File:Discovery reports (1959) (20342100214).jpg

Title: Discovery reports
Identifier: discoveryreports29inst (find matches)
Year: 1959 (1950s)
Authors: Institute of Oceanographic Sciences (Great Britain); National Institute of Oceanography of Great Britain; Great Britain. Colonial Office. Discovery Committee
Subjects: Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands
Publisher: London ; New York : Cambridge University Press
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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3i6 DISCOVERY REPORTS chaetognath Sagitta gazellae was present in both Antarctic and Subantarctic waters the catches were extremely small in a region loo miles north to 200 miles south of the convergence and he distinguished separate races in the population to the north and south of it. It will be clear from Fig. 3 that the pattern of distribution for E. triacantha is the reverse of that for S. gazellae and that the catches in fact reach a maximum in the vicinity of the convergence. David suggests that it is likely that the sudden changes in physical conditions, brought about by the fluctuations in the position of the Antarctic convergence, are unfavourable to S. gazellae. In the case of E. triacantha, however, such conditions are evidently favourable.
Text Appearing After Image:
-r 500 â fOO NORTH 200 too A NAUTICAL 100 200 MILES 300 400 500 SOUTH 600 800 Fig- 3- The number of adolescent and adult E. triacantha in a series of shallow oblique night hauls with the i m. net from north-south lines of stations plotted according to the distance in nautical miles from the Antarctic convergence. The number per 20 min. haul is expressed as a percentage of the total catch for each line. The position of the convergence has been taken from Mackintosh (1946, Table 9). Seasonal variation In Fig. 4 the distribution of adolescent and adult E. triacantha in relation to the Antarctic convergence is shown for each season of the year. The mean catch per 20 min. haul has been plotted at intervals of 50 miles north and south of the convergence. The crosses indicate the intervals for which no data are available. In order to obtain sufficient observations lines of stations from several different regions of the Southern Ocean have been used; the number taken from each sector in each season is shown in Table i. The exact position of the convergence was indeterminate for a line of stations (2311-2320) along the Greenwich meridian in April and the mean position of 49° 50' S, based on nine other lines along the same meridian, has been used as an approximation. This is unlikely to fall more than 20 miles from the actual position and as the observations are in 50-mile groups no significant error

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