SURFACE TEMPERATURE FIELD IN THE CROZET AND KERGUELEN WHALING GROUNDS

Transcription

1 SURFACE TEMPERATURE FIELD IN THE CROZET AND KERGUELEN WHALING GROUNDS SABURO MACHIDA Whale Reearch Intitute, Tokyo ABSTRACT Some oceanographic condition in the ummer eaon at the urface in the Crozet and Kerguelen Ridge region, where the good whaling ground of baleen whale occur, are dicued on the bai of the ditribution of the urface temperature oberved by the Japanee whaling fleet in the 1965/66 to 1972/73 Antarctic eaon. The urface iotherm bend northward over the ubmarine riing around the Prince Edward, Crozet and Kerguelen Iland. Thee bend of the iotherm ugget to reflect the bending of the urface current, and that it i preumably influenced by the bottom topography. They may be alo uggeted that the convergence efficiency of the current i comparatively intene north and eat of thee ubmarine riing. INTRODUCTION It i well known that the good whaling ground of baleen whale occur in the Crozet and Kerguelen Ridge region. In thee two region right whale were taken by the old American whaler mainly in the 19th century and pigmy blue whale were alo taken there in the early 19'. Recently the Japanee whaling fleet have been often earching for the favorite haunt of the ei and fin whale in the region. We have little knowledge of the general oceangoraphic condition in the Crozet and Kerguelen whaling ground, though the oceanographic condition are the cloe living evnvironment to the whale. A knowledge of oceanographic condition i fundamentally neceary to think ytematic tudy on the environment of the habit of variou marine organim. From thi point of view, therefore, the purpoe of the preent tudy i to dicu the oceanographic condition at the urface in the Crozet and Kerguelen Ridge region on the bai of the urface temperature ditribution, which wa oberved by the Japanee whaling fleet. MATERIAL AND METHOD The whaling fleet have been upplying u with the data of the oceanographic condition in the different whaling ground. They are temperature oberved by an electric thermometer, of which enor i fixed to the bottom of a factory hip (ea. 10 m depth) and a couting boat (ea. 5 m depth). A the urface layer down to a few,

2 272 MACHIDA ten meter in the Antarctic Ocean i roughly homogeneou in temperature, it eem to be reaonable to conider that there i no difference in the temperature between 5 and 10 m depth. Therefore, they are taken a ame and defined here a the urface temperature. The urface temperature were derived from " The urvey report of the whaling ground by a couting boat" in the 1965/66 to 1972/73 Antarctic eaon and " The weather and oceanographic condition at the noon poition of a factory hip " in the /58 to 1972/73 Antarctic eaon. A one degree quare grid wa adopted in making a monthly chart of the mean urface temperature, and iotherm were drawn by interpolation. The Far Sea Fiherie Reearch Laboratry, Fiherie Agency of Ja pan kindly upplied me with the material for thi tudy. 0 0 Fig. I. Chart of the Crozet Ridge region howing general bathymetry. Depth in the 100 fathom. (After U.S. Chart H.O. Mic. 15, ). The Crozet and Kerguelen Ridge region are hown with bathymetric contour in Fig. 1 and 2. Although the ubmarine riing around the Prince Edward and Crozet Iland i not generally termed the Crozet Ridge (Herdman, Eieman and Overy, 1965 ), the Crozet Ridge i named in thi tudy after "Atla zur Ozeanographie" by Dietrich and Ulrich (1968).

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4 274 MACHIDA LOCATION OF WHALING GROUNDS Before dicuing the feature of the temperature ditribution at the urface in the Crozet and Kerguelen Ridge region, the feature of the catch ditribution of the ei and fin whale, which are the mot important baleen whale a well a the minke whale for the recent whaling indutry, i ummarized. In thee two region right whale were abundantly caught by the old American whaler mainly in the l 9th century, and pigmy blue whale alo were bulkly caught there in the early 19'. The chart of the catch ditribution of the right whale by Townend (1935) and one of the pigmy blue whale by Ichihara (1966) are very uefull. According to them, the good whaling ground of the right whale were located in the water adjacent to the Crozet and Kerguelen Iland and one for the pigmy blue whale were rather ditributed over the Kerguelen and Crozet Ridge. Sei whale have been abundantly caught in thee region ince the 1964/65 Antarctic eaon and fin whale have been frequently caught in the north of S ince the 1957 /58 Antarctic eaon. The catch ditribution of the ei and fin whale are hown in Fig. 3, 4, 5 and SEI Fig. 3. Ditribution of ei whale caught by Japanee Antarctic whaling fleet in the Crozet Ridge region from the 1965/66 to the 1972/73 eaon. Light hading: depth le than 1,0 fathom (about 3,000 m).

