms.

50sFig. 7.

Surface temperature (°C) in December 1968.

The Crozet Ridge Region
The distibution of th emonthly mean surface temperature in this region are
shown in Figs. 7-14. The isotherms are remarkably bending, which is conspicuousin the submarine rising region around the Crozet Islands and less conspicuous in
the Prince Edward Islands than the former, namely northward on the rising andSci. Rep. Whales Res. Inst.,
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279

Jan

1968

Jan

1969

40

50

50

s

Fig. 8. Surface temperature (°C) in
January 1968.

40sFig. 9. Surface temperature (0 C) in
January 1969.

Feb

1967

40

50

s

Fig. 10.

Surface temperature (0 C) in February 1967.

southward on the west and the east sides of it, with some irregularities. Such tendency of the isothermal pattern is especially distinct in the Crozet Islands region,
where data are more abundant than in elsewhere. In the Prince Edward Islands
region, however, the similar bend are not so clear as in that region in a certain
months, perhaps owing to the lack of data.
The bend of isotherms in the adjacent waters to the Crozet Islands in winterSci. Rep. Whales Res. Inst.,
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MACHIDA

280

Feb
1968

40

6
50

s

Fig. 11.

30

Surface temperature (°C) in February 1968.

40
Fig. 12.

50

GOE

0

Surface temperature ( C) in February 1969.

have been already shown by Darbyshire (1964), Visser and Niekerk (1965), Orren(1966) and Nel (1968). By these charts, therefore, it appears that such feature of
the surface isotherms to be a permanent one. A steep temperature gradient still
occurs in the adjacent waters to south of the Subtropical Convergence. Its oceanographic conditions seem to intencify an effect of the convergent movement in accompany with the Subtropical Convergence, lying about 42° S in the South West
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281

Feb
1970

40

50

s

Fig. 13.

Surface temperature (0 C) in February 1970.

Mar
1966

40

.

8

50

s

Fig. 14.

Surface temperature (°C) in March 1966.

Indian Ocean (Deacon, 1937a; Orren, 1966). It also seems that the Subtropical
Convergence bends soutwards on the eastern side of the Crozet Islands, presumably
in approximately 60° E. The Subtropical Convergence by Deacon (1937a) also
meanders southwards in approximately 60° E.
The Antarctic Convergence, which is one of the major features in the Antarctic
Ocean, seems to run across the submarine rising around the Crozet Islands in DeSci. Rep. Whales Res. Inst.,
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MACHIDA

cember 1968, considering the location of the 4°C isotherm at the surface, which isone of the valid indication of the Antarctc Convergence (Deacon, 1937a; Mackintosh, 1946; Houtman, 1968). The 4°C isotherm, however, does not lie on the
Crozet Ridge in January, February and March. The greater parts of the Crozet
Ridge region, therefore, seems to be usually between the Subtropical and Antarctic
Convergences, and so this region is occupied by the major Subantarctic Surface
Water.
It is well known that the temperature distribution well reflects the feature of
the current. If we accept this general view, the current deflects to the left (north)on approaching a submarine rising around the Prince Edward and the Crozet Islands, and after having passed the rising it deflects to the right (south). Such current deflection over the submarine rising seems to be variable probably under the
influence of the bottom topography.
These findings support the view by Darbyshire (1964) and by Visser and Niekerk (1965), who described the current deflection to the left over the submarine rising around the Crozet Islands and the influence of the bottom topography on theocean current. Orren (1966) also indicated a northward flow of the cold Subantarctic Surface Water in the Crozet Islands region, probably occasioned by a northward movement of the Antarctic Convergence south of that islands.

The Kerguelen Ridge Region
Figs. 15-21 show the distribution of the monthly mean surface temperature inthis region. It is clear that the isotherms are bending in a similar way as in the
Crozet Ridge region, namely with a northward bend over the ridge and a southward
one on the east side of it. The 4°C isotherm lies near the 50° S parallel across theridge with bending from the west to the east. Furthermore after passing the ridge
the Antarctic Convergence bends down to about 55°S in approximately 90°E. Its
position roughly coincides with the convergence by Deacon (1937a) or by Mackintosh (1946). In addtion to this convergence, a sharp gradient in the surface temperature occurs on the north slope of the ridge.
The distriburion of the montly mean surface temperature suggests that thecurrent deflects to the left (north) on approaching the Kerguelen Ridge and after
having passed the ridge it bends to right (south). These deflection of the surface
current in the ridge region seems to be probably influenced by the bottom topography
and to be variable as well as in the Crozet Ridge region.
Deacon (1973a, b) and Sverdrup (1942) described the current bends to thenorth and to the south on passing over the Kerguelen Ridge, and that the current
deflection is probably under the influence of the bottom topography.
The deflection for a current on passing over the rising in the bottom topography may be anticipated on the theoritical grounds-in the southern hemisphere acurrent will deflect to the left as the sounding decreases and to the right as it increase(Deacon, 1937a, b; Sverdrup, 1941; Neuman, 1960), and in the case of eastern
flowing is the West Wind Drift a northward movement is expected. These features
are actually observed in many ridge regions, besides these two, in the Antarctic
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CROZET AND KERGUELEN WHALING GROUNDS

60

70

80

283

90E

Dec
1969

40

Fig. 15. Surface
temperature (°C)
in December 1969.

50

s

Jan
1968

4
50

Fig. 16. Surface
temperature (°C)
in January 1968.

60sSci. Rep. Whales Res. Inst.,
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MACHIDA

6~0~~~-.--~~-;7r0~~~-.-~~--"8~0~~~-.-~~~90E
Jan

1969

• 6
50

Fig. 17. Surface
temperature (°C)
in January 1969.

60

s

Feb

1967

50

Fig. 18. Surface
temperature (°C)
in February 1967.

2

60

s

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CROZET AND KERGUELEN WHALING GROUNDS

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Feb
1968

50

Fig. 19. Surface
temperature (°C)
in February 1968.

60
5

60

70
Feb
1969

40

50

s

Sci. Rep. Whales Res. Inst.,
No. 26, 1974

Fig. 20. Surface
temperature (°C)
in February 1969.

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MACHIDA

Mar

1968

50

4

·~4

60

s

Fig. 21.

Surface temperature (°C) in March 1968.

Ocean (Deacon, 1937a, b; Sverdrup et al., 1942; Midttun and Natvig, 1957; Burling,
1961; Harris, 1970) and they support the theory.
ACKNOWLEDGEMENTS
I wish to express my thanks to Dr. Keiji Nasu of the Far Seas Fisheries Laboratory,
Fisheries Agency ofJapan and Professor Michitaka U da of the Department of Marine
Science and Technology, Tokai University for suggesting this study. Thanks arealso due to Dr. Ichiro Yamanaka of the Far Seas Fisheries Laboratory, Fisheries
Agency ofJapan for some valuable suggestions and for reading this manuscript.
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DEACON, G. E. R., 1937b. Note on the dynamics of the Southern Ocean. Discovery Rep., 15: 125-152.
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