Discovery reports (1964) Discovery reports discoveryreports32inst Year: 1964 THE OLDER STAGES 207 5 or 6 days/ and for all we know in the sub-zero conditions in which it seems the krill eggs are laid the corresponding development might take longer. We have to consider, too, the period hatching to Metanauplius or First Calyptopis. We do not know this in E. superba, but in M. norvegica it seems (Heegaard, 1948) it might take up to 15 days or even more. Again, in the krill a longer period might elapse. Thus an unsegmented egg, liberated say in the slope waters of the south-western Weddell Fi
Discovery reports (1964) Discovery reports discoveryreports32inst Year: 1964 THE OLDER STAGES 207 5 or 6 days/ and for all we know in the sub-zero conditions in which it seems the krill eggs are laid the corresponding development might take longer. We have to consider, too, the period hatching to Metanauplius or First Calyptopis. We do not know this in E. superba, but in M. norvegica it seems (Heegaard, 1948) it might take up to 15 days or even more. Again, in the krill a longer period might elapse. Thus an unsegmented egg, liberated say in the slope waters of the south-western Weddell Fig. 31. Supposed influence of the sinking shelf water on the Hberated eggs. The Nauplii, Metanauplii and First Calyptopis are partly diagrammatic (see pp. 205-8). Sea, might spend a minimum of 21 days in the bottom water before, as a Metanauplius or First Calyptopis, it came within reach of our searching nets which in Weddell West and Weddell Middle did not go deeper than 1000 m. If the speed of the deep current were 2 knots the eggs and resultant larvae could, therefore, it seems, be carried at least 500 miles to the east. Although we do not know the speed of the bottom water there is some historical evidence (pp. 212-15) that it may be higher than is generally supposed. Bruce, for instance, was particularly impressed by the strength of the deep current that on occasion seemed to be sweeping his trawls, already heavily overweighted, off the bottom below the Weddell Sea, and he calls attention, too, to the famous occasion when Ross failed to strike bottom in this region, his sounding line evidently having been swept away by a current of similar force. It is possible in fact, as Deacon (1959) has recently said, that the bottom water has a transport comparable with that of the Gulf Stream. With fishes, as Simpson (1956) observes, an important source of error in positioning spawning from captures of eggs or larvae lies in the drift of the eggs and larvae away from the places where
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