5 CROZET AND KERGUELEN WHALING GROUNDS 275 The Crozet Ridge Region Sei whale were caught abundantly in the ubmarine riing around the Crozet Iland, though their few catche are ditributed widely on the Crozet Ridge. The good whaling ground of the ei whale are located in the adjacent water to the Crozet Iland. Although in the hallow water around the Prince Edward Iland it i omewhat imilar in appearance to the Crozet Iland region, catche of ei whale have been a little le than the former. The fin whale, on the other hand, alo ditributed widely on the ridge, and a great number of their catche i located on the far outh-wet water to the Prince Edward Iland FIN " Fig. 4. Ditribution of fin whale caught by Japanee Antarctic whaling fleet in the Crozet Ridge region from the 1957 /58 to the 1972/73 eaon. The Kerguelen Ridge Region The catche of ei and fin whale are widely ditributed on the ridge, though the feature of their eatch ditribution i to ome extent different from one on the outhern part of the ridge. There are two heavy catche area of ei whale over the ridge. It appear that the whaling ground of the ei and fin whale between 40 and 45 S are related to the Subtropical Convergence. The fin whale eem to be ditributed dominantly outh of about 53 S. Thee two pecie of whale have a 0 40

6 276 MACHIDA Fig. 5. Ditribution of ei whale caught by Japanee Antarctic whaling fleet in the Kerguelen Ridge region from the 1965/66 to the 1972/73 eaon. Light hading: depth le than 1,0 fathom (about 3,000 m).

7 CROZET AND KERGUELEN WHALING GROUNDS ' Fig. 6. Ditribution of fin whale caught by Japanee Antarctic whaling fleet in the Kerguelen Ridge region from the 1957/58 to the 1972/73 eaon.

8 278 MACHIDA trong tendency to be ditributed on to the eatern lope of the ridge and a few one have been caught on to the wetern lope of it, except in the higher latitude outh of about 56 S, where the fin whale are widely ditributed from wet to eat of the ridge. The different feature of the catch ditribution of the ei and fin whale a mentioned above may be partly caued by the difference of their food and habitat egregation. In the Subantarctic region of thee two whaling ground, the quantitatively important food organim of the ei whale i Parathemito gandichaudii, and Euphauia vallentini i important a a favorite food of the fin whale (Nemoto, 1959, 1962, 1970; Nau, 1966; Kawamura, 1970). I do not intend to mention further a pattern of their catch ditribution, becaue it i not the main purpoe of the preent tudy. SURFACE OCEANOGRAPHIC CONDITIONS Fig how the ditribution of the urface temperature in the 1957/58 to 1972/ 73 Antarctic whaling eaon. Some oceanographic condition in the Crozet and Kerguelen Ridge region are dicued on the bai of thee ditribution of the urface iotherm. Fig. 7. Surface temperature ( C) in December The Crozet Ridge Region The ditibution of th emonthly mean urface temperature in thi region are hown in Fig The iotherm are remarkably bending, which i conpicuou in the ubmarine riing region around the Crozet Iland and le conpicuou in the Prince Edward Iland than the former, namely northward on the riing and

9 CROZET AND KERGUELEN WHALING GROUNDS 279 Jan Jan Fig. 8. Surface temperature ( C) in January Fig. 9. Surface temperature ( 0 C) in January Feb Fig. 10. Surface temperature ( 0 C) in February outhward on the wet and the eat ide of it, with ome irregularitie. Such tendency of the iothermal pattern i epecially ditinct in the Crozet Iland region, where data are more abundant than in elewhere. In the Prince Edward Iland region, however, the imilar bend are not o clear a in that region in a certain month, perhap owing to the lack of data. The bend of iotherm in the adjacent water to the Crozet Iland in winter

10 280 MACHIDA Feb Fig. 11. Surface temperature ( C) in February Fig. 12. Surface temperature ( 0 C) in February GOE have been already hown by Darbyhire (1964), Vier and Niekerk (1965), Orren (1966) and Nel (1968). By thee chart, therefore, it appear that uch feature of the urface iotherm to be a permanent one. A teep temperature gradient till occur in the adjacent water to outh of the Subtropical Convergence. It oceanographic condition eem to intencify an effect of the convergent movement in accompany with the Subtropical Convergence, lying about 42 S in the South Wet

11 CROZET AND KERGUELEN WHALING GROUNDS 281 Feb Fig. 13. Surface temperature ( 0 C) in February Mar Fig. 14. Surface temperature ( C) in March Indian Ocean (Deacon, 1937a; Orren, 1966). It alo eem that the Subtropical Convergence bend outward on the eatern ide of the Crozet Iland, preumably in approximately E. The Subtropical Convergence by Deacon (1937a) alo meander outhward in approximately E. The Antarctic Convergence, which i one of the major feature in the Antarctic Ocean, eem to run acro the ubmarine riing around the Crozet Iland in De-

12 282 MACHIDA cember 1968, conidering the location of the 4 C iotherm at the urface, which i one of the valid indication of the Antarctc Convergence (Deacon, 1937a; Mackintoh, 1946; Houtman, 1968). The 4 C iotherm, however, doe not lie on the Crozet Ridge in January, February and March. The greater part of the Crozet Ridge region, therefore, eem to be uually between the Subtropical and Antarctic Convergence, and o thi region i occupied by the major Subantarctic Surface Water. It i well known that the temperature ditribution well reflect the feature of the current. If we accept thi general view, the current deflect to the left (north) on approaching a ubmarine riing around the Prince Edward and the Crozet Iland, and after having paed the riing it deflect to the right (outh). Such current deflection over the ubmarine riing eem to be variable probably under the influence of the bottom topography. Thee finding upport the view by Darbyhire (1964) and by Vier and Niekerk (1965), who decribed the current deflection to the left over the ubmarine riing around the Crozet Iland and the influence of the bottom topography on the ocean current. Orren (1966) alo indicated a northward flow of the cold Subantarctic Surface Water in the Crozet Iland region, probably occaioned by a northward movement of the Antarctic Convergence outh of that iland. The Kerguelen Ridge Region Fig how the ditribution of the monthly mean urface temperature in thi region. It i clear that the iotherm are bending in a imilar way a in the Crozet Ridge region, namely with a northward bend over the ridge and a outhward one on the eat ide of it. The 4 C iotherm lie near the S parallel acro the ridge with bending from the wet to the eat. Furthermore after paing the ridge the Antarctic Convergence bend down to about 55 S in approximately 90 E. It poition roughly coincide with the convergence by Deacon (1937a) or by Mackintoh (1946). In addtion to thi convergence, a harp gradient in the urface temperature occur on the north lope of the ridge. The ditriburion of the montly mean urface temperature ugget that the current deflect to the left (north) on approaching the Kerguelen Ridge and after having paed the ridge it bend to right (outh). Thee deflection of the urface current in the ridge region eem to be probably influenced by the bottom topography and to be variable a well a in the Crozet Ridge region. Deacon (1973a, b) and Sverdrup (1942) decribed the current bend to the north and to the outh on paing over the Kerguelen Ridge, and that the current deflection i probably under the influence of the bottom topography. The deflection for a current on paing over the riing in the bottom topography may be anticipated on the theoritical ground-in the outhern hemiphere a current will deflect to the left a the ounding decreae and to the right a it increae (Deacon, 1937a, b; Sverdrup, 1941; Neuman, 19), and in the cae of eatern flowing i the Wet Wind Drift a northward movement i expected. Thee feature are actually oberved in many ridge region, beide thee two, in the Antarctic

13 CROZET AND KERGUELEN WHALING GROUNDS E Dec Fig. 15. Surface temperature ( C) in December Jan Fig. 16. Surface temperature ( C) in January 1968.

14 284 MACHIDA 6~0~~~-.--~~-;7r0~~~-.-~~--"8~0~~~-.-~~~90E Jan Fig. 17. Surface temperature ( C) in January Feb 1967 Fig. 18. Surface temperature ( C) in February

15 CROZET AND KERGUELEN WHALING GROUNDS 285 Feb 1968 Fig. 19. Surface temperature ( C) in February Feb Fig. 20. Surface temperature ( C) in February 1969.

16 286 MACHIDA Mar ~4 Fig. 21. Surface temperature ( C) in March Ocean (Deacon, 1937a, b; Sverdrup et al., 1942; Midttun and Natvig, 1957; Burling, 1961; Harri, 1970) and they upport the theory. ACKNOWLEDGEMENTS I wih to expre my thank to Dr. Keiji Nau of the Far Sea Fiherie Laboratory, Fiherie Agency of Ja pan and Profeor Michitaka U da of the Department of Marine Science and Technology, Tokai Univerity for uggeting thi tudy. Thank are alo due to Dr. Ichiro Yamanaka of the Far Sea Fiherie Laboratory, Fiherie Agency of Japan for ome valuable uggetion and for reading thi manucript. REFERENCES BURLING, R. vv., Hydrology of circumpolar water outh of New Zealand. N.:(. Dep. ci. indutr. Re. Bull., 149 (N.<:,. Oceanogr. Int. Mem., 10), 66 pp. DEACON, G. E. R., 1937a. The hydrology of the Southern Ocean. Dicovery Rep., 15: DEACON, G. E. R., 1937b. Note on the dynamic of the Southern Ocean. Dicovery Rep., 15: DARBYSHIER, ]., A hydrological invetigation of the Agulha Current area. Deep-Sea Re., 11: DIETRICH, G. and ULRICH, J., Atla zur ozeanograhie. Bibliographiche lntitut LG Mannhim, 76 pp.

17 CROZET AND KERGUELEN WHALING GROUNDS 287 HERDMAN, H. F. P., EISEMAN, J. D. H. and OVERY, C. D., Propoed name of feature on the deepea floor. Deep-Sea Re., 3: HARRIS, T. F. vv., Planetary-type wave in the South Wet Indian Ocean. Nature, 227: HOUTMAN, TH. J., Surface temperature gradient at the Antarctic Convergence. N.z.J. Geol. Geophy., 7: !CHIHARA, T., The pygmy blue whale, Balaenoptera muculu brevicauda, a new ubpecie from the Antarctic. In Whale, Dolphin and Porpoie (Ed. K.S. Norri, Univ. Calif. Pre), KAWAMURA, A., Food of ei whale taken by Japanee whaling Expedition in the Antarctic eaon 1967/68. 22: l'viackintosh, N. A., The Antarctic Convergence and the ditribution of urface temperature in Antarctic Water. Dicovery Rep., 23: NAu, K., Fihery oceanographic tudy on the baleen whaling ground. 20: NEL, E. A., The microplankton of the South-Eat Indian Ocean. Invetl Rep. Div. Sea. Fih. S. Afr., 62: NEMOTO, T., Food of baleen whale with reference to whale movement. 14: NEMOTO, T., Food of baleen whale collected in recent Japanee whaling expedition. Sci. Rep. Whale Re. Int., 16: NEMOTO, T. and Yoo, K. I., An amphipod, Parathemito gaudichaudii a a food of the Antarctic ei whale. 22: NEUMAN, G., 19. On the effect of bottom topography on ocean current. Deut. Hydrograph. z., 13: ORREN, M.J., Hydrology of the South Wet Indian Ocean. Invet[ Rep. Div. Sea Fih. S. Afr., 55: SvERDRUP, H. U., The influence of bottom topography on ocean current. Appl. Mechanic. Th. Karman Ann. Vol., SVERDRUP, H. U., JoHNSoN, M. W. and FLEMING, R.H., The Ocean. Prentice-Hall, Inc., 1987 pp. TOWNSEND, C. H., The ditribution of certain whale a hwon by logbook record of American whalehip. Zoologica, 19: 1-. VISSER, G. L. and VAN NIEKERK, M. M., Ocean current and water mae at 1,000, 1,0 and 3,000 meter in the South-Wet Indian Ocean. Invetl Rep. Div. Sea Fih. S. Afr., 52: 1-46.